Biochemistry

1. CARBOHYDRATES METABOLISM–
TCA
&
GLYOXYLATE
CYCLE
Unit 3
MBH 103
Microbial Physiology & Biochemistry

2. Metabolism and regulation
 Glycolysis
 TCA cycle
 Glyoxylate cycle
 Pentose phosphate pathway
 Gluconeogenesis
 Entner – Doudoroff pathway
 Phosphoketolase pathway
 Biosynthesis of peptidoglycan

3. Catabolic pathways
1. Respiration
1) Aerobic (oxygen)
2) Anaerobic
- Nitrate
- Sulphate
- Iron
- Manganese
- carbon
2. Fermentation

5. Kreb cycle

6. Acetyl CoA

7. Acetyl CoA – fuel for TCA cycle
 Link between glycolysis & TCA
cycle.
 An Irreversible reaction
 Oxidative decarboxylation.
 Pyruvate dehyrogenas
complex
 Reactions in 3 steps:

9. Citrate from oxaloacetate and acetyl
coenzyme A
 Citrate synthase
 Condensation rxn.
 Oxaloacetate binds first
 Next acetyl CoA
 Thioester hydrolysed.
 Without role of ATP
 Compare - hexokinase

10. Citrate is Isomerized into
Isocitrate
 Aconitase is an iron-sulfur protein/ non heme iron protein
 4 iron atoms complexed to four inorganic sulfides
 3 cysteine sulfur atoms
 Hydration/ dehydration reactions

11. Isocitrate is oxidized and
decarboxylaed to α-Ketoglutarate
 Isocitrate dehydrogenase
 Oxidative decarboxylation
 Intermediate – oxalosuccinate (unstable
ketoacid)

12. Formation of Succinyl Coenzyme A
 α- ketoglutarate dehydrogenase
 Multienzyme complexes – E1 E2 E3
 Oxidative decarboxylation

13. Succinyl CoA – Energy rich thioester
compound
 Succinly CoA comparable to ATP
 Coupled to phosphorylation of purine GDP
 Example: Energy transformations
 Intermediate – succinyl phosphate
 Substrate level phosphoylation
 Succinyl CoA synthetase (succinate thiokinase)

14. Oxaloacetate is regenerated
 Rxn of 4 carbon compounds (oxidation, hydration, 2nd oxidation)
 A methylene group (CH2) converted to carbonyl (C=O) in 3 steps
 Step 1: Succinate dehydrogenase, iron-sulfur protein, membrane
bound
 Step 2: Fumarase
 Step 3: Malate dehydrogenase

17. Regulation of TCA cycle
 Acetyl CoA inhibits E2
(transacetylase)
 NADH inhibits E3;
dihydrolipoyl
dehydrogenase
 ATP inhibits E1; pyruvate
dehydrogenase
 Isocitrate dehydrogenase
 α-ketoglutarate
dehydrogenas

18. GLYOXLATE CYCLE

19. Glyoxlate cycle

20. 1
 Carbon-carbon bond is cleaved
 Aldehyde is released
 4 identical chains – requires Mg2+/Mn2+

21. Glyoxylate to malate
 3 substrates – acetyl CoA, H2O and glyoxlate
 Acyl transferase – transfers acyl into alkyl
 Exists as isomer A and B
 Thioester hydrolysis

22. Anaplerotic pathway

24. THANK
YOU