behaviour of enzymes, mechanisms and control Flashcards
allosteric greek term
other shape
Oligomer whose biological activity is affected by other substances binding to it
allosteric enzyme
oliger-diff subunits
enzyme activity alters it’s 4° structure
Substance that modifies the behavior of an allosteric enzyme by binding to it
allosteric effector
- allosteric inhibitor
- allosteric activator
it exhibit cooperative effects caused by subtle changes in quaternary structure
ATCase and hemoglobin
how does the allosteric enzymes have a different response to the presence of inhibitors from that of nonallosteric enzymes
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
briefly explain cooperative binding
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.
what is the end product when ATCase catalyzes the first step in a series of reactions
cytidine triphosphate (CTP)
ATCase - important forms in RNA and DNA
*energetically costly
what type of graph will ATCase and Hemoglobin will produce
ATCase: sigmoidal
Hemoglobin: sigmoidal
*myoglobin is hyperbolic
Process by which the final product of a series of reactions inhibits the first reaction in the series
feedback inhibition
*inhibits enzyme 1 only
*final product is the inhibitor to shut down the whole series
what type of curve describes the allosteric behavior
sigmoidal curve
Six protein subunits organized into two trimers
Six protein subunits organized into three dimers
Catalytic subunit (main function)
Regulatory subunit (alosteric function)
how can catalytic subunits can be separated from regulatory subunits
p-hydroxymercuribenzoate, which reacts with cysteines in the protein
what are the types of inhibition
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
Substrate, inhibitor, or activator that binds to an allosteric enzyme and affects its activity
what are the results of the effector
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)
this model is proposed by Monod, Wyman, and Changeux in1965
concerted model
Description of allosteric activity in which the conformations of all subunits change simultaneously
what are the conformations
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 ]
in the sigmoidal effects
higher L:
lower c:
higher L: high favorability of free T form
lower c: affinity btwn S and R form and more sigmoidal effects
Cooperative effect whereby binding of the first ligand to an enzyme or protein causes the affinity for the next ligand to be lower
negative cooperativity
can convert an inactive precursor into an active enzyme
Phosphorylation by ATP
sequential model of cooperative binding
ppt
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
2K+ in
3Na+out
^made possible by Phosphorylation by ATP
[2K in 3na out]
Inactive protein that can be activated by specific hydrolysis of peptide bonds
Zymogen
Synthesized and stored in the pancreas
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
Which amino acid residues on an enzyme are in the active site and catalyze the reaction?
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
what are the amino acids residues in the active site
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
Class of proteolytic enzymes in which a serine hydroxyl plays an essential role in catalysis
serine protease
*chymotrypsin is a serine protease
this catalytic triad is important for activation of chymotrypsin
His57
Electron-rich substance that tends to react with sites of positive charge or polarization
Nucleophile
*attacks carbonyl grp if peptide grp
SN1 vs SN2
SN1:
* Unimolecular nucleophilic substitution
* Rate of reaction follows first-order kinetics
SN2:
* Bimolecular nucleophilic substitution
* Rate of reaction follows second-order kinetics
Synthesized compounds that mimic the form of the transition state of an enzyme reaction
Transition-state analog
Antibodies that are produced against a transition-state analog and that have catalytic activity similar to that of a naturally occurring enzyme
Abzymes
Nonprotein substances that take part in enzymatic reactions and are regenerated at the end of the
reaction
coenzymes
Organic coenzymes
vitamins and derivatives
oxi-reduc reactions
B6 vitamins
Pyridoxal, pyridoxamine, and pyridoxine and their phosphorylated forms
coenzyme: transfer of amino grp - transamination
