Copyright © 2006 by Elsevier, Inc.

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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H3C (CH2)16 CO

OH

H2C-OH

H2C-OHHO-CH

Glycerol3 of these fatty acids (stearic acid) +

H3C (CH2)16 C-O-CH2

O

H3C (CH2)16 C-O-CH2

O

H3C (CH2)16 C-O-CH2

Oa triglyceride(tristearin, p. 840)

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Copyright © 2006 by Elsevier, Inc.

H2C-OH

H2C-OHHO-CH

H2C-OH

H2C-OPO3 2-

O CC

H2C-OPO3

HO-CH 2-

OH

H2C-OH

H2C-OPO3

HO-CH 2-

Glycerol Glycerol-3-P

Dihyroxyacetone-PGlyceraldehyde-3-PCopyright © 2006 by Elsevier, Inc.

Copyright © 2006 by Elsevier, Inc.

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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Pyruvate

Acetyl CoA

Ox.

OxaloacetateCitrate

Ketone BodiesAcetyl CoA

Malate

FACoA

Acetoacetyl CoA

HMG CoA

-3-hydroxybutyrate

acetoacetate

acetone

NADH

NAD+

CO2

NADH

Succ. CoA

Succinate

mitochondriaCopyright © 2006 by Elsevier, Inc.

Copyright © 2006 by Elsevier, Inc.

Problem Solving…

• What would be the net ATP gain from a triglyceride consisting of three palmitic acid chains (these are 16-C fatty acids…)?

Copyright © 2006 by Elsevier, Inc.

• Glycerol enters glycolysis as glyceraldehyde-3-phosphate – 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