Unit 1: Enzymes

Question 1

What is the equilibrium constant equation ?

Answer 1

K = Kf/ Kr

Question 2

What is the transition state ?

Answer 2

A part of any chemical reaction where old bonds are incompletely broken and new bonds are incompletely formed

Question 3

What are 3 ways enzymes lower the transition state of a reaction ?

Answer 3

• Proximity
• Orientation
• Microenvironment

Question 4

What is proximity in relation to enzymes and the transition state ?

Answer 4

When enzymes bring substrates together and this increases rate by 10^5-10^8

Question 5

What is orientation in relation to enzymes and transition state ?

Answer 5

When an enzyme orients substrates so that they can best attain the most favourable position to achieve transition state

Question 6

What is microenvironment in relation to enzymes and transition state ?

Answer 6

The idea that an active site can provide protection to a non aqueous environment

Question 7

What is the optimal conformation of a binding site ?

Answer 7

One that precisely contours the transition state of the reactants

Question 8

How is catalysis achieved ?

Answer 8

When amino acid residues are brought close together in their tertiary structure to form an active site

Question 9

What is the induced fit model of enzyme action ?

Answer 9

The idea that the active site moulds itself around the substrate. This leads to the enzyme changing conformation upon substrate binding

Question 10

What is the Michaelis-Menten theory of kinetics ?

Answer 10

That enzymes act by increasing the rates of both the forward and reverse reactions equally. This does not change the equilibrium constant

Question 11

What is the Michaelis-Menten kinetics equation ?

Answer 11

S + E <——> ES —–> P + E

Question 12

What does E stand for in the Michaelis-Menten kinetics equation ?

Answer 12

E = Enzyme

Question 13

What does S stand for in the Michaelis-Menten kinetics equation ?

Answer 13

S = Substrate

Question 14

What does ES stand for in the Michaelis-Menten kinetics equation ?

Answer 14

ES = Enzyme substrate complex

Question 15

What does P stand for in the Michaelis-Menten kinetics equation ?

Answer 15

P = Product

Question 16

What is a hyperbolic curve ?

Answer 16

The relationship between the rate of reaction and concentration of the substrate

Question 17

What is the term used for the effect of temperature on reaction rate ?

Answer 17

Fundamental

Question 18

What is the term used for the effect of temperature on denaturation rate ?

Answer 18

Consequential

Question 19

What does the PH optimum often reflect ?

Answer 19

PH sensitive events at the active site

Question 20

What is the idea of an enzyme pathway ?

Answer 20

That enzymes rarely operate alone, they are part of a chain of reactions known as a pathway.

Question 21

What is an allosteric enzyme ?

Answer 21

Type of enzyme that can change its activity or shape in response to the binding of a molecule at a site other than its active site

Question 22

What shape do allosteric enzymes display on a graph ?

Answer 22

A sigmoidal S-shaped curve

Question 23

What is the function of an allosteric inhibitor ?

Answer 23

• Stabilising the inactive state
• This decreases affinity of enzyme for the substrate

Question 24

What is the function of an allosteric activator ?

Answer 24

• Stabilising the active state
• This increases the affinity of the enzyme for the substrate

Question 25

How can enzyme activity be controlled/ regulated (4) ?

Answer 25

• Control by covalent modification, especially phosphorylation
• Control by regulatory proteins and/ or nucleotides
• Control through ion binding
• Control through proteolysis

Question 26

What are enzymes that bring about phosphorylation called ?

Answer 26

Kinases- they induce phosphorylation

Question 27

What are enzymes that cause dephosphorylation called ?

Answer 27

Phosphatases- they cause dephosphorylation

Question 28

What are the 2 forms of kinase ?

Answer 28

• Serine/threonine kinases
• Tyrosine kinases

Question 29

What is the EF hand motif ?

Answer 29

The hand motion that says the calcium binding site is located in a tight loop connecting two alpha helixes (E and F)