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MCAT Biochemistry > Chapter 11: Lipids and Metabolism > Flashcards

Chapter 11: Lipids and Metabolism Flashcards

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MCAT flashcards
1
Q

Where is the primary location of mechanical digestion in lipids?

A

Stomach

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2
Q

Where is the primary location of chemical digestion of lipids?

A

small intestine

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3
Q

In the small intestine, what fluid and enzymes help facilitate chemical digestion of lipids?

A

bile, pancreatic lipase, colipase, and cholesterol esterase

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4
Q

What do digested lipids form in order to be absorbed directly?

A

micelles

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5
Q

Where are short chain fatty acids absorbed?

A

Absorbed across the intestine into the blood

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6
Q

Where are long chain fatty acids absorbed and what are they assembled into for this to happen?

A

They are absbbored into the lymphatic system while they are assembled into chylomicrons

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7
Q

Lipids are mobilized from adipocytes by what enzyme?

A

Hormone sensitive lipase

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8
Q

lipids are mobilized by liporoteins by what enzyme?

A

Lipoprotein lipase

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9
Q

__ (1word) are the transport mechanism for dietary triacylglyerol molecules that are transported via the lymphatic system

A

Chylomicrons

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10
Q

__ Transports newly synthesized triacylglycerol molecules from the liver to peripheral tissues in the bloodstream

A

VLDL = Very low density lipoprotin

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11
Q

__ is a VLDL remnant in transition between triacylglycerol and cholesterol transport; it picks up cholesteryl esters from HDL

A

IDL = Intermediate density lipoprotein

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12
Q

__ primarily transports cholesterol for use by tissues

A

LDL = low density lipoprotein

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13
Q

__ Is involved in the reverse transport of cholesterol

A

HDL = High density

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14
Q

__ controls itneractions between lipoproteins

A

Apoproteins

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15
Q

How can cholsterol be obtained (2 ways)?

A

Through dietary sources or through de novo synthesis in the liver

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16
Q

What is the key enzyme in cholesterol biosynthesis?

A

HMG-CoA reductase

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17
Q

__ Catalyzes the formation of cholsteryl esters for transport with HDL

A

LCAT

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18
Q

__ catalyzes the transition of IDL to LDL by transferring cholesteryl esters from HDL

A

CETP

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19
Q

What are fatty acids?

A

they’re carboxylic acids with a single long chain, although can be branched

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20
Q

What is the difference between saturated fatty acids and unsaturated fatty acids?

A

Saturated = single bonds (no double bonds)

Unsaturated fatty acids = has double bonds (cis or trans)

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21
Q

Where are fatty acids synthesized in? From what molecule in the TCA?

A

FAs syn in the cytoplasm from acetyl-CoA trnapsorted out of the mitochondria

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22
Q

Lipid synthesis includes 5 steps: Name them

A

Activation, bond formation, reduction, dehydration, and a second reduction

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23
Q

WHen the steps of lipid synthesis is repeated eight times, what FA is made?

A

Palmitic acid (only human FA we can synthesize)

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24
Q

Where does FA oxidation occur?

A

Occurs in the mitochondira following transport by the carnitine shuttle

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25
Q

_-Oxidation uses cyles ofr oxidation, hydraiton, oxidation, and cleavage

A

B-oxidation

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26
Q

__ and __ FAs require special enzymes

A

Branched and unsatruated

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27
Q

Unsatuarated FAs use and __ and an additional __ during cleavage

A

Isomerase and a reducatase

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28
Q

When do ketone bodies form?

A

during prolonged starvaition state due to excess acetyl-CoA in the liver

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29
Q

Ketolysis regenerates __ for use as an energy source in peripheral tissues

A

Acetyl-CoA

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30
Q

The brain can derive up to __-thirds of its energy from ketone bodies during prolonged starvation

A

two-thirds

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31
Q

Where does protein digestion occur?

A

Primarily in small intestine

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32
Q

catabolism of cellular proteins occurs under what conditions?

A

starvation or fasting

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33
Q

Carbon skeletons of amino acids are used as fuel for which two metabolic pathways?

