TCA cycle and ETC Flashcards
what is the TCA cycle
- The TCA(krebs cycle) is a the centre of metabolism taking part in glucose, fatty acids and amino acids metabolism
what does the TCA need to function
- need a constant supply of substrate
- need oxygen
what substrates can be used in the TCA cycle
- amino acids from transamination to alanine which is converted to pyruvate
- glucose can feed in from glycolysis
- fatty acids can be converted to acetyl-CoA and this enters the TCA cycle
How does the Krebs cycle work briefly
- Oxaloacetate is combined with acetyl-CoA to make citrate, make intermediates including alpha ketoglutarate and this is then converted back to oxaloacetate
what does pyruvate dehydrogenase complex do
- This converts pyruvate into acetyl-CoA
- 3 carbons in pyruvate 2 carbons in acetyl-CoA
- Loose a carbon in terms of carbon dioxide
how many enzymes is pyruvate dehydrogenase made out of
- It is made up of 3 enzymes joined together that is why it is called a complex
what cofactor is used in pyruvate dehydrogenase
- A number of cofactors is used with it such as thiamine pyrophosphate which is derived from vitamin B1, without vitamin B1 this enzyme and a lot of other dehydrogenases do not work
what is vitamin B1 important in
important for energy generation in the cells and deficiency in this effects energy in the cells
whats the role of TCA
- Only occurs in oxidative metabolism
- allows further production of ATP from Amino acids, glucose and FA
- requires constant supply of substrates (carbon compounds in
cycle) and oxygen - occurs in the mitochondria
what is the first enzyme in the pyruvate dehydrogenase complex
pryruvate dehydrogenase
how is the pyruvate dehydrogenase complex controlled
- uses feedback inhibition for example if there are high levels of acetyl-CoA and NADH are high then it is inhibited
- controlled by covalent modification through phosphorylation by both PDH kinase and PKA
- The signalling pathways in terms of glucagon act to phosphorylate, this blocks down the cells need for sugar, insulin causes dephosphorylation of the enzymes and this activates pyruvate dehydrogenase and this turns on glucose metabolism when glucose is present in excess
what are the products of the TCA cycle
- 2 CO2 lost
- GTP produced via substrate level phosphorylation (direct energy of TCA cycle)
- Acetyl-CoA —> oxaloacetate
- 3NADH + FADH2 made (important co-factors used in the Electron transport chain)
what is the reduced NADH and FADH2 used in
- used in the electron transport chain and oxidised back this produces ATP
how does the electron transport chain work
- uses reduced cofactors e. NADH and FADH2 to move protons against their concentration gradient and allow ATP synthase to make ATP (due to passive transport of protons down concentration their new gradient) = PROTON MOTIVE FORCE
what are the complexes in the electron transport chain and what do they do
- Complex I – NADH to UQ
- Complex II – FADH to UQ
- Complex III – UQ to cytochrome C
- Complex IV – cytochrome C to O2 (this is the final electron acceptor and joins with hydrogens from the reduced NADH and FADH2 to produce water)
how do you generate energy from electrons
- Start from a very highly negative redox potential and move towards a more positive redox potential and you can get energy out
- Complex 1 3 and 4 have significant changes in redox potential so this is where energy can go out
what are 2 inhibitors of electron transport chain
- cyanide
- carbon monoxide gas
describe how cyanide works
it is a inhibitor of complex 4 of the electron transport chain
- It blocks this
- Electron transport chain shuts down
- Get back log of electrons
- This restricts the body in making energy, can no longer make energy using the ETC or TCA cycle
describe how the carbon monoxide works
- It acts as an inhibitor on complex 4 of the electron transport chain
- Not as potent as cyanide
- Inside complex 4 there are haem groups
what is coupling
- Coupling – chemosiomostic principle – and transport, uses the proton gradient made from the electron transport chain to drive the ATPase
what is uncoupling
- Coupling – chemosiomostic principle – and transport, uses the proton gradient made from the electron transport chain to drive the ATPase, if you use the hydrogen gradient for something else so it no longer drives the proton gradient then this is uncoupling
how do you uncouple
- Get rid of the hydrogen ion gradient – make hydrogen ion concentration equal on each side
- Get rid of the charge gradient – make charge equal on each side
what is useful uncoupling used for
- keeping us warm
- natural antibiotics
how does uncoupling keep us warm
- Non-shivering thermogenesis
- Uncoupling protein 1 – thermogenin
- Makes hydrogen ion ions to go through it (channel in the membrane) proton ions make heat instead of ATP
- Enables the baby to keep warm
- Brown adipose tissue
- Recently homologous in other tissues
how do uncoupling in natural antibiotics work
- Bacteria need to make energy
- Do the electron transport on their own cell membrane
- Antibiotics make ion channels in the bacterial cell membrane, this prevents them from being able to make a proton gradient as it flows back down into channels
