Biosynthesis of Fatty Acids & Eicosanoids

Question 1

Which statetement is incorrect?

A. Fatty acids are synthesized by an extramitochondrial system, which is responsible for the complete synthesis of palmitate from acetyl-CoA in the cytosol.

B. In most mammals, glucose is the primary substrate for
lipogenesis, but in ruminants it is acetate, the main fuel molecule they obtain from the diet

C. inhibition of lipogenesis occurs in type 2 diabetes mellitus

D. variations in the activity of the lipogenesis affect the nature and extent of obesity.

Answer 1

C.

inhibition of lipogenesis occurs in type 1
(insulin-dependent) diabetes mellitus,

Question 2

Which statement is incorrect?
A. Unsaturated fatty acids in phospholipids of the cell membrane are
important in maintaining membrane fluidity

B. high ratio
of saturated fatty acids to polyunsaturated fatty acids (S:P ratio) in the diet
is considered to be beneficial in preventing coronary heart disease

C. Animal tissues have limited capacity for desaturating fatty acids, and require certain dietary polyunsaturated fatty acids derived from plants.

D. essential fatty acids are used to form eicosanoic (C20) fatty acids, which
give rise to the eicosanoids prostaglandins, thromboxanes, leukotrienes,
and lipoxins

Answer 2

B

high ratio
of polyunsaturated fatty acids to saturated fatty acids (P:S ratio) in the diet
is considered to be beneficial in preventing coronary heart disease

Question 3

mediate inflammation, pain, induce sleep,

and also regulate blood coagulation and reproduction.

Answer 3

Prostaglandins

Question 4

act

by inhibiting prostaglandin synthesis

Answer 4

Nonsteroidal

anti-inflammatory drugs (NSAIDs)

Question 5

have muscle contractant and chemotactic properties and are important in allergic
reactions and inflammation.

Answer 5

Leukotrienes

Question 6

Which is true of lipogenesis?

A. Synthesis of fatty acids (lipogenesis) occurs in the cytosol
B. Lipogenesis cofactor includes NADPH, ATP, Mn2+, biotin, and HCO3
C. Acetyl-
CoA is the immediate substrate
D. free palmitate is the end product.
E. All of the above
F. None of the above

Answer 6

E. All of the above

Question 7

source of CO2 and is required in the initial reaction for the
carboxylation of acetyl-CoA to malonyl-CoA

Answer 7

Bicarbonate

Question 8

what enzyme is responsible for conversion of acetyl-CoA to malonyl-CoA

Answer 8

acetyl-CoA carboxylase

Question 9

Acetyl-CoA carboxylase has a requirement for what vitamin

Answer 9

B vitamin biotin

Question 10

Enzyme that involves in carboxylation of biotin involving ATP

Answer 10

Biotin carboxylase

Question 11

covalently linked to the BCP

Answer 11

Biotin

Question 12

a homodimer of
two polypeptide chains containing six enzyme
activities and the acyl carrier protein

Answer 12

Fatty Acid Synthase Complex

Question 13

ACP contains with vitamin as cofactor?

Answer 13

pantothenic acid

Question 14

Which one is the correct sequence of enzyme domains of fatty acid synthase

A. n-Ketoacyl synthase-Maolnyl/acetyl transacylase-ACP-enoyl reductase-dehydratase-thioesterase-c

B. n-Ketoacyl synthase-Maolnyl/acetyl transacylase-dehydratase-enoyl reductase-ketoacyl reductase-ACP-thioesterase-c

C. n-thioeterase-ACP-enoyl reductase-dehydratase-Maolnyl/acetyl transacylase-
keto acyl synthase-n

D. None of the above

Answer 14

B. n-Ketoacyl synthase-Maolnyl/acetyl transacylase-dehydratase-enoyl reductase-ketoacyl reductase-ACP-thioesterase-c

Question 15

This enzyme catalyzes

reactions to form acetyl (acyl)-malonyl enzyme.

