Biochemistry- Lipid Metabolism
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- Almost all fatty acids have ________ # of Carbon chains
- Even (f.e C16 or C18)
- Unsaturated fatty acids are those that have what? of what orientation?
- At least one double bond; ussually cis not trans
- What is the notation system for simple fatty acids?
- 20:4 (5,8,11,14) means there are 20 carbons in the fatty acid and it is unsaturated at 4 locations specifically the 5, 8, 11, and 14 carbons counting from the carbonyl carbon
- what are the 6 lipid classes
-
Simple fatty acids
mono di and tri glycerides
Glycerophospholipids
sphingolipids
Steroids
Prostoglandins - the lipid class (mono di or tri) glycerides is made up of what:
- 1, 2, or 3 fatty acid chains connected to a glycerol molecule.
- The lipid class glycerophospholipids are made up of what components (Hint: 4)
-
Glycerol
Fatty acids
phosphate
choline - The lipid class sphingolipids are made up of: what is unique?
-
Sphignosine
Fatty acids
phosphate
choline
NO GLYCEROL! - The lipid class steroids are made up of:
- fused rings
- The lipid class prostoglandins are made up of:
- variable but often have a ring structure and several unsaturations.
- What are the lipid class steroids generally used for? and give an example.
-
Hormone precursors
membranes
can be made as well as consumed
Cholesterol - What are prostoglandins generally used for?
-
function in signal transduction pathways.
contract muscles in the bronchi (malfunction causes asthma). - What are the functions of lipids? (6)
-
Structural (membranes)
storage forms of energy
transporters of fuel
emulsifying agents
vitamins and hormones
2nd messenger systems - what is a major component of cell membranes that accounts for their level of fluidity?
- Cholesterol and kinks in double bonds.
- What are the three proteins found in and around the membrane and how are they classified?
-
Inegral proteins- proteins incorporated within the membrane.
Peripheral proteins- those that are covalently attached to the polar heads of fatty acids and reside on the periphery of the membrane
trans-membrane proteins- those proteins that span the whole membrane. - Of the four lipid components of the membrane, which can be found as part of the "inner" and which are part of the "outer" leaflet?
-
Inner: Phosphatidylethanolamine and Phosphatidylserine
Outer:
Phosphatidylcholine and sphignomyelin - protein movement in the membrane is easy for ________ and difficult for _________.
-
latteral diffusion;
flip-floping - What lipid does the body use as its major source of energy in the body? where is it stored?
- Trigylcerides; stored in the adipocytes.
- triglycerides yield how much energy per gram
- 9 kcal more than 2x the energy in glucose
- VERY IMPORTANT: What happens to excess dietary carbohydrates (not glycogen synthesis)?
- it gets converted to triglycerides
- How are dietary fats digested?
- Bile salts and pancreatic lipases breakdown fats for absorption.
- Tissue TG are broken down by what enzyme?
- Hormone sensative lipase
- What is the reaction catalyzed by hormone sensative lipase?
- The conversion of tissue triacyl glycerol to glycerol and fatty acids (by hydrolysis).
- Fatty acid oxidation occurs when the body requires ____________. What is the overall reaction of fatty acid oxidation
-
More energy.
XC fatty acids + H20 + 7 CoASH -----> 8 acetyl CoA - Fatty acids flowing through the blood stream that are to be broken down must first undergo what reaction?
-
Fatty acids + ATP + CoASH -->
Fatty acyl CoA + AMP - Fatty acids to be broken down travel to the cytosol of a cell where they are converted to fatty acyl CoA, then what?
- They need to be shuttled into the matrix of the mitochondria by Carnitine Acyl Transferases I and II.
- Once carnitine transferases are used to shuttle acyl groups into the matrix of the mitochondrion what process takes place?
- Beta oxidation: the conversion of fatty acyl CoA's to Acetyl CoA for ketogenesis or TCA/oxidative phosphorylation.
