0226 The TCA cycle Flashcards
Metabolite entry to the mitochondria is regulated Entry to TCA cycle for catabolism is acetyl-CoA Multiple entry points for anapleurotic reactions TCA cycle produces NADH and FADH2 for energy production Discrete reactions subject to regulation by energy status Intermediates may for amino-acids, glucose and porphyrins
Where does ATP synthesis and the TCA cycle occur
Both occur in the mitochondrial matrix
What enzymes regulate the concentration of pyruvate that is destined for TCA cycle
Glycogen phosphorylase, glycogen synthase, hexokinase, PFK-1, Pyruvate kinase, GA3PDH
What are the cellular redox statuses that affect the primary pathway of carbohydrates to pyruvate (think ratios of energy molecules)
The ratios of [ATP]/[ADP] and [NADH]/[NAD+]
What type of transporter that carriers pyruvate into the mitochondria where it can be converted in acetyl CoA
OH- antiporter
What molecules inhibit the conversion of pyruvate to acetyl CoA in the mitochondria (hint: think products of the TCA cycle)
ATP, Acetyl CoA,NADH
True or False: conversion of pyruvate to acetyl CoA is a single step reaction in the mitochondria
False. It is actualyl a complex reaction involving 4 steps (decarboxylation, oxidation, transter of CoASH and oxidation again)
What is the entry point of the TCA cycle
The entry point is the formation of citrate from Acetyl CoA (2 carbon) and oxaloacetate (4 carbon)
Broadly describe the TCA cycle
A series of oxidative reactions in the mitochondrial matrix that produces reduced cofactors NADH and FADH2, GTP and CO2
How many molecules of CO2 are produced from one round of the TCA cycle
2 molecules of CO2 (remember starting point if citrate 6 carbon and ending point is oxaloacetate 4 carbon)
True or false: the concentrations of intermediates in the TCA cycle are relatively high
False. The concentrations of intermediates are low
What cellular redox statuses inhibit and stimulate the TCA cycle
Inhibits TCA = increased NADH or ATP (relative to NAD+ and ADP). Stimulates TCA = increased ADP (relative to ATP
What regulatory mechanisms are there for the TCA cycle (hint: there are 5 categories)
- Substrate supply (acetyl CoA)
- Committed Step (formation alpha KG)
- Metabolic branching points (e.g. citrate to FA synthesis)
- Feedback/forward loops (several products and late stage intermediates)
- Cellular energy status (NADH/NAD, ATP,ADP ratios)
What is the committed step in the TCA cycle
The commited step in the TCA cycle si the conversion of isocitrate to alpha-keto-glutarate
What are the potential branching points for TCA cycle
Fatty acid synthesis (citrate), Amino acid synthesis (alpha KG), glucose synthesis (oxaloacetate), porphryins (succinyl CoA)