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BIOC4331: Biochemistry I > Lipid Biosynthesis, Cholesterol, and Amino Acid Catabolism > Flashcards

Lipid Biosynthesis, Cholesterol, and Amino Acid Catabolism Flashcards

1
Q

Fatty acid oxidation occurs in the _____, but fatty acid synthesis occurs in the _____.

A

mitochondria; cytosol

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2
Q

The redox coenzyme used for fatty acid synthesis is _____.

A

NADPH

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3
Q

Fatty acid elongation reactions are repeated until the growing chain reaches __ carbons in length.

A

16

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4
Q

What catalyzes the first committed and a rate-controlling step of fatty acid synthesis?

A

Biotin-dependent enzyme in the ER

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5
Q

cAMP [inhibits/stimulates] acetyl CoA carboxylase (ACC) through phosphorylation by PKA.

Insulin [inhibits/stimulates] ACC activity through dephosphorylation.

A

inhibits; stimulates

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6
Q

Citrate [activates/inhibits] ACC, and palmitoyl-CoA (the product of fatty acid synthesis) [activates/inhibits].

A

activates; inhibits

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7
Q

What are the three regions of acetyl-CoA carboxylase? What are their functions?

A
  1. Biotin carrier protein: Swings CO2 from biotin carboxylase to transcarboxylase
  2. Biotin carboxylase: Attaches CO2 to a nitrogen in the biotin ring
  3. Transcarboxylase: Transfers CO2 from biotin to acetyl-CoA, producing malonyl-CoA
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8
Q

In fatty acid synthase, each monomer functions independently. True or false?

A

True

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9
Q

In fatty acid synthase, the starter unit is an acetyl group bound to the __, while a malonyl group is bound via a _____ to the ___.

A

KS; thioester; ACP

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10
Q

What are the four steps of fatty acid synthesis?

A
  1. Condensation: CO2 leaves; chain extends by two carbons
  2. Reduction: Uses NADPH; beta-keto group is reduced to an alcohol
  3. Dehydration: H2O leaves; creates double bond
    4: Reduction: Uses NADPH; double bond is reduced to from saturated fatty acyl group
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11
Q

The fatty acyl chain grow by __ carbons donated by malonate, which a loss of CO2 at each step.

A

2

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12
Q

In ACP, the __ group is the site of entry of malonyl groups during fatty acid synthesis.

A

SH

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13
Q

What system is used to create fatty acids longer than 16 carbons? Where is it located?

A

Fatty acid elongation system

Smooth ER

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14
Q

In the fatty acid elongation system, ACP is replaced by what?

A

Acyl-CoA

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15
Q

Can all cells synthesize cholesterol?

A

Yes

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16
Q

In certain cells, the cholesterol backbone is used for what two things?

A

Steroid hormone and bile acid biosynthesis

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17
Q

Is cholesterol oxidized to derive energy?

A

No

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18
Q

Mevalonate is converted to what activated isoprene units using how many ATPs?

A

IPP and DMAPP using 3 ATPs

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19
Q

What are statin drugs?

A

Competitive inhibitors of HMG-CoA Reductase

Reduced biosynthesis coupled with a low-fat diet reduces whole body cholesterol levels

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20
Q

Competitive inhibitors of HMG CoA Reductase are mimics of what molecule?

A

Mevalonate

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21
Q

Lipids are [more/less] dense than proteins.

A

less

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22
Q

What are chylomicrons?

A

Lipoproteins that transport lipids from the diet

(Lowest-density lipoproteins – more lipids, less protein)

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23
Q

What do very-low-density lipoproteins (VLDLs) do?

A

Carry triacylglycerols from the liver to peripheral tissues

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24
Q

What do low-density lipoproteins (LDLs) do?

A

Transport cholesterol from liver to peripheral tissues

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25
Q

High LDL values can lead to what?

A

Atherosclerosis

26
Q

High-density lipoproteins (HDLs) do what? Why are they good?

A

Transport cholesterol from dead/dying cells back to liver

They’re good because they remove cholesterol from tissues.

27
Q

List the four lipoproteins from smallest to largest.

A

HDL, LDL, VLDL, chylomicrons

28
Q

Which lipoprotein has the highest triacylglycerol composition? Chylomicron or VLDL?

A

Chylomicron

29
Q

Which lipoprotein has the highest cholesterol ester and cholesterol composition? HDL or LDL?

