3.1.4.2 MANY PROTEINS ARE ENZYMES

Question 1

What are enzymes?

Answer 1

• biological catalysts:
• speed up the rate if reaction without being used up
• provide an alternate pathway with lower activation energy

Question 2

Are enzymes globular or fibular proteins?

Answer 2

Globular proteins

Question 3

What can enzymes be?

Answer 3

Intracellular/ extracellular

Question 4

What are intracellular enzymes?

Answer 4

Produced and function inside the cell, made by free ribosomes

Question 5

What are extracellular enzymes?

Answer 5

• Secreted by cells and catalyst reactions outside cells
• made by ribosomes on the RER (eukaryotes)

Question 6

What is a catabolic reaction?

Answer 6

Involves the breakdown of complex molecules into simpler products:
- happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules
- e.g. cellular respiration and hydrolysis

Question 7

What is an anabolic reaction?

Answer 7

• involves the building of more complex molecules from simpler ones by drawing two or more substrates into the active site forming bonds between then and releasing a single products
• e.g. protein synthesis + photosynthesis

Question 8

What is the lock and key hypothesis?

Answer 8

The enzyme splits the substrate molecule into two smaller products, the enzyme can catalyse the reverse reaction

Question 9

What is the induced fit theory?

Answer 9

• as substrate is bonding
• triggers a change in active site
• tertiary structure change in the active site shape
• breaks hydrogen bonds- enzyme fits substrate more closely to give the enzyme- substrate complex

Question 10

6 Factors affecting rate of enzyme reaction?

Answer 10

1. Temp
2. PH
3. Conc of enzyme
4. Conc of substrate
5. Inhibitors (competitive and non-competitive)
6. Cofactors/ prosthetic group

Question 11

What is the temperature, kinetic energy and collision theory?

Answer 11

• higher temp= higher KE
• more KE= more collisions
• more ESC’s form= more product forms
• rate of reaction increases

Question 12

What is the Q10 theory?

Answer 12

• Q10 is the factor by which the rate of reaction increases for every 10 DC rise
• this is typically around 2, but varies between enzymes

Question 13

What is protein denaturing?

Answer 13

Breaking of the bonds holding the enzyme’s tertiary structure in place:
- e.g. London bonds + hydrogen forces will be the first to go- resulting in the tertiary structure being disrupted and the active site changing shape

Question 14

How could you change bonding in the enzyme to give greater thermostability?

Answer 14

Use stronger bonds such as covalent bonds:
- e.g. disulphide bridges

Question 15

How to reduce the effect of a competitive inhibitor?

Answer 15

Add more substrate

Question 16

What is a competitive inhibitor?

Answer 16

• inhibitor molecule similar shape to substrate
• therefore complementary shape to A.S.
• forms enzyme- inhibitor complex
• reduces number of active sites available for substrate
• brining can be reversible
• inhibitor is competing with substrate

Question 17

What is a non-competitive inhibitor?

Answer 17

• binds somewhere other than the active site - allosteric site

Question 18

Competitive vs non- competitive inhibitor:

Answer 18

COMPETITIVE:
- binds to active site
- similar structure to substrate
- doesn’t change shape of active site
- increasing substrate concentration means it can outcompete inhibitor
NON-COMPETITIVE:
- binds somewhere other than the active site- allosteric site
- does change shape of AS
- increasing substrate concentration has no effect

Question 19

Can competitive inhibitors denature the enzyme?

Answer 19

Yes because they bind permanently to the active site