ch 11 Lipid and Amino Acid Metabolism

Question 1

emulsification

Answer 1

mixing of two normally immiscible liquids. Liquids that won’t normally mix

Question 2

Dietary fat

Answer 2

consists mainly of triacylglycerols, but also has cholesterol, choleteryl esters, phospholipids and free fatty acids.

Question 3

Digestion path

Answer 3

minimal in mouth and stomach; small intestines, emulsification which is aided by bile (containing bile salts, pigments and cholesterol and is secreted by the liver and stored in gallbladder). Then pancreas secretes pancreatic lipase, colipase, and cholesterol esterase into small intestines which hydrolyze lipid to 2-monoacylglycerol, free fatty acids, and cholesterol

Question 4

micelles

Answer 4

formed to get absorbed in the small intestine (comprised of the free fatty acids, cholesterol and 2-monoacylglycerol) with water-soluble exterior and lipid interior

Question 5

Absorption of lipids in digestion

Answer 5

micelles diffuse to brush border (of intestinal muscosal cells) and are absorbed. pass brush border, absorbed into mucosa and are packaged into chylomicrons (re-esterified to form triacylglycerols and cholesteryl esters and packaged with apoproteins, fat-soluble vitamins and other lipids). Chylomicrons leave intestine by lacteals (lymphatic vessels) and reenter bloodstream by thoracic duct which empties into the left subclavian vein at base of neck

Question 6

hormone-sensitive lipase (HSL)

Answer 6

fall in insulin levels activates this. hydrolyzes triacylglycerols, yielding fatty acids and glcerol. Also activated by cortisol and epi

Question 7

lipoprotein lipase (LPL)

Answer 7

necessary for metabolism of chylomicrons

Question 8

albumin

Answer 8

carrier protein in blood transporting fatty acids

Question 9

lipoproteins

Answer 9

transport triacylglycerol and cholesterol in the blood, made of apolipoproteins and lipids

Question 10

chylomicrons

Answer 10

highly soluble in lymphatic fluid and blood; function to transport dietary tracyglycerols, cholesterol and cholesteryl esters to other tissues

Question 11

VLDL (very low density lipoprotein)

Answer 11

produced and assembled in liver cells; main function - transport tracylglycerols to other tissues; contain fatty acids also

Question 12

IDL (intermediate density lipoprotein)

Answer 12

VLDL remnant - what remains after triacyglycerol is removed from VLDL. Intermediate between chylomicrons and VLDL, and LDL and HDL, which transport cholesterol. This picks up cholesteryl esters from HDL to form LDL

Question 13

LDL (low density lipoprotein)

Answer 13

deliver cholesterol to tissues for biosynthesis; plays important role in cell membranes and bile acids and salts in liver and steroidogenesis

Question 14

HDL (high density lipoprotein)

Answer 14

cleans up excess cholesterol from blood vessels for excretion and delivers some cholesterol to steroidogenic tissues and transfers necessary apoliproteins to some of the other lipoproteins

Question 15

apoliproteins

Answer 15

also called apoproteins; receptor molecules involved in signaling

Question 16

de novo synthesis

Answer 16

form of synthesizing cholesterol other than LDL and HDL, occurs in liver and is driven by Acetyl-CoA and ATP

Question 17

citrate shuttle

Answer 17

carries mitochondrial Acetyl-CoA into cytoplasm where synthesis can occur.

Question 18

mevalonic acid

Answer 18

synthesis of this in the Smooth ER is rate limiting step of cholesterol biosynthesis

Question 19

3-hydroxy-3-methylglutaryl (HMG) CoA reductase

Answer 19

enzyme that catalyzes rate limiting step of cholesterol biosynthesis

Question 20

regulation of cholesterol synthesis

Answer 20

increased levels of cholesterol inhibit, insulin promotes, control of de novo synthesis depends on regulation of HGM-CoA reductase gene expression

Question 21

specialized enzymes for transport of cholesterol

Answer 21

Lecithin-cholesterol acyltransferase (LCAT), and cholesteryl ester transfer protein (CETP)

