What type of proteins are myoglobin and hemoglobin?
Both are globular proteins.
What essential group do myoglobin and hemoglobin contain?
Heme, a prosthetic group for reversible O2 binding.
What is the function of myoglobin?
Facilitates O2 diffusion and storage in muscle.
What is the function of hemoglobin?
Transports O2 in bloodstream.
How does myoglobin bind oxygen?
Binds based on oxygen concentration and follows a hyperbolic binding curve.
What is a prosthetic group?
A permanently attached non-protein factor essential for function.
What does heme contain that allows it to bind oxygen?
Fe2+, which binds O2 reversibly.
Why does biology use metal-containing cofactors like heme?
To solve the problem of oxygen transport due to poorly soluble free oxygen.
What is the structure of myoglobin?
Monomeric (single polypeptide) made of 153 amino acids and eight a-helices (A-H).
How many hemes does myoglobin contain?
One heme.
Where is myoglobin most concentrated?
In cardiac and skeletal muscle.
What is the globin fold?
A conserved structure across all globins (8 helices + connecting loops).
What role does His F8 (His93) serve in myoglobin?
It is the proximal His that binds directly to Fe.
What is the function of His E7 in myoglobin?
It is the distal His that hydrogen bonds to bound O2.
How does myoglobin prevent Fe2+ from oxidizing?
It encloses heme in a pocket.
How does distal His reduce CO toxicity?
Forces CO to bind at an angle, decreasing its preference for Fe2+.
What is unique about myoglobin's O2-binding curve?
It is hyperbolic due to having one O2-binding site.
What oxidation state must Fe2+ remain in to bind O2?
The ferrous state.
Which oxidation state of iron does not bind O2?
Fe3+ (ferric).
How many coordination bonds does heme iron have?
Six coordination bonds.
What are the coordination bonds of heme iron?
What optimizes O2 binding in the heme pocket?
Geometry and amino acids minimize risk of reactive oxygen species (ROS) formation.
How does free heme bind CO?
Extremely strongly; globin structure reduces CO affinity by 20,000-fold to ~40-fold.
What is Myoglobin?
A monomeric protein that facilitates muscle O2 diffusion.
What function does Hemoglobin serve?
Tetrameric protein responsible for blood O2 transport.
What is the role of Neuroglobin?
Protects neurons under low O2 conditions.
What does Cytoglobin regulate?
Involved in nitric oxide regulation.
What do all globins share?
They share the globin fold and similar tertiary structures despite low sequence identity.
What does the preserved globin fold indicate?
Indicates a common evolutionary origin.
What is divergent evolution in relation to globins?
Different globins specialize for different tissues and stress conditions.
What is the equation for association in ligand binding?
P + L = PL
What is the association constant (Ka) formula?
Ka = [PL] / ([P][L])
What is the dissociation constant (Kd) formula?
Kd = 1 / Ka
What does a lower Kd indicate?
Higher affinity.
What is the formula for fractional saturation (Y)?
Y = [L] / (Kd + [L])
At Y = 0.5, what is the relationship between [L] and Kd?
[L] = Kd.
What is the basic model for one binding site example?
Myoglobin.
What leads to hyperbolic behavior in ligand binding?
No cooperativity (no inter-subunit influence).
What is the equation for oxygen binding to myoglobin?
Y = pO2 / (pO2 + p50)
What does p50 represent in oxygen binding?
Partial pressure of O2 at 50% saturation.
What type of molecule is myoglobin?
Monomeric with a single binding site.
At what O2 pressure does myoglobin become saturated?
Relatively low O2 pressures.
What is the structure of hemoglobin?
Tetramer: α2β2.
How many globin folds does each hemoglobin subunit have?
1 globin fold.
What does each hemoglobin subunit contain?
1 heme.
How many residues are in the α1β1 (and α2β2) interface?
<blockquote>
30 residues.
</blockquote>
How many residues are in the α1β2 (and α2β1 interface?
~19 residues.
What forces hold the hemoglobin tetramer together?
What are the two conformational states of hemoglobin?
What characterizes the T state of hemoglobin?
What characterizes the R state of hemoglobin?
What causes the T to R transition in hemoglobin?
What happens during the T to R transition?
What is the effect of O2 binding on hemoglobin?
What type of binding does hemoglobin exhibit?
Cooperative binding due to tetrameric architecture.
What shape represents hemoglobin's O2 binding curve?
Sigmoidal
What shape represents myoglobin's O2 binding curve?
Hyperbolic
What is cooperative binding?
Binding of first O2 increases affinity for next O2 molecules.
What is the hallmark of conformational switching in proteins?
Sigmoid shape
Why is cooperativity important for hemoglobin?
It allows efficient release of O2 in tissues.
Is hemoglobin an allosteric protein?
Yes
What are homotropic modulators?
Normal ligand acts as modulator (e.g., O2).
What are heterotropic modulators?
Modulator ≠ ligand (e.g., H+, CO2, BPG).
What is allostery?
Binding at one site influences binding at another site.
What is the Hill equation?
log[Y/(1-Y)] = nH log[L] – log(Kd)
What does nH represent?
Hill coefficient reflecting cooperativity.
What does nH = 1 indicate?
No cooperativity (myoglobin).
What does nH > 1 signify?
Positive cooperativity (hemoglobin).
What does nH < 1 indicate?
Negative cooperativity.
What is the typical nH value for hemoglobin?
nH ~ 2.8 (not 4).
What are the two models of cooperative binding?
What does O₂ binding to hemoglobin favor?
Binding of O₂ favors the R state.
How does the binding of each subunit change?
Each subunit can change independently.
What effect does low pH have on oxygen release?
Low pH promotes more O₂ release.
What is the Bohr Effect equation?
