Enzymes

Question 1

Interaction of enzyme and substrate:

Answer 1

lock and key model

Question 2

protein catalyst

Answer 2

have great specificity for the reaction catalyzed and the molecules acted on

Question 3

substrates

Answer 3

reacting molecules

Question 4

products

Answer 4

substances formed by reaction

Question 5

How enzymes lower Activation energy Ea:

Answer 5

by increasing [substrates] at active site of enzyme

and by orienting substrates properly with respect to each other in order to form the transition state complex

Question 6

The effect of environment on enzyme activity

Answer 6

enzyme activity is significantly impacted by substrate concentration, pH, and temperature

Question 7

Effect of pH and temperature

Answer 7

each enzyme has specific pH and temperature optima
• denaturation
– loss of enzyme’s structure and activity when
temperature and pH rise too much above optima

Question 8

The regulation of metabolic pathways

Answer 8

pathways are regulated by adjusting the rate of one or more regulatory enzymes that governs the overall rate of the pathway

Question 9

types of enzyme regulation

Answer 9

allosteric enzymes

or covalent modification which can result in either positive or negative regulation of its activity

Question 10

allosteric enzymes have regulatory sites that are..

Answer 10

..not part of the active site

Question 11

allosteric effectors bind to sites on the enzyem …

Answer 11

…other than the active site

Question 12

allosteric enzyme

Answer 12

effector binding alters shape of active site

Question 13

patterns of regulation of metabolic pathways

Answer 13

feedback inhibition- regulates the pathway by using an end product allosterically inhibit an enzyme in the pathway (typically the first enzyme in the pathway or at a branch point_

Question 14

types of feedback inhibition

Answer 14

simple
concerted
cumulative

Question 15

simple feedback inhibition

Answer 15

A single end product inhibits an enzyme in a linear pathway.
• It is most efficient when it inhibits the first enzyme in the pathway. as product is used up, inhibition decreases and the pathway speeds up

Question 16

concerted feedback inhibition

Answer 16

occurs only in branched pathways

requires the binding of two end products simultaneously

Question 17

cumulative feedback inhibition

Answer 17

occurs only in branched pathways.
is incremental with each end product contributing some percentage of inhibition. each on its own may not be sufficient for complete inhibition. may not be additive though.

Question 18

isozyme

Answer 18

enzymes that perform the same catlytic reactions but differ by regulation or speed at which they perform the reaction are isozymes.Thus a branched pathway may be regulated by simple feedback inhibition when each isozyme is regulated by different end product

Question 19

generally pathways are regulated at..

Answer 19

..branch points

Question 20

regulatory enzymes are often

Answer 20

physiologically irreversible having a large negative delta G

Question 21

enzymes that follow simple michaelis-menten model of kinetics

Answer 21

non-regulatory

Question 22

michaelis-menten kinetics

Answer 22

When substrate concentrations [S] are plotted against initial velocity (v) a hyberbolic curve is produced which approaches the maximum rate of enzyme catalysis (Vmax)

Question 23

Km is calculated as

Answer 23

[S] at 1/2 Vmax

Question 24

When S is small compared to the Km

Answer 24

velocity is proportionality to S

Question 25

However when S is larger than Km,

Answer 25

cancels out and v approachs Vmax

Question 26

units for vmax

Answer 26

specific activity
and
turnover number

Question 27

specific activity =

Answer 27

micromoles of S converted per minute per mg of protein

Question 28

turnover=

Answer 28

micromoles of S converted per minute per micromole of enzyme

Question 29

effect of [substrate]

Answer 29

rate increases as
[substrate] increases
• no further increase occurs after all enzyme molecules are saturated with substrate

Question 30

Chapter 6
30
Regulatory Enzymes

Answer 30

Regulatory enzymes rarely follow Michaelis-Menten Kinetics
• They are typically multimeric • They may have more than one active site. • They may show positive cooperactivity meaning
that after one substrate binds, a second substrate binds more quickly because of increased affinity.
• Allosteric enzymes may have more than one regulatory site.
• They may show positive or negative cooperactivity due to binding of more than one effector.

Question 31

sigmoid kinetics of regulatory enzymes

Answer 31

Velocity (v) plotted against substrate concentration ([s])
• Curve 1 positive effect (faster or steeper rate compared to curve 2)
• Curve 2 no effector
• Curve 3 negative effector (slower rate compare to curve 2)

Question 32

Multimeric Enzymes

Answer 32

Catalytic subunits have the active site(s).
• Regulatory units bind the allosteric effectors.
• Low Km = high velocity • High Km = low velocity • Thus regulators (positive and negative)
alter the Km

Question 33

types of covalent modification

Answer 33

Adenylation (AMP binding to allosteric site) – Phosphorylation (Phosphate group binding) – Methylation (Methyl group binding) – Uridylylation (UMP group binding) – Acetylation (Acetyl group binding)

Question 34

Amino acids residues that are the usual sites involved in binding of the regulators

Answer 34

serine, threonine and tyrosine