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MCAT Biochem > Biochem #11 > Flashcards

Biochem #11 Flashcards

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1
Q

lipids are _____ when they reach the small intestine

A

pretty intact

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2
Q

emulsification

A

occurs in the duodenum.
 Aided by bile which is secreted from the liver and stored in the gallbladder. Bile contains bile salts, pigments, and cholesterol.

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3
Q

what does the pancreas secrete into the small intestine (specific to fats)

A

The pancreas secretes pancreatic lipase, colipase, and cholesterol esterase into the small intestine.

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4
Q

micelle

A

clusters of amphipathic lipids that are soluble in the aqueous environment of the intestinal lumen.
Contains free fatty acids, cholesterol, 2-monoacylglycerol, and bile salts contribute to them.

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5
Q

Any fat still remaining in the ileum will ____

A

pass into the colon and ends up in stool

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6
Q

chylomicrons

A

packages of triacylglycerols, cholesteryl esters, apoproteins, fat-soluble vitamins, and other lipids.
 These things get packaged into here after they pass through the brush border and are absorbed into the mucosa.
 Leave the intestine via lacteals, the vessels of the lymphatic system
• Re-enter the bloodstream via the thoracic duct, a long lymphatic vessel that empties into the left subclavian vein at the base of the neck.

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7
Q

where does the lymphatic system re-enter circulation?

A

lymphatic duct

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8
Q

short chain water soluble fatty acids can ____ during digestion

A

The more water-soluble short-chain fatty acids can be absorbed by simple diffusion directly into the bloodstream.

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9
Q

what are the drugs prescribed to treat high cholesterol?

A

statins

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10
Q

hormone sensitive lipase

A

Human adipose tissue does not respond directly to glucagon, but a fall in insulin levels activates hormone-sensitive lipase (HSL) that hydrolyzes triacylglycerols, yielding fatty acids and glycerol.
o Epinephrine and cortisol can also activate HSL

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11
Q

lipoprotein lipase

A

necessary for the metabolism of chylomicrons and very-low-density lipoproteins (VLDL).
o Can release free fatty acids from triacylglycerols in these lipoproteins.

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12
Q

what transports free fatty acid throughout the blood?

A

albumin

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13
Q

lipoproteins

A

transport triacylglycerol and cholesterol through the blood (also have a carrier protein)
o They are aggregates of apolipoproteins (bind lipids) and lipids.
o Names according to their density which is in direct proportion to the amount of protein present.

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14
Q

rank lipid transport molecules with respect to the ratio of fat to protein

A

Chylomicrons > VLDL (very low-density lipoprotein) > IDL (intermediate density) > LDL (low-density) > HDL (high density).

highest fat to protein ratio means least dense.

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15
Q

rank lipid transport molecules with respect to the ratio of fat to protein

A

Chylomicrons > VLDL (very low-density lipoprotein) > IDL (intermediate density) > LDL (low-density) > HDL (high density).

highest fat to protein ratio means least dense.

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16
Q

Chylomicrons and VLDL carry mostly ____.

LDL and HDL carry mostly _____l.

A

triacylglycerols

cholesterol

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17
Q

chylomicrons

A

 Highly soluble in lymphatic fluid and blood.
 Assembly occurs in the intestinal lining
 Carry dietary triacylglycerols, cholesterol, and cholesteryl esterase.

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18
Q

VLDL

A

 Similar to chylomicrons except it is produced and assembled in liver cells.
 Main job is to transport triacylglycerols.

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19
Q

IDL

A

 Once triacylglycerol is removed from VLDL  VLDL remnant or IDL.
 Some is reabsorbed by the liver.
 Can pick up cholesteryl esterase from HDL and become LDL. Exists as a transition particle.