Question 22

fatty acids

Answer 22

long-chain carboxylic acids. Carboxyl is C-1 and C-2 is alpha carbon

Question 23

Saturated fatty acids

Answer 23

no double bonds

Question 24

unsaturated fatty acids

Answer 24

one or more double bonds

Question 25

alpha-linolenic acid and linoleic acid

Answer 25

important essential fatty acids; poly-unsaturated, important in maintaining cell membrane fluidity

Question 26

omega number system

Answer 26

used for unsaturated fatty acids; omega designates the position of the last double bond relative to the end of the chain and identifies the major precursor fatty acid; double bonds in natural fatty acids are generally cis

Question 27

nontemplate synthesis

Answer 27

lipid and carb synthesis often referred to as this bc they don’t rely directly on coding of nucleic acid unlike protein and nucleic acid synthesis

Question 28

Palmitic acid

Answer 28

also called palmitate - primary end product of fatty acid synthesis

Question 29

acetyl-CoA carboxylase

Answer 29

rate-limiting enzyme for fatty acid biosynthesis; requires biotin and ATP; add CO2 to acetyl-CoA to form malonyl-CoA

Question 30

fatty acid synthase

Answer 30

better name is palmitate synthase bc palmiate is the only fatty acid that humans can synthesize de novo; 8 acetyl-coA groups are required to produce palmitate (16:0); many of rxns performed by fatty acid synthase are reversed by beta-oxidation

Question 31

triacylglycerol (triglyceride) synthesis

Answer 31

triacylglycerols are the storage form of fatty acids formed by attaching 3 fatty acids (as fatty acyl-CoA) to glycerol. formation occurs primarily in the liver and some in adipose.

Question 32

beta-oxidation

Answer 32

how most fatty acid catabolism proceeds; takes place in mitochondria or in the peroxisome. Directly inhibited by insulin and stimulated by glucagon

Question 33

alpha-oxidation

Answer 33

may occur in branch-chain fatty acids, depending on the branch points

Question 34

omega-oxidation

Answer 34

happens in ER and produces dicarboxylic acids

Question 35

pathway of beta-oxidation

Answer 35

fatty acids metabolized become activated by attachment to CoA which is catalyzed by fatty-acyl-CoA synthase produces fatty acyl-CoA. Then short (2-4 Cs) and medium (4-12 Cs) chain fatty acids diffuse freely into mitochondria while long (14-20 Cs) must use carnitine shuttle. Very long chains are oxidized elsewhere. in the mito, this processes reverses fatty acid synthesis, oxidizes and releases molecules of Acetyl-CoA, four step cycles each release one. and reduces NAD+ and FAD. NADH and FADH2 are oxidized in the ETC producing ATP. this process is used by liver to produce more acetyl-CoA

Question 36

rate limiting enzyme of beta-oxidation

Answer 36

carnitine acyltransferase I

Question 37

Four steps of beta-oxidation

Answer 37

1. oxidation of fatty acid to form double bond; 2. Hydration of the double bond to form a hydroxyl group; 3. oxidation of hydroxyl group to form a carbonyl (beta-ketoacid); 4. splitting of the beta-ketoacid into a shorter acyl-CoA and acetyl-CoA

Question 38

propionyl-CoA carboxylase

Answer 38

changes propionyl-CoA produced at end of beta oxidation by odd number carbon input to methylmalonyl-CoA which is then changed to succinyl-CoA by methylmalonyl-CoA mutase which requires B12 which is an intermediate in krebs or can be converted into malate for the gluconeogenic pathway

Question 39

enoyl-CoA isomerase

Answer 39

monosaturated fatty acids, this changes the configuration from cis to trans for oxidative enzymes to act on fatty acids; between Cs 2 and 3; in polyunsaturated further reduction is required by 2,4-dienoyl-CoA reductase

Question 40

steps in acetyl-CoA attachment to fatty acid chain

Answer 40

1. attachment to acyl carrier protein, 2. bond formation bt molecules, 3. reduction of a carbonyl group, 4. dehydration, 5. reduction of a double bond