lecture 4 Flashcards
negative delta G
spontaneous rxn
how can unfavourable rxns occur?
if they are coupled to a favourable one
for sequential rxns, standard free energy changes are
additive
the free energy is directly related to
the ratio of concentration of product and reactants
activation energy (Ea)
energy must be acquired by a molecule to undergo a chem rxn
what does delta G not tell us?
the speed of rxn
catalyst
lowers Ea of a rxn
Enzyme
biological catalyst. speeds up rxn rate by lowering Ea
Enzymes are
-not consumed in the process
-highly specific in terms of substate and rxn
-allow rxns to occur quickly
does delta G change w time?
yes, bc the concentration of products and reactants is changing
steady state equilibrium
relatively stable equilibrium. concentration of products and reactants vary slightly
are cells ever at a thermodynamic equilibrium?
no! unless dead
living cells are constantly exchanging
material with their environment
equilibrium constant
the ratio of substrates and product when the rates of the forward and reverse rxns are equal
equilibrium constant (K=?)
[products]/[reactants]
assume delta G is zero if not given
A + B –><– AB
if A and B bind non-covalently, is the free energy change positive or negative?
Negative bc rxn is favourable
-if A and B bind strongly, you need less of A and B to make product
chemical siphons
drives energetically unfavourable rxns
thermal motion
-molecules diffuse
-larger molecules diffuse slower than small ones
-random encounters between substrate and enzyme can lead to formation of an enzyme-substrate complex stabilized by noncovalent interactions
enzyme kinetics: velocity
rate of rxn
Vmax
the max velocity of a rxn for an enzyme. how quickly it can catalyze a rxn when fully saturated w substrate
Michaelis constant (Km)
concentration of substrate at which enzyme is at half Vmax
entropy
measure of a system’s disorder
do competitive enzymes bind reversibly or irreversibly to the substrate?
reversibly
turnover number for an enzyme definition
the maximum number of molecules of substrate that can be converted to product by one enzyme molecule per unit time
sugar cube dissolved in a cup of coffee. what happens to entropy of the sugar?
it increases.
sugar cube dissolves, more freedom of movement/random movement; increased entropy (more disordered)
what is the first law of thermodynamics?
energy can not be created or destroyed (law of conservation of energy)
states that energy can be transduced from one form to another
ATP carries stored potential energy and transfers it through the formation of
phosphate bonds
Reactions that have positive standard free energy changes (ΔG’°>0) can be made to occur in cells by:
both coupling them with exergonic reactions via a common intermediate and manipulating the concentrations of products and reactants such that ΔG’<0
To predict the direction in which a particular reaction will proceed at a given moment within a particular cellular compartment, one must know all of the following (4)
standard conditions.
the concentrations of reactants and products.
the ratio of [ADP] / [ATP].
the temperature at which the cell is found.
For a reaction with a standard free energy change, ΔG’° = +0.7 kcal/mole, how can we make the rxn occur?
The reaction could be made to occur by altering the concentrations of reactants and products
