Lipid Biosynthesis, Cholesterol, and Amino Acid Catabolism

Question 1

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

Answer 1

mitochondria; cytosol

Question 2

The redox coenzyme used for fatty acid synthesis is _____.

Answer 2

NADPH

Question 3

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

Answer 3

16

Question 4

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

Answer 4

Biotin-dependent enzyme in the ER

Question 5

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

Insulin [inhibits/stimulates] ACC activity through dephosphorylation.

Answer 5

inhibits; stimulates

Question 6

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

Answer 6

activates; inhibits

Question 7

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

Answer 7

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

Question 8

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

Answer 8

True

Question 9

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

Answer 9

KS; thioester; ACP

Question 10

What are the four steps of fatty acid synthesis?

Answer 10

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

Question 11

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

Answer 11

2

Question 12

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

Answer 12

SH

Question 13

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

Answer 13

Fatty acid elongation system

Smooth ER

Question 14

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

Answer 14

Acyl-CoA

Question 15

Can all cells synthesize cholesterol?

Answer 15

Yes

Question 16

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

Answer 16

Steroid hormone and bile acid biosynthesis

Question 17

Is cholesterol oxidized to derive energy?

Answer 17

No

Question 18

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

Answer 18

IPP and DMAPP using 3 ATPs

Question 19

What are statin drugs?

Answer 19

Competitive inhibitors of HMG-CoA Reductase

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

Question 20

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

Answer 20

Mevalonate

Question 21

Lipids are [more/less] dense than proteins.

Answer 21

less

Question 22

What are chylomicrons?

Answer 22

Lipoproteins that transport lipids from the diet

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

Question 23

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

Answer 23

Carry triacylglycerols from the liver to peripheral tissues

Question 24

What do low-density lipoproteins (LDLs) do?

Answer 24

Transport cholesterol from liver to peripheral tissues

Question 25

High LDL values can lead to what?

Answer 25

Atherosclerosis

Question 26

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

Answer 26

Transport cholesterol from dead/dying cells back to liver They're good because they remove cholesterol from tissues.

Question 27

List the four lipoproteins from smallest to largest.

Answer 27

HDL, LDL, VLDL, chylomicrons

Question 28

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

Answer 28

Chylomicron

Question 29

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

Answer 29

LDL

Question 30

Where is HDL made?

Answer 30

The liver and intestine

Question 31

LDL is [endocytosed/exocytosed].

Answer 31

endocytosed

Question 32

Nitrogen exists primarily in what two forms?

Answer 32

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

Question 33

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

Answer 33

Nitrate assimilation

Question 34

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

Answer 34

Nitrogen fixation

Question 35

Nitrogen is found where in the human body?

Answer 35

Nucleic acids and proteins

Question 36

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

Answer 36

Amino acids

Question 37

Largest cache of amino acids is in the what?

Answer 37

Skeletal muscles

Question 38

Where are amino groups metabolized?

Answer 38

The liver

Question 39

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

Answer 39

glutamine; alanine

Question 40

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

Answer 40

urea

Question 41

Which four amino acids are important in nitrogen metabolism?

Answer 41

Glutamate, glutamine, alanine, and aspartate

Question 42

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

Answer 42

glutamine; glutamate

Question 43

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

Answer 43

glutamate; glutamine Glutamine synthetase

Question 44

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

Answer 44

Glutaminase

Question 45

Alanine serves what two functions?

Answer 45

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

Question 46

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

Answer 46

Citrate

Question 47

Which enzyme produces acetyl-CoA for fatty acid synthesis?

Answer 47

Citrate lyase

Question 48

Malate is oxidized by malate dehydrogenase to generate what?

Answer 48

NADPH

Question 49

What are the four stages of cholesterol synthesis?

Answer 49

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

Question 50

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

Answer 50

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

Question 51

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

Answer 51

Alpha-ketoglutarate

Question 52

All aminotransferases have what as a cofactor/prosthetic group?

Answer 52

Pyridoxal phosphate (PLP)

Question 53

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

Answer 53

glutamate dehydrogenase; oxidative deamination; NAD+; NADP+

Question 54

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

Answer 54

arginine; urea

Question 55

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.

Answer 55

gastrin; HCl; pepsinogen; secretin

Question 56

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?

Answer 56

1. Glutaminase 2. Glutamate dehydrogenase 3. Aspartate aminotransferase

Question 57

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

Answer 57

Starving, diabetic, or on a low carb diet

Question 58

Proteases degrade ingested proteins in what two organs?

Answer 58

Stomach and small intestine

Question 59

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

Answer 59

True

Question 60

Name the ten essential amino acids

Answer 60

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