Enzymes And RegulationOf Enzyems Flashcards
All enzymes are proteins except
Ribozymes
-this is a catalytic ribonucleic acid triggering catalysis of RNA processing
Enzymes ___ transition state
Stabilize
If there were no enzyme how would the reaction proceed
Super slow or not at all
And it would take a tonnnn more energy
Εnzymes change the ____ energy but not the ______ energy
Activation
Overall
Enzymes _____ the rate of exergonic reactions by lowering the _______
Increase
Activation energy of the reaction
What 2 models describe the way enzymes work with substrates
Lock and key
Induced fit
See slide 8 W7
Which model is more common
Induced fit
What do enzymes need for catalysis
Active sites aka groove aka cleft
Cofactors - metal ions
Coenzymes - prosthetic groups
Compartmentalization
Specificity
Steps of induced fit
1 - enzyme active site has AA lining it
2 - the substrate binds (ES complex)
3 - additional bonds are formed to make the fit better (transition-state complex)
4 - products produced
Cofactors for enzymes are
Metal ions - which are INORGANIC
Small, non protein
Coenzymes for enzymes are
Prosthetic groups - tightly bound, does not dissociate away from enzyme
and co-substrates - associates with enzyme TEMPORARILY
They are ORGANIC
Cofactor examples
Mg, K, Ca, Zn, Fe, Cu
They are bond with enzyme molecule
Coenzymes examples
Vitamins!!!
NAD - B3/niacin
FAD - B2/riboflavin
Coenzyme A
Bind TEMPORARILY or permanently to enzyme NEAR active site
Water soluble vitamins are
Coenzymes
Thomas
Richard
Never
Pounded
PussySix
But
fondled
Chest
Enzymes need to be compartmentalized ___
Within the cell
Want to be in the ideal space for substrate + enzyme meeting
Enzymes have substrate specificity. Give 3 examples
Chymotrypsin has a hydrophobic active site for aromatic AA: trp, tyr, phen
Trypsin has a “-“ active site for “+” AA: lys, Arg
Elastase has a narrow active site for small uncharged AA: gly, ala, ser
What are the 3 types of enzymes
Isozymes
Allosteric enzymes
Proenzymes
Define isozyme
Multiple forms of an enzyme that catalyze the same reaction
Define allosteric enzymes
Multisubunit enzyme with identical or different polypeptide chains
Define proenzymes
biologically inactive substance which is metabolized into an enzyme
Zymogen -pancreas
What affects the activity of enzyme rxn and influence rate of rxn
- pH
- Temp
- Substrate conc/enzyme conc
What enzyme will activity will go up at acidic levels
Pepsin
what enzyme will go up at pH 7
Salivary amylase
What enzyme will go up at pH 9.5
Arginase
If temp is too low what happens to rate of enzyme activity
INACTIVE
If temp is too high what happens to rate of enzyme activity
Denatured
Which has a higher affinity for glucose hexokinase or glucokinase
HEXOKINASE
What would utilize hexokinase
Brain cuz it NEEDS glucose
Where is glucokinase found
Liver
Parenchyma cells
Pancreatic islet cells
What is the KM of hexokinase if we know it has a high affinity for glucose
0.1mM
This makes sure a supply of glucose for tissues is there even when the blood glucose is low
What is the KM of glucokinase if we know it has a low aff for glucose
10mM
This is 100x less aff compared to hexokinase
KM vs KD
KM = Michaelis constant
Kinetic constant
NOT equilibrium constant
Shows the affinity of substrates binding for the active site
KD = dissociation constant
thermodynamic constant
Equilibrium constant
Shows the affinity of the ligand towards an enzyme
What changes enzymes rate (regulates)
- Substrates/inhibitors
- Allosteric regulation of enzymes
- Covalent modification of enzymes via hormonal reg
Allosteric enzymes have _____ sites and _______. They show _______. And display ____ on a graph
Multiple active sites, change their conformation after they bind
Cooperative binding
Sigmoidal dependence
Where does an allosteric enzyme that causes inhibition and activation bind
NOT at the active site
___ are metabolic inhibitors or activators that affect activity of allosteric enzymes
Effectors
Positive Effectors characteristics
Once it binds it changes both subunits to a higher affinity for
Shifts graph to the left
Activators bind more tightly to R state
Negative effector characteristics
Binding both subunits to a low affinity form which inhibits activity
Bind more tightly to Tstate
____ is a good example of allosteric effects
Hemoglobin
Sigmoidal shape in allosteric curve is due to
Conformation change in enzyme
The cooperative binding
What is a common way to quickly adjust activity of enzymatic reactions
Covalent modification
Covalent modification is
Usually reversible
Phosphorylation
CAMP
Adding or removing phosphate groups is an example of
Covalent modification
Substrate availability results in _____ and take ______ long
Change in velocity
Seconds
Product inhibition results in ____ and takes ____ long
Change in Vm and/or Km
Seconds
Allosteric control results in _____ and takes _____ long
Change in Vm and/or Km
Seconds
What kind of bond is allosteric control utilizing
Non-covalent
Covalent modification results in ____ and takes ___ long
Change in Vm and/or Km
Seconds to minutes
Induction or repression results in ____ and takes ____ long
CHANGE IN AMOUNT
Min to hrs to days
Which regulator does not affect rate of reaction
Substrate availability
Allosteric control
Induction or repression
Covalent modification
Product inhibition
Induction or repression. It changes the amount of enzyme
Allosteric control effects
End product
Covalent modification affects
Another enzyme
Induction or repression effects
Hormone/metabolite
Induction or repression can alter
Protein sythesis
It takes a long time cuz its DNA and RNA
_____ resemble the substrate and bind reversibly at the active site
Competitive inhibitors
____ bind to the enzyme reversibly in a different domain than the active site changing the conformation of the enzyme
Non competitive inhibitors
What does a comp. Inhibitor effect
Raises the KM
Because you need more substrate to fight for spots
Vmax stays the same
What does a non competitive inhibitor effect
Lowers the vmax
KM stays the same
Cuz no one is interfering with the active site
What does uncompetitive inhibition effect
BOTH Km and Vmax
Lovastatin is an example of a _____ inhibitor. It effects the substrate ___
Competitive
HMG CoA
It decreases lipids
____ is an example of a non competitive inhibitor to pyruvate kinase
Alanine
Silver poisoning is an example of __
Non competitive inhibition
Examples of uncompetitive inhibition
Inhibition of Arya sulphatase by hydrazine
Inhibition of intestinal alkaline phosphatase by phenylalanine
What is the end result of a suicide inhibitor
Fewer enzyme molecules active to catalyze norm reactions - the vmax decreases
Suicide inhibitors aka and what do they do
Irreversible
Bind Supa tight to ACTIVE SITE forming covalent bond and permanently inactivate enzyme
Suicide inhibitors KM and VMAX effects
Vmax decreases
KM is unchanged
Examples of suicide inhibitors
NSAID-Aspirin
Penicillin
What kind of enzyme catalyzes irreversible metabolic reactions
Regulatory enzyme
Example of allosteric regulatory enzyme
Phosphofructokinase