Answer 15

malonyl acetyl

transacylase

Question 16

a priming molecule of acetyl-CoA combines with a? (REACTION 1A)

Answer 16

cysteine —SH group

Question 17

combines
with the adjacent —SH on the 4′-phosphopantetheine of ACP of the other
monomer (REACTION 1 B)

Answer 17

malonyl-CoA

Question 18

WHAT ENZYME catalyzeS REACTIONS 1A AND 1 B by , to form acetyl (acyl)-malonyl enzyme

Answer 18

malonyl acetyl transacylase

Question 19

The acetyl group attacks the methylene group of the malonyl residue, catalyzed by _____________ and liberates CO2, forming 3-ketoacyl enzyme
(acetoacetyl enzyme) (reaction 2), freeing the cysteine —SH group.

Answer 19

3- ketoacyl synthase

Question 20

The 3-ketoacyl group is reduced, dehydrated, and reduced again (reactions 3-5) to form the corresponding ______________________ (product of reaction 5).

Answer 20

saturated acyl enzyme

Question 21

A new malonyl-CoA molecule combines with the ___________, displacing the saturated acyl residue onto the free cysteine —SH group.

Answer 21

—SH of 4′- phosphopantetheine

Question 22

The sequence of reactions is repeated six more times
until a saturated 16-carbon acyl radical (palmitoyl) has been assembled. Then it is liberated from the enzyme complex by the activity of the _________

Answer 22

sixth enzyme

in the complex, thioesterase (deacylase).

Question 23

Which of the statement is incorrect?
A. The acetyl-CoA used as a primer forms carbon atoms 15 and 16 of palmitate.
B. The addition of all the subsequent C2 units is via malonyl-CoA.
C. Propionyl-CoA instead of acetyl-CoA is used as the primer for the synthesis of long-chain fatty acids with an odd number of carbon atoms
D. All of the above
E. None of the above

Answer 23

E. None of the above

Question 24

involved as a donor of reducing equivalents in the reduction of the 3-ketoacyl and the 2,3-unsaturated acyl derivatives

Answer 24

NADPH

Question 25

Which statement is incorrect?
A. The oxidative reactions of the pentose phosphate
pathway are the chief source of the hydrogen required for the synthesis of fatty acids.
B. tissues specializing in active
lipogenesis—that is, liver, adipose tissue, and the lactating mammary gland—also possess an active pentose phosphate pathway
C. both metabolic pathways are found in the cytosol of the cell, so there are no membranes or permeability barriers against the transfer of NADPH
D. All of the above
E. None of the above

Answer 25

E. None of the above

Question 26

Other sources of NADPH include the reaction that converts malate to pyruvate
catalyzed by ______________ and _____________________

Answer 26

NADP malate dehydrogenase (malic enzyme)
and
the extramitochondrial isocitrate dehydrogenase reaction

Question 27

the Principal Building Block of Fatty

Acids

Answer 27

Acetyl-CoA

Question 28

formed from glucose via the oxidation of pyruvate in the

matrix of the mitochondria

Answer 28

Acetyl-CoA

Question 29

the principal site of fatty acid synthesis

Answer 29

cytosol,

Question 30

After condensation of acetyl-CoA with
oxaloacetate in the citric acid cycle within mitochondria, the citrate produced can be translocated into the extramitochondrial compartment via the tricarboxylate transporter, where in the presence of CoA and ATP, it
undergoes cleavage to acetyl-CoA and oxaloacetate by what enzyme which increases in activity in the well-fed state.

Answer 30

ATP-citrate lyase

Question 31

Which statement is correct?
A. The acetyl-CoA is then
available for malonyl-CoA formation and synthesis of fatty acids and the oxaloacetate can form malate via NADH-linked
malate dehydrogenase, followed by the generation of NADPH and pyruvate via the malic enzyme.
B. The NADPH becomes available for lipogenesis, and the pyruvate can be used to regenerate acetyl-CoA after transport into the mitochondrion
C. This pathway is a means of transferring reducing equivalents from extramitochondrial NADH to NADP
D. malate itself can be transported into the mitochondrion, where it is able to reform oxaloacetate.
E. All of the above
F. None of the above

Answer 31

E. All of the above

Question 32

the citrate (tricarboxylate) transporter in the mitochondrial membrane requires ________ to exchange with citrate

Answer 32

malate

Question 33

Elongation of Fatty Acid Chains Occurs in the

Answer 33

Endoplasmic Reticulum

Question 34

This pathway (the “microsomal system”) elongates saturated and unsaturated fatty acyl-CoAs (from C10 upward) by two carbons, using malonyl-CoA as the acetyl donor and NADPH as the reductant, and is catalyzed by the microsomal ________________ system of enzymes

Answer 34

fatty acid elongase

Question 35

Elongation of _______________ in brain increases rapidly during myelination in order to provide C22 and C24 fatty acids for sphingolipids

Answer 35

stearyl-CoA

Question 36

TRUE OR FALSE

NADH may also be used by the reductases, but NADPH is
preferred.