- There are 4 steps in beta oxidation. What is the reactants, products and enzyme required by the first step? What kind of reaction is this?
- X Fatty Acid Acyl CoA in the presence of the enzyme Acyl CoA dehydrogenase makes Trans-(delta 2) Enoyl CoA in an OXIDATION reaction (a coenzyme is reduced in the process).
- There are 4 steps in beta oxidation. What is the reactants, products and enzyme required by the SECOND step? What kind of reaction is this?
- The product from the previous step Trans-Enoyl CoA in the presence of Enoyl CoA hydratase makes L-3Hydroxyacyl CoA in a HYDRATION reaction (obviously requiring H20).
- There are 4 steps in beta oxidation. What is the reactants, products and enzyme required by the THIRD step? What kind of reaction is this?
- The product from the last step L-3 Hydroxyacyl CoA in the presesnce of 3 -OH acyl CoA dehydrogenase is converted to 3 Ketoacyl CoA in an OXIDATION process (a conenzyme is reduced).
- There are 4 steps in beta oxidation. What is the reactants, products and enzyme required by the LAST step? What kind of reaction is this?
- 3-Ketoacyl CoA in the presence of Betta-Ketothiolase is converted to Acetyl CoA in a thiolysis reaction.
- How much ATP is produced per Carbon of a fatty acid that is broken down by Betta oxidation followed by TCA and oxidative phosphorylation? Are any used in the process?
- App 8 ATP's per carbon. Yes, recall it cost 2 ATP to activate the fatty acid to fatty Acid Acyl CoA (already taken into account)
- Recall that in betta oxidation carbons are cleaved off the fatty acid chain in pairs. What if the fatty acid chain has an odd number of carbons? what is the reaction that takes place?
- Odd Carbon in the chain reacts with CO2 (and ATP and Biotin cofactor) to form methylmalonyl CoA and ultimately Succinyl CoA to go through TCA and then Betta oxidation of even chain. (recall same reaction that makes oxaloacetate from pyruvate in gluconeogenesis)
- What is ketogenesis?
- the process by which Acetyl CoA (from pyruvate or betta oxidation) is converted to make Ketone bodies.
- What are the three ketone bodies?
-
Acetoacetate
Acetone
Betta Hydroxybutyrate - the ketone bodies acetoacetate and Betta-hydroxybutyrate are used for what...?
- used to produce ATP in the tissue and brain cells.
- What is the overall reaction that produces acetoacetate?
-
2 Acetyl CoA ----> AcetoAcetate
(reverse of cleavage step of Betta oxidation requiring Betta Ketothiolysis) - What is the overall reaction of the production of Acetone?
- 2 Acetyl CoA in the presence of the enzyme hydroxymethyl-glutaryl CoA synthase make HMG CoA (cholesterol precursor) which in the presence of HMG CoAlyase makes Acetoacetate (a ketone body). Finally H20 cleaves a bond on Acetoacetate to make Acetone (another ketone body).
- What is the overall reaction required to make the ketone body Betta-hydroxybutyrate?
- First the production of acetoacetate is required via the acetone synthesis pathway. Then in a totally reversible oxidation step catalyzed by beta-hydroxybutyrate dehydrogenase we make the product beta-hydroxybutyrate.
- The acetyl CoA produced in the beta oxidation of fatty acid in the matrix of the liver's mitochondrial cells cannot cross the blood-brain or blood-tissue barrier. What is the solution?
- To get the Acetyl CoA to the brain and tissue, it must undergo ketogenesis and form either acetoacetate or beta-hydroxybutyrate which can cross. Once in the brain or tissue, they can form acetoacetyl CoA (another ketone body) by the transfer of CoA from succinyl CoA to succinate. Finaly, the Acetoacetyl CoA can form 2 molecules of Acetyl CoA in the desired tissue for further oxidation to ATP.
- The transport of Acetyl CoA from the liver to the tissues and brain serves what function?
- To alleviate the emergency ATP requirement from falling squarely on glycogenolysis.