21 - Metabolism

Question 1

Metabolism

Answer 1

the set of chemical reactions that occur within a living organism in order to maintain life

Question 2

ΔG°

Answer 2

Standard free energy change. Difference in energy between substrates and products in a reaction at physiological pH, temp and pressure

Question 3

E’0

Answer 3

Standard reduction potential of redox half reactions

Question 4

Δ E’0

Answer 4

Difference in E’0 between two redox pairs

Question 5

Electron Transport Chain (ETC)

Answer 5

Series of linked half reactions having sequentially more positive E’0 values. Ensures that electrons are directed through chain to a terminal electron acceptor

Question 6

Proton Motive Force (PMF)

Answer 6

Energy that is generated by the transfer of protons or electrons across an energy-transducing membrane. Creates a potential difference across the membrane

Question 7

Electron carriers (ECs)

Answer 7

Molecules (NAD+, FAD) that transfer electrons to the electron transport chain (ETC)

Question 8

first law of thermodynamics

Answer 8

Energy can be neither created nor destroyed

Question 9

second law of thermodynamics

Answer 9

physical and chemical processes proceed in such a way that disorder (Entropy) increases

Question 10

3 types of work of bacteria

Answer 10

• Chemical work (synthesis of complex biological molecules from much simpler precursors)
• Transport work (take up nutrients, eliminate wastes, and maintain ion balances)
• Mechanical work (cell motility and the movement of structures within cells)

Question 11

Equilibrium constant (Eeq)

Answer 11

Keq = [C][D] / [A][B]

Question 12

Chemical reaction

Answer 12

A + B ⇌ C + D

Question 13

Keq greater than 1.0

Answer 13

Reaction is exergonic (favours forward reaction. C + D products)

Question 14

Keq less than 1.0

Answer 14

Reaction is endergonic (favours reverse reaction A + B products)

Question 15

Exergonic reaction

Answer 15

Net release of free energy (reaction is spontaneous). Negative ΔG. “earns ATP”

Question 16

Example of exergonic reaction

Answer 16

Respiration (generates energy) termed fuelling reactions

Question 17

Endergonic reaction

Answer 17

requires energy/energy is absorbed (positive ΔG). Requires a coupled exergonic reaction to supply energy. “spends ATP”

Question 18

Example of endergonic reaction

Answer 18

Anabolism (requires energy) and 3 types of work

Question 19

Cell energy cycle

Answer 19

Exergonic reactions power endergonic reactions through cycling ATP

Question 20

2 main ways of forming ATP

Answer 20

1. Substrate level phosphorylation
2. Oxidative phosphorylation

Question 21

Substrate level phosphorylation

Answer 21

Direct phosphorylation of ADP by substrates with high phosphate transfer potential

Question 22

Oxidative phosphorylation

Answer 22

Indirect production of ATP by ATP synthase. ATP synthase powered by proton gradient
(proton motive force)

Question 23

3 components of oxidative phosphorylation

Answer 23

1. Capture and transfer of energy as electrons by NAD+ and FAD
2. Transport of electrons to and along an electron transport chain
3. ATP synthase

Question 24

Why are electrons thought of as packets of energy in cells

Answer 24

1. Many essential biochemical reactions occur are driven by the transfer of electrons between reactants
2. Electron transfer is directly coupled to formation of electrochemical energy (the proton motive force, PMF)

Question 25

Redox reactions

Answer 25

• Electrons move from an electron donor to an electron acceptor (the reactants in the reaction)
• Produces an oxidised form of the
  donor and a reduced form of the acceptor
  (the products of the reaction)
• As electrons transfer from donor to
  acceptor, the donor becomes less energy
  rich and the acceptor becomes more
  energy rich

Question 26

Redox pair

Answer 26

Includes an electron donor and an electron acceptor.

Question 27

the oxidation half-reaction

Answer 27

The donor and its oxidised product form
one half of a redox pair in a redox reaction

Question 28

the reduction half-reaction

Answer 28

The acceptor and its reduced product form
the other half of a redox pair in a redox
reaction

Question 29

Lose electron

Answer 29

Oxidation (LEO)

Question 30

Gain electron

Answer 30

Reduction (GER)

Question 31

Are redox reactions reversible

Answer 31

Yes. Compounds can also act as a donor in a certain reaction but an acceptor in another

Question 32

What determines whether a compound acts as a donor or receptor

Answer 32

the standard reduction potential of the half-reactions (E’0). Measured in volts

Question 33

redox pairs with more negative E’0

Answer 33

Spontaneously donate electrons in a pair with more positive E’0

Question 34

ATP synthase

Answer 34

The proton motive force is used to generate ATP by the enzyme ATP snythase (ADP –> ATP)

Question 35

Electron flow

Answer 35

Flow from electron carrier with the most negative reduction potential to the most positive reduction potential

Question 36

Reduction potential

Answer 36

tendency of a chemical species to acquire electrons from or lose electrons to an electrode

Question 37

3 forms of biochemical pathways

Answer 37

Linear ( 1–>1), branched (1–>2) and cyclic (continuous)

Question 38

Different kinds of metabolites

Answer 38

• Metabolites that enter the pathway (substrates)
• Metabolites that exit the pathway (products)
• Metabolites in between are intermediates
• Metabolites from one pathway can serve as substrates in others

Question 39

enzymes

Answer 39

Biological catalysts that speed up metabolic reactions by reducing the activation energy. Can be stand-alone or holoenzymes (apo-enzyme plus a cofactor)

Question 40

proton motive force

Answer 40

1. Electron transfer between each adjacent redox pair generates energy
2. This energy is used to pump protons (H+) outside across a membrane to
   generate a proton motive force
3. This creates a potential difference across the membrane

Question 41

ETC in bacteria

Answer 41

ETC in bacteria are located in the plasma membrane (phospo bilayer)