biochem notecards Flashcards

Which statement about membranes is true?

a. Most plasma membranes contain more than 70% proteins.

b. Sterol lipids are common in bacterial plasma membranes.

c. Sterol lipids are common in human cell plasma membranes.

d. Sterol lipids are common in plant cell plasma membranes.

e. The plasma membranes of all cell types within a particular organism have basically the same lipid and protein composition.

The fluidity of the lipid side chains in the interior of a bilayer is generally increased by:

a. a decrease in temperature.
b. an increase in fatty acyl chain length.
c. an increase in the number of double bonds in fatty acids.

d. an increase in the percentage of phosphatidylethanolamine.

e. the binding of water to the fatty acyl side chains.

The fluidity of a lipid bilayer will be increased by:

a. decreasing the number of unsaturated fatty acids.

b. decreasing the temperature.
c. increasing the length of the alkyl chains.

d. increasing the temperature.

e. substituting 18:0 (stearic acid) in place of 18:2 (linoleic acid)

Which statement is true regarding the regulation of β oxidation?

1. AMPK activates acetyl-CoA carboxylase, which leads to the inhibition of β oxidation.
2. A buildup in the levels of acetyl-CoA inhibits the thiolysis reaction in β oxidation.
3. High levels of NADP+ activate β-hydroxyacyl-CoA dehydrogenase.
4. Malonyl-CoA inhibits carnitine acyltransferase 2, which leads to the inhibition of β oxidation.
5. β oxidation is enhanced in erythrocytes during starvation.

Fatty acids are activated to acyl-CoAs and the acyl group is further transferred to carnitine because:

1. acyl-carnitines readily cross the mitochondrial inner membrane, but acyl-CoAs do not.
2. acyl-CoAs easily cross the mitochondrial membrane, but the fatty acids themselves will not.
3. carnitine is required to oxidize NAD+ to NADH.
4. fatty acids cannot be oxidized by FAD unless they are in the acyl-carnitine form.

In β oxidation, which cofactor is required for the conversion of a β-ketoacyl-CoA to an acyl-CoA and an acetyl-CoA molecule?

1. NAD+
2. FAD
3. H2O
4. CoA-SH

In β oxidation, which cofactor is required for the conversion of a β-hydroxyacyl-CoA to a β-ketoacyl-CoA?

a. NAD+

b. FAD

c. H2O

d. CoA-SH

In β oxidation, which cofactor is required for the conversion of a trans-Δ2-enoyl-CoA to a β-hydroxyacyl-CoA?

a. NAD+

b. FAD

c. H2O

d. CoA-SH

What products from the oxidation of odd-numbered fatty acids enter the citric acid cycle?

a. acetyl-CoA and citrate
b. acetyl-CoA and malonyl-CoA
c. acetyl-CoA and propionyl-CoA

d. acetyl-CoA and succinyl-CoA
e. succinyl-CoA and propionyl-CoA

If the 16-carbon saturated fatty acid palmitate is oxidized completely to carbon dioxide and water (via the β-oxidation pathway and the citric acid cycle), and all of the energy-conserving products are used to drive ATP synthesis in the mitochondrion, the net yield of ATP per molecule of palmitate is:

a. 3.

b. 10.
c. 25.
d. 106.

e. 1,000.

Saturated fatty acids are degraded by the stepwise reactions of β oxidation, producing acetyl-CoA. Under aerobic conditions, how many ATP molecules would be produced as a consequence of removal of each acetyl-CoA?

a. two

b. three

c. four

d. five

e. six

Ketone bodies are formed in the liver and transported to the extrahepatic tissues mainly as:

a. acetoacetyl-CoA.
b. acetone.
c. β-hydroxybutyric acid.

d. β-hydroxybutyryl-CoA.

e. lactic acid.

Which statement is false regarding ketone bodies?

a. During prolonged starvation, the brain adapts to using ketone bodies as a fuel. b. Excess acetone production during ketoacidosis is exhaled through the lungs. c. Ketone bodies can be used as a carbon source for fatty acid synthesis.
d. Ketone bodies can be converted to glucose during ketosis.
e. Ketone bodies are formed when the glucagon/insulin ratio is high.

Which statement regarding ketone bodies is false?

1. The production of excess ketone bodies can cause a condition known as ketosis, which is associated with acidosis.
2. In hepatocytes, the production of ketone bodies is an anaplerotic process because the products of β-hydroxybutyrate oxidation can enter the citric acid cycle.
3. Ketone bodies are produced by the liver during starvation or in cases when insulin production is insufficient.
4. The production of ketone bodies increases when blood glucagon levels are elevated.