The equation is: \(HHb^+ + O_2 = HbO_2 + H^+\)
What happens to pH during CO₂ removal?
Removing CO₂ raises pH, promoting O₂ binding.
What does hemoglobin bind to aside from O₂?
Hemoglobin also binds H⁺ and CO₂.
What does high pH promote?
High pH promotes more O₂ binding.
How does CO₂ affect O₂ release?
Tissues produce CO₂, converting it to H⁺, promoting O₂ release.
Describe the effect of metabolism on O₂ delivery.
Couples O₂ delivery to metabolic activity.
What is BPG?
BPG (2,3-bisphosphoglycerate) is a heterotropic allosteric modulator that lowers hemoglobin's oxygen affinity.
Where does BPG bind in hemoglobin?
BPG binds to the central cavity between the β subunits, but only in the T state.
What happens to BPG levels at high altitude?
BPG levels increase at high altitude.
How does fetal hemoglobin interact with BPG?
Fetal hemoglobin (α2γ2) binds BPG more weakly, resulting in a higher O2 affinity.
What is the role of BPG in hemoglobin function?
BPG ensures hemoglobin releases sufficient O2 in tissues.
How does fetal hemoglobin extract O2?
Fetal hemoglobin extracts O2 from maternal blood by having weaker BPG binding and higher O2 affinity.
What causes hemoglobin variants?
Hemoglobin variants arise due to mutations in globin genes.
How are hemoglobin variants typically named?
Variants are usually named based on the location where they were first identified.
What can mutations alter?
How does hemoglobin's structure affect its function?
What molecular disease is associated with hemoglobin mutations?
Sickle cell anemia
What is the most important variant in sickle cell anemia?
HbS
What causes sickle cell anemia?
A mutation in the hemoglobin gene
What amino acid substitution occurs in the β-globin chain?
Glu6 is replaced by Val6
What type of residue replaces glutamate in the mutation?
A hydrophobic valine residue
What structure does the substitution form on hemoglobin?
A hydrophobic patch
What happens to hemoglobin under deoxygenated conditions?
The hydrophobic patch interacts with neighboring Hb, causing polymerization.
What is the result of hemoglobin polymerization?
Long fibers distort red blood cell shape.
What shape do red blood cells acquire due to the mutation?
Sickle-shaped
What happens to deoxygenated HbS?
It becomes insoluble and forms polymers.
What are the consequences of sickle-shaped cells?
What happens to sickled RBCs in deoxygenated state?
Polymerization occurs, leading to sickling.
What happens to sickled RBCs in oxygenated state?
Depolymerization occurs, restoring a more normal shape.
What causes pain crises in sickle cell disease?
Microvascular blockage due to sickled RBCs.
What causes anemia in sickle cell disease?
Destruction of red blood cells (RBCs).
What leads to organ damage in sickle cell disease?
Impaired blood flow caused by sickled cells.
Describe the shape of normal RBCs.
Flexible, biconcave discs.
Describe the shape of sickled RBCs.
Rigid, elongated crescent shapes.
What is a risk of sickled RBCs passing through capillaries?
Higher likelihood of rupturing.
What causes the shape change in sickled RBCs?
Polymerized hemoglobin pushing against the RBC membrane.
What is the primary factor leading to sickling in sickle cell disease?
Polymerization of mutated hemoglobin.
What does poor deformability decrease through narrow vessels?
Flow, leading to ischemia.
What does increased rupture reduce?
RBC lifespan, resulting in chronic hemolytic anemia.
Which hemoglobin variant is the most clinically important?
HbS.
How are hemoglobin variants usually named?
After cities or places where first identified.
What mutations do hemoglobin variants involve?
Different β-chain or α-chain mutations.
What is true about most hemoglobin variants?
What is essential to maintain hemoglobin function?
What is likely to produce disease in hemoglobin variants?
Mutations at critical sites.
What may some mutations change in hemoglobin?
Function and stability.
What key example is the slide focused on?
HbS
How do genetic variations affect proteins?
What factors affect protein function?
What condition is linked to genetic and molecular changes?
Sickle cell anemia
What happens due to changes in primary structure?
Altered tertiary and quaternary interactions lead to functional changes.
What do structural proteins maintain?
Shape, organization, and mechanical integrity of cells.
What are the three major cytoskeletal systems?
What is considered a major structural protein, although not cytoskeletal?
Collagen.
What are microfilaments primarily made of?
Polymers of globular actin (G-actin).
What do G-actin monomers self-assemble into?
A filament with directionality.
What structural formation does actin create?
A double-stranded helical chain (F-actin).
What kind of stability does the actin helix provide?
Structural stability and allows binding of regulatory proteins.
What is the direction of actin polymerization?
From G-actin to F-actin
At which end does actin assembly occur more rapidly?
(+) end
What characterizes the (-) end of actin assembly?
Slower addition or net loss
What are the three essential functions of actin dynamics?
What occurs during actin treadmilling?
What happens to filament length during treadmilling?
Filament length stays constant
What flows through the filament during treadmilling?
Monomers
What is the function of treadmilling in cells?
Allows actin to shift filaments within the cytoskeleton without full disassembly.
What are the components of tubulin dimers?
What is the structure of microtubules?
Hollow tubes made of 13 protofilaments arranged in a cylinder.
How do tubulin dimers affect microtubule dynamics?
The structural difference between α and ß subunits drives the dynamics.
How are tubulin dimers arranged in microtubules?
They assemble head-to-tail, imparting polarity to the microtubules.
How are microtubules visualized?
Visible by cryo-electron microscopy.
What geometry provides exceptional strength with minimal mass?
Cylindrical geometry
What are microtubules used for in cells?
How do microtubules behave in dividing cells?
They are abundant and highly dynamic.
What do microtubules interact with during mitosis?
Chromosomes
What is the dynamic behavior of microtubules during division?