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20
Q

LDL

A

 Mostly cholesterol particles
 The majority of cholesterol in blood is associated with LDL
 Many cells require cholesterol but main function of LDL is to deliver it to tissues for biosynthesis.
cholesterol used for: cell membranes, bile acids and salts (in liver), steroid hormone synthesis

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21
Q

HDL

A

 Synthesized in the liver and intestines and released as dense, protein-rich particles in the blood.
 Contains apolipoproteins which clean up excess cholesterol from blood vessels for excretion
delivers some cholesterol to steroidogenic tissues and transfers necessary apolipoprotiens to some of the other lipoproteins

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22
Q

apolipoproteins

A

protein component of lipoproteins
control interactions between lipoproteins.
 Apoproteins: form the protein component of the lipoproteins.
receptor molecules and are involved in signaling

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23
Q

most cells get their cholesterol from _______

A

HDL or LDL

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24
Q

citrate shuttle

A

carries mitochondrial acetyl-CoA to the cytoplasm where synthesis occurs.

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25
Q

where does the rate limiting step of cholesterol synthesis occur and what is the rare limiting step?

A

o Synthesis of mevalonic acid in the Smooth ER is the rate-limiting step and is catalyzed by 3-hydroxy-3-methylglutaryl (HMG) CoA reductase. HMG-CoA Reductase.

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26
Q

how does the presence of cholesterol effect cholesterol synthesis? how does insulin effect cholesterol synthesis?

A

inhibits it

promotes it

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27
Q

LCAT

A

found in the bloodstream and activated by HDL apoproteins.

• Adds a fatty acid to cholesterol to make cholesteryl esters which can be added to IDL.

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28
Q

CETP

A

facilitates the transfer process of fatty acid to cholesterol and the formation of LDL from IDL by addition of this cholesteryl ester.

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29
Q

naming fatty acids

A

carbons:double bonds

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30
Q

saturated fatty acids

A

no double bonds, straight

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31
Q

unsaturated fatty acids

A

have one or more double bonds.
 The human body can create some but the rest have to come from the diet.
 Two important ones are alpha-linolenic acid and linoleic acid.
• These and others are important for maintaining cell membrane fluidity.

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32
Q

acetyl-CoA shuttling

A

o After a big meal there is a buildup of acetyl-CoA in the mitochondrial matrix. After being converted into citrate by combining with OAA, it can use the citrate shuttle to get to the cytoplasm. There, it is broken back up into OAA and acetyl-CoA via citrate lyase.

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33
Q

acetyl-CoA carboxylase

A

carboxylase (biotin and ATP required to function) activates acetyl-CoA by converted it to malonyl-CoA. Adds CO2 to form malonyl CoA
o RATE LIMITING STEP of fatty acid synthesis.
o Activated by insulin and citrate.

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34
Q

what is the only fatty acid that humans can synthesize de novo?

A

palmitate synthase

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35
Q

fatty acid synthase

A

o Multienzyme complex that contains an acyl carrier protein (ACP) and requires vitamin B5.
o Need 8 acetyl-CoA groups to produce palmitate (16:0).
 After this is produced, can increase the length and add double bonds with other enzymes.
o Reactions occur over and over again until 16 carbons
 Reaction: activation of the growing chain and malonyl-CoA with ACP, bond formation between these activated molecules, reduction of a carbonyl to a hydroxyl group, dehydration, and reduction to a saturated fatty acid.

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36
Q

triacylglycerol synthesis

A

o Formed by combining 3 fatty acids with a glycerol.
o Triacylglycerol formation from fatty acids and glycerol-3-phosphate occurs primarily in the liver and somewhat in adipose tissue.

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37
Q

what is the name for fatty acid breakdown?

A

beta oxidation

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38
Q

glucagon and insulin affects on beta oxidation ____

A

o Insulin indirectly inhibits beta oxidation while glucagon stimulates it.

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39
Q

beta oxidation

A

 Fatty-acyl-CoA synthetase: attaches a fatty acid to CoA to activate it.
 Referred to as acyl-CoA
o Fatty acid entry into mitochondria
 Short chain fatty acids can diffuse freely into the mitochondria.
 Long chain fatty acids (14-20 C) must use the carnitine shuttle: carnitine acyltransferase I is the rate-limiting step of fatty acid oxidation.
 >20 C are oxidized elsewhere in the cell.
o Beta Oxidation in Mitochondria
 Pathway of 4 steps, each four step cycle releases one acetyl-CoA and reduces NAD+ and FAD. FADH2 and NADH are oxidized in the electron transport chain to produce ATP.
• 1. Oxidation of the fatty acid to form a double bond
• 2. Hydration of the double bond to form a hydroxyl group.
• 3. Oxidation of the carboxyl group to form a carbonyl
• 4. Splitting of the beta-ketoacid into a shorter acyl-CoA and acetyl-CoA
• Continues until the chain has been shortened to two carbons.

