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Michaelmas Term 1 > Charging The Cellular Batteries > Flashcards

Charging The Cellular Batteries Flashcards

1
Q

What is the ‘ATP battery’ charged with?

A
  • Catabolism of organic carbon substrates
  • photosynthesis
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2
Q

What does the ‘ATP battery’ discharge?

A

free energy coupled to thermodynamically unfavourable reactions for biosynthesis of cellular components

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3
Q

Why is ATP useful as an energy carrier?

A

Interconversion between ATP and ADP + Pi has an unusually high Keq

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4
Q

Keq

A
  • Equilibrium constant
  • concentration of products / concentration of reactants
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5
Q

How much ATP will there be at equilibrium?

A

Vanishingly small amounts

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6
Q

At what concentration is ATP maintained in a cell, relative to ADP

A

~3 fold greater

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7
Q

What are the typical concentration of ADP, ATP and Pi in a cell?

A

ADP = 1mM
ATP = 3mM
Pi = 10mM

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8
Q

How far is the ATP reaction displaced from equilibrium?

A

30,000 fold

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9
Q

Properties of ATP

A
  • thermodynamically unstable
  • kinetically stable
  • middling relative Gibbs free energy release on phosphoester hydrolysis (compared to other phosphate compound)
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10
Q

Why is the middling free energy of ATP hydrolysis important?

A

Unfavourable reverse reaction (condensation of ADP and Pi to form ATP) can be found oven by coupling to other phosphate compound hydrolysis

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11
Q

What are the two mechanisms to charge the ATP battery

A
  1. Substrate-level phosphorylation
  2. Oxidative phosphorylation
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12
Q

Substrate-level phosphorylation

A
  • metabolic reaction for ATP formation by direct transfer of PO3 to ADP, from another phosphorylated compound
  • Phosphate is passed from one substrate to another
  • requires large free energy coupling reactions, because of unfavourable synthesis
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13
Q

PO3

A

Phosphoryl group

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14
Q

NAD+

A

Nicotinamide adenine dinucleotide

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15
Q

NADH formation equation

A

NAD+ + H+ + 2e- -> NADH

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16
Q

Describe substrate-level phosphorylation

A

1) hexose sugar formed
2) double phosphorylated triose formed
3) phosphoryl transfer from triose to ADP

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17
Q

Why do you need fermentation in the absence of oxygen?

A

To maintain glycolysis, through NAD+ electron acceptor regeneration

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18
Q

Where is NAD+ regenerated?

A

As a byproduct of the transition of acetaldehyde to ethanol

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19
Q

Describe the electron transport chain

A
  • embedded into cell membrane
  • 4 separate protein complices
  • contains electron carriers
  • complices I, III and IV span the membrane
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20
Q

Give an example of an electron carrier

A

Cytochrome c

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21
Q

What supplies the electrons to the electron transport chain

A

The tricarboxylic acid cycle

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22
Q

What is the tricarboxylic acid cycle

A

An oxidative metabolic cycle

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23
Q

Describe the process of electron transport

A
  • each ETC complex is reduced the oxidised as it receives and passes on an electron pair to the proceeding complex (reduction-oxidative cycle)
  • oxygen is the terminal electron acceptor
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24
Q

Describe oxygen reduction to water as the terminal electron acceptor

A

1/2O2 + 2e- + 2H+ <-> H2O

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25
Q

Describe the action of complices I, III and IV

A
  • on each reduction-oxidation cycle, they pump a proton from the cytoplasm across the membrane
  • creates a proton gradient
26
Q

What does the proton gradient in oxidative phosphorylation represent?

A
  • a source of potential energy (chemical and charge gradient)
  • a proton motive force
27
Q

What does the proton motive force do?

A

Drives ATP synthesis via ATP synthase protein complex

28
Q

Why is oxidative phosphorylation called that?

