1. ALTERNATIVE METABOLIC PATHWAYS
SBI4U Biology

2. Glucose Metabolism Lack of Oxygen Lack of Glucose Too much Glucose
Cells rely primarily on the Glycolytic Pathway for most ATP. Carbs other than glucose need minimal modification before entering this pathway.
Alternate pathways deal with either:
Lack of Oxygen
Lack of Glucose
Too much Glucose

3. Lack of Oxygen Lactic Acid Fermentation
Low blood O2 = cell metabolism ‘backs up’
Pyruvate  Lactate
Regenerates NAD+

4. Lack of Oxygen Alcoholic Fermentation Yeast is an anaerobe
Pyruvate  Ethanol
Very simple!

5. GLYCOGENOLYSIS
Low blood Glucose = Glycogen broken down to glucose, for delivery to cells.
Daily Glycogen depletion/repletion cycle

6. GLYCOGENOLYSIS Involves several organs & tissues
Pancreas: Glucagon, Insulin
Liver: stores Glycogen
*Adipose cells: store body fat.

7. Gluconeogenesis Gluco = sugar Neo = new Genesis = formation
Making glucose or its intermediates, often from non-carb sources.

8. Amino Acids & Energy: glucose-Alanine Cycle
Amino Acid Alanine can be converted to glucose & vice versa.
Useful when proteins are plentiful but carbs in short supply.

9. Amino Acids & Energy
Various glucogenic amino acids can be metabolised to produce glucose in times of need.

10. Amino Acids & Energy
Glucogenic
*Act as Both:
Phe, Trp, Tyr, Ile
Ketogenic:
Leucine, Lysine
Ketogenic amino acids enter the regular pathway of metabolism indirectly, but still help yield ATP energy.

11. Amino Acids & Energy Proteins yield less energy than lipids or carbs
They are metabolised as a last resort in starvation

12. Amino Acids & Energy
Starvation is a more complex metabolic process than people imagine….

13. Lipid Metabolism Lipolysis: Glycerol enters glycolysis as PGAL
Fatty Acids enter Krebs as Acetyl CoA
Along the way, NADH & FADH2 are generated.

14. Lipids & Carbs: Cori Cycle
Uses energy derived from Fatty Acid metabolism drives this type of gluconeogenesis
Helps body clear lactate in a useful way.

15. Too much of a good thing!
After feeding, surplus protein & carbohydrate are converted via Krebs cycle intermediates into fats.
When fasting protein amino acids are converted into carbohydrates via the Krebs cycle & gluconeogenesis to maintain our blood glucose levels.
Fats provide energy and are mostly oxidized to CO2 and water

16. Lipogenesis from Glucose
So the fate of glucose after a meal is:
Fast Energy 2. Stored as Glycogen 3. Stored as Fat

17. Summary The body is resourceful, but frugal
It finds ways of getting energy when fuel is low
It directs molecules to their best possible use: energy, storage, or structure.
Catabolic & Anabolic processes are constant