In which cellular compartment are ketone bodies synthesized?

a. the cytosol
b. the mitochondrial matrix
c. the mitochondrial intermembrane space d. the endoplasmic reticulum
e. peroxisomes

Which pathway is likely to be affected by a deficiency in carnitine?

a. α oxidation

b. β oxidation

c. uptake of fatty acids from the bloodstream

d. All of the answers are correct.

Which statement is true regarding the regulation of β oxidation?

a. AMPK activates acetyl-CoA carboxylase, which leads to the inhibition of β oxidation.

b. A buildup in the levels of acetyl-CoA inhibits the thiolysis reaction in β oxidation.

c. High levels of NADP+ activate β-hydroxyacyl-CoA dehydrogenase.

d. Malonyl-CoA inhibits carnitine acyltransferase 2, which leads to the inhibition of β oxidation.

e. β oxidation is enhanced in erythrocytes during starvation.

Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires:

a. ATP, carnitine, and coenzyme A.
b. ATP, carnitine, and pyruvate dehydrogenase.
c. ATP, coenzyme A, and hexokinase.
d. ATP, coenzyme A, and pyruvate dehydrogenase.

The rate-limiting step in fatty acid synthesis is:

a. condensation of acetyl-CoA and malonyl-CoA.
b. formation of acetyl-CoA from acetate.
c. formation of malonyl-CoA from malonate and coenzyme A.
d. the reaction catalyzed by acetyl-CoA carboxylase.
e. the reduction of the acetoacetyl group to a D-β-hydroxybutyryl group.

Which statement is false concerning acetyl-CoA carboxylase?

a. It catalyzes the rate-limiting step in fatty acid synthesis.
b. This enzyme is inhibited by palmitate in mammals.
c. This enzyme is allosterically activated by citrate in mammals.
d. In mammals, this enzyme is inactivated under conditions when glycolysis is active.

What cofactor is required for acetyl-CoA carboxylase activity?

a. NADPH

b. thiamine pyrophosphate

c. lipoamide

d. biotin

Synthesis of malonyl-CoA from acetyl-CoA is MOST similar to what other reaction?

a. conversion of malate into fumarate
b. conversion of pyruvate into acetyl-CoA
c. conversion of phosphoenolpyruvate into 2-phosphoglycerate

d. conversion of glutamate into α-ketoglutarate
e. conversion of pyruvate into oxaloacetate

Which statement applies to synthesis of malonyl-CoA?

a. It is synthesized from acetyl-CoA and bicarbonate.
b. The reaction is catalyzed by acetyl-CoA carboxylase.
c. The three-step synthesis is irreversible.
d. In animal cells the synthesis takes place in the cytoplasm.
e. All of the statements apply to the synthesis of malonyl-CoA.

What cofactor is required for acetyl-CoA carboxylase activity?

a. NADPH

b. thiamine pyrophosphate

c. lipoamide

d. biotin

Which statement is false regarding acyl carrier protein (ACP)?

1. ACP is transiently attached to malonyl-CoA during fatty acid elongation.
2. ACP contains a pantothenate-derived prosthetic group.
3. ACP carries reaction intermediates from one active site to the next in fatty acid synthesis.
4. ACP associates as a separate polypeptide with fatty acid synthase I in vertebrates.

What statement is false regarding the regulation of HMG-CoA reductase?

1. HMG-CoA reductase is inhibited by phosphorylation.
2. Elevated levels of ATP will inhibit HMG-CoA reductase.
3. Elevated blood glucose will increase the activity of HMG-CoA reductase.
4. Statins act as competitive inhibitors for this enzyme.
5. Low cellular concentrations of cholesterol will increase expression of this enzyme and the LDL receptor.

The rate-limiting step in fatty acid synthesis is:

a. condensation of acetyl-CoA and malonyl-CoA.
b. formation of acetyl-CoA from acetate.
c. formation of malonyl-CoA from malonate and coenzyme A.
d. the reaction catalyzed by acetyl-CoA carboxylase.
e. the reduction of the acetoacetyl group to a D-β-hydroxybutyryl group.

In comparing fatty acid biosynthesis with β oxidation of fatty acids, which statement is incorrect?

a. A thioester derivative of crotonic acid (trans-2-butenoic acid) is an intermediate in the synthetic path, and in the degradative path.

b. A thioester derivative of D-β-hydroxybutyrate is an intermediate in the synthetic path, not in the degradative path.

c. Fatty acid biosynthesis uses NADPH exclusively, whereas β oxidation uses NAD+ exclusively.

d. Fatty acid degradation is catalyzed by cytosolic enzymes; fatty acid synthesis by mitochondrial enzymes.

