Biochem 406 up to midterm 1

Which of the following intermediates is the substrate for the enzyme catalyzing the committed step in cholesterol biosynthesis? A. Dimethylallyl pyrophosphate B. 3-hydroxy-3-methylglutaryl-CoA C. 3-isopentyl pyrophosphate D. Mevalonate

B. 3-hydroxy-3-methylglutaryl-CoA

In intestinal epithelial cells free fatty acids are A. stored in the plasma membrane until needed B. bound by fatty acyl binding proteins C. stored in lipid droplets until needed D. freely soluble

B. bound by fatty acyl binding proteins

The carbon skeletons of which two amino acids enter metabolism at the level of pyruvate? Choose the best answer(s) from the list below. 1- Alanine and Serine 2- Alanine and Cysteine 3- Serine and Asparagine 4- Alanine and Aspartate

1 & 2 1- Alanine and Serine 2- Alanine and Cysteine

Aminotransferases require the prosthetic group pyridoxal phosphate for activity. The pyridoxal phosphate 1- forms a covalent Schiff-base intermediate with an amino acid substrate. 2- remains covalently attached to the enzyme throughout catalysis of the reaction. 3- uses the phosphate group of the cofactor to modify the amino acid substrate.

1- forms a covalent Schiff-base intermediate with an amino acid substrate.

Choose the best answer(s) from the list below. The glucose alanine cycle involves: 1- the transfer of the amino group from alanine to glutamate to form glutamine in the liver. 2- the transport of pyruvate from muscle to liver in the form of alanine. 3- the transport of NH4+ from muscle to liver in the form of alanine.

2 & 3 2- the transport of pyruvate from muscle to liver in the form of alanine. 3- the transport of NH4+ from muscle to liver in the form of alanine.

In the Liver, the amino group of glutamate is released as the ammonium ion in a reaction catalyzed by glutamate dehydrogenase (GDH). Which of the following statements about GDH is TRUE? Choose the best answer(s) from the list below. 1- GDH is tightly regulated by N-acetyl-glutamate. 2-The products of the reaction are Gln, NADPH, and NH4+. 3-The products of the reaction are LaTeX: \alpha α -ketoglutarte, NADPH or NADH, and NH4+. 4-The GDH reaction is reversible, but in humans it usually proceeds in the direction of LaTeX: \alpha α -ketoglutarate production.

3 & 4 3-The products of the reaction are LaTeX: \alpha α -ketoglutarte, NADPH or NADH, and NH4+. 4-The GDH reaction is reversible, but in humans it usually proceeds in the direction of LaTeX: \alpha α -ketoglutarate production.

Which ONE of the following statements about the Proteasome is FALSE? A. 26S Proteasomes reside in the cytosol and the nucleus and are thus not able to degrade proteins that reside in the ER membrane. B. The 20S Proteasome is made up of four ring structures each of which has a seven-fold symmetry. C. The 19S Regulatory Particle has a AAA ATPase that is needed to unfold proteins and thread them into the 20S Core Particle. D. The 𝛃-subunits of the core particle contain threonine protease activity.

A. 26S Proteasomes reside in the cytosol and the nucleus and are thus not able to degrade proteins that reside in the ER membrane. (26S Proteasomes do reside in the cytosol, but due to the ERAD pathway proteins can be specifically extracted from the ER to be degraded in the cytosol.)

Which ONE of the following statements in FALSE? A. CDP-Diacylglyceride is an intermediate in the synthesis of Fats B. Phosphatidic Acid is an intermediate in the synthesis of both Fats and Phospholipids C. Glycerol-P can be synthesized from either Dihydroxyacetone Phophate or from Glycerol D. Both Acyl-CoA synthase and Acyl-Transferase are required for the synthesis of Phosphatidic Acid

A. CDP-Diacylglyceride is an intermediate in the synthesis of Fats

Which ONE of the following statements about Receptor-Mediated Endocytosis is FALSE? A. Clathrin triskelia are trimeric assemblies of protein subunits that are primarily composed of beta-sheet tertiary structures. B. Adaptor proteins bind both receptors loaded with cargo and clathrin triskelia. C. Adaptor proteins help sort and concentrate cargo-loaded receptors on the surface of the plasma membrane. D. Additional protein factors are required for the disassembly of the clathrin cage surround the internalized vesicle.

A. Clathrin triskelia are trimeric assemblies of protein subunits that are primarily composed of beta-sheet tertiary structures.

