Carbohydrates 3 And Lipids Flashcards
Explain how the TCA cycle is regulated.
The cycle is regulated at points where CO2 is produced as these steps are irreversible. Isocitrate dehydrogenase catalyses the reaction between isocitrate and a-ketoglutarate. It is activated by ATP and inhibited by ADP.
The whole cycle is also regulated by energy availability, levels of ATP/ADP, NAD/NADH.
Describe the roles of the Tricarboxylic acid cycle (TCA) in metabolism.
To produce biosynthetic reducing power for the electron transport chain (NADH FAD2H). To produce energy from substrate level phosphorylation (GTP). Produces precursors for biosynthesis (e.g. Part of converting one amino acid to another).
Describe the key features of oxidative phosphorylation
Electrons, donated by NADH and FAD2H, travel from PTC to PTC within the inner membrane of the mitochondrial matrix and finally are donated to oxygen. This process releases energy, 30% of which is used to pump H+ into the intermembrane space.
A H+ gradient is maintained by this and is called the size of the gradient is measured by the proton motive force (pmf) or potential difference.
H+ ions can then travel back across the membrane via ATPase. ATP uses the energy release from this to synthesis ATP from ADP. The greater the pmf, the more ATP can be synthesised. This is oxidative phosphorylation.
Explain the process of electron transport and ATP synthesis and how they are coupled.
Electrons, donated by NADH and FAD2H, travel from PTC to PTC within the inner membrane of the mitochondrial matrix and finally are donated to oxygen. Each time electrons reach a new PTC they lose energy. Electrons from NADH travel down 3 PTCs and electrons from FAD2H travel down 2 electrons. This process releases energy, 30% of which is used to pump H+ into the intermembrane space. This is electron transport.
H+ ions can then travel back across the membrane via ATPase. ATP uses the energy release from this to synthesis ATP from ADP. The greater the pmf, the more ATP can be synthesised. This is oxidative phosphorylation (ATP synthesis).
ATP synthesis via oxidative phosphorylation require the H+ gradient produced by electron transport.
Describe how, when and why uncoupling of these processes occurs in some tissues.
Uncoupling is the process of increasing the permeability of the mitochondrial inner membrane.
This causes more energy to be lost as heat which can be useful to warm hibernating animals and newborn babies.
Brown adipose tissue does this because of an uncoupling protein called UPC1 which is activated by fatty acids produced from lipases.
Compare the processes of oxidative phosphorylation (op) and substrate level phosphorylation (sp)
Op requires specific membrane associated complexes whereas sp requires solvable enzymes.
In op energy coupling coupling occurs indirectly due to the production of an H+ gradient. In sp energy coupling occurs directly through transferring energy from molecules to a high energy bond via a phosphorylation reaction.
Op cannot occur without O2 sp can.
Op is a major process in the production of ATP, sp is a minor process but both require lots of energy.
Describe the various classes of lipids
1) Fatty acid derivatives
A) Triacylglyerols - fuel storage and insulation
B) phospholipids - components of membranes and plasma lipoproteins.
C) Fatty acids - fuel molecules
D) Eicosanoids - local mediators known as ‘local hormones’ they function near the site of synthesis and are not transported.
2) Hydroxy-methyl-glutaric (HMG) acid derivatives
A) ketone bodies - water soluble fuel molecules
B) Cholesterol - membranes and steroid hormone synthesis.
C) Cholesterol esters - cholesterol storage
D) Bile acids and salts - lipid digestion
3) Vitamins A E D K
Describe how dietary triacylglycerols are processed to produce energy.
Triacylglycerols can be broken down into 3 fatty acids and glycerol by lipase (lipolysis).
Fatty acids are then transported by FA- albumin via the bloodstream to muscles where they enter cells. They become activated by reacting with CoA which requires energy from ATP. they then are transported across the mitochondrial membrane by a carnotine shuttle. Fatty acetylCoA -> fatty acetyl carnotine -> fatty acetyle CoA. This requires carnotine acyltransferase. The fatty acetyle CoA then undergo catabolism via a cycle of oxidative reactions. Each cycle produces 1 acetylCoA (2C), 1ATP, 1 NADH, H2O and FAD2H. Acetyl CoA can then enter glycolysis to produce energy and NADH and FAD2H can produce energy via oxidative phosphorylation. Fatty acids can be converted back into TAG from fatty acetylCoA reacting with glycerol-1-P, a product of glycolysis.
Glycerol can be converted to glycerol-1-P in the liver by glycerol kinase. This can then be converted to DHAP, reducing NAD, which can then enter glycolysis.
Explain how, when and why ketone bodies are formed.
Ketone bodies are produced in the liver from HMG-CoA, via lyase, which itself is made from AcetylCoA.
Ketones can travel from the liver to muscles where they can be converted back into acetylCoA to be used in glycolysis.
HMG-CoA can also be used to synthesise cholesterol via HMG-CoA reductase (can be reduced by statin drugs). Wether cholesterol or ketone bodies are produced by HMG-CoA depends on levels of insulin/ glucagon. Insulin is high if glucose is high and glucagon is high if glucose is low. Glucagon activates lyase and inhibits HMG-CoA reductase. Insulin activates HMG-CoA reductase and inhibits lyase.
This means when glucose is low, more ketone bodies are produced to supply energy for glycolysis.
Describe the central role of acetylCoA in metabolism.
AcetylCoA is the main convergence point for catabolic pathways. The CH3CO linked to CoA via an S atom means a high energy of hydrolysis.
It is used in the converting of different fuel molecules to products and different fuel molecules to other fuel molecules. This is because glucose, amino acids, ketone bodies, fatty acids, triglycerides, phospholipids and cholesterol all form acetylCoA at some point of their catabolism.
Acetyl CoA however cannot be used to create pyruvate.
