6.4 Chemical Reactions

Question 1

what is a chemical reaction?

Answer 1

the process by which molecules, called reactants, are transformed into other molecules, called products

Question 2

what changes during a chemical reaction?

Answer 2

the bonds linking the atoms

Question 3

most chemical reactions in the cell are readily reversible, what does that mean?

Answer 3

the products can react to form the reactants

Question 4

the way the reaction is written defines forward and reverse reactions:

Answer 4

a forward reaction proceeds from left to right, a reverse reaction proceeds from right to left

Question 5

the direction of a reaction can be influenced by:

Answer 5

the concentrations of reactants and products

Question 6

how to favour the forward reaction?

Answer 6

increase the concentration of the reactants or decrease the concentration of the products

Question 7

the effect of favouring the forward reaction can be found in the reactions of many metabolic pathways, how does that work?

Answer 7

the products of many reactions are quickly consumed by the next reaction, helping to drive the first reaction forward

Question 8

Gibbs free energy (G)

Answer 8

the amount of energy available to do work

Question 9

how does one determine whether the reaction releases energy that is available to do work?

Answer 9

you can compare the free energy of the reactants and products

Question 10

what is delta G (change in G)

Answer 10

the free energy of the products minus the free energy of the reactants

Question 11

if change in G is positive:

Answer 11

the products of a reaction have more free energy than reactants and a net input of energy is required to drive the reaction forward

Question 12

if change in G is negative:

Answer 12

the products of a reaction have less energy than reactants and energy is released and available to do work

Question 13

exergonic

Answer 13

describes reactions with a negative change in G that release energy and proceed spontaneously

Question 14

endergonic

Answer 14

describes reactions with a positive change in G that are not spontaneous and so require an input of energy

Question 15

spontaneous in the context of free energy means that:

Answer 15

a reaction releases energy

Question 16

non-spontaneous in the context of free energy means that:

Answer 16

a reaction requires a sustained input of energy

Question 17

the total amount of energy is equal to:

Answer 17

the energy available to do work plus the energy that is not available to do work because of the increase in entropy

Question 18

enthalpy (H)

Answer 18

the total amount of energy in a system

Question 19

entropy (S)

Answer 19

the degree of disorder in a system

Question 20

absolute temperature (T)

Answer 20

temperature measured on the kelvin scale

Question 21

the formula for the total amount of energy (H) is:

Answer 21

energy available to do work (G) + energy lost to entropy (TS)

Question 22

the formula to determine energy available to do work (G) is:

Answer 22

H - TS

total amount of energy - energy lost to entropy

Question 23

the value of change in G depends on BOTH the:

Answer 23

change in enthalpy and the change in disorder

Question 24

catabolic reactions are those in which the products have :

Answer 24

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)

Question 25

anabolic reactions are the opposite of catabolic reactions so:

Answer 25

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

Question 26

if the change in enthalpy and entropy are both positive or both negative, whether or not the reaction is spontaneous is determined by:

Answer 26

the absolute value of these parameters which then determines whether delta G is positive or negative

Question 27

what effect does increasing temperature have on the free energy (delta G) of a chemical reaction?

Answer 27

increasing the temperature increases the value of (TS) which decrease G (G=H-TS)

Question 28

hydrolysis reactions consist of a chemical reaction in which a water molecule is split into:

Answer 28

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

Question 29

the reaction of ATP with water is an exergonic reaction because:

Answer 29

there is less free energy in the products compared to the reactants

Question 30

why is the reaction of ATP an exergonic reaction?

Answer 30

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

Question 31

the free energy difference for ATP hydrolysis is approximately: (under lab conditions)

Answer 31

-7.3 kcal per mole of ATP

Question 32

the value of the free energy difference for ATP hydrolysis is influenced by several factors including:

Answer 32

the concentration of reactants and products, the pH of the solution, and the temperature and pressure

Question 33

in cell conditions, the free energy difference is approximately:

Answer 33

-12 kcal per mole of ATP

Question 34

the release of free energy during ATP hydrolysis comes from:

Answer 34

breaking weaker bonds (with more chemical energy) in the reactants and forming more stable bonds (with less chemical energy in the products)

Question 35

the change in G for the forward and reverse reactions have the same:

Answer 35

absolute value but opposite signs

Question 36

energetic coupling

Answer 36

the driving of a non-spontaneous reaction by a spontaneous reaction

Question 37

energetic coupling requires that the net change in G of the two reactions be:

Answer 37

negative and the two reactions must occur together or share an intermediate

Question 38

the synthesis of ATP from ADP and inorganic P is an:

Answer 38

endergonic reaction with a positive change in G requiring an input of energy

Question 39

in some cases, the synthesis of ATP can be driven by:

Answer 39

exergonic reactions through energetic coupling

Question 40

hydrolysis reactions can be ranked by:

Answer 40

their free energy differences (change in G)

Question 41

ADP is an energy:

Answer 41

ACCEPTOR

Question 42

ATP is an energy:

Answer 42

DONOR

Question 43

reactions with a free energy difference more negative than that of ATP hydrolysis transfer:

Answer 43

a phosphate group to ADP by energetic coupling (helping to drive ATP synthesis because it is more exergonic)

Question 44

reactions with a free energy differences less negative than that of ATP hydrolysis receive:

Answer 44

a phosphate group from ATP by energetic coupling (because it is less exergonic compared to ATP hydrolysis)

Question 45

the free energy difference for ATP hydrolysis compared to hydrolysis of common phosphorylated molecules is:

Answer 45

intermediate which allows ATP to drive reactions as well as be replenished