Download Metabolic Biochemistry

1.
Insulin production by ß-cells of the pancreas involves each of the following processes
EXCEPT:
A.
B.
C.
D.
E.
2.
Cholera toxin causes massive and often fatal diarrhea by:
A.
B.
C.
D.
E.
3.
Inhibition of guanylate cyclase
Its synthesis is increased by the drug Viagra
It activates guanylate cyclase
It is a gaseous signaling molecule that can diffuse from one cell to another
It results in relaxation of smooth muscle
Its nitrogen atom comes from arginine
A cell population in culture is treated with a membrane-permeable analog of cyclic AMP
in the absence of hormone treatment. What is the most likely effect of adding this
compound?
A.
B.
C.
D.
E.
5.
Inactivating Gi protein
Irreversibly activating adenylate cyclase
Locking Gs protein into an inactive form
Rapidly hydrolyzing G protein GTP to GDP
All of the following are true of nitric oxide EXCEPT:
A.
B.
C.
D.
E.
4.
Glycosylation of the polypeptide
Packaging of the hormone in secretory granules
Removal of the signal peptide and formation of disulfide bonds to form proinsulin
Removal of the C-peptide
Transcription of mRNA encoding pre-proinsulin
Activation of a G protein
Activation of protein kinase A
Binding of arrestin to a receptor
Activation of adenylate cyclase
Activation of protein kinase C
Which of the following is TRUE of proteoglycans and glycoproteins?
A.
B.
C.
D.
E.
The polysaccharide component of both proteoglycans and glycoproteins can be
branched
The polysaccharide component of both proteoglycans and glycoproteins can be
elongated in the Golgi
Polysaccharides can be linked to protein via asparagine for both proteoglycans and
glycoproteins
Polysaccharides of both proteoglycans and glycoproteins can contain sialic acid
Polysaccharides of glycoproteins are made up of repeating disaccharide units
while the
polysaccharides of proteoglycans are more complex
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6.
All of the following molecules contain carbons obtained from the tetrahydrofolate onecarbon pool EXCEPT:
A.
B.
C.
D
E
7.
The major regulatory step in the biosynthesis of cholesterol involves formation of:
A.
B.
C.
D.
E.
8.
Aspartate
Glycine
Glutamine
Serine
S-Adenosylmethionine
Insulin binds its receptor on the plasma membrane to regulate cell metabolic activity. All
of the following statements about the insulin receptor are true EXCEPT:
A.
B.
C.
D.
E.
10.
Squalene
Lanosterol
Mevalonate
Hydroxymethyl-glutaryl CoA
Acetoacetyl CoA
Which of the following provides carbon atoms in the biosynthesis of the
pyrimidine base structure?
A.
B.
C.
D.
E.
9.
The purine ring
Methylcobalamin
dTMP
The pyrimidine ring
Serine
The receptor is composed of polypeptide chains joined by disulfide bonds
Insulin binding to the receptor activates a tyrosine kinase domain in the receptor
The receptor is internalized into the cell following insulin binding
The receptor requires a trimeric G protein for signaling
The receptor undergoes autophosphorylation
Which of the following statements concerning vitamin B 12 is FALSE?
A.
B.
C.
D.
E.
It is enriched in animal by-products
It is used in the conversion of methylmalonyl CoA to succinyl CoA
It is utilized in the direct formation of methionine from homocysteine
It binds intrinsic factor that is produced by parietal cells
It is utilized in the direct formation of cystathionine from homocysteine
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11.
A young child is in an automobile accident that requires surgical intervention and
substantial recovery time in the hospital. Consultation with a nutritionist results in a
specific dietary plan that includes supplementation with an amino acid typically
considered to be non-essential. Which of the following amino acids is an essential
amino acid under conditions of enhanced growth or surgical recovery?
A.
B.
C.
D.
E.
12.
The major function of HDLs is to:
A.
B.
C.
D.
E.
13.
