Enzymes Flashcards
isozymes
different molecular forms of the same enzyme synthesized by different tissues of the same organism
classifications of enzymes
oxidoreductases (often names dehydrogenase) transferases hydrolases lyases (cleave C-C, C-S and some C-N) isomerases ligases
enzyme kinetic curve compares what parameters?
the rate of reaction to the substrate concentration (how many molecules of subtrate are converted ever min)
What can speed up a reaction? (besides catalyst/enzymes)
Temperature - to an extent if its too hot it’ll denature the proteins
A particular pH that assist in the ionization of residues at the active site - extreme pH levels will denature
Vmax and Km of emzymatic kinetics
higher Km means a weaker affinity for substrate and enzyme
the Km is equal to the concentration of subtrate at half the Vmax.
Vmax - the fastest the reaction will go regardless of substrate concentration
irreversibile inhibition
enzyme is destroyed when inhibitor reacts covalently with it
Aspirin inhibits prostaglandin synthetase
reversible inhibition
nonconvalently interaction with enzyme, can be competitive inhibition and noncompetitive
competitive inhibitor
usually a substrate analog, binds in the active site where the substrate
affinity of enzyme for substrate decreases (Km inc)
ex. statins that competitively inhibit HMG-CoA (synthesis of cholesterol)
non-competitive inhibition
binds enzyme at a different site than active site,
decreases Vmax
allosteric control of enzyme
allosteric enzyme have an allosteric site, effector binds noncovalently and reversibly at the allosteric site
allosteric binding changes the enzyme activity: increases - positive, decreases - negative
covalent modification
reversible
often phosphorylation, by kinase or dephosphorylation, phosphatase
quick
feedback control
feedback inhibition - when the final product of a pathway circulates back to inhibit an earlier enzyme in the pathway
hormonal control
hormones change the physiological state of target organs through activation or inactivation of enzymes in the organs.
ex - insulin, glucagon
nuclear receptor
intracellular receptor activation - steriod hormones, either enter nucleus to bind receptor or on membrane which detaches and relocates to neucles
ex - estrogen receptor, progesterone receptor, thyroid hormone receptor
how does cholera toxin work?
taken into cell and activated by proteolysis
transfers ADP-Ribosyl to G-alpha-s
this permanently activates G-protein
increase cAMP level intracellularly
keeps CFTR open, Cl- pours out of the cells and water follows
