Pii: Describe the Carbohydrate Metabolism
Definitions
Metabolism = the chemical ∆ in a cell when there is breakdown & synthesis of stored E
Carbohydrate Metabolism
- 40 – 50% E requirements from oxidation of carbs
- Glucose = main product of carb digestion & absorption
- Glucose is absorbed via Portal System & either:
a. Utilised for E
b. Stored as Glycogen
- Glucose is metabolised by:
- Glycolysis
- Kreb’s Cycle
- Electron Transport Chain (ETC)
Glycolysis
- Sequence of reactions which convert GIucose → Pyruvate
- With concomitant production small amount ATP
- Occurs in cytoplasm
Glucose (6C) + 2Pi + 2ADP + 2NAD+ → 2 Pyruvate (3C) + 2ATP + 2NADH + 2H+ + 2H2O
- Under aerobic conditions, pyruvate enters mitochondria & is oxidised in Kreb’s cycle
- To enter Kreb’s; pyruvate → Acetyl CoA
- Occurs inside mitochondria
- Regulated by [NADH]
- ↑[NADH] inhibits Pyruvate Dehydrogenase
Citric Acid Cycle
- Final common pathway for oxidation of fuel molecules (amino acids, carbs, fats)
- Fuel enters Krebs as Acetyl CoA
- Takes place in matrix of mitochondria
- Main purpose of Krebs is to produce NADH & FADH2 which then enters ETC
Acetyl CoA + 3NAD+ + FAD + GDP + Pi + 2H2O → 2CO2 + 3NADH + FADH2 + GTP + 2H+ + CoA
- Although O2 doesn’t participate directly in Krebs, it can only operate in aerobic conditions because NAD+ & FAD can be regenerated in mitochondria only by transfer of e– to molecular O2
- Krebs also provides one GTP per glucose, which can convert ADP → ATP
ETC
- NADH & FADH2 formed from Krebs is E rich
- Each contains pair e– with high E
- When these e– are donated to O2, a large amount of free E is liberated
- Electrons flow from NADH & FADH2 to molecular O2 through protein complexes on inner mitochondria membrane
- Causes H+ to be pumped out of mitochondria matrix, generating a H+ motive force
- ATP is synthesised when H+ flow back into mitochondrial matrix by ATPase
- Overall 1 glucose will generate 32ATP
C6H12O6 + O2 → 6H2O + 6CO2 + 23ATP
ATP Balance Sheet
Glycolysis 2
Krebs 2
ETC 34
- ATP = a nucleic acid. Each ATP has 3 phosphate groups which yield high E when broken ∴when a cell needs E, it removes Pi from ATP by hydrolysis
- Respiration = process of making ATP
Glycogen Synthesis
- When glucose enters a cell it can be used immediately to release E
- OR stored as glycogen
- Glycogen = large glucose polymer
- All cells can store glycogen but main stores are liver & skeletal m.
- Glucagon, adrenaline → stimulate glycogenolysis