They allow for 'search and capture' of chromosomes.
What is the effect of some drugs on microtubules?
Why are drugs targeting microtubules used in therapy?
They disrupt cell division.
What is keratin?
An intermediate filament protein.
What structure does keratin adopt?
A left-handed coiled coil structure with two a-helices.
What role do intermediate filaments play?
Provide mechanical stability, especially in stress-experiencing tissues.
What pattern is seen in the coiled coil structure?
Heptad repeat (seven-residue pattern).
How do the residues align in a coiled coil?
Hydrophobic residues align to maintain coil stability.
What ensures tight packing between a-helices?
The arrangement of residues in the coiled coil.
What does the geometry of a structure enhance?
Tensile strength
How are intermediate filaments depicted?
How do real filaments behave?
They are twisted instead of straight
What gives keratin high durability?
Multiple coiled coils bundle into larger fibers
What is unique about collagen's amino acid composition?
It has a repeating pattern rich in Glycine, Proline, and hydroxyproline
What do small glycine residues allow in collagen?
Tight packing
Which amino acids stabilize helix geometry in collagen?
What is the structure of collagen?
Collagen forms a triple helix.
How do the chains of collagen interact?
Three chains wind around each other.
What does the collagen triple helix resist?
Stretching
What connective tissues is collagen ideal for?
When does cross-linking occur in collagen?
After polypeptide synthesis.
What stabilizes collagen fibrils?
Covalent cross-links
How does cross-linking affect tensile strength?
Increases strength over time.
What happens if there are defects in cross-linking?
Weakens connective tissue integrity.
What do motor proteins convert into mechanical movement?
Chemical energy (ATP)
What are essential processes of motor proteins?
What type of motor protein is myosin?
Actin-based
What are the two parts of myosin's structure?
What does each myosin head contain?
A binding site for actin
What type of nucleotide does myosin bind to?
Adenine nucleotide (ATP or ADP)
What does the two-headed structure of myosin allow?
Where does myosin bind ATP?
At the nucleotide-binding pocket in its head domain
What happens when ATP binds to myosin?
Reduces myosin's affinity for actin, causing detachment
What provides energy for myosin's conformational changes?
ATP hydrolysis
What role does myosin play in movement?
Myosin acts as a lever
What causes the lever arm to swing?
ATP hydrolysis
What does the swinging motion generate along?
Actin filament
What is core to force production in muscle contraction?
Myosin-actin reaction cycle
What is the first step in the Myosin-Actin reaction cycle?
ATP binding
What happens after ATP hydrolysis in the cycle?
Myosin is energized ('cocked back')
What triggers the power stroke in the Myosin-Actin cycle?
Phosphate release
What happens when ADP is released?
Myosin is tightly bound ('rigor state')
What converts chemical energy into mechanical work?
Myosin-actin reaction cycle
What type of protein is kinesin?
Kinesin is a microtubule-associated protein.
Which direction does kinesin move its cargo?
Toward the (+) end of a microtubule.
What type of transport does kinesin generally mediate?
Kinesin mediates anterograde transport (away from center).
How does kinesin's movement occur?
Movement occurs stepwise.
What are the structural components of kinesin?
What is the function of kinesin with regard to cargo?
Kinesin transports cargo processively along microtubules.
Describe the movement of kinesin.
What does processivity mean in kinesin movement?
Kinesin can take many steps without detaching, facilitating long-distance transport.
Why is processivity important for kinesin?
It allows kinesin to transport cargo over long distances, such as along axons.
What is the significance of the kinesin reaction cycle?
It details the stepping mechanism for kinesin as it moves along a microtubule.
What does ATP binding cause in kinesin movement?
Rear head swings ahead.
What follows ATP binding in kinesin?
Hydrolysis enables the next step.
What coordinates kinesin head movements?
ATP binding, hydrolysis, and product release.
How does kinesin 'walk'?
By alternating binding, hand-over-hand.
What energy do motor proteins convert?
Chemical to mechanical energy.
What changes allow motor proteins to function?
Conformational changes and nucleotide cycles.
Which filaments does myosin move on?
Actin filaments.
Which structure does kinesin move on?
Microtubules.
What is essential for kinesin's forward stepping?
ATP.
What do both myosin and kinesin require for movement?
ATP hydrolysis.
What do cytoskeletal tracks and motor proteins facilitate?
Intracellular transport and movement mechanisms
What is an enzyme?
A catalyst that is specific for its substrates and products
Name a way to increase reaction rates in living systems.
Why is increasing temperature not practical in cells?
Cells have a narrow viable temperature range
What is a challenge of increasing reactant concentrations in cells?
What is the effect of adding a catalyst?
It increases the rate of chemical reactions
What do catalysts do?
They accelerate reactions without being permanently changed.
What are biological catalysts called?
Enzymes.
How do temperature and concentration increases work?
By raising the effective collision frequency of molecules.
Can biological systems drastically change temperature or concentration?
No, they cannot.
How do enzymes help biological systems?
What are most enzymes composed of?
Proteins.
What are RNA enzymes called?
Ribozymes.
What is the active site of an enzyme?
The region where the reaction takes place.
What conditions do enzymes operate under?
Mild conditions.
How do enzymes differ from chemical catalysts?
Enzymes require milder conditions compared to many chemical catalysts.
What are the conditions that can affect enzyme activity?
How is enzyme activity regulated?
What is the active site of an enzyme?
A specialized microenvironment precisely shaped for the substrate.
Why is enzyme regulation important?
How do chemical catalysts compare to enzymes?
Chemical catalysts cannot adapt or respond; enzymes can.
What is the benefit of enzymatic rate enhancement?
Enzymes significantly speed up biochemical reactions.
How much do enzymes accelerate reactions?
