Chapter 2- Enzymes Flashcards
zymogen
inactivated form of enzyme
Oxidoreductases
catalyze oxidation-reduction reactions (transfer of electrons between biological molecules). typically have cofactor that acts as electron carrier (ex: NAD+ or NADP+) reductant (electron donor), oxidant (electron acceptor)
oxidase
catalyze oxidation reduction reactions and typically have oxygen as the final electron acceptor
Transferases
catalyze movement of a functional group from one molecule to another. (kinases are included in this group- transfer of phosphate group, generally from ATP to another molecule)
Hydrolases
catalyze breaking of a compound into two molecules using the addition of water (ex: phosphatase- cleaves phosphate group from another molecule)
Lyases
catalyze cleavage of single molecule into two products. dont require water. typically referred to as synthases. (ex: ATP into AMP and inorganic phosphate)
Isomerases
catalyze rearrangement of bonds within a molecule.
ligases
catalyze addition or synthesis reactions generally b/w large similar molecules. often require ATP.
two enzyme theories (also note which is more supported)
lock and key theory induced fit model (more supported)
lock and key theory
enzymes active site (lock) is already in appropriate conformation for the substrate (key) to bind.
induced fit model
substrate induces a change in shape of the enzyme. requires energy so its endergonic to change shape, but to release the substrate from the enzyme is exergonic.
cofactors/coenzymes
nonprotein molecules that participate in catalysis of reaction. typically carry charge and recruited only when needed.
apoenzymes
enzymes without their cofactors
holoenzymes
enzymes containing cofactors
prosthetic groups with respect to enzymes
tightly bound cofactors or coenzymes that are necessary for enzyme function
cofactors
inorganic molecules/ metal ions (often ingested as dietary minerals)
coenzymes
small organic groups, vast majority are vitamins or derivatives of vitamins such as NAD+, FAD, and coenzyme A.
water-soluble enzymes
Vitamin B and C (ascorbic acid) are important and must be replenished regularly b/c they are easily excreted.
fat-soluble vitamins
Vitamin A, D, E, and K are better regulated by partition coefficients (quantify ability of a molecule to dissolve in polar/nonpolar environments.
saturation
when all available enzymes are working with substrates. this is where the enzymes are working at a maximal velocity as long as enzyme concentration stays constant.
Michaelis-Menten equation (with enzyme concentration constant)…how to find velocity of an enzyme
v = Vmax [S] / Km + [S]
when reaction rate is equal to half of Vmax
Km = [S]
Km (Michaelis constant)
substrate concentration at which half of the enzymes active sites are full
Km and enzymes affinity for substrate
low Km = high affinity high Km = low Km *note: Km cannot be changed, its an intrinsic property
Lineweaver-Burk plots
x-intercept: -1/Km y-intercept: 1/Vmax
T vs. R state
T (low affinity Tense state) R (high affinity Relaxed state)
enzymes and temperature
reaction rate doubles in velocity for every 10degree increase in temperature until optimum temperature is reached. (37 degrees for human body).
optimal pH in body
stomach- 2 pancreas- 8.5 rest of body- 7.4
feedback regulation
regulation of enzymes by products further down a given metabolic pathway
feed-forward regulation
regulation of enzymes by intermediates in the pathway
negative feedback
feedback inhibition, which helps to maintain homeostasis
4 types of reversible inhibition
- competitive- inhibition by occupying active site, can be overcome by adding more substrate (larger Km and same Vmax) 2. noncompetitive- bind to allosteric site instead of active site, which induces a change in enzyme conformation, cannot be overcome (same Km and larger Vmax) 3. mixed- inhibitor can bind to enzyme or enzyme-substrate complex, but has different affinity for each, binds at allosteric site 4. uncompetitive- bind only to enzyme-substrate complex and essentially lock substrate in the enzyme, bind at allosteric site
glycosylation
covalent attachment of sugar moieties (an enzyme modification that can tag an enzyme for transport within a cell or can modify protein activity/selectivity)
how to tell if an enzyme is a zymogen?
it will end in -ogen
hydrolysis
breaking a bond by adding water
