Key Concepts - Week 8 - Thermodynamics

Question 1

Bioenergetics studies…?

Answer 1

energy relationships and energy conversions in biological systems

Question 2

Cells are constantly performing work to maintain their _______________. They require energy to perform work and maintain this organised structure, to ________________, and transport _______________ across membranes.

Answer 2

function and structure

synthesise cellular components

small molecules and ions

Question 3

Biomolecules (e.g. lipids, sugars and proteins) store ________ in their ___________

Answer 3

energy

chemical bonds

Question 4

To obtain energy from biomolecules they are converted into other ________, such as _____, after several ________________.

Answer 4

molecules

ATP

biochemical reactions

Question 5

ATP is known as the __________, and is the principal molecule for ____________________ in cells.

Answer 5

energy currency

storing and transferring energy

Question 6

Energy transformations in biological systems obey the…?

Answer 6

laws of thermodynamics

Question 7

Biochemical reactions are influenced by two forces: what are they?

Answer 7

the tendency to achieve the most stable bonding state (expressed as enthalpy, H) and the tendency to achieve the highest degree of randomness (expressed as entropy, S).

Question 8

The driving force in a reaction is…? Which is the…?

Answer 8

ΔG, the free-energy change, which represents the net effect of enthalpy and entropy: ΔG=ΔH−T ΔS.

Question 9

The standard free-energy change, ΔG′°, is a ________ and is a characteristic for …?

Answer 9

constant

a given reaction and can be calculated from the equilibrium constant for the reaction: ΔG′°=−RT  ln Keq′.

Question 10

The free-energy change,_______, is a variable that…?

Answer 10

ΔG

Depends on ΔG′° and on the experimental conditions, such as temperature, concentrations of reactants and products: ΔG=ΔG′°+RT  ln([products]/[reactants]).

Question 11

When ΔG is negative, the reaction is…?

Answer 11

thermodynamically favourable and tends to go in the forward direction; when ΔG is positive, the reaction is thermodynamically unfavourable and tends to go in the reverse direction; and when ΔG=0, the system is at equilibrium

Question 12

Free-energy changes are ________; the net chemical reaction that results from successive reactions has an…?

Answer 12

additive

overall free-energy change that is the sum of the ΔG values for the individual reactions.

Question 13

In cells, endergonic processes are coupled with…?

Answer 13

exergonic reactions of high energy compounds to be thermodynamically favourable (i.e. to create free energy)

Question 14

The rate of a reaction depends on the…?

Answer 14

Activation energy (i.e. the energy required to reach the transition state and start a reaction), and is independent from ΔG

Question 15

Enzymes accelerate biochemical reactions by…?

Answer 15

Lowering their activation energy (EA). Enzymes don’t change the ΔG of a reaction.

Question 16

Living systems use biochemical reactions that can be classified into five general types: list them all and describe

Answer 16

reactions that make or break carbon–carbon bonds; internal rearrangements and eliminations; free-radical reactions; group transfers; and oxidation-reduction reactions

Question 17

Phosphoryl transfer reactions are especially important in cells, as they are required for…?

Answer 17

the activation of molecules in reactions that would be thermodynamically unfavourable (see coupling of reactions in previous lesson).

Question 18

Oxidation-reduction reactions involve…?

Answer 18

the loss or gain of electrons: one reactant gains electrons and is reduced, while the other loses electrons and is oxidised

Question 19

Biological oxidation-reduction reactions can be described as ____ reactions, each with a characteristic…?

Answer 19

two

standard reduction potential, E′°

Question 20

The standard free-energy change, _______ , for an oxidation-reduction reaction is directly proportional to…?

Answer 20

ΔG′°

the difference in standard reduction potentials of the two reactions via the correlation: ΔG′°=−nFΔE′°

Question 21

Oxidation-reduction reactions in living cells use specialised ______________ __________. ______ and _____ are coenzymes of many ____________. _____ and _____ accept two electrons and one proton.

Answer 21

electron carriers

NADH and NADPH

dehydrogenases

NAD+ and NADP+

Question 22

Electron carriers, such as NADH and NADPH, provide ________ _________ in the cell

Answer 22

reducing power

Question 23

The ________________ in reduction-oxidation reactions is responsible, directly or indirectly, for all work done by living organisms

Answer 23

flow of electrons