Answer 36

TRUE

Question 37

The process in which it converts surplus glucose

and intermediates such as pyruvate, lactate, and acetyl-CoA to fat, assisting the anabolic phase of this feeding cycle

Answer 37

Lipogenesis

Question 38

the main factor regulating the rate of lipogenesis

Answer 38

The nutritional state of the organism

Question 39

TRUE OR FALSE

Lipogenesis is increased when sucrose is fed instead of glucose because fructose bypasses the phosphofructokinase control point in glycolysis and floods the lipogenic pathway

Answer 39

TRUE

Question 40

Which statement is incorrect?
A. Long-chain fatty acid synthesis is controlled in the short term by allosteric and covalent modification of enzymes
B. Long-chain fatty acid synthesis is controlled in the long term by changes in gene expression governing rates of synthesis of enzymes.
C. All of the above
D. None of the above

Answer 40

D. None of the above

Question 41

Most Important Enzyme in the Regulation of Lipogenesis

Answer 41

Acetyl-CoA Carboxylase

Question 42

Acetyl-CoA Carboxylase is an allosteric enzyme and is activated by _____

Answer 42

citrate

Question 43

increases in concentration in the well-fed state and is an

indicator of a plentiful supply of acetyl-CoA

Answer 43

citrate

Question 44

promotes the conversion of the enzyme from an inactive dimer (two subunits of the enzyme complex) to an active polymeric form, with a molecular mass of several million.

Answer 44

citrate

Question 45

inhibits the mitochondrial tricarboxylate transporter, thus preventing activation of the enzyme by egress of citrate from the mitochondria into the cytosol

Answer 45

Acyl-CoA

Question 46

Which statement is correct?
A. Acetyl-CoA carboxylase is activated by citrate, which promotes the conversion of the enzyme from an inactive dimer to an active polymeric form
B. Inactivation is promoted by phosphorylation of the enzyme and by long-chain acyl-CoA molecules such as palmitoyl-CoA
C. acyl-CoA inhibits the tricarboxylate transporter, which transports citrate out of mitochondria into the cytosol, thus decreasing the citrate concentration in the cytosol and favoring inactivation of the enzyme.
D. All of the above
E. None of the above

Answer 46

D. All of the above

Question 47

Which hormone does not regulate Acetyl-CoA carboxylase  via changes in its phosphorylation state:
A. Glucagon
B. Insulin
C. Epinephrine 
D. Dopamine 
E. All of the above 
F. None of the above

Answer 47

D. Dopamine

Question 48

Which is true regarding regulation of Acetyl-CoA carboxylase by phosphorylation/dephosphorylation
A. The enzyme is inactivated by phosphorylation by AMP-activated protein kinase (AMPK),
B. AMP-activated protein kinase (AMPK) is phosphorylated and activated by AMP-activated protein kinase kinase
(AMPKK)
C. Glucagon and epinephrine increase cAMP, and thus activate this latter enzyme via cAMP-dependent protein kinase.
D.Insulin activates acetyl-CoA carboxylase via dephosphorylation of AMPK.
E. All of the above
F. None of the above

Answer 48

E. All of the above

Question 49

causes an inhibition of pyruvate dehydrogenase by inhibiting the ATP-ADP exchange transporter of the inner mitochondrial membrane, which leads to increased intramitochondrial (ATP)/(ADP) ratios and therefore to conversion of active to inactive pyruvate dehydrogenase

Answer 49

Acyl-CoA

Question 50

stimulates lipogenesis by several other mechanisms as well as by increasing acetyl-CoA carboxylase activity.

