Enzymes

Question 1

What are enzymes

Answer 1

• Enzymes are catalysts
• Increase reaction rate
• Do not alter the equilibrium
  of a chemical reaction
• Accelerate attainment of
  equilibrium
• they lower the activation energy

Question 2

What is the Transition state

Answer 2

This is the activation energy

Question 3

What is the formation of an enzyme-substrate complex

Answer 3

• Binding of enzyme to a substrate is key to enzymatic catalysis
• Substrates bind to a specific region of an enzyme –
  the active site

Question 4

How is the active site formed

Answer 4

The active site is formed by amino acids from different parts of the primary sequence

Question 5

How large is the active site

Answer 5

The active site occupies a small part of the enzyme

Question 6

Where are active sites found in the enzyme
Why are they found there

Answer 6

Active sites are clefts (Between Subunits) or crevices (folds in the enzyme)
They are clefts or crevices so they can be hidden from water as water can cause problems for chemical reactions

Question 7

What is the induced fit model

Answer 7

THE Active site of the enzyme is changed slightly to better fit the substrate after the substrate binds
This allows proper catalytic function

Question 8

How are substrates bound to enzymes

Answer 8

Substrates are bound to enzymes by multiple weak bonds
NOT STRONG COVALENT INTERACTION

Question 9

How are substrates bound to enzymes?

Answer 9

Substrates are bound to enzymes by multiple weak bonds
NOT STRONG COVALENT INTERACTION

Question 10

Why do enzyme substrates have a weak bond

Answer 10

A weak bond so substrate can bind and product can be released effectively

Question 11

How is the initial rate of reaction taken

Answer 11

V0 = initial rate of reaction
Rate is taken from Zero and Tangent is used.

Question 12

How does substrate concentration affect the rate of reaction

Answer 12

The rate of reaction depends on the substrate concentration
Higher conc higher rate of reaction

Question 13

What is the Michaelis-Menten equation

Answer 13

V0 = Vmax [S] / Km + [S]

Km = Michaelis constant (M)
Vmax = maximal velocity (mol/min)
[S] = concentration of substrate

Question 14

What is Km

Answer 14

Km is the concentration of substrate which permits the enzyme to achieve half Vmax.

Question 15

What does a Low Km Value mean

Answer 15

The lower the Km value the higher the affinity of the enzyme for the substrate

Question 16

What is Vmax

Answer 16

the rate of the reaction at which the enzyme shows the highest turnover

Question 17

What is “1 Unit”

Answer 17

1 unit = the amount of enzyme that produces 1mmol of product per min under standard conditions
* Often expressed as a standardised rate
e.g. per litre (L) of serum or per gram (g) of tissue

Question 18

How is the rate of reaction affected by enzymes

Answer 18

The rate of an enzyme-catalysed reaction is proportional to the concentration of enzyme
* If you double the concentration of enzyme present then the measured rate of reaction doubles

Question 19

How to make the
The Lineweaver-Burk plot

Answer 19

1/V0 = km/Vmax .1/(S) + 1/ Vmax = Y= mx + c

Question 20

What is a competitive inhibitor

Answer 20

• Binds at the active site
• Reduces the proportion of enzyme molecules bound to a substrate
• Similar shape as substrate thus binds instead of substate.

Question 21

What is a non-competitive Inhibitor?

Answer 21

• Binds at free enzyme away from the active site
• Changes the shape of the active site
• Decreases concentration of functional enzyme

Question 22

What happens when more substrate is added to a competitive inhibitor

Answer 22

Adding enough substrate will always overcome the effect of the inhibitor, so no effect on Vmax

Question 23

What happens to the Km and Vmax in competitive inhibitors when more substrate is added

Answer 23

Km increases; As higher CONC outcompetes inhibitor
Vmax is unaffected; Vmax doesn’t change

Question 24

What happens when more substrate is added to a NON- competitive inhibitor

Answer 24

Inhibitor lowers the effective concentration of free enzyme so adding more substrate will not overcome the effect

Question 25

What happens to the Km and Vmax in NON- competitive inhibitors when more substrate is added

Answer 25

Km unaffected; Adding more Conc won’t affect outcompete inhibitor
Vmax decreases; As the rate of reaction decreases

Question 26

What is Enzyme Activity

Answer 26

Enzyme activity is measured in units which indicate the rate of the reaction catalysed by that enzyme expressed as micromoles of substrate transformed