Enzyme - controlling rates - regulating and inhibiting

Question 1

effect of temp on V

Answer 1

increase temp - add heat energy - easier to reach Ae
speed molecule increase therefore collide more per second
opt 37-40 over - decreases rate because denature - unravel protein E

Question 2

effect of pH on V

Answer 2

e.g. lysozyme - pH7
pepsin - acidic
alkaline phosphatase - alkaline
denature above/below opt pH

Question 3

effect [E] on V

Answer 3

[S] - constant
V = (Vmax*[S]) / (Km+[S])
increase in [E] = increase Vmax = increase V

Question 4

enzyme regulation

Answer 4

covalent

non-covalent

Question 5

covalent - enzyme regulation

Answer 5

break/make covalent bond - alter activity of enzyme - change bond
irreversible process

Question 6

covalent - zymogen

Answer 6

cleave peptide chain - made in cell and released - turn full mature E = active

Question 7

covalent - zymogen - example

Answer 7

digestive enzyme in gut - convert zymogen in gut

Question 8

covalent - reversible process

Answer 8

phosphorylation - on and off

Question 9

phosphorylation - covalent

Answer 9

phosphate -ve therefore bind to side chain = repel/attract groups = distortion
reverse - use phosphatase - return to original shape

Question 10

non-covalent - enzyme regulation

Answer 10

reversible binding of molecules of specific site
increase/decrease activity
regulation can be at binding/catalysis steps or both

Question 11

enzyme regulation - equations

Answer 11

E + S <> ES -> E + P

Question 12

E + S <> ES

Answer 12

K type - B

Question 13

ES -> E + P

Answer 13

V type - C

Question 14

cooperativity (K-type regulation)

Answer 14

S binding to one side - increase affinity at another binding site

Question 15

cooperativity examples -

Answer 15

2 enzymes = dimer act as regulator of each other
start at low affinity and when S binds - affects propagate
most S not affect - [S] regulate E activity - independent to [S] = increase V

Question 16

M-M kinetics

Answer 16

Michaelis-Menten kinetics

Question 17

non-M-M kinetics

Answer 17

sigmoidal curve

1/2 Vmax - K0.5 for non-M-M kinetics

Question 18

sigmoidal curve

Answer 18

multiple subunit E with cooperative changes in S affinity between subunit - decrease activity due to decrease [S]

Question 19

allosteric enzyme (K-type)

Answer 19

regulated by binding to another molecules not S - completely different

Question 20

allosteric activator

Answer 20

low affinity - no bind at active site

high affinity - caused by another molecule on regulatory subunit

Question 21

allosteric inhibitor

Answer 21

low affinity - molecule bind to regulatory subunit

high affinity - no binding

Question 22

allosteric enzyme - Km

Answer 22

altered easily by changing conc of allosteric molecule

Question 23

allosteric enzyme (V-type)

Answer 23

less common
effect catalytic step - speed not binding
Vmax changes depending on V type allosteric enzyme conc
while all will have same K0.5

Question 24

unwanted regulation

Answer 24

all through allosteric E - set up to be regulated by changing level of molecules

Question 25

unwanted regulation - in cell - principle

Answer 25

molecules that naturally vary therefore enzyme matched to changing levels of natural molecules

Question 26

unwanted regulation - decrease activity

Answer 26

molecules outside body has nothing to do with body - can bind to E and change activity

Question 27

enzyme inhibitor

Answer 27

decrease decrease E activity - irreversible/reversible - decrease V and compared to absence of molecule - might resemble S or different
various different forms = different

Question 28

irreversible inhibitor

Answer 28

suicide S
e.g. aspirin
penicillin

Question 29

aspirin

Answer 29

close to S - binds at active site and starts to catalysis

never finishes therefore permanent covalent alteration of enzyme

Question 30

penicillin

Answer 30

bond breaks and attaches to end to active site - block
stop bacteria from building cell wall
therefore E is no longer functional therefore must move more E for reaction to occur

Question 31

reversible inhibitor

Answer 31

competitive
non-competitive
uncompetitive
mixed

Question 32

competitive inhibitor

Answer 32

loss of binding process - similar shape to S bind to active site and block
bind somewhere else - distort active site therefore cannot bind
Vmax stays same and V decreases
Km - larger (poor binding) as if [S] was less

Question 33

equation of competitive inhibitor

Answer 33

V = (Vmax[S]) / (KmIf)+[S]

where If is at E + S - decreases V

Question 34

If

Answer 34

inhibition factor

= I + [I]/Ki

Question 35

non-competitive inhibitor

Answer 35

loss of catalysis process - prevent reaction when E binds to S
Vmax is smaller
Km is same and 1/2 Vmax is changed
as if [E] was less

Question 36

equation of non-competitive inhibitor

Answer 36

V = (Vmax/If)[S] / (Km+[S])

where If is at E+S (EI) and ES(ESI) - decreases V

Question 37

uncompetitive inhibitor

Answer 37

bother Vmax and Km seem smaller

forces E to hold onto S even if reaction doesn’t occur

Question 38

equation of uncompetitive inhibitor

Answer 38

V = (Vmax[S]) / Km+([S]If)

where If is at ES(ESI)

Question 39

mixed inhibitor

Answer 39

bind to either but with different affinity of E and ES

line crosses but not at the axis - on graph