Answer 50

Insulin

Question 51

All statements are true of insulin regulating lipogenesis except:
A. It increases the transport of glucose into the cell (eg, in adipose tissue), increasing the availability of both pyruvate for fatty acid synthesis and glycerol-3-phosphate for
triacylglycerol synthesis via esterification of the newly formed fatty acids
B. also converts the inactive form of pyruvate
dehydrogenase to the active form in liver , but not in adipose tissue
C. Has an ability to depress the level of intracellular cAMP—inhibits lipolysis in adipose tissue, reducing the concentration of plasma-free fatty acids and, therefore, long-chain acyl-CoA, which are inhibitors of lipogenesis.
D. All of the above
E. None of the above

Answer 51

B.

also converts the inactive form of pyruvate
dehydrogenase to the active form in adipose tissue, but not in liver

Question 52

Which statement is true:

A. the fatty acid synthase complex & acetyl-CoA
carboxylase are adaptive enzymes and adapt to the body’s physiologic needs via changes in gene expression which lead to increases in the total amount of enzyme protein
present in the fed state and decreases during intake of a high-fat diet and in conditions such as starvation, and diabetes mellitus

B. Insulin plays an important role, promoting gene expression and induction of enzyme biosynthesis, and glucagon (via cAMP) antagonizes this effect

C. Feeding fats containing polyunsaturated fatty acids coordinately regulates the inhibition of expression of key enzymes of glycolysis and lipogenesis.

D. All of the above

E. None of the above

Answer 52

D. All of the above

Question 53

Which statement is true:

A. Palmitoleic and oleic acids are not essential in the diet
because the tissues can introduce a double bond at the Δ9 position of a saturated fatty acid.

B. Linoleic and α-linolenic acids are the only fatty acids
known to be essential for the complete nutrition of many species of animals, including humans, and are termed the nutritionally essential fatty acids.

C. Double bonds can be introduced at the Δ4, Δ5,
Δ6, and Δ9 positions in most animals, but never beyond the Δ9 position.

D. plants are able to synthesize the nutritionally
essential fatty acids by introducing double bonds at the Δ12 and Δ15 positions.

E. All of the above

F. None of the above

Answer 53

E. All of the above

Question 54

Which statement is incorrect?

A. Several tissues including the liver are considered to be responsible for the formation of saturated fatty
acids from nonessential monounsaturated fatty acids

B. The first double bond introduced into a saturated fatty acid is nearly always in the Δ9 position

C. An enzyme system—Δ9 desaturase—in the endoplasmic reticulum catalyzes the conversion of palmitoyl-CoA or stearoyl-CoA to palmitoleoyl-CoA or oleoyl-CoA

D. Oxygen and either NADH or NADPH are necessary for the reaction.

E. All of the above

F. None of the above

Answer 54

A.

Several tissues including the liver are considered to be responsible for the formation of nonessential monounsaturated fatty acids from saturated fatty
acids.

Question 55

Which statement is correct?

A. animals have a Δ9 desaturase, they are able to synthesize the ω9 (oleic acid) family of unsaturated fatty acids completely by a combination of chain elongation and desaturation after the formation of saturated fatty acids

B. linoleic (ω6) or α-linolenic (ω3) acids are required for the
synthesis of the other members of the ω6 or ω3 families and must be supplied in the diet.

C. Linoleic acid is converted to arachidonic acid (20:4 ω6) via γ-linolenic acid (18:3 ω6)

D. The nutritional requirement for arachidonate may be dispensed with if there is adequate linoleate in the diet.

E. All of the above

F. None of the above

Answer 55

E. All of the above

Question 56

Which statement is incorrect?

A. Essential fatty acids are required for prostaglandin, thromboxane, leukotriene, and lipoxin formation, and they also have various other functions that are less well defined.

B. They are found in the structural lipids of the cell, often
in the position 1 of phospholipids, and are concerned with the structural integrity of the mitochondrial membrane.

C. Arachidonic acid is present in membranes and accounts for 5 to 15% of the fatty acids in phospholipids.

D. Docosahexaenoic acid (DHA; ω3, 22:6),
which is synthesized to a limited extent from α-linolenic acid or obtained directly from fish oils, is present in high concentrations in retina, cerebral cortex, testis, and sperm

E. All of the above

F. None of the above

Answer 56

B.

They are found in the structural lipids of the cell, often in the position 2 of phospholipids, and are concerned with the structural integrity of the mitochondrial membrane.

Question 57

Patients with this condition are reported to have low blood levels of DHA.

