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BCT Enzymes
Enzymes Learning Objectives
15
Biochemistry
Professional
11/03/2013

Additional Biochemistry Flashcards

 


 

Cards

Term
First and Second Law of Thermodynamics
Definition
1st: Energy is conserved; cannot be created or destroyed
2nd: Entropy (S) tends to increase
Term
Define the change in free energy (delta G) and delta G for a reaction.
dG=0 is...
dG<0 is...
dG>0 is...
Definition
-Amount of free energy consumed or liberated during a chemical reaction

dG=0 is...Equilibrium
dG<0 is...Spontaneous (Exergonic)
dG>0 is...Energy needed (Endergonic)
Term
Equation relating dG (and dG0') to [products] and [reactants]
Definition
[image]
Term

How do enzymes acts as catalysts?

 

How do they affect Gibbs free energy of activation?

Definition

-Do not change eq of chemical rxn, but stabilize transition state

-Lower activation energy

Term
Induced Fit vs Lock-and-Key
Definition

Induced Fit: substrate binds to the enzyme's activation site in which it mostly fits, enzyme then changes shape to better fit the substrate

 

Lock and Key: substrate binds to a specific enzyme at the activation site in which it fits perfectly

 

In reality, both of these occur

Term
4 properties of enzyme catalysts
Definition

1. Specificity

2. Stabilize transition state, do not change thermodynamics

3. Do not change [S] and [P] at Keq, but decrease amount of time required to reach eq

4. Bring substrates together at optimal orientation in the active site

Term
Draw the Michaelis-Mentin kinetics profile of an enzyme
Definition
[image]
Term

Define and give units for:

 

Vmax

Km

Kcat

 

Definition

Vmax (μmol product/min/mg enzyme) is velocity of reaction when all enzyme active sites are filled

Km (mM or μM) is [S] at (1/2)Vmax and measures affinity for substrate (High Km=Weak Binding, Low Km=Strong Binding)

Kcat (s-1) is turnover rate

Kcat/Km (s-1M-1) measures catalytic efficiency

Term
Why are enzymes with very high Kcat/Km ratios efficient catalysts?
Definition

·         A high Kcat indicates a high number of enzymatic reactions catalyzed per second.

A low Km indicates strong binding between substrates and enzymes


High divided by low gives very high ratio indicating that a large number of reactions can be catalyzed at maximum efficiency

Term
Explain the kinetics of Zero, First, an Second order reactions
Definition

Zero: independent of [S]

First: 1 substrate, rxn rate dependent on [S] and decreases over time as less substrate is available (half life)

Second: 2 substrates, rxn rate dependent on both [S]s

Term
Reversible vs Irreversible Inhibition
Definition

Reversible: non-covalent bond b/w inhibitor and enzyme; can be removed and enzyme reused

 

Irreversible: covalent bond between inhibitor and enzyme; permanently inhibits enzyme

(Ex: Penicillin, Sarin)

Term

Reversible Inhibition: Competitive 


What is it? Effect on Km and Vmax?

Definition

Inhibitor structurally resembles substrate and binds to active site

 

Increase Km

No change Vmax

Term

Reversible Inhibition: Noncompetitive

What is it? Effect on Km and Vmax?

Definition

Inhibitor binds to allosteric site, affecting shape of active site so substrate doesn't quite fit

 

No change Km

Decrease Vmax

Term
Why is phosphorylation by kinases linked to the energy status of the cell?
Definition

-Kinases phosphorylate Serine, Threonine, or Tyrosine (have OH groups)

 

Term

Catalytic Triad


What is it? What's the mechanism? What does it do?

Definition

-Refers to three amino acid residues functioning together at active site of certain hydrolase and transferase enzymes

 

-Generates nucleophilic residue for covalent catalysis by creating charge-relay network to polarize and activiate the nucleophile, which attacks the substrate, forming a covalent intermediate which is then hydrolyzed to regenerate the free enzyme.

 

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