Factors of \(10^0\) to \(10^{12}\) (hundreds of millions to trillions times faster).
What happens to reactions without enzymes?
They proceed too slowly to sustain life.
How do enzymes affect thermodynamic favorability?
They increase the reaction rate without altering overall $ riangle G$ (thermodynamic favorability).
What do enzymes specifically recognize?
What allows enzymes to discriminate between similar molecules?
Active site functional groups.
What arises from shape complementarity?
Specificity in enzyme binding.
What arises from chemical complementarity?
Specificity in enzyme binding.
What is essential to avoid unwanted side reactions in cells?
Specificity in enzyme binding.
How many major classifications of enzymes are there?
Seven major classifications.
What do most biochemical reactions involve?
What can prevent binding in enzyme specificity?
Subtle differences, e.g., one methyl group.
What do translocases catalyze?
Movement of ions/molecules across membranes.
What is the classification system for enzymes based on?
Type of reaction, not structure.
What does the movement category in enzymes indicate?
Some enzymes catalyze transport, not chemical transformation.
How are many enzymes named?
After the reaction they catalyze.
What is an example of enzyme naming?
Chymotrypsin is named for its substrate, chymotrypsinogen.
What system assigns a unique four-level EC number to enzymes?
The EC number system.
What does the EC number system categorize enzymes by?
What is an example of an EC number?
Chymotrypsin = EC 3.4.21.1
What must occur for a biochemical reaction to proceed?
What is activation energy (AG‡)?
Energy required for reactants to undergo changes to become products.
How do enzymes affect reaction rates?
Enzymes accelerate reactions by lowering the activation energy.
List the three catalytic mechanisms of enzymes.
What roles do amino acid side chains play in enzymes?
They participate in catalytic mechanisms to facilitate chemical reactions.
What is essential for a reaction to proceed even if it's thermodynamically favorable?
Reactants must be able to approach closely.
What does AG represent in thermodynamics?
Free energy change
What is required to reorganize bonds in a reaction?
Activation energy (AG‡)
What does AG < 0 indicate?
Spontaneous reaction
What does AG > 0 indicate?
Non-spontaneous reaction
Does AG describe speed of a reaction?
No, it describes thermodynamics.
Why are enzymes essential in reactions?
They lower AGI but do not change AG.
What is the Transition State (TS)?
A high-energy state during a reaction.
What is the transition state in a reaction?
The highest-energy point on the reaction pathway.
What is the activation energy represented as?
The energy difference between reactants and the transition state (AG‡).
How does activation energy affect reaction rate?
What fraction of molecules reach the transition state at a given moment?
Only a small fraction of molecules.
How do enzymes affect the transition state?
They stabilize the transition state, increasing the reaction rate.
What happens when there are more transition state molecules present?
More product formation and a faster reaction.
What do enzymes do to activation energy?
They lower AG‡, thereby increasing the reaction rate.
Does lowering activation energy change the AG of the reaction?
No, it does not change AG of the reaction.
What do enzymes accelerate?
Both forward and reverse reactions, by stabilizing the transition state.
What are cofactors?
Groups required for catalytic functions not available in amino acids.
What types of cofactors exist?
Why are cofactors important?
They broaden the chemical capabilities of proteins.
What reactions would be impossible without cofactors?
What is Acid-Base Catalysis in enzymes?
What does Acid Catalysis do?
What does Base Catalysis do?
What is the purpose of Acid-Base Catalysis?
What is Covalent Catalysis in enzymes?
What are the steps in Covalent Catalysis?
What does a reaction coordinate represent?
It has two energy barriers.
What effect does covalent catalysis have on the reaction pathway?
It changes to one with lower overall activation energy.
What is true about the intermediate in covalent catalysis?
It is more stable than the TS but still transient.
How do metal ions assist catalysis?
How do metals influence reaction energetics?
By holding substrates in specific conformations or stabilizing charged intermediates.
What type of catalysis involves amino acids?
Acid-base and covalent mechanisms.
Which amino acids can act in acid-base catalysis?
Amino acids with side-chain groups that can donate/accept H+.
What determines if an amino acid can act as an acid or base?
The pKa values of the side chains.
What can amino acids do during catalysis?
Change protonation states strategically.
What do nucleophilic amino acids provide?
Electron-rich groups capable of forming covalent intermediates.
What is the role of nucleophilicity in catalysis?
Enables formation of enzyme-substrate covalent intermediates.
How does context affect amino acids in active sites?
Amino acid context enhances reactivity.
What enzyme converts acetaldehyde to ethanol?
Alcohol dehydrogenase
What metal ion stabilizes the negative charge on oxygen in alcohol dehydrogenase?
Zinc ion
What role do metal ions play in chemical reactions?
They stabilize intermediates or TS species, lowering \(ΔG^‡\).
What does zinc do during hydride transfer?
It interacts electrostatically with the oxygen atom.
What is the catalytic triad of chymotrypsin?
What does Ser195 require to be nucleophilic enough for catalysis?
His57 removes Ser195's proton, activating it as an alkoxide.
What role does Asp102 play in the activation of Ser195?
It stabilizes the positively charged His57 during catalysis.
What does the triad involving Ser195 achieve?
Why is the positioning of the substrate's scissile bond important?
It must be near Ser195 for effective catalysis.
How does the enzyme active site contribute to catalysis?
It precisely orients substrates to reduce entropy cost.
What ensures efficient cleavage in enzymatic reactions?
Positioning combined with triad chemistry enhances the process.
What are the core mechanistic features of chymotrypsin?
What are the steps involved in the reaction of chymotrypsin?
What is the role of the oxyanion hole in the chymotrypsin mechanism?
It stabilizes the tetrahedral intermediate.
What is formed during the acylation step of chymotrypsin's mechanism?
The enzyme becomes acylated.