What effect does the hormone glucagon have on fatty acid metabolism? A. It triggers the mobilization of stored fats B. It triggers the conversion of glucose into triacylglycerols C. It triggers the storage of triacylglycerols D. It triggers the conversion of triacylglycerols to glucose

A. It triggers the mobilization of stored fats

Enzymes exist that allow interconversion of different forms of THF carrying 1-carbon units except A. N5-Methyl THF B. N5,N10 Methylene THF C. N5,N10 Methenyl THF D. N10-Formyl-THF

A. N5-Methyl THF

Which ONE of the following statements about digestive enzymes is TRUE? A. The highly acidic milieu of the stomach helps to unfold proteins for enzymatic degradation. B. Zymogen activation of Chymotrypsin requires the reduction of 3 disulfide bonds. C. Chymotrypsin activates most other proteases in the small intestine through degradation of their respective inhibitors. D. Pepsin is secreted by the pancreas and has pH optimum at around pH 10.

A. The highly acidic milieu of the stomach helps to unfold proteins for enzymatic degradation.

Which of the following is NOT a difference in the pathways by which fatty acids are degraded and synthesized? A. an intermediate with a double bond B. the molecule to which the chain being synthesized or degraded is attached C. the location of the process

A. an intermediate with a double bond

Choose the best answer. Cholesterol is stored: A. as cholesterol esters in lipid droplets. B. in the ER membrane. C. in the gallblader as bile salts.

A. as cholesterol esters in lipid droplets.

A common signal recognized by the Proteasome for degradation of a cellular protein is: A. covalent modification by K48-linked poly-ubiquitin chains. B. covalent modification by K63-linked poly-ubiquitin chains. C. reduction of a protein's disulfide bonds. D. protein phosphorylation at a serine reside near the C-terminus.

A. covalent modification by K48-linked poly-ubiquitin chains.

The propionyl-CoA produced by β-oxidation of long-chain odd-number fatty acids enters the citric acid cycle as A. succinyl-CoA B. oxaloacetate C. acetyl-CoA D. malonyl-CoA

A. succinyl-CoA

Squalene, the 30 carbon precursor of cholesterol, is synthesized from: A. 5 molecules of mevalonate B. 6 molecules of isoprene pyrophosphate C. 15 molecules of acetyl-CoA D. 3 molecules of farnesyl pyrophosphate

B. 6 molecules of isoprene pyrophosphate

Terrestrial vertebrates use the urea cycle to convert the ammonium ion to urea such that the urea can be excreted. In the production of urea, only one of the nitrogens in the product comes directly from ammonium ions. What is the source of the other nitrogen? A. Fumarate B. Aspartate C. Carbamoyl-Phosphate D. Glutamate E. Ornithine

B. Aspartate

Which of the following statements regarding the Cobalamin cofactor are TRUE? Choose the best answer. A. A genetic defect in the human enzymes required for Cobalamin synthesis from Glycine and Succinyl-CoA result in the disease known as Pernicious Anemia. B. Cobalamin is used in only two metabolic reactions in humans: 1) Synthesis of Methionine from Homocysteine, and 2) the reaction that converts Methyl-Malonyl-CoA to Succinyl-CoA. C. Methyl-Cobalamin is an intermediate in the reaction catalyzed by Methionine Synthase. The methyl group of methyl-Cobalamin originates from S-adenosylmethionine

B. Cobalamin is used in only two metabolic reactions in humans: 1) Synthesis of Methionine from Homocysteine, and 2) the reaction that converts Methyl-Malonyl-CoA to Succinyl-CoA.

Which ONE of the following statements about Lysosomes is FALSE? A. Lysosomal enzymes include Lipases, Amylases, Proteases, and Nucleases. B. F-type ATPase in the Lysosomal membrane use the low pH inside the Lysosome for the production of ATP. C. The concentration of H+ inside the lysosome is ~100 times higher than in the cytosol. D. Lysosomes provide the only known way for the cell to degrade large cellular structures.

B. F-type ATPase in the Lysosomal membrane use the low pH inside the Lysosome for the production of ATP. (Lysosomal V-type ATPases create the low pH inside Lysosomes by using ATP.)