How many phosphoanhydride bonds (net) are consumed in the conversion of mevalonate into the activated isoprene compound dimethylallyl pyrophosphate?

a. zero

b. one

c. two

d. three

e. four

Which compound is NOT an intermediate in the synthesis of lanosterol from acetyl-CoA?

a. isopentenyl pyrophosphate

b. malonyl-CoA

c. mevalonate

d. squalene

Cholesterol is synthesized from:

a. acetyl-CoA.

b. choline.

c. lipoic acid.

d. malate.

e. oxalate.

A 30-carbon precursor of the steroid nucleus is:

a. farnesyl pyrophosphate.

b. geranyl pyrophosphate.

c. isopentenyl pyrophosphate.

d. lysolecithin.

e. squalene.

Which statement about cholesterol synthesis is true?

1. Cholesterol is the only known natural product whose biosynthesis involves isoprene units.
2. Only half of the carbon atoms of cholesterol are derived from acetate.
3. Squalene synthesis from farnesyl pyrophosphate results in the release of two molecules of PPi for each molecule of squalene formed.
4. The activated intermediates in the pathway are CDP-derivatives.
5. The condensation of two five-carbon units to yield geranyl pyrophosphate occurs in a "head-to-head" fashion.

Which statement is a step in the uptake of cholesterol from the bloodstream into cells?

a. LDL containing ApoB-100 is recognized by the LDL receptor.

b. LDL bound to the LDL receptor leads to endocytosis of the complex.

c. The cholesteryl esters in the LDL are hydrolyzed to release free cholesterol.

d. The ApoB-100 protein is degraded.

e. All of the above are steps in the uptake of cholesterol.

Which statement about the regulation of cholesterol synthesis is NOT true?

a. Cholesterol acquired in the diet has essentially no effect on cholesterol synthesis in the liver.

b. Failure to regulate cholesterol synthesis predisposes humans to atherosclerosis.

c. High intracellular cholesterol stimulates the formation of cholesteryl esters.

d. Insulin stimulates HMG-CoA reductase.

e. Some metabolite or derivative of cholesterol inhibits HMG-CoA reductase.

Which apolipoprotein is found in chylomicrons but not in other lipoproteins?

a. ApoB-48

b. ApoB-100

c. ApoC-II

d. ApoC-III

e. ApoE

Reverse cholesterol transport is primarily associated with which lipoprotein?

a. chylomicrons

b. VLDL

c. IDL

d. LDL

e. HDL

Conversion of VLDL into LDL is associated with what changes?

a. depletion of cholesteryl esters

b. an increase in particle diameter

c. an increase in the protein-lipid ratio

d. ApoE-mediated receptor interactions

Which apolipoprotein binds to the LDL receptor?

a. ApoB-100

b. ApoC-I

c. ApoC-II

d. ApoD

e. ApoE

Which lipoproteins do NOT originate from the liver?

a. chylomicrons and VLDL

b. VLDL and HDL

c. LDL and HDL

d. chylomicrons

e. VLDL and LDL

Lipoprotein particles in human blood do NOT contain:

a. an apolipoprotein B isoform.

b. cholesterol.

c. cholesteryl esters.

d. phosphatidylcholine.

e. triglycerides.

What statement is false regarding the regulation of HMG-CoA reductase?

1. HMG-CoA reductase is inhibited by phosphorylation.
2. Elevated levels of ATP will inhibit HMG-CoA reductase.
3. Elevated blood glucose will increase the activity of HMG-CoA reductase.
4. Statins act as competitive inhibitors for this enzyme.
5. Low cellular concentrations of cholesterol will increase expression of this enzyme and the LDL receptor.

Which statement about membranes is true?

1. Most plasma membranes contain more than 70% proteins.
2. Sterol lipids are common in bacterial plasma membranes.
3. Sterol lipids are common in human cell plasma membranes.
4. Sterol lipids are common in plant cell plasma membranes.
5. The plasma membranes of all cell types within a particular organism have basically the same lipid and protein composition.

Which statement about the composition of biological membranes is false?