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40
Q

what is the acetyl-CoA from fatty acid breakdown used for in muscle, liver, and adipose tissue?

A

 In muscle and adipose tissue, the produced acetyl-CoA is used in the citric acid cycle.
 In the liver, acetyl-CoA stimulates gluconeogenesis.

41
Q

odd numbered chain fatty acids and breakdown

A

 Odd numbered chain fatty acids: can be converted to succinyl CoA and malate and enter the gluconeogenic pathway.

42
Q

what are the common ketone bodies?

A

acetoacetate and 3-hydroxybutyrate.

43
Q

what are the common ketone bodies?

A

acetoacetate and 3-hydroxybutyrate.

44
Q

In the fasting state, the liver converts excess ____ from ____ of fatty acids into ____ which can be used for energy in various tissues.

A

acetyl-CoA
beta oxidation
ketone bodies

45
Q

ketogenesis

A

occurs in the mitochondria of liver cells when excess acetyl-CoA accumulates in the fasting state.
o Acetone is a minor side product that is formed.

46
Q

what is produced as a side product from ketopgenesis

A

acetone

47
Q

ketolysis

A

o Ketone bodies picked up in blood and they are converted to acetyl-CoA in the mitochondria.
o Liver lacks this enzyme so it cannot catabolize the ketone bodies that it produces.
o Ketolysis in the Brain
 During a prolonged fast, the brain begins to derive up to two-thirds of its energy from ketone bodies.
 When ketones are metabolized, pyruvate dehydrogenase is inhibited.

48
Q

can ketolysis be done in the liver?

A

NO. Does not have the enzyme for it.

49
Q

under extreme energy deprivation, _____ can be used for energy

A

• Under extreme energy deprivation, proteins can be used for energy.

50
Q

proteolysis

A

breakdown of proteins

51
Q

when does proteolysis occur?

A

begins in the stomach with pepsin and continues with the pancreatic proteases trypsin, chymotrypsin, and carboxypeptidases A and B.
o Completed by the small intestine brush-border enzymes dipeptidase and aminopeptidase.
o Main product is amino acids, dipeptides, and tripeptides.

52
Q

amino acids and energy

A

• Amino acids released from proteins lose their amino groups: transamination or deamination.
o Remaining carbon skeleton is used for energy.

53
Q

what are the glucogenic amino acids

A

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

54
Q

ketogenic amino acids

A

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

55
Q

how are amino groups rid from the body?

A

urea

56
Q

urea cycle

A

o Urea cycle occurs in the liver and is the body’s primary way of removing excess nitrogen from the body.

57
Q

what are micelles actually made of?

A

they are made out of lipids that have their hydrophobic portions pointing in (interact with lipids) and their hydrophilic parts pointing out (interact with water/aqueous environment)

58
Q

in addition to a decrease in insulin, what else activates hormone-sensitive lipase?

A

epinephrine and cortisol

59
Q

what is the ratio of glycerol to free fatty acid when a triacylglycerol is broken down?

A

3 fatty acid for every 1 glycerol

60
Q

what do lipoproteins consist of?

A

carrier protein, triacylglycerol and cholesterol

61
Q

apolipoproteins

A

proteins that bind lipids (to make lipoproteins)

62
Q

the more dense the lipoprotein, the more ____ (protein or fat) is in it

A

protein

63
Q

what are steroidogenic tissues

A

adrenal gland and gonads

64
Q

cholesteryl ester

A

ester of cholesterol

forms when an ester group is formed on the hydroxyl group of a cholesterol

65
Q

what is considered “good cholesterol”

A

HDL

66
Q

where are lipoproteins mostly sythesized?