Answer 57

retinitis pigmentosa

Question 58

ratio in plasma lipids can be used to diagnose the extent of essential fatty acid deficiency

Answer 58

triene:tetraene

Question 59

In this condition nonessential polyenoic acids of the ω9
family, particularly Δ5,8,11-eicosatrienoic acid (ω9 20:3),
replace the essential fatty acids in phospholipids, other complex lipids, and membranes.

Answer 59

essential fatty acid deficiency

Question 60

true or false:

EICOSANOIDS ARE FORMED FROM C20 POLYUNSATURATED FATTY ACIDS

Answer 60

true

Question 61

Which statement is true:

A. Arachidonate and some other C20 polyunsaturated fatty acids give rise to eicosanoids, physiologically and pharmacologically active compounds known as prostaglandins (PG), thromboxanes (TX), leukotrienes (LT),
and lipoxins (LX)

B. they are considered to act as local hormones functioning through G-protein–linked receptors to elicit their biochemical effects

C. There are three groups of eicosanoids that are synthesized from C20 eicosanoic acids derived from the essential fatty acids linoleate and α- linolenate, or directly from dietary arachidonate and eicosapentaenoate

D. Arachidonate, which may be obtained from the diet, but is
usually derived from the position 2 of phospholipids in the plasma membrane by the action of phospholipase A2, is the
substrate for the synthesis of the PG2, TX2 series (prostanoids) by the cyclooxygenase pathway, or the LT4 and LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate

E. All of the above

F. None of the above

Answer 61

E. All of the above

Question 62

TRUE OR FALSE

THE CYCLOOXYGENASE PATHWAY IS RESPONSIBLE FOR PROSTANOID SYNTHESIS

Answer 62

TRUE

Question 63

Which statement is true regarding CYCLOOXYGENASE PATHWAY?

A. In the first reaction, catalysed by cyclooxygenase (COX)
(also called prostaglandin H synthase), an enzyme that has two activities, a cyclooxygenase and peroxidase, two molecules of O2 are consumed.

B. COX is present as two isoenzymes, COX-1 and COX-2.

C. The product, an endoperoxide (PGH), is converted to prostaglandins D and E as well as to a thromboxane (TXA2) and prostacyclin (PGI2)

D. Each cell type produces only one type of prostanoid.

E. All of the above

F. None of the above

Answer 63

E. All of the above

Question 64

are synthesized in platelets and upon release cause

vasoconstriction and platelet aggregation.

Answer 64

Thromboxanes

Question 65

Thromboxane synthesis is inhibited by?

Answer 65

low-dose aspirin

Question 66

are produced by blood vessel walls and are potent inhibitors of platelet aggregation.

Answer 66

Prostacyclins (PGI2)

Question 67

they are formed from eicosapentaenoic acid (EPA) and inhibit the release of arachidonate from phospholipids and the formation of PG2 and TX2

Answer 67

PG3 and TX3

Question 68

is as potent an antiaggregator of platelets as PGI2

Answer 68

PGI3

Question 69

is a weaker aggregator than TXA2

Answer 69

TXA3

Question 70

Which statement is incorrect?

A. The role of essential fatty acids in membrane formation is unrelated to prostaglandin formation

B. Prostaglandins do not relieve symptoms of essential fatty acid deficiency

C. An essential fatty acid deficiency is not caused by inhibition of prostaglandin synthesis

D. All of the above

E. None of the above

Answer 70

D. All of the above

Question 71

Which of the following is true?

A. the inactivation of prostaglandins by 15 hydroxyprostaglandin dehydrogenase is rapid.

B. “Switching off” of prostaglandin activity is partly achieved by a remarkable property of cyclooxygenase—that of self-catalyzed destruction; that is, it is a “suicide enzyme.”

C. Blocking the action of this enzyme with sulfasalazine or indomethacin can prolong the half-life of prostaglandins in the body.

D. All of the above

E. None of the above

Answer 71

D. All of the above

Question 72

These medications can prolong the half-life of prostaglandins in the body.

Answer 72

sulfasalazine or indomethacin

Question 73

True or False?