What does His57 do in the chymotrypsin mechanism?
It facilitates proton transfers in acid-base catalysis.
What are the two main steps in the catalytic mechanism of chymotrypsin?
What are the intermediates formed in the chymotrypsin reaction?
Which bond is broken in the chymotrypsin mechanism?
Peptide bond
What bond is formed with Ser195 during chymotrypsin action?
Covalent bond
What bond breaks during hydrolysis in chymotrypsin?
Acyl-enzyme bond
What are the products formed after chymotrypsin action?
New peptide fragments
What does chymotrypsin demonstrate in enzymatic strategy?
General enzymatic strategy
What is the role of substrate orientation in chymotrypsin?
Facilitates reaction
What is covalent catalysis in context of chymotrypsin?
Temporary covalent bonds formed
How does chymotrypsin achieve transition-state stabilization?
Lowers activation energy
What aspect does acid-base chemistry provide in chymotrypsin?
Proton transfer facilitates reaction
What does the lock-and-key model in enzymatic action fail to explain?
Flexibility of active site
What does the Lock-and-Key Model imply?
The substrate fits precisely into the active site, like a key into a lock.
What is a limitation of the Lock-and-Key Model?
It doesn't explain how the active site can bind products.
What is transition-state stabilization?
It's the process of lowering the energy of the transition state to enhance catalysis.
What does proximity/orientation refer to?
Positioning substrates correctly to promote reaction.
What is induced fit?
The active site adjusts to better fit the substrate upon binding.
What is electrostatic catalysis?
The stabilization of charged transition states using complementary charges in the active site.
What contributes to product binding in enzymes?
Binding energy induces conformational change.
How do inhibitors bind to enzymes?
They often resemble transition states rather than substrates.
What is a key characteristic of active sites?
They are dynamic and not rigid.
What is essential for enzyme catalysis?
Flexibility during substrate binding.
What do enzymes stabilize in enzymology?
The transition state, lowering activation energy.
How do enzyme-transition state interactions compare to enzyme-substrate interactions?
They are stronger than enzyme-substrate interactions.
What does TS in biochemistry refer to?
TS stands for transition state, a high-energy configuration in enzymatic reactions.
Why do enzymes bind most tightly to the transition state?
Do enzymes stabilize substrates?
No, enzymes stabilize the transition state.
What are the key features of serine proteases?
How do serine proteases optimize their active sites?
They stabilize negatively charged transition states.
What is the role of Ser195 in Serine Protease mechanism?
It facilitates a rapid nucleophilic attack.
What characterizes the tetrahedral intermediate in the transition state?
What stabilizes the negatively charged oxyanion?
How does stabilizing the transition state (TS) affect AG‡?
Stabilizing the TS more than the enzyme-substrate complex (ES) lowers AG‡.
What is the function of the oxyanion hole?
It provides electrostatic stabilization to an unstable structure.
What type of bond forms during catalysis in chymotrypsin?
A low-barrier hydrogen bond may form.
Which residue is involved in stabilizing the positively charged His57?
The low-barrier hydrogen bond forms between residues involved in His57 stabilization.
How do low-barrier hydrogen bonds compare to normal hydrogen bonds?
They are stronger than normal hydrogen bonds.
What effect do low-barrier hydrogen bonds have on the transition state?
They lower the energy of the transition state.
What role do low-barrier hydrogen bonds play in the catalytic cycle?
They help maintain charge stabilization.
What is the proximity effect in enzyme catalysis?
Bringing substrates close together increases the reaction rate.
How does the proximity effect influence reactants?
It increases the effective concentration of reactants.
Why do reactions often fail?
Molecules collide rarely or incorrectly.
How do enzymes affect reaction rates?
Enzymes hold molecules in direct contact, reducing entropy and speeding up reactions.
What is a key function of enzymes?
They orient substrates in the proper alignment for reactions.
What happens with improper orientation of substrates?
No reaction occurs.
What is the impact of enzymes on molecule collisions?
Enzymes prevent random collisions by ensuring correct alignment.
What does the Induced Fit Model explain?
The substrate binding causes a conformational change in the enzyme.
What occurs to the enzyme during substrate binding?
The enzyme almost fully encloses the substrate.
What is the concept of induced fit in enzymes?
Enzymes undergo conformational changes to better fit substrates.
What are the four aspects of the conformational changes in enzymes?
How do enzymes reduce the energy barriers during catalysis?
By shielding from solvent, enzymes lower the ordered water shell.
Why is flexibility important in enzymes?
What does induced fit ensure about enzyme activity?
Enzymes are complementary to the transition state, not just the substrate.
What is a risk of tight binding to substrates?
It can lead to inhibitor-like effects during catalysis.
What does hexokinase catalyze?
Phosphorylation of glucose by ATP.
What phenomenon is described by the significant conformational change of hexokinase?
Induced fit.
What are the shape changes of hexokinase used for?
When does phosphate transfer occur in hexokinase's process?
Only when glucose is properly bound.
What residues normally donate hydrogen bonds in the active-site oxyanion hole of the protease?
What is the impact of the Gly → Asp mutation in the protease?
Enzyme activity decreases to 55%.
What charge does Asp carry?
Negatively charged
What is the charge of the oxyanion?
Negatively charged
What effect does charge repulsion have on stability?
Reduces stability of the transition state
Why is transition-state stabilization important?
Essential to catalytic efficiency
What happens when Gly is replaced with Asp?
What is chymotrypsin an example of?
Enzyme evolution and physiology
Define divergent evolution.
Proteins evolve from a common ancestor
What are the determinants of substrate specificity?
Involves various structural and chemical interactions.
What does enzyme activation refer to?
The process that activates a dormant enzyme.
What is enzyme inhibition?
Process by which enzyme activity is decreased.
What leads to different substrate specificities among enzymes?
