Enzymes

Question 1

6.6.What are enzymes?

Answer 1

Tertiary structure, globular proteins that are catalysts

• not changed by reaction
• can be used repeatedly so - effective in small amounts
• hv a high turn-over (catalyse many reactions per sec)

Question 2

What is a catalyst?

Answer 2

a molecule that speeds up a chemical reaction but remains unchanged/isn’t used up at the end

Question 3

Why will each enzyme only catalyse one specific reaction?

Answer 3

• enzyme, so active site has a specific 3D tertiary structure/shape
• so - active site only complementary to & will bind to 1 substrate
• to form an e-s complex

Question 4

What are the 2 types of metabolism?

Answer 4

(all reactions in the body)
1. Anabolic reactions: building up molecules e.g. protein synthesis
2. Catabolic reactions: breaking molecules down e.g. digestion

Question 5

How are enzymes secreted from cells?

Answer 5

by exocytosis

Question 6

Induced fit?

Answer 6

• Before reaction, active site is not complementary to substrate
• as substrate binds, the active site changes shape to become complementary to substrate - forming e-s complex
• this stresses/distorts bonds in substrate (due to enzyme moulding around substrate) - lowering the activation energy
  *accepted model

Question 7

Induced fit&raquo_space;> lock and key model, why?

Answer 7

Lock and key suggest AS is rigid structure & substrate is exact fit to AS…
Induced fit matches current observations that AS changes shape slightly upon binding to become a more exact fit

Question 8

For an enzyme to catalyse a reaction it must…?

Answer 8

• come into physical contact w substrate
• substrate must be complementary to active site
• they must collide w enough energy & suitable orientation

Question 9

How do enzymes speed up the rate of reactions?

Answer 9

Lower the activation energy needed for reactions to take place
(the minimum amount of energy required to activate a reaction)

Question 10

Temperature?

Answer 10

• too low: not enough kinetic energy (to move fast enough) for successful collisions between enzyme + substrate so - fewer e-s complexes
• too high: enzyme denatures, active site changes shape so - e-s complexes can’t form

Question 11

Why do enzymes denature if there’s too much kinetic energy?

Answer 11

• bonds holding amino acids in fixed 3D tertiary structure in active site broken

Question 12

pH?

Answer 12

too