Session 2 Flashcards
(40 cards)
What are the requirements for the TCA cycle?
- NAD+
- FAD+
- Oxaloacetate
- Acetyl CoA
Where does the TCA cycle occur?
Mitochondria
What is the main function of the TCA pathway?
- Oxidise carbon atoms to CO2
- Transfer of H+ and e- to NAD+ and FAD
- Breaking of C-C bonds in acetate
- Production of ATP
What can the TCA cycle not function without?
-Oxygen
What does the intermediates in the TCA cycle allow for in terms of biosynthesis?
- Amino acids
- Haem synthesis
- Fatty acid synthesis
What enzyme catalyses the conversion of pyruvate to oxaloacetate?
Pyruvate Carboxylase
What are the characteristics of pyruvate dehydrogenase?
- Exist in the Mitochhondrial matrix
- Large multi complex (5 enzymes)
- Co-factors required leads to PDH being sensitive to vitamin B1 deficiency.
- Reaction is irreversible so is a key regulatory step
What is the result of PDH deficiency?
Lactic acidosis
What are the ways in which isocitrate dehydrogenase is regulated?
- Stimulated by ADP
- Inhibited by NADH and ATP
What are the ways in which alpha-ketoglutarate dehydrogenase is regalated?
Inhibited by NADH, ATP, and Succinyl-CoA
What are the key characteristics of stage 4 catabolism of carbohydrates?
- Mitochondrial
- Electron transport
- NADH & FADH2 re-oxidised
- O2 required which is reduced to H2O
- Large amounts of energy int he form of ATP is produced
What is the use of reducing power in ATP synthesis?
- Electrons on NADH and FADH2 transferred through a series of carrier molecules to oxygen (ELECTRON TRANSPORT)
- Free energy released used to drive ATP synthesis (OXIDATIVE PHOSPHORYLATION)
What is the process of oxidative phosphorylation?
- Electrons are transferred from NADH and FADH2 through a series of carrier molecules to O2 with release of energy
- Energy used to move H+ across membrane
- H+ gradients is established across inner mitochondrial membrane. Proton motive force established
- Return of protons is favoured energetically by the electrochemical potential
- Protons can only return across membrane via the ATP synthase and this drives ATP synthesis
Electrons in NADH have more energy than in FADH2. true/false
True
How is oxidative phosphorylation regulated?
- When ATP is high (therefore ADP low) no substrate for ATP synthase
- Inward flow of H+ stops
- Concentration of H+ in the intermitochondrial space increases
- Prevents further H+ pumping - stops electron transport
What is an example of an inhibitor of oxidative phosphorylation?
- Cyanide, Carbon monoxide
- Blocks electron transport therefore prevents acceptance of electrons. Therefore no proton motive force so no oxidative phosphorylation
What are examples of uncouplers of oxidative phosphorylation?
How do they work?
-Dinitrophenol, Dinitrocresol, Fatty Acids
- Increases the permeability of membrane of H+
- H+ enters mitochondria without driving ATP synthase so dissipates proton motive force. No phosphorylation of ADP as a result so no inhibition of electron transport
What happens to energy lost during oxidative phosphorylation?
- It is lost as heat.
- Efficiency of oxidative phosphorylation depends on the tightness of coupling
What does brown adipose tissue contain that allows for heat generation in response to the cold?
-Contains thermogenin (UCP1)
- In response to the cold, noradrenaline activates
- Lipase triggers release of fatty acids from TAG
- Fatty acid oxidation occurs so NADH and FADH2 are formed.
- Electron transport can occur
- UCP1 transport H+ back into mitochondria
- Electron transport is uncoupled from ATP synthesis. Energy from the p.m.f is released as EXTRA HEAT
Oxidative VS Substrate level Phosphorylation
Oxidative phosphorylation
- Requires membrane associated complexes
- Energy coupling occurs indirectly through generation & subsequent utilisation of proton gradients
- Cannot occur in the absence of O2
- Major process for ATP synthesis in cells requiring large amounts of energy
Substrate level phosphorylation
- Requires soluble enzymes
- Energy coupling occurs directly through formation of high energy hydrolysis bone
- Can occur to a limited extent in the absence of O2
- Minor process for ATP synthesis in cells requiring large amounts of energy
What are the benefits of TAGs that allow it to be stored?
How is storage and mobilisation control?
- Hydrophobic therefore stored in anhydrous form in a specialised tissue called adipose tissue.
- Controlled by hormones
When are TAGs utilised?
- Utilised in prolonged exercise, starvation and during pregnancy
- Released as fatty acids when need and carried to tissues as albumin-fatty acid complex
How are TAGs in the diet metabolised and transported?
- TAGs in diet are hydrolysed by pancreatic lipase in small intestine to fatty acids and glycerol
- They are recombined back to TAGs in the G.I tract and packaged into lipoprotein particles (CHYLOMICRONS)
- They are released into circulation via lymphatics
- They are then carried to adipose tissue and stored as TAGs
How does fatty acid catabolism occur?
-Occurs in the mitochondria
- Fatty acid is activated by linkage to co-enzyme A outside the mitochondrion by the action of ‘fatty acyl CoA synthase’
- The fatty acids is transported across the inner mitochondria membrane using a carnitine shuttle
- Fatty Acid cycles through a sequence of oxidative reactions with 2 carbons being removed each cycle