1. In a given eukaryotic cell type (e.g., a hepatocyte), all intracellular membranes have essentially the same complement of lipids and proteins.
2. Carbohydrate is found in membranes as part of either a glycolipid or glycoprotein.
3. The plasma membranes of the cells of vertebrate animals contain more cholesterol than the mitochondrial membranes.
4. The ratio of lipid to protein varies widely among cell types in a single organism.
5. Triacylglycerols are not commonly found in membranes.

Which statement about the composition of membranes is true?

a. All biological membranes contain cholesterol.
b. Free fatty acids are major components of all membranes.
c. The inner and outer membranes of mitochondria have different protein compositions. d. The lipid composition of all membranes of eukaryotic cells is essentially the same.
e. The lipid:protein ratio is similar in most membranes.

Which lipid compound is NOT at least partially made from the condensation of isoprene units?

a. sterols

b. limonene

c. beta-carotene

d. vitamin E

e. phosphatidylinositol

Which eicosanoids contains a five-carbon ring as part of its structure?

a. thromboxanes

b. prostaglandins

c. lipoxins

d. leukotrienes

e. arachidonates

Fatty acids are a component of:

a. carotenes.

b. cerebrosides.

c. sterols.

d. vitamin D.

e. vitamin K.

Biological waxes are all:

a. triesters of glycerol and palmitic acid.

b. esters of single fatty acids with long-chain alcohols.

c. triesters of glycerol and three long-chain saturated fatty acids.

d. sphingolipids.

e. None of the answers is correct.

Which statement is true of lipids?

a. Many contain fatty acids involved in ester or amide linkages.

b. Most are classified as polymers.

c. Testosterone is an important sphingolipid found in myelin.

d. They are more soluble in water than in chloroform.

e. They play only passive roles as energy-storage molecules.

Fatty acids are a component of:

a. carotenes.

b. cerebrosides.

c. sterols.

d. vitamin D.

e. vitamin K.

Which statement is true about fatty acids?

a. Fatty acids with longer chains have lower melting points.

b. Fatty acids with longer chains have higher solubility in water.

c. Fatty acids with more double bonds have higher melting points.

d. Fatty acids with longer chains have higher melting points and lower solubility in water. e. None of the statements is true.

What is the abbreviated nomenclature for a 14-carbon omega-3 fatty acid that contains no other double bonds?

a. 14:1 (Δ11)

b. 17:1 (Δ14)

c. 14:1 (Δ3)

d. 13:1 (Δ11)

e. 14:0 (Δ11)

Which type of chemical linkage is used to join fatty acids to glycerol?

a. ether linkage

b. peptide bond

c. ester linkage

d. double bond

e. peroxide bond

Commercial vegetable oils can be converted from liquid forms to solid forms and have their shelf lives increased due to which process?

a. partial desaturation

b. unsaturation

c. partial hydrogenation

d. hydrolysis

e. complete esterification

Waxes are BEST described as:

a. esters of glycerol and three fatty acids.

b. esters of one long-chain fatty acid and one long-chain alcohol.

c. polyunsaturated long-chain fatty acids.

d. esters of two long-chain fatty acids.

e. ethers of glycerol and short-chain alcohols

In neutral fats, three fatty acids are generally linked to a _____ backbone.

a. glycogen

b. glycerol

c. sphingosine

d. glucose

e. phosphoglycerol

Which term BEST describes the polarity of membrane lipids?

a. ambidextrous

b. completely nonpolar

c. amphipathic

d. completely polar

e. amphibolic

Which statement describes a distinct difference between membrane lipids in archaea and membrane lipids in eukaryotes?

a. Archaeal membrane lipids have alkyl acids that are ether-linked to glycerol at both ends.

b. Eukaryotic membrane lipids consist of glycerol that is ester-linked to three fatty acids.

c. Only eukaryotic membrane lipids are amphipathic.

d. Archaeal membrane lipids always contain sphingosine.

e. Eukaryotic membrane lipids always have a phosphate group attached to glycerol.

Which compound is NOT a type of membrane lipid?

a. sphingolipid

b. glycerophospholipid

c. sulfolipid

d. sterol

e. triacylglycerol

Platelet-activating factor is much more water soluble than most other glycerophospholipids due to which feature?

a. its ether-linked alkyl chain at the C-1 of glycerol

b. its ester-linked acetic acid at the C-2 of glycerol

c. its ethanolamine head group

d. its lack of any long alkyl chains linked to glycerol

e. the presence of sphingosine, rather than glycerol, as a lipid backbone

Fatty acids are attached to sphingosine by what type of chemical linkage?

a. ether

b. amide

c. ester

d. peroxide

e. alkyl