1. Carbohydrate, Lipid, and Protein Metabolism
Combined Chapters
Carbohydrate, Lipid, and Protein Metabolism

2. Stage 1: Digestion of Carbohydrates
In the mouth, salivary amylase hydrolyzes a-glycosidic bonds in polysaccharides to give smaller polysaccharides (dextrins), maltose, and some glucose.
In the small intestine, pancreatic amylase hydrolyzes dextrins to maltose and glucose.
The disaccharides maltose, lactose, and sucrose are hydrolyzed to monosaccharides.
The monosaccharides enter the bloodstream for transport to the cells.

3. Summary of carbohydrate digestion in the human body.

4. Metabolism
Section of the small intestine, showing its folds and the villi that cover the inner surface of the folds.
© Ed Reschke / Peter Arnold, Inc.

5. Glycolysis: Splitting Sugar
In Stage 2, the metabolic pathway called glycolysis degrades glucose (6C) obtained from digestion to pyruvate (3C)

6. Glycolysis: Energy-Investment
In reactions 1-5 of glycolysis:
Energy is used to add phosphate groups to glucose and fructose
Glucose is converted to two three-carbon molecules

7. Glycolysis: Energy-Production
In reactions 7 and 10, the hydrolysis of triose phosphates generates four ATP molecules

8. phosphoglucoisomerase
Step 1: Formation of Glucose 6-phosphate Step 2: Formation of Fructose 6-Phosphate
ATP
ADP
Step 1
Hexokinase
Step 2
phosphoglucoisomerase

9. Step 3: Formation of Fructose 1,6-bisphosphate Step 4: Formation of Triose Phosphates
ATP
ADP
Step 3
phosphofructokinase C O H 2 P + 1 4 1
Step 4 6 5 2 2 5 6 4 3
Aldolase 3
dihydroxyacetonephosphate
glyceraldehyde 3-phosphate

10. Step 5: Isomerization of Triose Phosphates2
Triosephosphate isomerase
By the end of Step 5, we have:
1. Used two molecules of ATP so we can
2. Break Glucose (6C) into 2 3C units of glyceraldehyde 3-phosphate

11. phosphoglycerokinase
Step 6: Formation of 1,3-Bisphosphoglycerate Step 7: Formation of 3-Phosphoglycerate
Step 6
+ 2NAD+ +2Pi 2 2
+ 2NADH + 2H+
Glyceraldehyde phosphate dehydrogenase
Step 7
2ADP
2ATP 2 2
phosphoglycerokinase

12. Step 8: Formation of 2-Phosphoglycerate Step 9: Formation of Phosphoenolpyruvate
phosphoglyceromutase
Step 9 2 2
enolase
+2H2O

13. Step 10: Formation of Pyruvate
2ADP
2ATP 2 2
pyruvate kinase
By the end of Step 10, we have:
1. Generated 4 ATP molecules (2 net)

14. Glycolysis: Overall Reaction
Glycolysis generates 2 ATP and 2 NADH
Two ATP are used in energy-investment to add phosphate groups to glucose and fructose-6-phosphate
Four ATP are formed in energy-generation by direct transfers of phosphate groups to four ADP.
Glucose + 2ADP + 2Pi + 2NAD+ 
2Pyruvate + 2ATP + 2NADH + 4H+

15. Carbohydrate Metabolism

16. Regulation of Glycolysis
Reaction 1 Hexokinase is inhibited by high levels of glucose-6-phosphate (feedback)
Reaction 3 Phosphofructokinase, an allosteric enzyme, is inhibited by high levels of ATP and activated by high levels of ADP and AMP
Reaction 10 Pyruvate kinase, another allosteric enzyme is inhibited by high levels of ATP or acetyl CoA

17. Pathways for Pyruvate
When oxygen is present in the cell, pyruvate from glycolysis is decarboxylated to produce acetyl CoA (enters TCA cycle) and CO2
Pyruvate + HS-CoA + NAD+  acetyl CoA + CO2 + NADH + H+

18. Lactate Formation
When oxygen is not available, pyruvate is reduced to lactate, which replenishes NAD+ to continue glycolysis
Pyruvate + NADH + H+  lactate + NAD+

19. Lactate in Muscles Under anaerobic conditions (strenuous exercise):
Oxygen in the muscles is depleted
Lactate accumulates in the muscles
Muscles tire and become painful
Rest is needed to repay the oxygen debt and to reform pyruvate in the liver

20. Fermentation Fermentation:
Occurs in anaeobic microorganisms such as yeast
Decarboxylates pyruvate to acetaldehyde, which is reduced to ethanol.
Regenerates NAD+ to continue glycolysis
Pyruvate + NADH + H+  ethanol + NAD+ + CO2

21. All three of the common fates of pyruvate from glycolysis provide for the regeneration of NAD+ from NADH.

22. Carbohydrate Metabolism
Structural relationships among glycerol and acetone and the C3 intermediates.

23. Metabolism
Entry points for fructose and galactose into the glycolysis pathway.
Note: Glycolysis functions in the cytosol.

24. NADH SHUTTLE
The dihyroxyacetone phosphate-glycerol 3-phosphate shuttle.
Cytosolic NADH can not cross mitochondrial membrane.
Shuttle brings cytosolic electrons into mitochondria in form of mitochondrial FADH2

25. Carbohydrate Metabolism
The processes of glycogenesis, storage of glucose and glycogenolysis, liberating glucose, are contrasted.

26. Cori Cycle
The Cori Cycle

27. Metabolism

28. Carbohydrate Metabolism
Saturn Stills / SPL / Photo Researchers
A diabetic giving himself a blood glucose test.

29. Lipid Metabolism
The events that must occur before triacylglycerols can reach the bloodstream through the digestive process.

30. Lipid Metabolism
Chylomicron, a type of lipoprotein

31. Lipid Metabolism
Structural characteristics of the adipose cell.

32. Lipid Metabolism
Fatty acids are transported across the inner mitochondrial membrane in the form of acyl carnitine.

33. Reactions of the fatty acid spiral for an 18:0 fatty acid.

34. Lipids cont’d

35. Protein Metabolism
Summary of protein digestion in human body.

36. Protein Metabolism

37. Protein Metabolism
Possible fates for amino acid degradation products.

38. Protein Metabolism
Key compounds in the transamination / oxidative deamination process include three keto acid/amino acid pairs.

39. The four-step urea cycle.

40. Protein Metabolism
Fates of the carbon skeletons of amino acids.

41. Protein Metabolism
The starting materials for the biosynthesis of the 11 nonessential amino acids.

43. Human body response to feasting, fasting, and starving.