Transport cholesterol to peripheral tissue
Promote recycling of the LDL receptor
Bind cholesterol released from peripheral cell membranes
Transport dietary triglycerides to intestinal epithelial cells
Activate cholesterol esterification by acyl-CoA:cholesterol acyltransferase
(ACAT)
All of the following statements about phosphatidylethanolamine are true EXCEPT:
A.
B.
C.
D.
E.
14.
Alanine
Arginine
Glycine
Serine
Tyrosine
Can be made by decarboxylation of phosphatidylserine
Can be used to make phosphatidylserine by displacement of ethanolamine by
serine
Can be converted to phosphatidylcholine by methylation
Can be used to make phosphatidylcholine by displacement of ethanolamine by
choline
Can be used to produce ethanolamine from an amino acid in a net fashion
The major function of the LDL receptor is to:
A.
B.
C.
D.
E.
Mediate the uptake of LDLs into cells
Transfer cholesterol esters from LDLs to HDLs
Transfer cholesterol esters from the cytoplasm to the plasma membrane
Prevent conversion of cholesterol to cholesterol esters
Recycle apoproteins from LDLs back to HDLs
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15.
Before the introduction of vitamin D-fortified milk, children who spent most of their time
indoors often developed rickets. In these vitamin D-deficient children, the most likely
explanation for their bone malformations is:
A.
B.
C.
D.
E.
16.
The most direct route to cardiolipin biosynthesis is:
A.
B.
C.
D.
E.
17.
Phosphatidylglycerol + phosphatidic acid
CDP-glycerol + phosphatidylglycerophosphate
CDP-diacylglycerol + phosphatidylglycerol
Phosphatidylinositol + phosphatidylglycerol
Diacylglycerol + ATP + glycerol phosphate
A patient presents with extreme swelling and tenderness in the joints of the
extremities. Examination of synovial fluid extracted from a big toe reveals the presence
of urate crystals and confirms the diagnosis of gouty arthritis. The drug allopurinol is
prescribed in order to inhibit which of the following enzymes?
A.
B.
C.
D.
E.
18.
Excessive deposition of calcium in bone
Excessive renal excretion of phosphate ion
Inadequate uptake of calcium in the intestine
Lack of weight-bearing exercise
Excessive renal tubular reabsorption of calcium
Adenosine deaminase
AMP deaminase
Nucleoside phosphorylase
Uricase
Xanthine oxidase
All of the following play an important role in biosynthesis of many integral membrane
proteins EXCEPT:
A.
B.
C.
D.
E.
Clathrin
Signal recognition particle
Chaperones
GTP
ATP
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19.
A patient presents in your office with very high levels of serum cholesterol despite
following the diet and exercise regimen you prescribed last year. You decide that this
patient would benefit from a drug such as Lipitor (atorvastatin). This class of drugs is
effective in treating hypercholesterolemia because it:
A.
B.
C.
D.
E.
20.
All of the following statements regarding the water-soluble vitamins are true EXCEPT:
A.
B.
C.
D.
E.
21.
Many electron transfer reactions use cofactors derived from Vitamins B2 or B3
(riboflavin and niacin)
Vitamin B1 (thiamine) is a precursor for a catalytic component of alphaketoglutarate dehydrogenase
Excess amounts of water-soluble vitamins are usually excreted in the urine
Biotin is used to carry C 1 units at the same oxidation level as that in S-adenosyl
methionine
Deficiency in Vitamin C (ascorbate) disrupts modification of proline residues in
connective tissue protein
All of the following statements about genetically inherited defects are true EXCEPT:
A.
B.
C.
D.
E.
22.
