Boehmer Lecture 8
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- What is allostery in enzymes?
- Activity of enzyme modulated by positive or negative allosteric effectors.
- What are isozymes?
- Distinct polypeptides that catalyze the same reaction to fine tune metabolism (e.g.: muscle isozyme works for anerobic and high Km, heart isozyme works for aerobic at low Km)??
- What are three ways to activate enzyme activity?
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1) Phosphorylation (eg: Pyrvuate kinase)
2) Proteolytic (eg: zymogen activation by trypsin and blood coagulation cascade)
3) Cooperativity and alloery (hemoglobin) - What happens if there is a pyruvate kinase deficiency?
- Anemia - Atp required for biconcave shape, deficiency causes reduction in glycolysis and lowered ATP levels, which causes cells to be lost rapidly with anemia since precursor cells cnanot compensate sufficiently
- What important zymogens does trypsin activate?
- Proelastase to Elastase and chymotrypsinogen to chymotrypsin.
- What is the significance of the step between thrombin and fibrin in the blood coagulation cascade for blood clot formation?
- Thrombin will cleave at alpha and beta chain to remove tails, which allows fibrin to undergo polymerization to form a clot.
- What is the difference between homotropic and heterotropic effectors?
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Homotropic is where the molecule that induces the effect is similar to the substrate
Heterotropic is when the molecule that induces the effect is different from substrate. - What are the two models of homotropic effectors?
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1) Concerted - dimeric enzyme, binding of first substrate has effect on binding of second substrate
2) Sequential -four subunits, binding of 1st substrate facilitates binding of following substrates - What are the inactive and active states called?
- T and R
- For a protein to exhibit cooperativity, what must its Hill plot slope be? for non-cooperativity
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greater than 1 to be cooperative
Non-cooperative=1 - Describe monomeric heterotropic effects.
- 3 binding sites - substrate, activator and inhibitor. Activator or inhibitor can bind, and then substrate either can bind or cannot bind to the one subunit (monomeric).
- What is heterotropic allostery?
- Involves molecules other than substrate in pathway.
- What are the two types of heterotropic allostery?
- Monomeric and oligomeric.
- Will increase in BPG (2,3-Biphosphoglycerate) increase or decrease the O2 affinity of hemoglobin, and how is this advantageous at high altitudes?
- It will lower the affinity of hemoglobin for oxygen. This will allow more oxygen to be delivered to the tissues at high altitudes.
- What is the difference b/n non-competitive inhibition and allostery?
- You don't change the Km value in non-competitive inhibition, whereas in allostery you prevent substrate from binding in the first place.
- Protein-protein interactions have what consequence for regulation, specifically with Protein Kinase A and cAMP?
- keep enzyme in inactive state until activated
- What is the mechanism of ubiquitinization for degradation of proteins in proteasomes to smaller peptides?
- Ubiquitin added to lysine sidechain via isopeptide bond. Involves three distinct enzymes in a multi-step process.