behaviour of enzymes, mechanisms and control

Question 1

allosteric greek term

Answer 1

other shape

Question 2

Oligomer whose biological activity is affected by other substances binding to it

Answer 2

allosteric enzyme

oliger-diff subunits
enzyme activity alters it’s 4° structure

Question 3

Substance that modifies the behavior of an allosteric enzyme by binding to it

Answer 3

allosteric effector

• allosteric inhibitor
• allosteric activator

Question 4

it exhibit cooperative effects caused by subtle changes in quaternary structure

Answer 4

ATCase and hemoglobin

Question 5

how does the allosteric enzymes have a different response to the presence of inhibitors from that of nonallosteric enzymes

Answer 5

Nonallosteric enzymes:
Direct inhibition at the active site
Gradual, often linear decrease in activity

Allosteric enzymes:
Inhibition at a separate regulatory site
More sensitive and cooperative response
Often shows a sharp, nonlinear change in activity

Question 6

briefly explain cooperative binding

Answer 6

binding of one O2 molecule helps or “cooperates” in the binding of subsequent O2 molecules. It results in a rapid transition from the unbound to the fully bound state once the process begins, allowing for more sensitive and efficient oxygen uptake and release in the case of hemoglobin.

Question 7

what is the end product when ATCase catalyzes the first step in a series of reactions

Answer 7

cytidine triphosphate (CTP)

ATCase - important forms in RNA and DNA
*energetically costly

Question 7

what type of graph will ATCase and Hemoglobin will produce

Answer 7

ATCase: sigmoidal

Hemoglobin: sigmoidal
*myoglobin is hyperbolic

Question 8

Process by which the final product of a series of reactions inhibits the first reaction in the series

Answer 8

feedback inhibition
*inhibits enzyme 1 only
*final product is the inhibitor to shut down the whole series

Question 9

what type of curve describes the allosteric behavior

Answer 9

sigmoidal curve

Question 10

Six protein subunits organized into two trimers
Six protein subunits organized into three dimers

Answer 10

Catalytic subunit (main function)
Regulatory subunit (alosteric function)

Question 11

how can catalytic subunits can be separated from regulatory subunits

Answer 11

p-hydroxymercuribenzoate, which reacts with cysteines in the protein

Question 12

what are the types of inhibition

Answer 12

K system:
sub conc. yields one-half Vmax (aka K0.5) is altered
V system:
maximal velocity of the enzyme but not the substrate

=these will alter quaternary structure and reflects it in the behavior

Question 13

Substrate, inhibitor, or activator that binds to an allosteric enzyme and affects its activity

what are the results of the effector

Answer 13

allosteric effector

homotropic effects:
identical molecules bound to protein
(bind of aspartate to ATCase)

heterotopic effects:
different subs r bound to a protein
(inhibition of ATCase by CTP and activation of ATP)

Question 14

this model is proposed by Monod, Wyman, and Changeux in1965

Answer 14

concerted model

Question 15

Description of allosteric activity in which the conformations of all subunits change simultaneously

what are the conformations

Answer 15

concentrated model
“one for all, all for one”

active R (relaxed):
bind substrate tightly

inactive T (tight or taut):
bind substrate less tightly

*absence of substrate, enzyme r inactive, T form
*presence, shifts the equilibrium from T form to R form:
2 types - free form and bound form.(if bound, decrease in free form)
[T to R and vice versa, change simultaneously ]

Question 16

in the sigmoidal effects
higher L:
lower c:

Answer 16

higher L: high favorability of free T form
lower c: affinity btwn S and R form and more sigmoidal effects

Question 17

Cooperative effect whereby binding of the first ligand to an enzyme or protein causes the affinity for the next ligand to be lower

Answer 17

negative cooperativity

Question 18

can convert an inactive precursor into an active enzyme

Answer 18

Phosphorylation by ATP

Question 19

sequential model of cooperative binding

Answer 19

ppt

Question 20

Phosphorylation of the Sodium–Potassium Pump Is Involved in Cycling the Membrane Protein between the Form That Binds to Sodium and the Form That Binds to Potassium

Answer 20

2K+ in
3Na+out
^made possible by Phosphorylation by ATP

[2K in 3na out]

Question 21

Inactive protein that can be activated by specific hydrolysis of peptide bonds

Answer 21

Zymogen

Question 22

Synthesized and stored in the pancreas

Answer 22

Chymotrypsinogen (this is a zymogen)
-when it bcs activated, undergoes function in small intestine = it then cleaves a polypeptide from Nterminal end to give active pi-chymotrypsin
consists of 245 amino acid residues cross-linked by five disulfide (—S—S—) bonds

Question 23

Which amino acid residues on an enzyme are in the active site and catalyze the reaction?

Answer 23

Functional groups that can play a catalytic role include:
* imidazole ring of histidine
* hydroxyl group of serine
* carboxyl side chains of aspartate & glutamate
* sulfhydryl group of cysteine
* amino side chain of lysine
* phenol group of tyrosine

Question 24

what are the amino acids residues in the active site

Answer 24

catalytic triad:
Ser195
His57
^those 2 must be close to e/o
Asp102
^involve in catalysis at the AS

ultimate goal: Ser to act as a Nu to attack the peptide bond

Question 25

Class of proteolytic enzymes in which a serine hydroxyl plays an essential role in catalysis

Answer 25

serine protease
*chymotrypsin is a serine protease

Question 26

this catalytic triad is important for activation of chymotrypsin

Answer 26

His57

Question 27

Electron-rich substance that tends to react with sites of positive charge or polarization

Answer 27

Nucleophile
*attacks carbonyl grp if peptide grp

Question 28

SN1 vs SN2

Answer 28

SN1:
* Unimolecular nucleophilic substitution
* Rate of reaction follows first-order kinetics

SN2:
* Bimolecular nucleophilic substitution
* Rate of reaction follows second-order kinetics

Question 29

Synthesized compounds that mimic the form of the transition state of an enzyme reaction

Answer 29

Transition-state analog

Question 30

Antibodies that are produced against a transition-state analog and that have catalytic activity similar to that of a naturally occurring enzyme

Answer 30

Abzymes

Question 31

Nonprotein substances that take part in enzymatic reactions and are regenerated at the end of the
reaction

Answer 31

coenzymes

Question 32

Organic coenzymes

Answer 32

vitamins and derivatives
oxi-reduc reactions

Question 33

B6 vitamins

Answer 33

Pyridoxal, pyridoxamine, and pyridoxine and their phosphorylated forms

coenzyme: transfer of amino grp - transamination