Stimulates phosphorylation of ß-hydroxy-ß-methylglutaryl-CoA reductase
Increases degradation of ß-hydroxy-ß-methylglutaryl-CoA reductase
Binds cholesterol and prevents it from being absorbed by the intestinal mucosa
Directly prevents the deposition of cholesterol on artery walls
Inhibits ß-hydroxy-ß-methylglutaryl-CoA reductase
Hunter syndrome is due to deficient degradation of a glycosaminoglycan in the
lysosomes
I-cell disease results in impaired targeting of extracellular proteins to the
lysosomes for degradation
Leukocyte adhesion deficiency Type II results in improper modification of the
carbohydrate portion of glycoproteins
Tay-Sachs disease results in accumulation of a ganglioside in the lysosomes
Niemann-Pick disease results in accumulation of sphingomyelin in the lysosomes
Which of the following statements about the fat-soluble vitamins is TRUE?
A.
B.
C.
D.
E.
Excess Vitamin A is oxidized in the liver for excretion as a component of bile
In most people, exposure of the skin to sunlight decreases the amount of Vitamin
D needed in the diet
A major function of Vitamin E (tocopherol) is to facilitate electron transfer from
NADH to oxygen in the mitochondrial membrane
Vitamin K is required for activation of clotting factors by carboxylation of
selected aspartate residues
Regulation of bone mineralization is disrupted by Vitamin A deficiency
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23.
The ionophore valinomycin greatly increases the permeability of K+ across membranes
by acting as a carrier for the ion. This action requires diffusion in the membrane. Which
ONE of the following is most likely to INCREASE valinomycin-mediated K+ flux
across the membrane?
A.
B.
C.
D.
E.
24.
Which of the following best describes the mechanism by which cholesterol (or a
metabolite) represses the expression of enzymes involved in cholesterol biosynthesis?
A.
B.
C.
D.
25.
It acts directly as a transcription factor
It directly inhibits a protease that releases a transcription factor
It binds to the Steroid Regulatory Element Binding Protein (SREBP) and inhibits
its action
It prevents the movement of the pre-SREBP from the endoplasmic reticulum to the
Golgi
Trace amounts of 3H-thymidine were added for 2 hours to a nonsynchronized culture
of cells doubling in number every 24 hours. Then, unincorporated label was removed
by washing and radioactivity was visualized by autoradiography of cells fixed on
coverslips. Which one of the following is most likely to be observed?
A.
B.
C.
D.
E.
26.
A decrease in temperature
A decrease in average chain length of fatty acid residues of membrane lipids
An increase in saturated fatty acid residue content of membrane lipids
An increase in carbohydrate residue content of membrane proteins
A decrease in the content of essential fatty acyl residues in membrane lipids
Radioactivity is present in nuclei of all cells
Radioactivity is present in the cytoplasm of all cells
Radioactivity is present in the nuclei of 10-30% of the cells
Radioactivity is present in the cytoplasm of 10-30% of the cells
No radioactivity is incorporated
All of the following statements concerning apoptosis are true EXCEPT:
A.
B.
C.
D.
E.
A proteolytic cascade is activated
It can involve release of a mitochondrial protein into the cytoplasm
It can be triggered by ligand binding to the cell surface
Nuclear DNA remains intact after apoptosis is triggered
Apoptosis is required for normal embryological development
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27.
Which of the following statements about serine is FALSE:
A.
B.
C.
D.
E.
28.
All of the following statements about sialic acid (N-acetyl neuraminic acid) are true
EXCEPT:
A.
B.
C.
D.
E.
29.
Diacylglycerol
Inositol trisphosphate (IP3)
Cyclic AMP
Protein kinase C
Calmodulin
Sphingolipids:
A.
B.
C.
D.
E.
31.
It is present in gangliosides but absent from cerebrosides
Its attachment to some molecules regulates their lifetime in the circulation
It can be a component of both glycolipids and glycoproteins
It is formed by isomerization of glucuronic acid
It is removed by enzymes in the lysosome
Which ONE of the following acts directly to trigger release of Ca 2+ from the endoplasmic
reticulum?
A.
B.
C.
D.
E.
30.