A

Gluconeogeneis or ketone body formation

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34
Q

Amino acid groups are fed into which cycle?

A

The Urea cycle for excretion.

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35
Q

dietary fat consists of ___ with the remainder comprised of ___, ___ esters, ___ and free ___ acids

A

triacylglycerols with the remainder comprised of cholesterol, cholesteryl esters, phospholipids and free fatty acids

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36
Q

lipid digestion is minimal in ___ and ___ but are transported to the small ___ for digestion

A

minimal in mouth and stomach but are transported to the small itnestine for digestion

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37
Q

What occurs in the duodenum?

A

Emulsification which is mixing of two normally immiscible liquids (fat and water)

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38
Q

Formation of an emulsion increases the ____ area of the lipid, which permits greater ___ interaction and processing

A

increases surface area

greater enzymatic interaction

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39
Q

Emulsification is aided by what three things?

A

bile salts, pigments and cholesterol

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40
Q

Bile is secreted by ___ and stored in ___

A

secreted by liver and stored in gallbladder

41
Q

Pancreas secretes what three enzymes? Where?

A

Pancreatic lipase, colipase, and cholesterol esterase

Into small intestine

42
Q

What do both liver and pancratic enzymes do to the lipid componenets?

A

They hydrolyze lipid to 2-monoacylglycerol, free fatty and cholesterol

43
Q

Emulsification is followed by ___ of fatys by intestinal cells

A

absoprtion

44
Q

Micelles

A

clusters of amphipathic lipids that are soluble in the aqueous or water spehres iwth lipid soluble itnerior

45
Q

As micelles travel down the duodenum to the ilem, what happens to bile salts?

A

bile salts are reabsobred and recyled while any fat remains goes to colon and becomes part of stool

46
Q

In absorption, where do micelles get absorbed?

A

Micelles diffuse to brush border of intesitnal mucosal cells

47
Q

When lipids are absobred what is the chemical process?

A

Re-esterified to form triacylglycerols and cholesteryl esters and packaged with certain apoproteins , fat soluble vitamins and other lipids in chylomicrons

48
Q

What do chylomicrons leave the intesine by? And how do they re-enter bloodstream?

A

Leave via Lacteals: vessels of lymphatic system

re-enter via thoracic duct: long lymphatic vessel that empties into left subclavian vein at base of neck

49
Q

Role of hormone sensitive lipase (HSL)

A

Hydrolyzes triacyleglycerols from adipose tissues yielding glycerol and fatty acids

50
Q

Regulation of hormone-sensitive lipase

A

increase in Epinephrine and cortsol activate HSL

Decrease in insulin (higher glucagon) also activates HSL

51
Q

lipoprotein lipase (LPL) is for the metabolism of chylomicronsa and very ___ density lipoproteins

A

very low density lipoproteins (VLDL)

52
Q

LPL is an enzyme that release free fatty acids from ___ in these lipoproteins

A

from triacylglycerols in these lipoproteins

53
Q

released glycerol can go into ___

A

gluconeogeneis (high glucagon and cortisol)

54
Q

What is the ratio of free fatty acids to glycerol produced through lipid mobilization?

A

ratio of free FAs to glycerol is 3:1 since a triacylglycerol is made of glycerol and 3 fatty acids anyway

55
Q

What conditions and hormones promote lipid mobilization from fat stores?

A

In the postabsorptive and prolonged fasting states, lipid mobilization is favored. A decrease in insulin levels, and increase in epinephrine and cortisol will increase lipid mobilization from adipocytes.

56
Q

Free fatty acids are trnasproted though blood in association with ____
While triacylglycerols and choelsterol are transproted in blood as ___ / ___

A

albumin

transproted in blood as liporptoteins/apolipoproteinswith lipids

57
Q

VLDL (very low dentisty liportoteins

A

transports triacylglycerols from liver to tissues

58
Q

IDL (Intermediate density lipoproteins VLDL remnants)

A

Picks up cholesterol from HDL to become LDL –> picked up by liver

59
Q

LDL (low density liporteins

A

delivers cholsterol into cells

60
Q

HDL (high Density Lipoproteins)

A

picks up cholesterol accumulating in blood vessels; delivers cholesterol to live and steroidogenic tissues

61
Q

What is the primary method of transporting free fatty acids in the blood?

