Enzymes 1 & 2 Flashcards
what is activation energy?
the energy required to go from reactants to products
stabilizing transition states makes it more favorable and reduces ___________
delta G
definition of an enzyme
increases the rate or velocity of a chemical reaction without changing itself in the process
classic enzyme nomenclature
substrate +action+ase
systematic enzyme nomenclature
substrate(s) + enzyme type
oxidoreductase function
catalyze oxidation-reduction reactions
ex. lactate to pyruvate
transferase function
catalyze transfer of C N or P containing groups
ex. serine to glycine
hydrolase function
catalyze cleavage of bonds by addition of water
ex. urea
Renin
role in regulation of blood pressure
pepsin
digestive enzyme
how do enzymes accelerate reactions?
-create an alternate reaction pathway in which the transition state has lower free energy
-decreases free energy of activation and lowers the activation barrier of delta G
-increase the concentration of substrate in the transition state and thus increases the rate of the reaction
describe the active site of an enzyme
-small 3D cleft or crevice formed by different parts of amino acid sequence
-complementarity of substrate for site
-noncovalent interactions
Lyases
catalyzes cleave of C-C, C-S, and C-N bonds
ex. pyruvate to acetylaldehyde
Isomerases
catalyze racemization of optical or geometric isomers
ex, methylmalonyl CoA to Succinyl CoA
ligases
catalyze formation of bonds between carbon and S, O, N coupled to hydrolysis of high energy phosphates
ex. pyruvate to oxaloacetate
what are the noncovalent interactions that hold enzyme and substrate complexes together
-H bonding
-ionic
-van der waals
-hydrophobic
what happens at Vmax
all of the enzyme present in the system is saturated
what is km
km is the amount of substrate is takes to reach half Vmax
Vmax/2
what is kcat
how many substrate molecules are transformed into products per unit time by a single enzyme
how to calculate enzyme efficiency
kcat/km
at high concentrations of substrate, the velocity of the reaction is ___________________, constant and independent of substrate concentration
zero order
at low concentrations of substrate, the velocity of the reaction is ___________, proportional to substrate concentration
first order
large Km=
low affinity of enzyme for substrate
small Km=
high affinity of enzyme for substrate
competitive inhibition
-inhibitor binds to active site
-Km increases and Vmax stays the same
how can competitive inhibition be overcome?
flooding the reaction with substrate
noncompetitive inhibition
-binds to allosteric site
-Km stays the same and Vmax decreases
graph makes a v shape
uncompetitive inhibition
-binds to enzyme-substrate complex
-Km decreases and Vmax decreases
lines run parallel
modifies transpeptidase and prevents bacterial cell wall synthesis
penecillin
modifies cyclooxygenase (1&2) & reduces inflammatory signals
Aspirin
cooperative binding
binding at one site enhances binding at another
Aspartate transcarbamyolase (ATCase)
first committed step of nucleotide biosynthesis
-CTP is end product and feeds back to inhibit the enzyme
what amino acids can be phosphorylated
serine, threonine, tryosine
histidine in bacteria
enzymes that add phosphates
kinases
regulatory proteins involved in muscle contractility
Troponins T and I
released in the plasma in response to cardiac damage
-gold standard in diagnosing MI
Cardiac specific isoforms (cTn)
cleaves all accessible peptide bonds (serine protease)
subtilisin
cleaves after all accessible Lys or Arg (serine protease)
trypsin
cleaves only after Arg in a specific sequence
thrombin
statins block the 1st committed step in cholesterol synthesis because they are…..
competitive inhibitors in Hydroxymethylglutaryl (HMG) CoA reductase
serious side affects of statins
-reduced testosterone
-memory loss
-transiant global amnesia
-muscle pain
formulas for delta G
ΔG=ΔH-TΔS
ΔG=ΔG0’+1.36log products/reactants
formula for standard state ΔG
ΔG0’= -1.36(logKeq)
how can unfavorable biosynthetic reactions proceed?
can be accomplished by coupling reaction to a favorable reaction
the overall ΔG of a reaction its the sum of….
free energy changes of the individual steps
many unfavorable biosynthetic reactions are coupled to ________________
ATP hydrolysis (strong phosphate bonds)
hexokinase couples reaction by ……
transferring phosphate directly from ATP to glucose—-aided by proximity of both reactants binding to adjacent sites on the enzyme