What are the key reasons for the conserved structure of enzymes?
What are examples of serine proteases?
What do chymotrypsin, trypsin, and elastase share?
What does the evolutionary specialization of serine proteases reflect?
Their different substrate preferences
What is the substrate preference for Chymotrypsin?
What substrate does Trypsin prefer?
What is the substrate preference for Elastase?
What is convergent evolution?
What does natural selection favor in convergent evolution?
Give an example of convergent evolution.
What type of enzyme is subtilisin?
Bacterial serine protease
Does subtilisin show similarity to chymotrypsin?
No sequence or structural similarity
What catalytic triad does subtilisin share?
Asp-His-Ser catalytic triad
What is the purpose of the specificity pocket in serine proteases?
Determines fit of amino acid side chain on substrate
What does the specificity pocket accommodate?
The residue N-terminal to the scissile bond
Why is the catalytic triad significant in evolution?
It was rediscovered independently due to its power
What does the presence of the catalytic triad indicate?
Functional constraints shape enzyme active sites
What contributes to substrate specificity in enzymes?
How do slight changes in residues affect enzyme specificity?
They dramatically alter enzyme specificity.
What is a zymogen?
Inactive precursors of enzymes.
What regulates protease activity in organisms?
How are zymogens activated?
By proteolysis after secretion into the small intestine.
What triggers conformational changes in zymogens?
Proteolysis.
What is the inactive form of chymotrypsin?
Chymotrypsinogen
What process activates chymotrypsinogen?
Proteolytic cleavages
What are the key components aligned during chymotrypsin activation?
What changes occur during the activation of chymotrypsinogen?
Why do proteases remain inactive until activation?
To prevent tissue digestion.
What happens if the activation changes do not occur?
The zymogen remains inactive.
What does activation of the enzyme make it?
Catalytically competent.
What synthesizes digestive zymogens and protease inhibitors?
What organ produces additional protease inhibitors?
How do protease inhibitors protect tissues?
What do protease inhibitors mimic?
What do protease inhibitors block?
What is a characteristic of protease inhibitors?
How do protease inhibitors affect the active site?
What does the safety mechanism in proteases prevent?
What is the key mechanism of blood coagulation?
A protease cascade.
What causes a blood clot to form?
What happens without blood clotting?
Cells and plasma would leak out of the vessel.
What do clots contain?
What does the fibrin mesh do?
What is the role of platelets in clotting?
Provide rapid initial plugging.
What is the function of fibrin in a clot?
Forms a structural scaffold that stabilizes the clot.
What does clot formation prevent?
Prevents blood loss and allows time for healing.
What is the molecular mass of fibrinogen?
~340,000.
What is the structure of fibrinogen?
Contains three pairs of polypeptide chains.
What is the process of converting fibrinogen to fibrin called?
Coagulation.
What is removed from fibrinogen to trigger polymerization?
What happens to fibrinogen after peptide removal?
What role does proteolysis play in fibrin assembly?
It exposes binding sites for self-assembly.
What is the function of the polymerized fibrin network?
What defines a cascade in coagulation?
What is the result of a small initial trigger in the coagulation cascade?
It produces large activation at the pathway's end.
What are the key features of cascades in biological processes?
How does Factor Xa relate to prothrombin?
Factor Xa catalyzes the conversion of prothrombin to thrombin.
Which factors activate Factor X?
What role does tissue factor play in the body?
Tissue factor exposes itself when a blood vessel is broken, triggering the coagulation cascade.
What reaction does thrombin catalyze?
Thrombin converts fibrinogen into fibrin.
Why is Factor Xa crucial in the clotting process?
Factor Xa is an upstream activator that leads to the formation of thrombin.
How do protease cascades compare to the blood coagulation cascade?
Blood coagulation cascades are more regulated than protease cascades seen in digestion.
What is one form of hemophilia caused by?
A deficiency in Factor IX.
What occurs without Factor IX?
How do human coagulation factors function?
They circulate as inactive precursors until activated by proteolysis.
What ensures the regulation of coagulation factors?
List some human coagulation factors.
What does Antithrombin do?
Inhibits clotting.
What happens with a deficiency of Antithrombin?
What balance does Antithrombin help maintain?
What condition does a deficiency of Antithrombin lead to?
Hypercoagulation.
What essential group do myoglobin and hemoglobin contain?
Heme, a prosthetic group for reversible O2 binding.
How does myoglobin bind oxygen?
Binds based on oxygen concentration and follows a hyperbolic binding curve.
Why does biology use metal-containing cofactors like heme?
To solve the problem of oxygen transport due to poorly soluble free oxygen.
What is the structure of myoglobin?
Monomeric (single polypeptide) made of 153 amino acids and eight a-helices (A-H).
How does distal His reduce CO toxicity?
Forces CO to bind at an angle, decreasing its preference for Fe2+.
What is unique about myoglobin's O2-binding curve?
It is hyperbolic due to having one O2-binding site.
What optimizes O2 binding in the heme pocket?
Geometry and amino acids minimize risk of reactive oxygen species (ROS) formation.
How does free heme bind CO?
Extremely strongly; globin structure reduces CO affinity by 20,000-fold to ~40-fold.
What do all globins share?
They share the globin fold and similar tertiary structures despite low sequence identity.
What is divergent evolution in relation to globins?
Different globins specialize for different tissues and stress conditions.
What forces hold the hemoglobin tetramer together?
What causes the T to R transition in hemoglobin?
What is the effect of O2 binding on hemoglobin?
What are the two models of cooperative binding?
What is BPG?
BPG (2,3-bisphosphoglycerate) is a heterotropic allosteric modulator that lowers hemoglobin's oxygen affinity.
Where does BPG bind in hemoglobin?
BPG binds to the central cavity between the β subunits, but only in the T state.