A

Free fatty acids remain in the blood, bound to albumin and other carrier proteins. A much smaller amount will remain unbound.

62
Q

Order the lipoproteins from greatest percentage of protein to least percentage of protein. Circle the molecules that are primarily involved in triacylglycerol transport.

A

HDL > LDL > IDL > VLDL > chylomicrons;
VLDL and chylomicrons are the primary triacylglycerol transporters. HDL and LDL are mostly involved in cholesterol transport.

63
Q

Lipoproteins are synthesized primarily by which two organs?

A

Lipoproteins are synthesized primarily by the intestine and liver

64
Q

Chylomicrons

A

transports triacylglycerols and cholesterol from intesine to tissues

65
Q

Under what conditions is HMG-CoA reductase most active? In what cellular region does it exist?

A

HMG-CoA reductase is most active in the absence of cholesterol and when stimulated by insulin. Cholesterol reduces the activity of HMG-CoA reductase, which is located in the SER.

66
Q

What proteins are specific to the transport and release of cholesterol, and what are their functions?

A

LCAT catalyzes the esterification of cholesterol to form cholesteryl esters. CETP promotes transfer of cholesteryl esters from HDL to IDL, forming LDL.

67
Q

Acetyl-CoA Carboxylase

A

in the cytoplasm;
rate limiting enzyme of fatty acid biosynthesis;
requires ATP and biotin;
adds CO2 to acetyl-CoA to form malonyl CoA;
(+) insulin and citrate

68
Q

Fatty Acid Synthase or Palmitate Synthase

A

palmitate is the only fatty acid that humans can synthesize de novo;
Action:
1. activation of the growing chain and malonyl CoA
2. attachment of ACP (malonyl-ACP)
3. reduction of carbonyl group to hydroxyl group
4. dehydration
5. reduction to saturated fatty acid

69
Q

Fatty acid synthesis and b-oxidation

A

reverse process;
both involve transport across the mitochondrial membrane, followed by a series of redox reactions, but always in the opposite direction of one another

70
Q

b-oxidation

A 
mitochondria;
activated by glucagon and inhibited by insulin;
reverse process of fatty acid synthesis;
repetition of 4 steps:
1. releases 1 acetyl-CoA
2. reduces NAD+ and FAD
71
Q

Long chain (14-20C) fatty acids transport

A

requires carnitine shuttle in the mitochondria

72
Q

Carnitine acyltransferase I

A

rate-limiting enzyme of fatty acid oxidation

73
Q

4 steps of b-oxidation

A
  1. oxidation of fatty acid to form a double bond
  2. hydration of the double bond to form hydroxyl
  3. oxidation of hydroxyl to carbonyl (b-ketoacid)
  4. splitting of the b-ketoacid into a shorter acyl-CoA and acetyl-CoA
74
Q

Propionic acid pathway

A

Odd fatty acid –> Propionyl-CoA— (propionyl-CoA carboxylase (biotin))—> Methylmalonyl-CoA —- (methylmalonyl-CoA mutase (B12)) —> Succinyl-COA —> Citric Acid Cycle

*exception to the rule that fatty acids cannot be converted to glucose in humans!

75
Q

2 Enzymes for Oxidation of Unsaturated Fatty Acids

A
  1. enoyl-CoA isomerase

2. 2,4-dienoyl-CoA reductase

76
Q

Enoyl-CoA Isomerase

A

rearranges cis double bonds at the 3,4 position to trans double bonds at 2,3 position (last step)

77
Q

2,4-Dienoyl-CoA Reductase

A

convert two conjugated double bonds to one double bond at 3,4 position (2nd step)

78
Q

What are the 5 steps in the addition of acetyl-CoA to a growing fatty acid chain?

A

The five steps in the attachment of acetyl-coA to a growing fatty chain are:

  1. attachment to ACP
  2. bond formation between molecules
  3. Reduction of a carboxyl to hydroxyl
  4. Dehydration
  5. Reduction of a double bond
79
Q

How does b-oxidation of unsaturated fatty acids differ from that of saturated fatty acids?