A

Because it relies on oxidative metabolism, not oxygen involvement

29
Q

Describe the composition of protein complices

A
  1. Flavin mononucleotide
  2. Fe-S clusters
  3. Ubiquinone
30
Q

From where is flavin derived

A

Vitamin B2

31
Q

Ubiquinone aka

A

Coenzyme Q10

32
Q

Describe e- transport and H+ pumping by complex I

A
  • chain of redox centres (mostly Fe-S) allow electron jumping
  • oxidised Ubiquinone binds to channel
  • 2e- from NADH to ubiquinone releases much free energy
  • drives a series of piston like conformational changes
  • 4H+ channels open towards inside of cell
  • protons enter connected water river running through centre of membrane arm
  • conformational change pushes protons to the left; opens channels to the outside of the cell
  • proton ejected
33
Q

Describe electron jumping

A

Occurs over a precise position and distance

34
Q

Describe the Ubiquinone channel

A

Tight

35
Q

Redox active metals and organic compounds facilitate

A

Electron transfer

36
Q

Haem

A

A tetrapyyrole ring with Fe atom in centre

37
Q

As you go down the ETC

A
  • electron carrier reduction potential increases (from -0.420V to + 0.031V)
  • decreasing tendency to donate electrons
38
Q

How does e- transport drive proton pumping?

A
  • electron transport releases free energy
  • drives conformational change in ETC complices - protons pumped from inside cell, across cell membrane, into periplasmic space
39
Q

Carboxylic acids were most likely

A

The first molecules to spontaneously arise from CO2 and H2

40
Q

Conditions required for carboxylic acid synthesis

A
  • high temp (40-70)
  • high pressure
  • reduced redox-active metals (Fe, No£
41
Q

ATP Synthase is a

A
  • rotary motor
  • subunit a provides a periplasmic space half channel and à cytosolic half channel
  • subunit c ring and aspartic acid (conserved)
42
Q

Summary of OP

A
  • oxidative glycolysis metabolism and TCA cycle provide electrons from carbon substrates carried by NADH and FADH2
  • electrons pass down ETC
  • ETC reduction-oxidation cycles release free energy
  • free energy coupled to proton pumping through respiratory complices
  • electrochemical gradient powers ATP synthase rotary motor
  • oxygen is reduced to water, as terminal electron acceptor
43
Q

ETC

A

series of large membrane spanning protein complices connect by mobile electron carriers

44
Q

Examples of mobile electron carriers

A
  • ubiquinone (Q)
  • cytochrome c
45
Q

Advantages of proton gradients

A
  1. Flexible
  2. Efficient
46
Q

Describe the flexibility of proton gradients

A

Energy sources (fuel) is irrelevant as long as electrons can be extracted and given to universal electron carriers for proton gradient generation for ATP Synthesis

47
Q

Give an example of a universal electron carrier

A

NAD+

48
Q

Substrate level phosphorylation is

A
  • tied to a specific chemistry
  • less flexible than oxidative phosphorylation
49
Q

Describe the efficiency of proton gradients

A

Regeneration of NAD+ allows more energy to be extracted from carbon sources as they pass down ETC

50
Q

What generates the cellular battery?

A

Displacement of ATP:ADP ratio from equilibrium

51
Q

What is the cellular battery?

A

The chemical energy store

52
Q

All chemical reactions tend towards

A

Equilibrium

53
Q

What does it mean if something is kinetically unstable?

A
  • Slow, needs catalysis
  • means you can control its coupling
54
Q

Pyruvate

A

Triose

55
Q

Oxygen is an

A

Abundant, relatively available electron acceptor that is easy to reduce, and gives the benign product, water

56
Q

Synthesis of CoA requires

A

Vitamin B5

57
Q

Examples of carboxylic acids

A
  1. Fatty acids
  2. Amino acids
58
Q

What are carboxylic acids the result of?

A

Spontaneous chemistry at the evolution of life

59
Q

Carboxylic acids are

A

Conserved universally, in all branches of the evolutionary tree

60
Q

Where do the conformational changes occur in the ATP synthase rotary motor?

A

In the head group

61
Q

The C ring in the ATP synthase rotary motor is made up of

A

Multiple c subunits

62
Q

What did the occurrence of oxygen in the atmosphere allow?

A

increased efficiency of fuel extraction

Michaelmas Term 1 (42 decks)

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