How does fetal hemoglobin interact with BPG?
Fetal hemoglobin (α2γ2) binds BPG more weakly, resulting in a higher O2 affinity.
What is the role of BPG in hemoglobin function?
BPG ensures hemoglobin releases sufficient O2 in tissues.
How does fetal hemoglobin extract O2?
Fetal hemoglobin extracts O2 from maternal blood by having weaker BPG binding and higher O2 affinity.
How are hemoglobin variants typically named?
Variants are usually named based on the location where they were first identified.
What can mutations alter?
How does hemoglobin's structure affect its function?
What happens to hemoglobin under deoxygenated conditions?
The hydrophobic patch interacts with neighboring Hb, causing polymerization.
What are the consequences of sickle-shaped cells?
What happens to sickled RBCs in oxygenated state?
Depolymerization occurs, restoring a more normal shape.
What causes the shape change in sickled RBCs?
Polymerized hemoglobin pushing against the RBC membrane.
What is the primary factor leading to sickling in sickle cell disease?
Polymerization of mutated hemoglobin.
What is true about most hemoglobin variants?
What is essential to maintain hemoglobin function?
How do genetic variations affect proteins?
What factors affect protein function?
What happens due to changes in primary structure?
Altered tertiary and quaternary interactions lead to functional changes.
What are the three major cytoskeletal systems?
What kind of stability does the actin helix provide?
Structural stability and allows binding of regulatory proteins.
What are the three essential functions of actin dynamics?
What is the function of treadmilling in cells?
Allows actin to shift filaments within the cytoskeleton without full disassembly.
What are the components of tubulin dimers?
What is the structure of microtubules?
Hollow tubes made of 13 protofilaments arranged in a cylinder.
How do tubulin dimers affect microtubule dynamics?
The structural difference between α and ß subunits drives the dynamics.
How are tubulin dimers arranged in microtubules?
They assemble head-to-tail, imparting polarity to the microtubules.
What are microtubules used for in cells?
What is the dynamic behavior of microtubules during division?
They allow for 'search and capture' of chromosomes.
What role do intermediate filaments play?
Provide mechanical stability, especially in stress-experiencing tissues.
What is unique about collagen's amino acid composition?
It has a repeating pattern rich in Glycine, Proline, and hydroxyproline
What are essential processes of motor proteins?
What type of transport does kinesin generally mediate?
Kinesin mediates anterograde transport (away from center).
What is the function of kinesin with regard to cargo?
Kinesin transports cargo processively along microtubules.
Describe the movement of kinesin.
What does processivity mean in kinesin movement?
Kinesin can take many steps without detaching, facilitating long-distance transport.
Why is processivity important for kinesin?
It allows kinesin to transport cargo over long distances, such as along axons.
What is the significance of the kinesin reaction cycle?
It details the stepping mechanism for kinesin as it moves along a microtubule.
What do cytoskeletal tracks and motor proteins facilitate?
Intracellular transport and movement mechanisms
Name a way to increase reaction rates in living systems.
What is a challenge of increasing reactant concentrations in cells?
How do temperature and concentration increases work?
By raising the effective collision frequency of molecules.
How do enzymes help biological systems?
How do enzymes differ from chemical catalysts?
Enzymes require milder conditions compared to many chemical catalysts.
What is the active site of an enzyme?
A specialized microenvironment precisely shaped for the substrate.
Why is enzyme regulation important?
How do chemical catalysts compare to enzymes?
Chemical catalysts cannot adapt or respond; enzymes can.
What is the benefit of enzymatic rate enhancement?
Enzymes significantly speed up biochemical reactions.
How much do enzymes accelerate reactions?
Factors of \(10^0\) to \(10^{12}\) (hundreds of millions to trillions times faster).
How do enzymes affect thermodynamic favorability?
They increase the reaction rate without altering overall $ riangle G$ (thermodynamic favorability).
What do most biochemical reactions involve?
What does the movement category in enzymes indicate?
Some enzymes catalyze transport, not chemical transformation.
What must occur for a biochemical reaction to proceed?
What is activation energy (AG‡)?
Energy required for reactants to undergo changes to become products.
How do enzymes affect reaction rates?
Enzymes accelerate reactions by lowering the activation energy.
List the three catalytic mechanisms of enzymes.
What roles do amino acid side chains play in enzymes?
They participate in catalytic mechanisms to facilitate chemical reactions.
What is essential for a reaction to proceed even if it's thermodynamically favorable?
Reactants must be able to approach closely.
What is the activation energy represented as?
The energy difference between reactants and the transition state (AG‡).
How does activation energy affect reaction rate?
What fraction of molecules reach the transition state at a given moment?
Only a small fraction of molecules.
How do enzymes affect the transition state?
They stabilize the transition state, increasing the reaction rate.
What happens when there are more transition state molecules present?
More product formation and a faster reaction.
Does lowering activation energy change the AG of the reaction?
No, it does not change AG of the reaction.
What do enzymes accelerate?
Both forward and reverse reactions, by stabilizing the transition state.
What is Acid-Base Catalysis in enzymes?
What does Base Catalysis do?
What is the purpose of Acid-Base Catalysis?
What is Covalent Catalysis in enzymes?
What are the steps in Covalent Catalysis?
What effect does covalent catalysis have on the reaction pathway?
It changes to one with lower overall activation energy.
What is true about the intermediate in covalent catalysis?
It is more stable than the TS but still transient.
How do metal ions assist catalysis?
How do metals influence reaction energetics?
By holding substrates in specific conformations or stabilizing charged intermediates.
Which amino acids can act in acid-base catalysis?
Amino acids with side-chain groups that can donate/accept H+.
What do nucleophilic amino acids provide?
Electron-rich groups capable of forming covalent intermediates.