A

There is an additional isomerase and an additional reductase for the b-oxidation of unsaturated fatty acids, which provide the stereochemistry necessary for further oxidation

80
Q

Fatty acids are synthesized in the

A

cytoplasm

81
Q

Fatty acids are modified by enzymes in the

A

smooth endoplasmic reticulum

82
Q

Ketone bodies

A

transportable forms of acetyl-CoA;

produced by the liver and used by other tissues during prolonged starvation

83
Q

Ketogenesis

A

occurs in the mitochondria of liver cells when excess acetyl-CoA accumulates in the fasting state

84
Q

Ketolysis

A

occurs in mitochondrial matrix of muscle, renal cortex, and brain in prolonged fast;

acetoacetate is picked up from the blood and activated by thiophorase (only in liver), 3-hydroxybutarate is oxidized to acetoacetate

85
Q

Why are fatty acids used to create ketone bodies instead of creating glucose?

A

Fatty acid degradation results in large amounts of acetyl-CoA, which cannot enter the gluconeogenic pathway to produce glucose. Only odd-numbered fatty acids can act as a source of carbon for gluconeogenesis; even then, only the final malonyl-CoA molecule can be used. Energy is packaged into ketone bodies for consumption by the brain and muscles.

86
Q

What conditions and tissues favor ketogenesis?

A

Ketogenesis is favored by a prolonged fast and occurs in the mitochondria of the liver. It is stimulated by increasing concentrations of acetyl-CoA

87
Q

What conditions and tissues favor ketolysis?

A

Ketolysis is favored by a prolonged fast and is stimulated by a low-energy state in muscle and brain tissues.

88
Q

Glucogenic Amino Acids

A

all but leucine and lysine can be converted into glucose through gluconeogenesis

89
Q

Ketogenic Amino Acids

A

leucine, lysine, isoleucine, phenylalanine, threonine, tryptophan, tyrosine can be converted into acetyl-CoA and ketone bodies

90
Q

T or F: Bodily proteins will commonly be broken down to provide acetyl-CoA for lipid synthesis

A

False. Proteins are more valuable to the cell than lipids, thus, they will not commonly broken down for lipid synthesis

91
Q

Where does bulk of protein digestion occurs?

A

Bulk of protein digestion occurs in the small intestines

92
Q

During protein processing, what is the fate of carbon skeleton? amino group? side chains?

A

Carbon skeleton: transported into the liver for processing into glucose or ketone bodies

Amino group: urea cycle for excretion

Side chains: processed depending on composition; basic side chains will be processed like amino groups and other functional groups will be treated like carbon skeleton

93
Q

Lipids are mobilized from adipocytes by

A

hormone-sensitive lipase (HSL)

94
Q

Lipids are mobilized from lipoproteins by

A

Lipoprotein lipase (LPL)

95
Q

Apoproteins

A

control interactions between lipoproteins;
increases ability to remove excess cholesterol from blood vessles; edocytose lipoprotein, secrete lipid transport lipoproteins

96
Q

True or False: All lipids enter the circulation through the lymphatic system

A

False. Small free fatty acids enter the circulation directly

97
Q

Describe the structure of a micelle

A

Micelles are collections of lipids with their hydrophobic ends oriented toward the center and their charged ends oriented toward the aqueous environment. They collect lipids within their hydrophobic centers.

98
Q

What conditions and hormones promote lipid mobilization from fat stores?

A

In the postabsorptive and prolonged fasting states, lipid mobilization is favored. A decrease in insulin levels, and increase in epinephrine and cortisol will increase lipid mobilization from adipocytes.

99
Q

When lipids leave the stomach, what stages of digestion have been accomplished? What enzymes are added to accomplish the next phase?

A

Physical digestion is accomplished in the mouth and the stomach, reducing the particle size. Beginning in the small intestine, pancreatic lipase, colipase, cholesterol esterase, and bile assist in the chemical digestion of the lipids. In the more distal portion of the small intestine, absorption occurs.

MCAT Biochemistry (3 decks)

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