LEUKOTRIENES & LIPOXINS ARE FORMED BY
THE LIPOXYGENASE PATHWAY

Answer 73

True

Question 74

family of conjugated trienes formed from eicosanoic acids in leukocytes, mastocytoma cells, platelets, and macrophages by the lipoxygenase pathway in response to both immunologic and nonimmunologic stimuli

Answer 74

leukotrienes

Question 75

Which is true?

A. Three different lipoxygenases
(dioxygenases) insert oxygen into the 5, 12, and 15 positions of arachidonic acid, giving rise to hydroperoxides (HPETE).

B. Only 5- lipoxygenase forms leukotrienes

C. Lipoxins are a family of conjugated tetraenes also arising in leukocytes. They are formed by the combined action of more than one lipoxygenase

D. All of the above

E. None of the above

Answer 75

D. All of the above

Question 76

are a family of conjugated tetraenes also arising in leukocytes. They are formed by the combined action of more than one lipoxygenase

Answer 76

Lipoxins

Question 77

infants receiving formula diets low in fat and patients maintained for long periods exclusively by
intravenous nutrition low in essential fatty acids show deficiency symptoms that can be prevented by an essential fatty acid intake of 1 to 2% of the total caloric requirement.

Answer 77

1 to 2%

Question 78

This condition produces elevated levels of very-long-chain

polyenoic acids in the brains

Answer 78

Zellweger syndrome

Question 79

Which statement is true:

A. Diets with a high P:S (polyunsaturated:saturated fatty acid) ratio reduce serum cholesterol levels and are considered to be beneficial in terms of the risk of development of
coronary heart disease.

B. Abnormal metabolism of essential fatty acids, which may be connected with dietary insufficiency, has been noted in cystic fibrosis, acrodermatitis enteropathica, hepatorenal syndrome, Sjögren-Larsson syndrome, multisystem neuronal degeneration, Crohn disease, cirrhosis and
alcoholism, and Reye syndrome

C. All of the above

D. None of the above

Answer 79

C. All of the above

Question 80

True of trans fat:

A. They are structurally similar to saturated fatty acids and have comparable effects in the promotion of hypercholesterolemia and atherosclerosis

B. Trans fatty acids compete with essential fatty acids and may exacerbate essential fatty acid deficiency.

C. All of the above

D. None of the above

Answer 80

C. All of the above

Question 81

a nonsteroidal anti-inflammatory drug (NSAID) that inhibits COX-1 and COX-2

Answer 81

Aspirin

Question 82

drugs that usually inhibit cyclooxygenases by competing with arachidonate.

Answer 82

indomethacin and ibuprofen

Question 83

Transcription of _____________ is completely inhibited by anti-inflammatory corticosteroids.

Answer 83

COX-2

Question 84

is a potent sleep-promoting substance

Answer 84

PGD2

Question 85

potent constrictor of the bronchial airway musculature

Answer 85

Slow-reacting substance of anaphylaxis (SRS-A)

leukotrienes C4, D4, E4

Question 86

The synthesis of long-chain fatty acids (lipogenesis) is carried out by two enzyme systems which are?

Answer 86

acetyl-CoA carboxylase and fatty acid synthase

Question 87

True or false:

The pathway converts acetyl-CoA to palmitate and requires NADPH, ATP, Mn2+, biotin, and pantothenic acid as cofactors

Answer 87

True

Question 88

converts acetyl-CoA to malonyl-CoA,

Answer 88

Acetyl-CoA carboxylase

Question 89

a multienzyme complex consisting of two
identical polypeptide chains, each containing six separate enzymatic activities and ACP, catalyzes the formation of palmitate from one acetyl-CoA and seven malonyl-CoA molecules

Answer 89

fatty acid synthase,

Question 90

regulated at the acetyl-CoA carboxylase step by
allosteric modifiers, phosphorylation/dephosphorylation, and
induction and repression of enzyme synthesis

Answer 90

Lipogenesis

Question 91

acetyl-CoA carboxylase:

allosterically activated by________ and deactivated by

Answer 91

citrate

long-chain acyl- CoA.

Question 92

Biosynthesis of unsaturated long-chain fatty acids is achieved by

Answer 92

desaturase and elongase enzymes

Question 93

Higher animals have Δ4, Δ5, Δ6, and Δ9 desaturases but cannot insert new double bonds beyond the position _______ of fatty acids

Answer 93

9