How does aspirin, a nonsteroidal antiinflammatory drug (NSAID), reduce inflammation? A. It inhibits the action of prostaglandins B. It blocks the synthesis of prostaglandins C. It inhibits the conversion of prostagladins into molecules that cause inflammation

B. It blocks the synthesis of prostaglandins

Which of the following is TRUE about human Fatty Acid Synthase (FAS)? A. Some of the reactions catalyzed by FAS generate NADPH B. It has a flexible phosphopantetheine arm covalently attached to the Acyl-Carrier Protein domain of the FAS C. It is a complex of seven different polypeptides D. Its principal product is stearate

B. It has a flexible phosphopantetheine arm covalently attached to the Acyl-Carrier Protein domain of the FAS

Which of the following molecules does not result from decarboxylation of an amino acid? A. gamma-aminobutyrate (GABA) B. L-dopa C. Histamine D. Serotonin

B. L-dopa

Which amino acids are purely ketogeneic? Choose the best answer. A. Lysine and Isoleucine. B. Lysine and Leucine. C. Leucine and Phenylalanine. D. Leucine and Tryptophan.

B. Lysine and Leucine.

Which ONE of the following statements is True? A. In the organization of metabolic pathways, a metabolite generated along a particular pathway can only be used for that pathway B. The activity of enzymes that catalyze committed steps in a metabolic pathway are often tightly controlled C. The activity of each enzyme in a pathway can only be controlled by one type of allosteric regulation (eg. Phosphorylation, product inhibition, etc)

B. The activity of enzymes that catalyze committed steps in a metabolic pathway are often tightly controlled

The cleavage of a peptide bonds is an exergonic process, yet protein degradation by the UPS requires energy. Which ONE of the following statements is NOT a reason for this? A. The 19S proteasome requires ATP for unfolding of proteins to be degraded. B. The cleavage poly-Ubiquitin chains for recycling at the Proteasome requires ATP. C. The biochemical process of tagging proteins with Ubiquitin as a signal for the proteasome requires ATP. D. Protein degradation by the UPS is highly specific and non-random, i.e. it decreases entropy. Previous

B. The cleavage poly-Ubiquitin chains for recycling at the Proteasome requires ATP. (Cleavage of an (iso-)peptide bond in poly-Ubiquitin chains in an exergonic process and does not require ATP.)

Which ONE of the following statements is FALSE about amino acid metabolism? A. Amino acids can be used in energy metabolism. B. The first step for the use of amino acids used in energy metabolism is oxidation of the amine group. C. Amino acids contain nitrogen, but most organisms have no storage form of nitrogen and thus rely on consistent dietary intake. D. Amino acids from degraded proteins can be recycled for new protein synthesis.

B. The first step for the use of amino acids used in energy metabolism is oxidation of the amine group. (The first step for the use of amino acids used in energy metabolism is transamination and not oxidation of the amine group.)

Which ONE of the following statements about Ubiquitin is FALSE? A. Ubiquitin is an 8.5 kDa protein with 76 amino acids. B. The very N-terminus of Ubiquitin features two glutamate residues that are important for conjugation to substrate proteins. C. The amino acids sequence of Ubiquitin is highly conserved among different eukaryotes. D. The 7 lysine residues and the N-terminus of Ubiquitin provide attachment sites for other Ubiquitin molecules during chain formation.

B. The very N-terminus of Ubiquitin features two glutamate residues that are important for conjugation to substrate proteins. (The very C-terminus of Ubiquitin features two glycine residues that are important for conjugation to substrate proteins.)

What happens to ketone bodies after they are synthesized? A. They are used in gluconeogenesis B. They are exported to other tissues to be used for fuel C. They are converted to acetyl-CoA and exported to tissues D. They are oxidized in the liver mitochondria to produce ATP for other tissues

B. They are exported to other tissues to be used for fuel

Which ONE of the following is FALSE regarding the regulation of cholesterol synthesis? A. Glucagon stimulates AMPK-dependent phosphorylation of both HMG-CoA reductase and Acetyl-CoA carboxylase. B. When cholesterol levels are low SREBP, SCAP, and INSIG form a stable complex localized in the ER membrane. C. Two different proteases working sequentially in the Golgi membrane release the bHLH domain (a transcriptional activator) from SREBP D. When cholesterol levels are high, a complex formed with INSIG in the ER membrane promotes the degradation of HMG-CoA Reductase.

B. When cholesterol levels are low SREBP, SCAP, and INSIG form a stable complex localized in the ER membrane.

Arginine and Methionine are considered essential dietary amino acids because A. humans lack enzymes that can synthesize arginine and methionine. B. humans lack the capacity to synthesize arginine and methionine in the amounts necessary. C. Trick question. Arginine and Methionine are non-essential amino acids for humans.

B. humans lack the capacity to synthesize arginine and methionine in the amounts necessary.

Human Pancreatic Lipase A. is activated upon contact with mono-acylglycerides B. requires a protein called colipase for activity C transports free fatty acids into intestinal epithelial cells D. solubilizes fatty acids for transport into intestinal epithelial cells

B. requires a protein called colipase for activity

Which of the following is NOT observed in the response to glucagon? A. Increased glycogen breakdown B. Increased glucogeogenesis C. Activation of Acetyl-CoA Carboxylase D. Activation of Hormone Sensitive Lipase E. Increased mobilization of fatty acids for use as fuel.

