Lecture 3 - Enzymes Flashcards
What is the definition of enzymes?
-biological catalysts
-made of protein
-increase rate of chemical reaction
-specific to their action with 1 substrate
-need to maintain structure to keep function
What is a cofactor?
non-protein inorganic (metal ion) that helps enzyme
What is an organic cofactor called?
coenzyme
What are the 2 types of coenzymes?
prosthetic groups: permanently bound
cosubstrates: temporarily bound
What are important coenzymes?
ATP/GTP
NAD
FAD
coenzyme A
What are examples of cofactors?
Mg2+
Ca2+
What is the difference between an apoenzyme and a holoenzyme?
apoenzyme = inactive (enzyme WITHOUT cofactor)
holoenzyme = active (apoenzyme + cofactor)
What is the active/catalytic site of an enzyme?
site where substrate must fit and bind to activate enzyme
How many classes of enzymes exist?
- oxidoreductase
- transferase
- hydrolase
- lyase
- isomerase
- ligase/synthetase
- translocase
What is an exergonic and endergonic reaction?
exergonic = release energy
endergonic = requires energy
What is the Michaelis-Menten formula used for?
-formula to interpret behavior of enzymes (regulatory enzymes)
-calculate rate of catalysis of enzyme at some particular substrate
What happens in the catalytic reaction of the concentration of substrate is increased?
low [S] = velocity increases 1:1
high [S] = no change in velocity (plateaus)
Can enzymes catalyze 2 or more substrates?
yes, many enzymes catalyze reactions with 2+ substrates
Is the pH different for different enzymes?
yes, every enzyme has optimum pH for maximal activity
What are the factors affecting enzymatic activity?
temp
water (required reactant)
pH
[substrate]
[enzyme]
inhibitors
end products
activators
radiation
What kinds of enzyme inhibitors exist?
reversible
irreversible
What are the kinds of reversible enzyme inhibition?
competitive
uncompetitive
mixed
non-competitive
What is an irreversible enzyme inhibitor?
bind covalently to enzyme’s active site (blockage) –> can destroy functional groups that are needed for enzyme’s function
What is competitive inhibition?
binds to substrate active site
What is non-competitive inhibition?
binds to enzyme-substrate complex –> changes shape of active site –> can’t bind
What is the difference between competitive and non-competitive and uncompetitive inhibition?
competitive competes directly with substrate (increasing substrate can overcome)
non-competitive/uncompetitive do NOT compete directly with substrate (increasing substrate CANNOT overcome)
What is an allosteric site?
site other than enzyme’s active site
What is allosteric regulation?
binding regulator molecule to allosteric site
What is an allosteric activator?
effectors/regulators that enhance protein’s activity
What is an allosteric inhibitor?
effectors/regulators that decrease protein’s activity?
What is a reversible covalent modification of an enzyme?
between non-protein group and enzyme to turn it on or off
What are examples of reversible covalent modification of an enzyme?
-phosphorylation (can be dephosphorylated)
-adenylation
-uridylation
What is proteolytic activation?
enzymes, hormones, proteins made as inactive proteins
activation = cleavage of 1 or a few specific peptide bonds (no ATP required)
irreversible!
What are zymogens?
inactive precursor of protein
