1. Lipid metabolism

2. Roles of lipids Largest energy store Insulation Structural components
Membranes
Hormones
Carrier
Fat-soluble vitamins

3. Types of lipids Simple lipids Triglyceride Mostly triglycerides
Principal storage form
>95% of body fat
Mostly in adipose cells
Some in liver and skeletal muscle
Triglyceride
One glycerol
3 fatty acids
All have linear C chain
14-22 C long
Saturated or unsaturated

4. Types of lipids Compound lipids Neutral fats with other chemicals
Glycolipids
Sphingolipids
Phosphoglycerides
Lipoproteins
Glycerol, two fatty acids and one sugar group
Involved in cell recognition
One fatty acid and one molecule of sphingosine
Sphingomyelin
Signal transmission and cell recognition
Glycerol, two fatty acids, one phosphate group and one alcohol group
Important component of cell membranes

5. Lipoproteins Formed mainly in the liver Consist of
Triglycerides
Phospholipids
Cholesterol
Protein
Main transport form of lipids in the blood
Fats are insoluble in water
The protein and phospholipids allow the insoluble fatty acids to be carried in the core of the lipoprotein

6. Lipoproteins Classified according to their density
HDL: Least amount of cholesterol
Carry cholesterol back to the liver
Converted to bile
Most recycled, some excreted

7. Lipoproteins LDL and VLDL: Chylomicrons: Carry most of the cholesterol
Have the greatest affinity for the arterial walls
Particularly oxidized LDL
Chylomicrons:
Largest amount of triglycerides
Produced in small intestinal cells
Elevated after high fat meals

8. Lipid metabolism Triglycerides Not taken up directly into the cells
Must be broken down first
Fatty acids and glycerol
Lipoprotein lipase
Located on capillary endothelium
Glycerol goes to liver

9. Lipid metabolism Phospholipase A2
Capillary endothelium
Breaks down surface lipoproteins
Lecithin-cholesterol acyltransferase (LCAT)
Plasma
Forms a fatty acid-cholesterol ester
This is transferred to chylomicron or VLDL
Helps maintain stability of those molecules as triglycerides are removed
Lipid metabolism

10. Derived lipids Cholesterol Only in animal products
In every cell of the body
Cell membrane
Vitamin D
Hormones
Testosterone
Estrogen
Cortisol
Bile
Fat metabolism
Found in
Egg yolks
Meats, shellfish and dairy
Diets high in saturated fats
Increase cholesterol synthesis

12. Fatty acid synthesis Occurs in the liver and adipose tissue
Essentially
Acetyl-CoA + 7 Malonyl-CoA + NADPH + 14H+ → Palmitic Acid + 8CoA + 14 NADP+ + 6H2O
Acetyl-CoA and Malonyl-CoA are reduced to Palmitic acid
NADPH is the reducing agent
Dehydration Rx
Malonyl-CoA
Created from Acetyl-CoA
Acetyl-CoA carboxylase
Thus, anything that increases Acetyl-CoA levels can lead to fat synthesis

13. Triglyceride synthesis
Fatty acyl CoA

14. Triglyceride synthesis
Glycerol 3 phosphate + 2 Fatty acyl-CoA
Phosphatidic acid
Phosphatidic acid converted to diacylglycerol
Phosphatase
Diacylglcerol + fatt acyl CoA
Triglyceride
Acyl transferase

15. Triglyceride metabolism
Stored in
Adipose tissue, liver, muscle
Breakdown process
Lipolysis
Whether or not triglycerides come from muscle or liver, same basic steps occur
Mobilization
Circulation
Uptake
Activation
Translocation
B-oxidation
Aerobic metabolism

16. Lipid mobilization Hormone sensitive lipase Fatty acids
Breaks down stored triglycerides
Fatty acids and glycerol released
Into blood (adipose tissue)
Glycerol
Goes to liver
Gluconeogenesis
Glycogenesis
Lipid biosynthesis
Fatty acids
Require a carrier
Albumin

17. Lipid Mobilization Activation of Hormone sensitive lipase Epinephrine
Activates G protein
Stimulates adenylate cyclase
Adenylate cyclase
Produces cAMP
Activates Protein kinase A

18. Lipid circulation Fatty acids bound to albumin
Circulate around to active tissues
How do they know?

19. Fatty acid uptake Uptake Directly related to circulating concentration
Rate of blood flow
Increased flow, increased delivery, increased uptake and utilization
Requires
Fatty acid transporter (FAT) and Fatty acid binding protein (FABP)
Costs
Two ATP

20. Fatty acid activation Fatty acids must be activated
ATP + CoA
Fatty acyl-CoA
Fatty acyl-CoA must be translocated
From cytoplasm to mitochondria
Carnitine acyl transferase 1 and 2

21. Fatty acid oxidation B-oxidation Total for 16C palmitic acid?
Sequential events which
Convert fatty acyl-CoA to
Acetyl-CoA
NADH
FADH
Number of cycles
(Number of carbon atoms/2)-1
16C FA
7 cycles
Each cycle produces 1 acetyl-CoA, 1 NADH and 1 FADH
Each acetyl CoA = 12 ATP
Each NADH = 3 ATP
Each FADH = 2 ATP
Total for 16C palmitic acid?