C. Activation of Acetyl-CoA Carboxylase

Newborn infants sometimes develop jaundice because of an accumulation of A. Urobilin B. Heme C. Bilirubin D. Biliverdin

C. Bilirubin

Which ONE of the following statements about pyridoxal-phsophate (PLP) is TRUE? A. In reactions at the \alpha-carbon of amino acids, the bond to be broken is dictated by the PLP cofactor B. PLP is only used by the class of enzymes known as aminotransferases. C. In PLP-dependent reactions the \alpha-carbon \sigma-bond to be broken is oriented perpendicular to the plane of the PLP cofactor. D. PLP is only used to catalyze transformations at the \alpha-carbon of amino acids.

C. In PLP-dependent reactions the \alpha-carbon \sigma-bond to be broken is oriented perpendicular to the plane of the PLP cofactor.

Which of the following molecules is not derived from glycine? A. Glutathione (GSH) B. Phosphocreatine C. Serotinin D. Heme

C. Serotinin

Which of the following is NOT observed in the response to insulin? A. Activation of Acetyl-CoA Carboxylase B. Dephosphorylation of Acetyl-CoA Carboxylase C. Stimulation of Carnitine Acyl Transferase 1 activity D. Enhanced storage of fatty acids as triacylglycerides

C. Stimulation of Carnitine Acyl Transferase 1 activity

Which ONE of the following statements is False? A. Anabolic and Catabolic pathways can be regulated by hormones such as glucagon and insulin B. Control of enzyme levels through the regulation of gene expression is one example of long-term regulation of a metabolic pathway C. The flow of metabolites in Anabolic and Catabolic pathways is primarily controlled by changes in metabolite concentrations because the anabolic pathways are simply the reverse of catabolic pathways D. To generate products, an anabolic or catabolic pathway must overall be exergonic

C. The flow of metabolites in Anabolic and Catabolic pathways is primarily controlled by changes in metabolite concentrations because the anabolic

The reaction catalyzed by aminotransferases (transaminases): A. Always use LaTeX: a-ketoglutarate as an amino group acceptor. B. Generates free ammonia. C. Uses two substrates and generates two products. D. Are highly exergonic.

C. Uses two substrates and generates two products.

Acetyl groups to be used for fatty acid biosynthesis are transferred across the mitochondrial membrane in what form? A. acetyl-carnitine complexes B. acetyl-coenzyme A C. citrate D. malate

C. citrate

Choose the best answer. Linoleate and \alpha α -linolenate are "essential fatty acids" because: A. mammals can use them to make other fatty acids B. mammals cannot synthesize fatty acid chains with more than 16 carbons C. mammals can only introduce double bonds in fatty acid chains at certain positions D. mammals cannot introduce double bonds into fatty acid chains

C. mammals can only introduce double bonds in fatty acid chains at certain positions

Which of the following fatty acids will require enoyl-CoA isomerase in order to undergo complete β-oxidation? A. 18C with 2 trans X2 bonds on C's 14 and 10. C1 has a double bond to O and a bond to S-CoA B. 17C with 1 trans X2 bond on C 14. C1 has a double bond to O and a bond to S-CoA C. 18C. C1 has a double bond to O and a bond to S-CoA D. 18C with 1 cis X2 bond on C9. C1 has a double bond to O and a bond to S-CoA

D. 18C with 1 cis X2 bond on C9. C1 has a double bond to O and a bond to S-CoA

Which ONE of the following statements about Acetyl-CoA carboxylase (ACC) is TRUE? A. The dimeric form of ACC is the most active form. B. Citrate inhibits the activity of ACC. C. Palmitoyl-CoA is an allosteric activator of ACC. D. Assembly of ACC into long filaments increases activity.

D. Assembly of ACC into long filaments increases activity.

Choose the best answer from the list below. The NADPH used in the reductive steps of fatty acid biosynthesis comes from: 1. NADPH is generated as citrate is is converted to pyruvate in the cytosol. 2. the conversion of glucose-6-P to ribulose-5-P in the pentose phosphate pathway. 3. NADPH generated in the TCA cycle. A. 1 only B. 2 only C. 3 only D. Both 1 and 2 E. Both 2 and 3

D. Both 1 and 2

Which ONE of the following occurs during uptake of cholesterol by extra-hepatic tissues? A. LDL receptors on the cell surface recognize cholesterol in LDL particles. B. Recycling of the LDL receptor occurs after degradation of LDL in the lysosome C. The apoB-100 protein in LDL particles is not internalized, but is recycled. D. Cholesterol is released from LDL particles when they are degraded in the lysosome.

