Transcript Introduction to Physiology: The Cell and General Physiology

Lipids
• Fatty Acids (FA) and Triglycerides (TG)
– high density energy store
• Phospholipids
– major components of membranes
– contain precursors of many biologically active substances, such as:
prostaglandins, thromboxane, inositol trisphosphate
– modulate the activities of membrane enzymes and transporters
• Cholesterol (not really a lipid, but lipid soluble and lipid
derived)
– prominent part of membranes, control fluidity and protein function
– precursor for bile acids and steroid hormones
– most cells can synthesize it from Acetyl CoA; liver makes most of it
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H2C-OH
HO-CH
H2C-OH
O
H3C (CH2)16 C
OH
3 of these fatty acids (stearic acid)
+
O
H3C (CH2)16 C-O-CH2
O
H3C (CH2)16 C-O-CH2
O
H3C (CH2)16 C-O-CH2
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Glycerol
a triglyceride
(tristearin, p. 840)
H2C-OH
HO-CH
H2C-OH
Glycerol
H
2H2C-OPO3
Glycerol-3-P
O
C
HO-CH
2H2C-OPO3
Glyceraldehyde-3-P
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H2C-OH
HO-CH
H2C-OH
O C
2H2C-OPO3
Dihyroxyacetone-P
The Liver & Lipids
• oxidize triglycerides (fatty acids) for energy
• production of ketone bodies from triglycerides
(FA)
– exported to other cells as energy source (Acetyl CoA)
• synthesize triglycerides, mainly from glucose
– some from amino acids as well
• synthesize other lipids, mainly phospholipids and
cholesterol, from fatty acids
• de-saturate fatty acids (most FA in TG’s in
adipose tissue are saturated)
– saturated means no double bonds, chock full o’ hydrogens
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Beta Oxidation of Fatty Acids
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Ketone Bodies
FA
CoA
 Ox.
Pyruvate
Acetyl CoA
Acetyl CoA
Acetoacetyl CoA
Citrate
HMG CoA
Succ. CoA
NADH
Oxaloacetate
NADH
Malate
acetoacetate
Succinate
NAD+
CO2
-3-hydroxybutyrate acetone
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mitochondria
Problem Solving…
• What would be the net ATP gain from a
triglyceride consisting of three palmitic
acid chains (these are 16-C fatty acids…)?
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• Glycerol enters glycolysis as glyceraldehyde-3phosphate – worth ~ 36 ATP
• Palmitic acid – 16 carbons = 8 acetyl-CoA, 7
NADH, & 7 FADH2
• 8 acetyl-CoA = 12 ATP each = 96 ATP
• 7 NADH = 3 ATP each = 21 ATP
• 7 FADH2 = 2 ATP each = 14 ATP
• Palmitic acid then worth 131 ATP – but 2 ATP
equivalent required to start beta-oxidation, so
actually worth approximately 129 ATP.
• Three palmitic acid chains in a triglyceride – 129 x 3
= ~ 387 ATP, plus ~ 36 ATP from glycerol = ~ 423
ATP
Copyright © 2006 by Elsevier, Inc.