What is the role of nucleophilicity in catalysis?
Enables formation of enzyme-substrate covalent intermediates.
What role do metal ions play in chemical reactions?
They stabilize intermediates or TS species, lowering \(ΔG^‡\).
What does Ser195 require to be nucleophilic enough for catalysis?
His57 removes Ser195's proton, activating it as an alkoxide.
What role does Asp102 play in the activation of Ser195?
It stabilizes the positively charged His57 during catalysis.
What does the triad involving Ser195 achieve?
Why is the positioning of the substrate's scissile bond important?
It must be near Ser195 for effective catalysis.
How does the enzyme active site contribute to catalysis?
It precisely orients substrates to reduce entropy cost.
What ensures efficient cleavage in enzymatic reactions?
Positioning combined with triad chemistry enhances the process.
What are the core mechanistic features of chymotrypsin?
What are the steps involved in the reaction of chymotrypsin?
What is the role of the oxyanion hole in the chymotrypsin mechanism?
It stabilizes the tetrahedral intermediate.
What does His57 do in the chymotrypsin mechanism?
It facilitates proton transfers in acid-base catalysis.
What are the intermediates formed in the chymotrypsin reaction?
What does the Lock-and-Key Model imply?
The substrate fits precisely into the active site, like a key into a lock.
What is a limitation of the Lock-and-Key Model?
It doesn't explain how the active site can bind products.
What is transition-state stabilization?
It's the process of lowering the energy of the transition state to enhance catalysis.
What is electrostatic catalysis?
The stabilization of charged transition states using complementary charges in the active site.
How do enzyme-transition state interactions compare to enzyme-substrate interactions?
They are stronger than enzyme-substrate interactions.
What does TS in biochemistry refer to?
TS stands for transition state, a high-energy configuration in enzymatic reactions.
Why do enzymes bind most tightly to the transition state?
What are the key features of serine proteases?
How do serine proteases optimize their active sites?
They stabilize negatively charged transition states.
What is the role of Ser195 in Serine Protease mechanism?
It facilitates a rapid nucleophilic attack.
What characterizes the tetrahedral intermediate in the transition state?
What stabilizes the negatively charged oxyanion?
How does stabilizing the transition state (TS) affect AG‡?
Stabilizing the TS more than the enzyme-substrate complex (ES) lowers AG‡.
What is the function of the oxyanion hole?
It provides electrostatic stabilization to an unstable structure.
Which residue is involved in stabilizing the positively charged His57?
The low-barrier hydrogen bond forms between residues involved in His57 stabilization.
How do low-barrier hydrogen bonds compare to normal hydrogen bonds?
They are stronger than normal hydrogen bonds.
What effect do low-barrier hydrogen bonds have on the transition state?
They lower the energy of the transition state.
What role do low-barrier hydrogen bonds play in the catalytic cycle?
They help maintain charge stabilization.
What is the proximity effect in enzyme catalysis?
Bringing substrates close together increases the reaction rate.
How does the proximity effect influence reactants?
It increases the effective concentration of reactants.
How do enzymes affect reaction rates?
Enzymes hold molecules in direct contact, reducing entropy and speeding up reactions.
What is the impact of enzymes on molecule collisions?
Enzymes prevent random collisions by ensuring correct alignment.
What does the Induced Fit Model explain?
The substrate binding causes a conformational change in the enzyme.
What is the concept of induced fit in enzymes?
Enzymes undergo conformational changes to better fit substrates.
What are the four aspects of the conformational changes in enzymes?
How do enzymes reduce the energy barriers during catalysis?
By shielding from solvent, enzymes lower the ordered water shell.
Why is flexibility important in enzymes?
What does induced fit ensure about enzyme activity?
Enzymes are complementary to the transition state, not just the substrate.
What is a risk of tight binding to substrates?
It can lead to inhibitor-like effects during catalysis.
What residues normally donate hydrogen bonds in the active-site oxyanion hole of the protease?
What happens when Gly is replaced with Asp?
What are the determinants of substrate specificity?
Involves various structural and chemical interactions.
What leads to different substrate specificities among enzymes?
What are the key reasons for the conserved structure of enzymes?
What do chymotrypsin, trypsin, and elastase share?
What does the evolutionary specialization of serine proteases reflect?
Their different substrate preferences
What is the purpose of the specificity pocket in serine proteases?
Determines fit of amino acid side chain on substrate
Why is the catalytic triad significant in evolution?
It was rediscovered independently due to its power
What does the presence of the catalytic triad indicate?
Functional constraints shape enzyme active sites
What contributes to substrate specificity in enzymes?
How do slight changes in residues affect enzyme specificity?
They dramatically alter enzyme specificity.
What are the key components aligned during chymotrypsin activation?
What changes occur during the activation of chymotrypsinogen?
What does the safety mechanism in proteases prevent?
What does the fibrin mesh do?
What happens to fibrinogen after peptide removal?
What is the function of the polymerized fibrin network?
What defines a cascade in coagulation?
What is the result of a small initial trigger in the coagulation cascade?
It produces large activation at the pathway's end.
What are the key features of cascades in biological processes?
How does Factor Xa relate to prothrombin?
Factor Xa catalyzes the conversion of prothrombin to thrombin.
What role does tissue factor play in the body?
Tissue factor exposes itself when a blood vessel is broken, triggering the coagulation cascade.
Why is Factor Xa crucial in the clotting process?
Factor Xa is an upstream activator that leads to the formation of thrombin.
How do protease cascades compare to the blood coagulation cascade?
Blood coagulation cascades are more regulated than protease cascades seen in digestion.
How do human coagulation factors function?
They circulate as inactive precursors until activated by proteolysis.
What ensures the regulation of coagulation factors?
What happens with a deficiency of Antithrombin?
What balance does Antithrombin help maintain?
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