Citric Acid Cycle Flashcards
Citric Acid Cycle other names
krebs Cycle, Tricarboxylic acid (TCA) cycle
What is the citric acid common for?
Common metabolic pathway for all “fuel” molecules (carbs/FA/AA)
Where does the CAC occur
Mitochondrial matrix
What happens in the citric acid cycle in terms of energy
yealis mich energy that is passed on to other biochemical system (ETC) which produces large amounts of ATP - part of catabolic processes
Give some key facts/points about the CAC
- gateway to aerobic metabolism of any molecule that can be transformed into an acetyl group or component of the cycle
- Cycle doesn’t produce ATP directly (removes e- and passes them on to form NADH and FADH2
- Cycle in collaboration with oxidative phosphorylation
- Very effeicinet: cyclical, small no. of CA molecules make many NADH and FADH2
how has respiration evolved
used to be glycolsis (but since NADH recycled no osidation of glucose occured). Thereforec can’t yeild all the Ep glucose contains, so only got 2ATP per Glc. Then evolved use of O2 in breakdown of high energy food moleules - evolutionary advantage
How else can we look at the CAC in terms of its evolution - why has it evolved
To harvest e- that could then be used to completely oxidise food molecules to CO2 and H2O
How is Acetyl CoA formed - brief
Pyruvate from glycolysis and/or FA are oxidised further to Acetyl CoA in the mitochondrial matrix
Why is Acetyl so important and at the “centre of energy production” for the cell
Allows different intermediates into the main E producing pathway of the CAC
What enzyme makes Acetyl CoA from pyruvate
pyruvate dehydrogenase
Give formation of Acetyl CoA in more detail
Involves decarboxylation of pyruvate, then oxidation, followed by transfer of CoA complex - decarboxylation step releases 2 e- (in form of 2H- ions) which can pass to O2 to produce more TAP through NADH intermediates
Pyruvate dehydrogenase
E catalysing pyruvate to acetyl CoA
Multiple copies of each od the 3 subunits each catalysing diff part of reaction:
E1: decarboxylation of pyruvate
E2: transfers acteyl group to coenzyme A
E3: process… passes e- to NAD+ making NADH
What happens for each turn of the CAC?
2C’s enter (acetyl CoA) followed by removal of two different C’s as 2xCO2
What is acetyl CoA oxidised to
CO2 and H2O
Is CoA used again in the cycle
Yes: used in step 4 then removed step 5
What is the a-ketoglutarate dehydrogenase reation similar to
pyruvate dehydrogenase
How is entry into the CAC controlled?
Pyruvate dehydrogenase is regulated by it’s immediate products and the endo point of cellular respiration, ATP
how is the CAC regulated - explain
Bases on the needs of the cell:
1. If has enough E: NADH and ATP negatively regulate PDH on it’s allosteric site, stopping conversion of pyruvate to acetyl CoA
2. If cell needs E: ADP and Pyruvate +vely regulate PDH to catalysise conversion of Pyruvate to Acetyl CoA
Give 2 other non-reversible reactions (exergonic steps) and points of control of CAC
- Isocitrate dehydrogenase - E allostreically controlled through ATP and NADH conc (-vely regulate) and ADP +ve regulate
- a-ketoglutarate dehydrogenase - ATP and NADH -vely regulate, also succintly CoA -vely regulates
What do the 2 other control points of the CAC allow?
Re-direction of cellular resources:
* blocking isocitrate dehydrogenase causes citrate build up which shuttles citrate into cytoplasm causing phosphofructokinase to stop glycolysis
* a-ketoglutarate builds up when a-ketoglutarate dehydrogenase is inactive, which switches it’s use to production of AA
amphibilic pathway: definition and example
pathway which serves both catabolic and anabolic processes: CAC
What other metabolic processes are each major molecule in the CAC involved in?
- Citrate: FA, steroids - fats
- A-ketogluterate: Glutamate… Diff AA/P - AA/purine bases
- Succinyl-CoA: porphyrins, heme (groups)- heam group, phorphyrin group
- Oxaloacetate: aspartate, asparagine –> pyrimidines - nucleotide bases - Glucose, AA, purine bases, pyrimidine bases
What ahppens when energy neets are met through the CAC
it can then produce building blocks of nucleotide bases, heme groups and proteins
- however this depleties the cell of CAC intermediates
If the cell is depleted of CAC intermediates and an exercising muscle cells requires ATP, what happens?
- Depleadted amount of oxaloacetate
- Pyruvate can be converted to oxaloacetate by enzyme pyruvate carboxylase
- Enzyme only active when acetyl CoA is present, so build up of acetyl CoA triggers this
- Know as anaplerotic reaction
Which reactions involve electron carreirs, and which release CO2
SEE SHEET
What regulates pyruvate dehydrogenase
- ATP
- NADH
- Acetyl CoA
