TCA cycle Flashcards
Metabolism (3)
- the sum of all the chemical transformations
- takes place in a cell or organism
- occurs through a series of enzyme- catalyzed reactions
Catabolism
Degradative phase of metabolism in which organic molecules are converted into smaller, simpler end products
Catabolism
-characteristics (2)
- release energy
- energy which is conserved in the formation of ATP and reduced electrons carriers (NADH, NADPH, FADH2)
Anabolic pathways
Small, simple precursors are bulit up into larger and more complex molecules (lipids, proteins)
Anabolism
-characteristics (1)
Require an input of energy, generally in the form of the phosphoryl group transfer potential of ATP and the reducing power of NADH, NADPH, FADH2
Anabolism and Catabolism
- precursor molecules
- end product
A: amino acids, sugars, fatty acid
C: carbohydrate, fats, proteins
A: proteins, lipids, nuclei acids
C: CO2, H2O, NH3
TCA cycle
- substrate for this cycle
- substrate is generated in
- 2-carbon acetly group is…
- energy is conserved as..
- acetly CoA
- the pathways for oxidation of fatty acids, glucose, amino acids
- oxidized to two molecules of CO2
- NADH, FADH2, GTP
TCA cycle
-function
-conserve the energy from the oxidation of acetyl CoA to CO2 by transferring electrons from intermediates of the cycle to NAD+ and FAD
TCA cycle
- number of electrons donated by the acetyl group and what it forms
- where does the cycle occur?
8 electrons donated –> 3 molecules of NADH and 1 of FAD
-mitochondria
Step 1-3
-only name and enzyme involved
- Formation of citrate/ Enzyme – citrate synthase
- Conversion of citrate to isocitrate/ Enzyme – acotynase
- Oxidation and decarboxylation of isocitrate/ Enzyme – isocitrate dehydrogenase
Step 4-6
-only name and enzyme involved
- Oxidative decarboxylation of a- ketoglutarate/ Enzyme – a- ketoglutarate dehydrogenase complex.
- Cleavage of succinyl CoA/ Enzyme – succinate thiokinase
- Oxidation of succinate/ Enzyme – succinate dehydrogenase
Step 7-8
-only name and enzyme involved
- Hydration of fumarate/ Enzyme – fumarase
8. Regeneration of oxaloacetate/ Enzyme – malate dehydrogenase
Energy produced by the TCA cycle (2)
- Two carbon atoms enter the cycle as acetyl CoA and leave as CO2.
- Four pairs of electrons are transferred during one turn of the cycle (3 reduce NAD+ to NADH, 1 reduce FAD to FADH2)
Oxidation of one NADH yields:
Oxidation of FADH2 yields:
- 5 ATP
1. 5 ATP
Total ATPs
10
Regulation of the TCA cycle
Regulated to correspond to the rate of the electron transport chain, which is regulated by the ATP/ADP ratio and the rate of ATP utilization.
Regulation of the TCA cycle
-two major messengers
- the phosphorylation state of ATP
- the reduction state of NAD+ (ratio NADH/NAD+).
Regulation of Citrate Synthase
- It has no allosteric regulators.
- Regulated by: concentration of citrate (=a product inhibitor).
Regulation of Isocitrate Dehydrogenase
- Is one of the rate-limiting steps.
- Regulated allosterically: activated by ADP, Ca2+
- inhibited by NADH.
Regulation of α-ketoglutarate dehydrogenase
- Inhibited by: NADH and succinyl CoA.
- Activated by Ca2+.
Precursors of Acetyl CoA (3)
- Compounds that enter as acetyl CoA are oxidized to CO2.
- Compounds that enter the TCA cycle as acetyl CoA or as an intermediate that can be converted to malate or oxaloacetate
- Compounds that enter as TCA cycle intermediates replenish intermediates that have been used but cannot be fully oxidized to CO2.
Acetyl CoA
- characteristics
- it can be generated from…. (4)
-common point of convergence for the major pathways of fuel oxidation
- the β-oxidation of fatty acids
- degradation of the ketone bodies
- Pyruvate is oxidized to acetyl CoA
- amino acids, such as leucine and isoleucine are also oxidized to acetyl CoA
Pyruvate
the end- product of aerobic glycolysis
Pyruvate is oxidized to acetyl CoA by which complex?
the pyruvate dehydrogenase complex.
