CARBOHYDRATE METABOLISM: How the total ATP's are generated from carbohydrate

1. Presented by:
HACKMAN, DESMOND PAA KWESI
(BSc Nutrition & Food Sci., MSc Dietetics, Student Dietitian)
College of Health Sciences
University of Ghana, Legon

2. Introduction
Glycolysis
Krebs’ (Tricarboxylic acid) Cycle
Electron Transport Chain/Oxidative
Phosphorylation
Total ATP Generation
Factors Influencing CHO Metabolism
References

3. Cn(H2O)n
digestion monosaccharides
C6H12O6 is the principal product
of almost all digestible CHO;
main fuel for energy.
After absorption: glucose G6P;
destined to follow one of these:
- Glycolysis
- Kreb’s Cycle
- Pentose Phosphate Pathway
- Glycogenolysis
- Glucogenesis
- Gluconeogenesis
catabolic
anabolic

5. Under aerobic conditions: Under anaerobic conditions:
Lactate Dehydrogenase
O
C
C
CH3
O
O
O
C
HC
CH3
OH
O
NADH + H+ NAD+
pyruvate lactate
In aerobic conditions, the acetyl-CoA produced enters the TCA.
However, in low O2 tension or ‘O2 debt’, such as during intense exercises, the
muscle & RBC generate lactate from pyruvate. Increased lactic acid causes
fatigue & cramps. If it occurs in the myocardium due to coronary thrombosis, it
could have damaging effect on the heart.

6. Each produces 1ATP, 3NADH and 1FADH2
Thus for 1C6H12O6 2ATP, 6NADH and 2FADH2

7. Series of redox reactions in the
mitochondria
NADH and FADH2 produced in
TCA & Glycolysis donate their
electrons to a series of electron
accepting compounds found on
the inner membrane of the
mitochondrion.
NADH and FADH2 passes their
electrons to 3 and 2 acceptor
molecules respectively.
Each transfer generate a proton
electrochemical gradient which
powers:
ADP+Pi ATP
Thus:
1NADH = 3ATPs
1FADH2 = 2ATPs

8. NADH FADH2 Direct ATP
Glycolysis 2 - 2 (net)
PDH (Pyruvate to
Acetyl CoA)
2 - -
TCA 6 2 2
Sub Total 10 2 4
TOTAL ATP = 10(3) + 2(2) + 4 = 38 ATPs
Not all these 38ATPs are realised due to:
Losses such as the cost of moving Pyruvate,
Phosphate, ADP into the mitochondria. All are actively
transported using carriers which utilise the stored
energy in the proton electrochemical gradient.

9. Pathways depend on:
Nutritional Status
◦ Glycogenolysis predominant in starvation & untreated DB.
◦ Glycogenesis predominant in fed state.
◦ Supply of adequate B-vitamins & minerals (Fe2+, Fe3+, Mg2+ )
◦ Alcohol intake
Oxygen Status
◦ In adequate O2, TCA is activated.
◦ When demand exceeds supply, glycolysis is activated in active
muscle
Tissue ⁄ cell type
◦ In tissue damage or Fatty acid synthesis, PPP is activated.
◦ Mature RBCs lack mitochondria & solely depend on glycolysis
for energy.

10. Adjimani, J.P.(2006). MOLECULES OF LIFE:
Energetics And Metabolism At A Glance. First edition.
Beno Publications, N.T., Accra. Pp 26-40.
Lehninger, M.M., Nelson, D.L. and Cox (2005).
Principles of Biochemistry. Fourth edition. Worth
Publishers, U.S.A. Pp 524-526.