D. Cholesterol is released from LDL particles when they are degraded in the lysosome.

Which ONE of the following statements about protein turnover is TRUE? A. Protein synthesis is generally a much quicker process then protein degradation. B. All proteins have a fixed, intrinsic half-life that does not change throughout the cell cycle. C. Degradation by Carboxypeptidase A is the major mechanism involved in intracellular protein turnover. D. Constant protein turnover prevents the accumulation of acquired protein defects over time.

D. Constant protein turnover prevents the accumulation of acquired protein defects over time.

The reactions of the urea cycle: A. All take place in the mitochondrial matrix. B. Generate ATP C. Start with the entry of ornithine. D. Convert ammonia to urea.

D. Convert ammonia to urea.

Which of the following lipoproteins participates in reverse cholesterol transport? A. chylomicrons B. VLDL C. LDL D. HDL

D. HDL

What is the committed step in fatty acid synthesis? A. The condensation step catalyzed by the \beta-KetoAcyl- ACP Synthase of the Fatty Acid Synthase Complex. B. Cleavage of the fatty acid from the acyl carrier protein (ACP) catalyzed by Thioesterase C. The attachment of a malonyl group to the acyl carrier protein (ACP) D. The formation of malonyl-CoA

D. The formation of malonyl-CoA

Which ONE of the following is TRUE of the lipoprotein particles that transport dietary fats? A. They carry fats, but are most important for delivering cholesterol to tissues B. They are the smallest of the lipid carriers C. They only contain one type of apolipoprotein D. They are synthesized in intestinal cells

D. They are synthesized in intestinal cells

Which of the following is true of the properties of triacylglycerols? A. They are readily transported across cell membranes B. They are soluble in water C. They are chemically unstable D. They generate more energy than the same weight of carbohydrate

D. They generate more energy than the same weight of carbohydrate

Dietary triacylglycerols are emulsified in the intestine by A. lipases B. Apolipoproteins C. chylomicrons D. bile salts

D. bile salts

Ketone bodies are formed in: A. adipocytes B. myocytes C. all cells D. hepatocytes

D. hepatocytes

Fatty acid biosynthesis depends on the presence of CO2 (or HCO3-) to generate malonyl-coenzyme A from acetyl-coenzyme A. If a culture of cells is grown in the presence of 14C-labeled bicarbonate, which carbons of the newly synthesized fatty acids would be expected to be radiolabeled? A. the even-numbered carbons B. the odd-numbered carbons C. all the carbons D. none of the carbons

D. none of the carbons

Choose the best answer. High concentrations of cholesterol in tissues leads to: 1- Decreased expression of the gene for HMG-CoA Reductase 2- Decreased expression of the gene for the LDL receptor 3- Activation of Acyl-CoA Cholesterol Acyltransferase (ACAT) A. 1 only B. 2 only C. 3 only D. 1 and 2 E. 1, 2, & 3

E. 1, 2, & 3 (Decreased expression of the gene for HMG-CoA Reductase; Decreased expression of the gene for the LDL receptor; Activation of Acyl-CoA Cholesterol Acyltransferase (ACAT))

Intermediates generated during cholesterol biosynthesis can be used to synthesize: A. Steroid hormones B .Co-enzyme Q (ubiquinone) C. Vitamin D3 D. Geranyl-geranyl E. All of the above

E. All of the above (Steroid hormones, Co-enzyme, (ubiquinone), Vitamin D3, Geranyl-geranyl)

Choose the best answer. High circulating levels of cholesterol: A. can be treated with statin drugs. B. can result in atherosclerosis. C. can be caused by a genetic mutation that reduces the number of functional LDL receptors. D. can be treated with drugs that block dietary absorption of cholesterol. E. All of the above about high circulating levels of cholesterol are TRUE.

E. All of the above about high circulating levels of cholesterol are TRUE. (can be treated with statin drugs; can result in atherosclerosis; can be caused by a genetic mutation that reduces the number of functional LDL receptors; can be treated with drugs that block dietary absorption of cholesterol.)

The conversion of serine to glycine utilizes which of the following pairs of cofactors? A. B12 & THF B. PLP & NADH C. Biotin & B12 D. SAM (also known as adoMet) & ATP E. PLP & THF

E. PLP & THF