HLSC 2110U Lecture Notes - Lecture 10: Fluid Mosaic Model, Membrane Lipids, Adipocyte
19 Feb 2019
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Fatty Acids
- Exist in free fatty acids and TAG
- Low levels of free fatty acids occur in all tissues but substantial amounts can be found in plasma
(usually during fasting)
- Plasma free fatty acids are transported by serum albumin from point of origin (TAG, fat, or
circulating lipoproteins) to site of consumption (most tissues)
Functions of Fatty Acids
- Free fatty acids can be oxidized by many tissues for energy (mainly liver and muscle)
- Structure of cell membrane (glycolipids and phospholipids)
- Attached to intracellular proteins to enhance ability of proteins to associate with membrane
- Precursor of hormone-like prostaglandins
- Energy reserves in body (TAGs in adipose cells)
Structure of Fatty Acids
- - Hydrophobic hydrocarbon chain and a terminal carboxyl group
Saturation of Fatty Acids
- No double bonds = saturated
- If they do, then they are mono- or polyunsaturated
- Double bonds decrease the melting point of fatty acid
- Membrane lipids contain LFCA with double bonds
Membrane Structure
- Phospholipids and glycolipids
- Fluid mosaic model
- Not stable structure
- Contains mobile structures that allow flex and movement
Essential Fatty Acids
- Dietary essential in humans
- Linoleic acid (precursor of arachidonic acid – substrate for prostaglandin synthesis)
- Alpha-linoleic acid (precursor of omega fatty acids – needed for growth and development)
- Arachidonic acid becomes essential if linoleic acid is deficient in diet
De Novo Synthesis of Fatty Acids
- Large portion of fatty acids supplied by diet
- Carbs, proteins, and other molecules in excess can be converted to fatty acids, stored as TAGs
Precursor for Fatty Acid Synthesis
- Acetyl-CoA
- Can be formed from dietary precursors of glucose, fructose, or amino acids
Fatty Acid Synthesis in Adults
- Occurs primarily in the liver, lactating mammary glands, and sometimes in adipose tissue
- Process incorporates carbons from acetyl CoA into growing fatty acid chain, using ATP and
NADPH
Production of Fatty Acids from Acetyl CoA
- Acetyl CoA will be carboxylated into malonyl CoA
- Fatty synthase is a multi-catalytic enzyme with 7 sites which will act on malonyl CoA to convert it
in a number of repeated steps into fatty acid
- Steps consist mainly of addition of carbon residues in repeated steps to end up with a 4-carbon
compound-butyryl-ACP
- Cycles are repeated 4-5 times where 2 carbon units derived from malonyl CoA, are added in
each cycle until the chain length of the final selected fatty acid is reached
- NADPH used extensively
- Derived mostly from the hexose monophosphate pathway
Regulation of Fatty Acid Synthesis
- Pathway enhanced by increased in ATP and citrate in the mitochondria
- In cytosol, citrate (allosterically) activates acetyl CoA carboxylase to produce malonyl CoA
- Enzyme can be (allosterically) inactivated by long chain fatty acids and regulatory hormones (epi
and glucagon)
- In presence of insulin, enzyme is dephosphorylated and activated
Long Term Regulation
- Prolonged consumption of diets with excess calories, specifically high calorie and high carb,
there is an increase of acetyl CoA carboxylase synthesis which increased fatty acid synthesis
- Low calorie diets or fasting causes a reduction of fatty acid synthesis decreasing the acetyl CoA
carboxylase synthesis
Document Summary
Low levels of free fatty acids occur in all tissues but substantial amounts can be found in plasma (usually during fasting) Plasma free fatty acids are transported by serum albumin from point of origin (tag, fat, or circulating lipoproteins) to site of consumption (most tissues) Free fatty acids can be oxidized by many tissues for energy (mainly liver and muscle) Attached to intracellular proteins to enhance ability of proteins to associate with membrane. Energy reserves in body (tags in adipose cells) Hydrophobic hydrocarbon chain and a terminal carboxyl group. If they do, then they are mono- or polyunsaturated. Double bonds decrease the melting point of fatty acid. Membrane lipids contain lfca with double bonds. Contains mobile structures that allow flex and movement. Linoleic acid (precursor of arachidonic acid substrate for prostaglandin synthesis) Alpha-linoleic acid (precursor of omega fatty acids needed for growth and development) Arachidonic acid becomes essential if linoleic acid is deficient in diet.
