L17: Intro To Metabolism

Question 1

Energy

Answer 1

Organisms acquire energy from sources in surroundings

Energy obtained from sources via exergonic chemical reactions (energy yielding)

Cells trap released energy & store for later use

Most commonly used and stored form of cellular energy: chemical adenosine 5’ triphosphate (ATP)

Question 2

Fuelling reactions

Answer 2

Reactions that supply ATP, precursers and reducing power for biosynthesis

Question 3

Structure of ATP

Answer 3

Cells store energy their energy sources by adding phosphate group to ADP

Energy is stored in bond

Question 4

Hydrolysis

Answer 4

When energy is required to drive reaction in cell: ATP hydrolysed to ADP

Hydrolysis of bond between terminal and second to terminal phosphate groups-> releases stored energy -> energy available go do work in cell

Standard free energy change of reaction: measure of energy released

Question 5

Role of ATP

Answer 5

High energy molecule

Exergonic (energy releasing) breakdown of ATP coupled with endergonic (energy requiring) reactions to make more favourable

In cells, other nucleoside phosphates in addition to ATP (guanosine 5’ triphosphate, cytosine 5’- triphosphate, uridine 5’- triphosphate) also apply some energy

Question 6

ATP formation

Answer 6

1. Through process: substrate level phosphorylation (SLP). Inorganic phosphate group (Pi) can be added to compound that has high phosphate transfer potential. Compounds readily give up their phosphate groups. Reaction of compound with ADP -> ATP
2. By oxidative phosphorylation. Energy (as electrons) is harvested during fuelling reactions in redox reactions

Specialised e carriers pass e to an e transport chain, where energy is used to produce unique energy form: proton motive force (PMF)

PMF is used to add Pi to ADP (enzyme involved: ATP synthase)

Question 7

Electrons as energy

Answer 7

Electrons: ‘packets of energy in cells’

1. Many essential biochemical reactions occur (driven by transfer of e between reactants)
2. E transfer in some of reactions is directly coupled to formation of electrochemical energy (proton motive force)

Involve movement of e from e donors to e acceptors (reducing reaction), chemicals acquiring e: have reducing power

Question 8

Redox reactions

Answer 8

Capture & retention of energy from energy source usually involve redox reactions

E move from e donor to e acceptor (reactants)

Produces oxidised form of donor and reduced form of acceptor (products of reaction)

Donor and oxidised product -> one redox pair (oxidation half-reaction)

Acceptor and its reduced product -> another redox pair (reduction half reaction)

Do not always proceed in only one direction

Each half reaction: reversible

Compound acts as donor or acceptor determined by reduction potential of half reaction

Redox pair with more negative reduction potential -> spontaneously donate e

NADH: e donor, O2: e acceptor

Difference between reduction potential: how much free energy is released in reaction

Question 9

Proton motive force

Answer 9

Energy released between each adjacent redox pair (e flow through ETC) provides energy that is used by cell to pump protons to outside of plasma membrane ( prokaryotes) or mitochondrial inner membrane (eukaryote)

-> potential difference across membrane

Question 10

Electron transport chains

Answer 10

Redox reactions often linked together to form ETC

Ensures e are directed through chain to terminal e acceptor -> prevents loss of e in random redox reactions and ensures energy released between each adjacent redox pair in chain is released in controlled manner