What is the TCA cycle?
cyclic metabolic pathway that oxidizes acetyl CoA to carbon dioxide in the presence of oxygen, generating ATP and the reduced coenzymes NADH and FADH2
What does acetyl CoA look like?
two carbon acetate group from pyruvate linked to a carrier called coenzyme A
Where does Acetyl CoA come from?
oxidative decarboxylation of pyruvate or by the stepwise oxidative breakdown of fatty acids
What course does Acetyl CoA take during the TCA cycle (what does it turn into)?
Acetyl CoA transfers its acetate group to oxaloacetate (4C) which thereby generates citrate
citrate undergoes two successive decarboxylations and several oxidation steps
oxaloacetate is regenerated, and can accept two more carbons from Acetyl CoA
- therefore it is a cycle
What occurs during each round of the TCA cycle?
release of two CO2 molecules
entry of two carbons
regeneration of oxaloacetate
How many times does oxidation occur during the TCA cycle?
oxidation occurs at five steps:
four in the cycle itself and one in the reaction that converts the pyruvate to Acetyl CoA
- electrons are always accepted by coenzyme molecules
How does pyruvate get to the spot where the TCA cycle occurs?
the pyruvate molecule passes through the porin proteins, to pass the second membrane (inner) a symporter transports pyruvate across the membrane into the matrix along with a proton
How is pyrivate converted into Acetyl CoA?
pyruvate dehydrogenase complex - oxidation because two electrons are transferred to NAD+ to form NADH
Summarize the TCA cycle in 5 steps.
1. Two carbons enter as Acetyl CoA, this joins the four carbon molecule oxaloacetate and forms cirtrate
2. Decarboxylation occurs at two steps in the cycle so that the input of two carbons as Acetyl CoA is balanced by the loss of two carbons as CO2
3. Oxidation occurs at 4 steps, with NAD+ as the electron acceptor in 3 cases and FAD as the electron acceptor in one
4. ATP is generated at one point, with GTP as an intermediate in animal cells - this is substrate level phsophrylation where an accidental ATP is made
5. One turn of the cycle is completed upon regeneration of oxaloacetate
What is proteolysis?
degradation of proteins by hydrolysis of the peptide bonds between amino acids
What are the enzymes called that are responsible for proteolysis?
Give some example of amino acids that can be converted into steps of the TCA cycle to generate ATP
Alanine - pyruvate
Aspartase - Oxaloacetate
Glutamate - alpha-ketoglutarate
What are triacylglycerols?
neutral triesters of glycerol and long-chain fatty acids
How are triacylglycerols catabolized?
this begins with their hydolysis of glycerol and free fatty acids
glycerol is channeled into glycolytic pathway by oxidative conversion to dihydroxyacetone phosphate
fatty acids are linked to coenzyme A to form fatty acyl CoAs, which are then degraded by beta-oxidation
What is beta-oxidation?
a catabolic process that generates acetyl CoA and the reduced coenzymes NADH and FADH2
What does the beta-oxidation pathway involve?