A

LDL

30
Q

Where is HDL made?

A

The liver and intestine

31
Q

LDL is [endocytosed/exocytosed].

A

endocytosed

32
Q

Nitrogen exists primarily in what two forms?

A

N2 in the atmosphere or nitrate (NO3-) in the soil or ocean

33
Q

The reduction of NO3- to NH4+ in plants, fungi, and bacteria is called what?

A

Nitrate assimilation

34
Q

The formation of NH4+ from N2 gas in prokaryotes is called what?

A

Nitrogen fixation

35
Q

Nitrogen is found where in the human body?

A

Nucleic acids and proteins

36
Q

Largest cache of nitrogen in the human body is in what?

A

Amino acids

37
Q

Largest cache of amino acids is in the what?

A

Skeletal muscles

38
Q

Where are amino groups metabolized?

A

The liver

39
Q

Amino groups are shuttled to the liver in the form of _____ from most tissues and as _____ from the muscle.

A

glutamine; alanine

40
Q

Amino groups are converted to ____ in mammals for excretion in urine.

A

urea

41
Q

Which four amino acids are important in nitrogen metabolism?

A

Glutamate, glutamine, alanine, and aspartate

42
Q

Ammonia is transported from other tissues in the form of _____, then converted back to _____ in the liver.

A

glutamine; glutamate

43
Q

Excess ammonia in tissues is added to _____ to form _____. This reaction is catalyzed by what enzyme?

A

glutamate; glutamine

Glutamine synthetase

44
Q

After transport in the bloodstream, glutamine enters the liver and NH4+ is liberated in the mitochondria by what enzyme?

A

Glutaminase

45
Q

Alanine serves what two functions?

A
  1. Carrier of ammonia
  2. Carbon skeleton of pyruvate from skeletal muscle to liver
46
Q

Acetyl-CoA groups pass out of the mitochondrion as what?

A

Citrate

47
Q

Which enzyme produces acetyl-CoA for fatty acid synthesis?

A

Citrate lyase

48
Q

Malate is oxidized by malate dehydrogenase to generate what?

A

NADPH

49
Q

What are the four stages of cholesterol synthesis?

A
  1. Condensation of 3 acetate groups to form a 6-carbon mevalonate
  2. Conversion of melavonate to activated 5-carbon isoprene units (Requires 3 ATP)
  3. Polymerization of six 5-carbon isoprene units to form a 30-carbon linear squalene
  4. Cyclization of squalene to form a 4-ring steroid nucleus
50
Q

How does the protein NPC1L1 help with the intestinal absorption of cholesterol?

A

NPC1L1 binds free cholesterol, which is then packaged into chylomicrons and delivered to the liver.

51
Q

In many aminotransferase reactions, what is the amino group acceptor?

A

Alpha-ketoglutarate

52
Q

All aminotransferases have what as a cofactor/prosthetic group?

A

Pyridoxal phosphate (PLP)

53
Q

In the liver, _____ catalyzes ammonium production by _____ in mitochondria using either ___ or ___ as the cofactor.

A

glutamate dehydrogenase; oxidative deamination; NAD+; NADP+

54
Q

In the urea cycle, ammonia and CO2 are made into _____, and then into _____.

A

arginine; urea

55
Q

When proteins and amino acids enter the stomach, they induce the production of the hormone _____. This hormone causes the secretion of _____ and _____ to initiate digestion. Later on in the intestine, the hormone _____ induces the pancreas to produce bicarbonate.

A

gastrin; HCl; pepsinogen; secretin

56
Q

What three different enzymes, expressed in the liver mitochondrial matrix, catalyze the removal of
nitrogen from an amino acid that can end up in urea?

A
  1. Glutaminase
  2. Glutamate dehydrogenase
  3. Aspartate aminotransferase
57
Q

Humans derive a small fraction of oxidative energy from amino acids unless they’re what?

A

Starving, diabetic, or on a low carb diet

58
Q

Proteases degrade ingested proteins in what two organs?

A

Stomach and small intestine

59
Q

True or false? Individual amino acids are absorbed by the body.

A

True

60
Q

Name the ten essential amino acids

A
  1. Histidine
  2. Isoleucine
  3. Leucine
  4. Lysine
  5. Methionine
  6. Phenylalanine
  7. Threonine
  8. Tryptophan
  9. Valine

BIOC4331: Biochemistry I (9 decks)

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