enzyme regulation and bioenergetics Flashcards
catabolic pathway
enzymes in a pathway can function to breakdown biomolecules and release energy
anabolic pathway
enzymes in a pathway can also make complex biomolecules, needed by the cell, from small precursors
pathways may contain unfavorable reactions
an unfavorable reaction can be driven forward by a favorable reaction
pathways are regulated
substrates or products of one step in the pathway can interact with one of the enzymes to effect its activity and alter the efficiency of the entire pathway
cells do not waste energy, or building blocks, …
making biomolecules that are already plentiful enough, or that are not needed under a given environmental condition; down-regulated to decrease production of end-product
if a cell needs more energy, or more of a particular biomolecule, under a given set of circumstances…
the cells will produce more; up regulated to increase production of end product
what is usually the first enzyme and why?
often the regulatory enzyme; more efficient since other steps do not waste energy unnecessarily
what do enzymes in a pathway do that regulatory enzymes do not?
follow Michaelis-Menten kinetics
what are the two main types of regulation?
allosteric and reversible covalent modification
allosteric regulation
reversibly bind regulatory molecules that alter enzyme activity
reversible covalent modification
a group is added to the enzyme to modulate its activity, and this group can be removed to reverse the effect
what is true about positive regulators and negative regulators?
binding of positive regulator increases activity and the absence of a negative regulator increases activity
what is the substrate concentration that gives 1/2Vmax
K0.5
how can an enzyme regulate the activity of a second enzyme in regulation by reversible covalent modification?
by covalently modifying the enzyme
bioenergetics
study of energy transductions in living systems
what obeys the laws of thermodynamics?
biological energy
gibbs free energy, G
measure of the amount of work a system can perform at constant temperature and pressure
exergonic reaction
releases free energy, -delta G (favorable)
endergonic reaction
gains free energy, +delta G (not favorable)
enthalphy, H
reflects the number and kind of bonds in reactants (substrate, S) and product, P
exothermic reaction
heat is released, -delta H
endothermic reaction
heat is absorbed, +delta H
entropy, S
measures randomness or disorder
change in gibbs free energy equation
deltaG= deltaH-TdeltaS
what do reacting systems tend to move towards?
equilibrium
delta G naut
measure of how far a reaction must go to reach equilibrium, when initial concentrations of each component are 1M, with standard state conditions; constant for a given reaction
what does actual free energy change for a reaction depend on?
initial concentrations of substrates and products, and on the temperature
when deltaG<0, reaction tends to go
forward direction
when deltaG>0, reaction tends to go
reverse direction
when deltaG=0, reaction tends to go
it is at equilibrium
______ DO NOT affect equilibrium, only the reaction rate and rate of approach to equilibrium
enzymes
standard free energy changes for sequential reactions are additive therefore
thermodynamicaly unfavorable reaction can be coupled to a thermodynamically favorable reaction to drive the unfavorable reaction forward
the deltaGnaut for ATP hydrolysis is
large and negative
in metabolism, it is not _________, but ________, that couples the energy of ATP breakdown to endergonic reactions
ATP hydrolysis; group transfer
for some mechanoenzymes, energy of ATP hydrolysis drives..
conformational changes to drive reactions
what is the “true” cellular substrate?
Mg*ATP^2-
in thermodynamics, what really matters?
relative energies of the reactants and the products
