Enzymes 1

Question 1

how do enzymes act as catalysts

Answer 1

lower activation energy by providing alternative transition state

Question 2

5 key features

Answer 2

1. Globular proteins
2. Show specificity
3. Catalysts
4. Sensitive to changes in physical and chemical environment
5. Their activity can be controlled

Question 3

Lysozome

2 points

Answer 3

1. enzyme in tears and secretions on exposed surfaces of body
2. attacks bacterial cell walls killing the bacteria (natural antibiotic)

Question 4

Lysozome

shape

Answer 4

includes a cleft into which part of the bacterial cell wall (made of peptidoglycan) can fit

Question 5

Lysozome

which bond does it break

Answer 5

bond between sugars 4 and 5 of a hexamer

Question 6

2 parts of AS

Answer 6

Substrate Binding Site

Catalytic Site

Question 7

lock and key

Answer 7

binding site has complementary shape to substrate(s)]

Question 8

induced fit

Answer 8

contact between part of the binding site and the substrate induces a change in shape of the active site to bind to the substrate

Question 9

4 levels of enzyme specificity

Answer 9

absolute

bond

group

stereo

Question 10

catalysts lower

Answer 10

activation energy

Question 11

catalysis

proximity

Answer 11

substrate molecules close together

Question 12

catalysis

orientation

Answer 12

substrates have correct relative orientation

Question 13

catalysis

Strain/distortion

Answer 13

binding puts strain on bond making it easier for reaction to occur

Question 14

acid-base catalysis

Answer 14

protons (H+) donated/accepted

Question 15

Covalent catalysis

Answer 15

temporary covalent bond between enzyme and substrate

Question 16

effect of time

start of reaction

Answer 16

very quick

Maximum ratio of S/E so greatest chance of collision

Question 17

effect of time

middle of reaction

Answer 17

amount of S decreases (it is converted to P) less chance of S colliding with E so rate of reaction decreases

Question 18

effect of time

end of reaction

Answer 18

Rate decreases until reaction reaches equilibrium (no net change in amount of S or P) when graph reaches plateau. Rate = 0

Question 19

dont understantd inital reaction velocity on graph

Answer 19

?

Question 20

IRV

Initial Reaction Velocity (t=0) =

Answer 20

x/y

used to compare enzyme activities

Question 21

Katal

Answer 21

1 Katal of enzyme activity produces 1 mole of product per second

or utilises one mole of substrate per second

(1 Katal = 1 mole/sec)

Question 22

Unit

Answer 22

1 Unit of enzyme activity produces 1 umole of product per minute

or utilises 1 umole of substrate per min

(1 Unit = 1 mmole/min)

Question 23

Turnover number (kcat)

Answer 23

the number of substrate molecules that can be converted to product by 1 enzyme molecule in 1 second

Question 24

Changes in pH affect

Answer 24

electrostatic bonds

Question 25

pH will decrease enzyme activity if

5 points

Answer 25

1. Overall 3-D structure of active site is altered
2. Group involved in binding to substrate changes charge
3. Group involved in the catalytic act changes charge
4. Group on substrate involved in binding to enzyme changes charge
5. Group on substrate involved in catalytic act changes charge

Question 26

Optimum pH range not always ~pH 7

e.g.

Answer 26

pepsin

Question 27

Two effects of temperature

Answer 27

kinetic

denaturing

Question 28

temperature
kinetic effect
3 points

Answer 28

1. Increased motion of molecules
2. Increased collisions between enzyme/substrate
3. Increased rate of reaction

Question 29

temperature
denaturing effect
5 points

Answer 29

1. Proteins take on the 3-D structure with lowest potential energy - increases their stability
2. Increased energy causes increased motion within the molecule as well as between molecules
3. Weak bonds in the tertiary structure (hydrogen bonds) are broken and new bonds form in different positions
4. New 3-D structures form
5. If the change in 3-D structure alters the active site of the enzyme so that it cannot catalyse the reaction it is said to be denatured

Question 30

Denaturing effect is due to both

Answer 30

temperature and time of exposure to that temperature

Question 31

Optimum temperature is not always ~37 ºC

Answer 31

depends on location and what reaction occurs