A

intestine and liver

67
Q

cholesterol plays a major role in the synthesis of ______

A

cell membranes, steroid hormones, bile acids, and vitamin D

68
Q

where does de novo synthesis of cholesterol occur?

A

liver

69
Q

fatty acid

A

long-chain carboxylic acid

70
Q

how many double bonds do saturated fatty acids have?

A

none

71
Q

where does fatty acid biosynthesis occur and where are the products transported?

A

occurs in the liver and products are transported to adipose tissue
adipose tissue can also synthesize smaller quantities of fatty acids

72
Q

what are the major enzymes of fatty acid synthesis?

A

acetyl-coA carboxylase and fatty acid synthase

73
Q

palmitic acid (palmatate)

A

primary end product of fatty acid synthesis

74
Q

what is the rate limiting step of fatty acid synthesis?

A

acetyl-CoA carboxylase: acetyl-CoA to malonyl-CoA

75
Q

what activates acetyl-coA carboxylase?

A

insulin and citrate

76
Q

what comes together to make a triacyleglycerol?

A

glycerol-3-phosphate and 3 fatty acids

77
Q

oxidation of fatty acids

A

primarily occurs in the mitochondria (as beta oxidation) but there are other types that exist such as alpha and omega oxidation in other locations as well.

78
Q

are very long chain fatty acids (over 20 carbons) oxidized in the mitochondria?

A

no, elsewhere in the cell

79
Q

what is the rate limited step of fatty acid oxidation?

A

carnitine acyltransferase I

80
Q

what acts as the exception to the rule that fatty acids cannot be converted to glucose in humans?

A

odd-carbon fatty acids

81
Q

enoyl-CoA isomerase and 2,4-dienoyl-CoA reductase

A

help beta oxidation occur with unsaturated fatty acids

goal is to get the double bond between the 2 and 3 carbons and then beta oxidation can go as normal.

82
Q

omega naming system

A

w-designation describes the position of the last double bond relative to the end of the chain

83
Q

where are fatty acids modified after they are synthesized?

A

smooth ER

84
Q

in thew fasting state, the liver converts excess acetyl-CoA from Beta oxidation of fatty acids into the ketone bodies ______ and ______

A

acetoacetate

3-hydroxybutyrate

85
Q

What are acetoacetate and 3-hydroxybutyrate converted into by cardiac and skeletal muscle?

A

acetyl-CoA

86
Q

what enzymes produce acetoacetate from acetyl-CoA

A

HMG-CoA synthase
HMG-CoA lyase

HMG-CoA is the intermediate

87
Q

what is a side product of the conversion of acetyl-CoA to acetoacetate?

A

acetone

88
Q

can the liver catabolize the ketone bodies that it produces?

A

no

89
Q

what organ produces ketone bodies?

A

the liver

90
Q

at what point does the brain begin to use ketone bodies?

A

after a fast longer than one week

91
Q

ketogenesis is stimulated in the _____ by a prolonged ______ and buildup of _____

A

liver
fast
acetyl-coA

92
Q

what are the enzymes for protein breakdown released by the pancreas? what are the enzymes for protein breakdown in the brush-border?

A

pancreas: trypsin, chymotrypsin, carboxypeptidase A and B

brush border: aminopeptidase and dipeptidase

93
Q

where does the urea cycle occur?

A

liver

94
Q

what are amino groups removed from peptides converted to that is potentially dangerous to the body and how is it removed?

A

converted to ammonia

removed as urea

95
Q

transamination or deamination

A

proteins lose their amino groups (during protein catabolism)

96
Q

how are the side chains of amino acids processed during protein catabolism?

A

basic side chains go thru the urea cycle

other side chains act like the carbon skeleton and produce energy through gluconeogenesis or ketone production.

97
Q

how many carbons and double bonds does palmatic acid have?

A

16 C’s

0 double bonds

98
Q

the majority of triacylglycerols stored in adipocytes originate from where?

A

the liver

99
Q

are proteins ever broken down for fatty acid storage?

A

no

MCAT Biochem (12 decks)

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