- Gramicidin – forms 2 half channels
- Nigericin – enables proton to permeate membrane
- Valinomycin – enables dissipation of charge through movement of potassium ions
describe dinitro-phenol
- Dinitro-phenol is able to exsit in two states, state with a hydrogen ion and state without a hydrogen ion
- Has a large benzene ring, in state without hydrogen ion it has a negative charge which is spread throughout the whole molecule
- Both states are membrane soluble
describe what dintiro-phenol does
- Both states are membrane soluble
- Can get into the mitochondria
- It picks up a hydrogen ion and goes across mitochondria membrane and loses a hydrogen
- Alternative group for hydrogen ions to go across the mitochondria membrane
- Dissipates the hydrogen ion gradient and loose the energy as heat
what is the danger of dinitrophenol
- Used as a pesticide in the UK as it is good at uncoupling the electron transport chain and killing insects
- Low does is probably safe but therapeutic window is tiny, electron transport chain becomes uncoupled and you produced loads amount of heat and you are unable to make ATP and you die
what are the intermediates of TCA used to make
amino acids, fatty acids, steroids and nucleotides
if we are taking things out of the cycle…
we are no longer regenerating oxaloacetate
- This is solved by using pyruvate carboxylase
what are the ways in which the TCA cycle can be regenerated
- pyruvate carboxylase allows us to take pyruvate and make oxaloacetate, this allows us to make more oxaloacetate and therefore it is still there to combine with acetyl-CoA so it can flow around the cycle and make citrate
- citrate from the TCA cycle can be exported to the cytosol where it is converted back to the acetyl CoA and oxaloacetate
- the acetyl CoA and this can be used for fat synthesis
what is acetyl CoA used to make in the mitochondria virus in the TCA cycle
- Acetyl CoA in the cytoplasm is used to make things such as fatty acids and cholesterol
when it is in the mitochondria it is used in the TCA cycle
what does beta oxidation do
breaks FA to make acetyl-CoA
Beta-oxidation basically removes 2C (acetyl Co A) from long carbon chain of FA
what is the acetyl-CoA used for when it is made from beta oxidation
Acetyl-CoA used in energy production for gluconeogenesis (not directly for gluconeogenesis)
what to glucogenic amino acids do
- Glucogenic amino acids feed into the TCA cycle beyond alpha ketoglutarate
- The oxaloacetate produced can be used to synthesis glucose in gluconeogenesis
where to glycogenic amino acids feed into the TCA cycle
beyond alpha ketoglutarate
how is the TCA regulated
- It is regulated only be substrates high levels of ATP and high levels of acetyl CoA inhibit the cycle
- Conversely levels of NAD and ADP promote the TCA cycle
- Respond to the energy depend of the cell
- In muscle tissue – dehydrogenases respond to levels of calcium, they are stimulated by calcium linking it to contract
what is hypoxia
- This is the state at which oxygen levels are reduced in the body
what causes hypoxia
- altitude
- trauma
- trying to exercise too much
what does hypoxia do to the ETC
- In hypoxia state it is a problem as you need oxygen for the electron transport chain to run
- Block at complex 4 this means that there is a build up of electrons in complex 4 and whole system backs up,
what does hypoxia cause at complex 1 in the ETC
- Complex 1 – the electrons flow through the complex through the surface of complex 1 and in normal situations this is fine but if the electorns are not allowed to move on, and we end up producing reactive oxygen species
- Reactive oxygen species are oxygen with extra electrons, these can damage parts of our cells
how does the Body reduce the number of reactive oxygen species that is produced by hypoxia
- Reduces the amount of electron transport chain is one way to do this
- Do this by reducing the number of mitochondria inside the cell
- Therefore need less oxygen therefore you are less likely to get reactive oxygen species building up
- Produce the as much as possible by anaerobic metabolism
- Do this by transcription factor called HIF1a
what does HIFa do in normal conditions
- Under normal conditions the alpha subunit of HIF becomes hydroxylated – alcohol groups are added to it, causes another protein to bind and creates a gel and this causes the degradation of alpha subunit
what happens when oxygen is not present to HIFa
- There is no hydroxylation so protein cannot bind
- Alpha subunit binds to the beta subunit
- This binds to HREs
- This turns on a number of genes include GLUT-1, VEGF and EPO
- HIF1 downregulates mitochondria respiration during hypoxia which promotes loss of mitochondrial (autophagy) and supressing biogenesis (via PGC-1)
Why does HIF1 destroy mitochondria
- prevents the formation of reactive oxygen species which causes damage
what do hypoxic adaptations aim to do
- limit ATP use by switching off non-essential cell functions
- improve anaerobic ATP production efficiency
- limit oxidative stress, providing protection against ischaemia
