6.4 Chemical Reactions Flashcards
what is a chemical reaction?
the process by which molecules, called reactants, are transformed into other molecules, called products
what changes during a chemical reaction?
the bonds linking the atoms
most chemical reactions in the cell are readily reversible, what does that mean?
the products can react to form the reactants
the way the reaction is written defines forward and reverse reactions:
a forward reaction proceeds from left to right, a reverse reaction proceeds from right to left
the direction of a reaction can be influenced by:
the concentrations of reactants and products
how to favour the forward reaction?
increase the concentration of the reactants or decrease the concentration of the products
the effect of favouring the forward reaction can be found in the reactions of many metabolic pathways, how does that work?
the products of many reactions are quickly consumed by the next reaction, helping to drive the first reaction forward
Gibbs free energy (G)
the amount of energy available to do work
how does one determine whether the reaction releases energy that is available to do work?
you can compare the free energy of the reactants and products
what is delta G (change in G)
the free energy of the products minus the free energy of the reactants
if change in G is positive:
the products of a reaction have more free energy than reactants and a net input of energy is required to drive the reaction forward
if change in G is negative:
the products of a reaction have less energy than reactants and energy is released and available to do work
exergonic
describes reactions with a negative change in G that release energy and proceed spontaneously
endergonic
describes reactions with a positive change in G that are not spontaneous and so require an input of energy
spontaneous in the context of free energy means that:
a reaction releases energy
non-spontaneous in the context of free energy means that:
a reaction requires a sustained input of energy
the total amount of energy is equal to:
the energy available to do work plus the energy that is not available to do work because of the increase in entropy
enthalpy (H)
the total amount of energy in a system
entropy (S)
the degree of disorder in a system
absolute temperature (T)
temperature measured on the kelvin scale
the formula for the total amount of energy (H) is:
energy available to do work (G) + energy lost to entropy (TS)
the formula to determine energy available to do work (G) is:
H - TS
total amount of energy - energy lost to entropy
the value of change in G depends on BOTH the:
change in enthalpy and the change in disorder
catabolic reactions are those in which the products have :
less chemical energy (lower enthalpy) in their bonds than reactants have, the products are more disordered (higher entropy) than the reactants are-have a negative value of change in H and a positive value for change in S (releases energy-spontaneous)
anabolic reactions are the opposite of catabolic reactions so:
increasing chemical energy (positive delta H) and decreasing disorder (negative delta S0, synthesis of macromolecules, positive value of delta G, requires a net input of energy
if the change in enthalpy and entropy are both positive or both negative, whether or not the reaction is spontaneous is determined by:
the absolute value of these parameters which then determines whether delta G is positive or negative
what effect does increasing temperature have on the free energy (delta G) of a chemical reaction?
increasing the temperature increases the value of (TS) which decrease G (G=H-TS)
hydrolysis reactions consist of a chemical reaction in which a water molecule is split into:
a proton (H+) and a hydroxyl group (OH-), hydrolysis reactions often break down polymers into their subunits and in the process one product gains a proton and the other gains a hydroxyl group
the reaction of ATP with water is an exergonic reaction because:
there is less free energy in the products compared to the reactants
why is the reaction of ATP an exergonic reaction?
ADP is more stable than ATP, contains less chemical energy in its bonds (negative H), and because there is two molecules (ADP and P), there is increased entropy (H), so G is negative and the reaction is spontaneous and releases energy
the free energy difference for ATP hydrolysis is approximately: (under lab conditions)
-7.3 kcal per mole of ATP
the value of the free energy difference for ATP hydrolysis is influenced by several factors including:
the concentration of reactants and products, the pH of the solution, and the temperature and pressure
in cell conditions, the free energy difference is approximately:
-12 kcal per mole of ATP
the release of free energy during ATP hydrolysis comes from:
breaking weaker bonds (with more chemical energy) in the reactants and forming more stable bonds (with less chemical energy in the products)
the change in G for the forward and reverse reactions have the same:
absolute value but opposite signs
energetic coupling
the driving of a non-spontaneous reaction by a spontaneous reaction
energetic coupling requires that the net change in G of the two reactions be:
negative and the two reactions must occur together or share an intermediate
the synthesis of ATP from ADP and inorganic P is an:
endergonic reaction with a positive change in G requiring an input of energy
in some cases, the synthesis of ATP can be driven by:
exergonic reactions through energetic coupling
hydrolysis reactions can be ranked by:
their free energy differences (change in G)
ADP is an energy:
ACCEPTOR
ATP is an energy:
DONOR
reactions with a free energy difference more negative than that of ATP hydrolysis transfer:
a phosphate group to ADP by energetic coupling (helping to drive ATP synthesis because it is more exergonic)
reactions with a free energy differences less negative than that of ATP hydrolysis receive:
a phosphate group from ATP by energetic coupling (because it is less exergonic compared to ATP hydrolysis)
the free energy difference for ATP hydrolysis compared to hydrolysis of common phosphorylated molecules is:
intermediate which allows ATP to drive reactions as well as be replenished
