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Flashcards in Enzymes Deck (59)
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1

What is the activation energy?

The minimum amount of energy required for a reaction to occur

2

Why are enzymes better for increasing the rate of a reaction rather than temperature and concentration

You want to maintain the temperature and concentration at a set point

3

What are enzymes?

Biological catalysts that increase the rate of reaction by lowering the activation energy

4

Why don't enzymes affect the reaction equilibrium

It catalysed the reaction equally forwards and backwards

5

What is the active site?

The place where substrates bind and the chemical reaction occurs

6

What is the lock and key hypothesis

Where active sites are complementary in shape to the substrate

7

What is the INDUCED fit hypothesis

Binding of substrates cause conformational changes in the enzyme

8

What type of bonds are formed between the active site and substrate?

Week hydrogen binds which hold the substrate in the correct orientation but also allows it to be released

9

What does the Michaelis-Menton model propose?

That a specific complex between the enzyme and the substrate is a necessary intermediate. Represents that the rate is related to concentration of substrate

10

What is Vmax

The maximal rate when all enzymes active sites are saturated with substrate

11

What is Km?

The substrate concentration that gives half maximal velocity

12

What does a low Km value tell you?

The enzyme has a high affinity for the substrate

13

What is the lineweaver-Burk plot

Reciprocal graph that gives -1/Km at the X intercept and 1/Vmax at the y intercept

14

What is an enzyme inhibitor?

Molecules that slow down or prevent an enzyme reaction

15

What are the 2 types of inhibitors?

1. Irreversible - bind very tightly forming covalent bonds
2. Reversible - can freely dissociate as they don't form covalent bonds

16

What are the 2 types of reversible inhibitors

1- competitive (binds to active site. Affects Km not Vmax)
2- Non-competitive (bind to another site in the enzyme. Affects Vmax not Km)

17

Why do competitive inhibitors not affect Vmax?

Adding enough substrate will overcome the affect of the inhibitor so the maximum rate can still be reached

18

Why do competitive inhibitors affect Km?

The inhibitor competes with the substrate for the active site so the affinity decreases

19

Why do competitive inhibitors lower Vmax?

They decrease the turnover rate of the enzyme

20

Why does the active site of an enzyme only occur a small area?

A large proportion of the enzyme is needed to hold the shape of the active site

21

What is the units of enzyme activity

Micromoles per minute per litre

22

What affect does doubling the enzyme concentration have on the rate

It doubles the rate of reaction

23

Why does enzyme activity stay the same despite changes the enzyme concentration

The enzymes always work to the same activity. The rate at which they work doesn't not change.

24

What are the 2 long term regulation methods for enzymes

1. Change in protein synthesis
2. Change in protein degradation

25

What are the 2 short term regulation methods for enzymes

1. Changes in substate/product concentration
2. Change in enzyme conformation

26

State 3 ways in which enzyme conformation can be changed

1. Allosteric regulation
2. Covalent modification
3. Proteolytic cleavage

27

What graph shape do allosteric enzymes show

Sigmoidal

28

Why do allosteric enzymes show a sigmoidal graph for rate vs substrate concentration.

As the enzyme can exist in 2 forms (T and R state)

29

What do allosteric activators do

Increase the proportion of enzyme in the R state

30

What direction do allosteric activators shift the binding curve

Left