Enzymes Flashcards
how do enzymes catalyze reactions?
- increase chemical reaction rate
- reduce the free energy needed to drive a chemical reaction
- increase the probability of reaction occurence
describe simple enzymatic reactions
- enzyme reacts with a substrate
- enzyme reacts with a product
- can be bidirectional or unidirectional
vast majority of enzymes are?
large globular proteins, with the exception of catalytic RNAs
are substrates and binding pockets selective?
- yes
- once bound, conformational change occurs
what do coenzymes do?
bind to protein to allow binding of substrate
what are cofactors?
inorganic ions that bind to enzymes to allow binding of substrate
what is a holoenzyme?
- a catalytically active enzyme with coenzymes and cofactors bound
- classified by reaction type
what do oxidoreductases do?
-transfer of electrons
what do transferases do?
group transfer reactions
what do hydrolases do?
hydrolysis reactions
what do lyases do?
cleavage of C-C, C-O, C-N, or other bonds
what do isomerases do?
transfer of groups within molecules to yield isomeric forms
what do ligases do?
formation of C-C, C-S, C-O, and C-N bonds by condensation reactions
How do enzymes enhance reaction rates?
-reduce activation energies by lowering free energy thresholds
T or F:
enzymes covalently change chemical structure
true
T or F:
substrate complementation would decrease free energy demands
false
increase
T or F:
enzymes shift substrates into the transition state
true
T or F:
strong bonding is optimal in the transition state
false
weak binding
T or F:
strong bonding releases free energy
false
weak bonding
T or F:
weak bonding drives enzyme catalysis
true
Name the 4 activation barriers that enzymes overcome
- entropy of molecules in a solution
- solvation shell
- substrate conformation
- substrate orientations
Name the 4 binding energies needed for enzymes to overcome the 4 activation barriers
- organize substrates, reduce entropy to overcome entropy of molecules in a solution
- weak bonds desolvate substrates to overcome solvation shell
- weak bonds alter conformation to overcome substrate conformation
- enzymes induce fit to overcome substrate orientations
what do enzyme kinetics do?
-they regulate the rate at which enzymes create products
what do kinetic studies allow?
- identification of mechanism
- rate limiting steps of product formation
- identification of inhibitors
- this all measures the velocity
what is velocity?
- the primary measure of reaction rate
- initial velocity (rate within first few second of reaction) and maximum velocity (max speed at which reaction can occur)
what is velocity affected by?
- [enzyme]
- [substrate]
- cofactors and coenzymes
- enzyme modifications
- pH
- temperature
what is the Michaelis-Mentin constant?
-the substrate concentration needed for initial velocity to reach 1/2 of the maximum velocity
what are the 4 assumptions in Michaelis-Mentin kinetics?
1) single substrate enzyme reaction
2) free diffusion of substrate
3) substrate concentration is below Vmax
4) constant conditions
what do allosteric enzymes do?
- increase or decrease enzyme efficiency by binding and changing conformation
- do not follow Michaelis-Menten kinetics
- consequence of globular proteins having complex structures
in what ways are allosteric enzymes post-translationally modified?
- phosphorylation
- methylation
- myristoylation
- acetylation
- ubiquitination
in what way do allosteric enzymes not follow michaelis-menten kinetics?
- homotropic and heterotropic regulation
- regulation occurs at a separate site from substrate binding
what is the difference between homotropic regulation and heterotropic regulation
- homotropic regulation - substrate regulates enzyme function
- heterotropic regulation - non-substrate molecule regulates enzyme function
what 2 major processes do enzymes drive?
metabolism and signal transduction
name 7 characteristics of enzymes
1) most commonly globular proteins, with the exception of catalytic RNAs
2) substrate selective
3) can have coenzymes
4) weak interactions
5) cofactors
6) classified by reaction type
7) can become holoenzymes
