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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
Describe the action of complices I, III and IV
- on each reduction-oxidation cycle, they pump a proton from the cytoplasm across the membrane - creates a proton gradient
26
What does the proton gradient in oxidative phosphorylation represent?
- a source of potential energy (chemical and charge gradient) - a proton motive force
27
What does the proton motive force do?
Drives ATP synthesis via ATP synthase protein complex
28
Why is oxidative phosphorylation called that?
Because it relies on oxidative metabolism, not oxygen involvement
29
Describe the composition of protein complices
1. Flavin mononucleotide 2. Fe-S clusters 3. Ubiquinone
30
From where is flavin derived
Vitamin B2
31
Ubiquinone aka
Coenzyme Q10
32
Describe e- transport and H+ pumping by complex I
- 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
Describe electron jumping
Occurs over a precise position and distance
34
Describe the Ubiquinone channel
Tight
35
Redox active metals and organic compounds facilitate
Electron transfer
36
Haem
A tetrapyyrole ring with Fe atom in centre
37
As you go down the ETC
- electron carrier reduction potential increases (from -0.420V to + 0.031V) - decreasing tendency to donate electrons
38
How does e- transport drive proton pumping?
- electron transport releases free energy - drives conformational change in ETC complices - protons pumped from inside cell, across cell membrane, into periplasmic space
39
Carboxylic acids were most likely
The first molecules to spontaneously arise from CO2 and H2
40
Conditions required for carboxylic acid synthesis
- high temp (40-70) - high pressure - reduced redox-active metals (Fe, No£
41
ATP Synthase is a
- rotary motor - subunit a provides a periplasmic space half channel and à cytosolic half channel - subunit c ring and aspartic acid (conserved)
42
Summary of OP
- 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
ETC
series of large membrane spanning protein complices connect by mobile electron carriers
44
Examples of mobile electron carriers
- ubiquinone (Q) - cytochrome c
45
Advantages of proton gradients
1. Flexible 2. Efficient
46
Describe the flexibility of proton gradients
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
Give an example of a universal electron carrier
NAD+
48
Substrate level phosphorylation is
- tied to a specific chemistry - less flexible than oxidative phosphorylation
49
Describe the efficiency of proton gradients
Regeneration of NAD+ allows more energy to be extracted from carbon sources as they pass down ETC
50
What generates the cellular battery?
Displacement of ATP:ADP ratio from equilibrium
51
What is the cellular battery?
The chemical energy store
52
All chemical reactions tend towards
Equilibrium
53
What does it mean if something is kinetically unstable?
- Slow, needs catalysis - means you can control its coupling
54
Pyruvate
Triose
55
Oxygen is an
Abundant, relatively available electron acceptor that is easy to reduce, and gives the benign product, water
56
Synthesis of CoA requires
Vitamin B5
57
Examples of carboxylic acids
1. Fatty acids 2. Amino acids
58
What are carboxylic acids the result of?
Spontaneous chemistry at the evolution of life
59
Carboxylic acids are
Conserved universally, in all branches of the evolutionary tree
60
Where do the conformational changes occur in the ATP synthase rotary motor?
In the head group
61
The C ring in the ATP synthase rotary motor is made up of
Multiple c subunits
62
What did the occurrence of oxygen in the atmosphere allow?
increased efficiency of fuel extraction

Michaelmas Term 1 (42 decks)

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