Session 2-Energy Production: Carbs Flashcards
What is another name for the tricarboxylic acid cycle?
Krebs cycle
Where is pyruvate dehydrogenase (PDH) located?
Mitochondrial matrix
How many enzymes is PDH made up of?
5 enzymes
What does PDH deficiency lead to?
Lactic acidosis
What is PDH activated by? (5)
Pyruvate CoASH NAD+ ADP Insulin
What is PDH inhibited by? (4)
Acetyl-CoA
NADH
ATP
Citrate
True or false: PDH activators work by phosphorylation
FALSE - dephosphorylation
Which two reactions in the TCA cycle are irreversible?
1) isocitrate (C6) -> alpha-ketoglutarate (C5)
2) alpha-ketoglutarate (C5) -> succinyl-CoA (C4)
How many TCA cycles occur per glucose molecule?
2
How is the TCA cycle regulated?
Energy availability ie ATP/ADP ratio and NADH/NAD+ ratio
Which two enzymes are allosterically regulated by NADH and ATP in the TCA cycle?
1) isocitrate dehydrogenase
2) alpha-ketoglutarate dehydrogenase
True or false: TCA supplies biosynthetic processes
TRUE
True or false: TCA cycle is only catabolic
FALSE - also anabolic
TCA cycle is the central pathway in the catabolism of which substances? (5)
Sugars Fatty acids Ketone bodies AA Alcohol
How is ATP produced in the TCA cycle?
Substrate level phosphorylation
True or false: TCA cycle can function in the absence of O2
FALSE
Where does electron transport and ATP synthesis occur?
Inner membrane of the mitochondria
Which coenzymes are re-oxidised in stage 4 of catabolism?
NADH
FADH2
What is O2 reduced to in stage 4 of catabolism?
Water
Why does stage 4 of catabolism occur in small steps?
To retain energy
Which two processes use reducing power to synthesise ATP?
1) Electron transport
2) Oxidative phosphorylation
What happens in electron transport?
Electrons on NADH and FADH2 are transferred through a series of carrier molecules to oxygen
What happens in oxidative phosphorylation?
Free energy released is used to drive ATP synthesis
True or false: the inner membrane of a mitochondrion is impermeable
TRUE
What happens to electrons as they are passed from proton translocating complex (PTC) 1 to PTC3?
Lose energy
In the electron transport chain, why do protons want to reenter the matrix and what prevents them from doing so?
- Concentration gradient and electrical gradient
- Membrane is impermeable so can only enter through ATP synthase
Approximately what % of energy is used to move H+ across the membrane in the electron transport chain?
~30%
What is the H+ gradient across the inner mitochondrial membrane called?
Proton motive force (pmf)
Where are electrons transferred to from NADH and FADH2?
Molecular oxygen
Complete the sentence:
Energy from the dissipation of the pmf is coupled to the synthesis of ___ from ___
ATP
ADP
True or false: electrons in FADH2 have more energy than in NADH
FALSE - other way round
How many PTCs does NADH use?
3
How many PTCs does FADH2 use?
2
True or false: the greater the pmf, the _______ ATP is synthesised
More
How is oxidative phosphorylation regulated?
When [ATP] is high ([ADP] is low), no substrate for ATP synthase so the inward flow of H+ stops. The concentration of H+ in the intermitochondrial space increases, preventing further H+ pumping. Electron transport is therefore stopped
Complete the sentence:
Inhibitors ______ electron transport, preventing the acceptance of electrons by _________
Block
Oxygen
Give examples of an inhibitor of oxidative phosphorylation
Cyanide
Carbon monoxide
What do uncouplers of oxidative phosphorylation do?
Increase permeability of the inner mitochondrial membrane to protons. This dissipates the proton gradient, thereby reducing the pmf so there is no drive for ATP synthesis
Give an example of uncouplers
Fatty acids
What does the efficiency of coupling of oxidative phosphorylation depend on?
Tightness of coupling
What controls the degree of coupling in brown adipose tissue and what does this allow?
Fatty acids
Allows extra heat generation
What does brown adipose tissue contain that is usually inactive?
Thermogenin (UCP1) = naturally-occurring uncoupling protein
What is activated in UCP1’s response to cold and noradrenaline? (2)
1) lipase which releases fatty acids from triacylglycerol
2) fatty acid oxidation -> NADH/FADH2 -> electron transport
Apart from cold and noradrenaline, what else activates UCP1 and what effect does this have?
- Fatty acids
- UCP1 transports H+ back into mitochondria so electron transport is uncoupled from ATP synthesis and the energy of pmf is released as extra heat.
In which organisms can brown adipose tissue be found in?
Newborn infants
Hibernating animals
In what way are the enzymes used in oxidative phosphorylation different to those used in substrate level phosphorylation?
In oxidative, enzymes are membrane-associated whereas in substrate level, enzymes are soluble
True or false: energy coupling occurs indirectly through the generation and subsequent utilisation of a proton gradient in substrate level phosphorylation
FALSE - ^ in oxidative
How does energy coupling occur in substrate level phosphorylation?
Directly through formation of high energy hydrolysis bond
True or false: oxidative phosphorylation can occur to a limited extent in the absence of O2
FALSE - ^ is substrate level
Which is the major process for ATP synthesis?
Oxidative phosphorylation
How many moles of ATP are produced per mole of glucose?
32
The reaction catalysed by PDH is sensitive to the deficiency of which vitamin?
B1
Which reaction does PDH catalyse?
Pyruvate -> acetyl-CoA + CO2