It contributes carbon to the one-carbon pool
It is a three carbon amino acid formed from 3-phosphoglycerate
It is converted to glycine by a reaction requiring tetrahydrofolate
It controls its own production by feedback inhibition of 3-phosphoglycerate
dehydrogenase
It is synthesized from glucose via an intermediate of the TCA cycle
Contain a backbone that derives its carbons from condensation of palmitic acid
and glycine
Have two fatty acyl chains, one as an amide, one as an ester
Are conjugated with taurine prior to entering the gut
Are stored with triglycerides in intracellular lipid droplets
Can be sulfated using an adenosine-based carrier molecule
All of the following are important functions of bile acids and bile salts EXCEPT:
A.
B.
C.
D.
E.
Help to dissolve biliary cholesterol
A significant component of chylomicrons
Absorption of fat-soluble vitamins
Emulsify triglycerides taken in the diet
Removal of cholesterol from the body
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32.
Which one of the following statements about heme biosynthesis is TRUE?
A.
B.
C.
D.
E.
33.
A patient presents in your office with very high levels of serum cholesterol. After a
series of tests you conclude that the patient has elevated LDL cholesterol, but has
normal levels of liver LDL receptor. The most likely explanation for this situation is:
A.
B.
C.
D.
E.
34.
Dysfunctional apoprotein B-100
Inability to remove cholesterol from the LDL complex
Defective lipoprotein lipase
Decreased acyl-CoA:cholesterol acyltransferase activity
Altered phosphorylation of the LDL receptor
All of the following statements about O-linked glycoproteins are true EXCEPT:
A.
B.
C.
D.
E.
35.
Some carbons of heme are furnished by S-adenosyl methionine
Defects in the enzymes of heme biosynthesis are usually asymptomatic in
heterozygotic individuals
Accumulation of heme biosynthetic intermediates can result in photosensitivity
The iron atom is inserted before the porphyrin ring is closed
All steps in heme biosynthesis take place in the cytoplasm
The carbohydrate component can be branched and can contain many different
monosaccharides
The carbohydrate is attached directly to a growing oligosaccharide linked to the
protein through either serine or threonine
Activated sugars are added one at a time to the protein in the endoplasmic
reticulum
Degradation of both the protein and polysaccharide components occurs in
lysosomes
The oligosaccharide component of O-linked glycoproteins in the plasma
membrane faces the extracellular matrix
Which of the following is NOT found as a major constituent in biological membranes?
A.
B.
C.
D.
E.
Sphingomyelin
Cholesterol
Free fatty acids
Phosphatidylcholine
Phosphatidylethanolamine
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36.
Which of the following statements concerning tyrosine is FALSE:
A.
B.
C.
D.
E.
37.
All of the following statements regarding iron metabolism are true EXCEPT:
A.
B.
C.
D.
E.
38.
Ferritin is the major storage form of iron
Iron is transported in the bloodstream as ferrous ion (Fe 2+) complexed with
transferrin
Iron uptake by peripheral cells is limited by the number of transferrin receptors at
the cell surface
Reactive oxygen species can be produced in reactions involving iron
Mobilization of stored iron and its transport in the bloodstream requires both
oxidation and reduction of the iron
All of the following statements about N-linked glycoproteins are true EXCEPT:
A.
B.
C.
D.
E.
39.
It is the product of phenylalanine hydroxylase
It is used together with glycine in the formation of creatine
It is utilized in the formation of epinephrine
It is an essential amino acid in patients with phenylketonuria
Its formation utilizes tetrahydrobiopterin
The carbohydrate component contains a common oligosaccharide made up of
mannose and N-acetyl glucosamine (G1cNAc)
Synthesis of the carbohydrate component can occur in both the endoplasmic
reticulum and the Golgi
Elongation of the protein-linked oligosaccharide in the Golgi requires
sugar-nucleotide:nucleotide antiporters
Dolichol phosphate shuttles activated sugars from the cytoplasm into the
endoplasmic reticulum lumen
The polysaccharide chain remains attached to the protein during degradation in
the lysosomes
Conversion of nucleoside diphosphates to deoxynucleoside diphosphates is carried out
by:
A.
B.
C.
D.
E.
Dihydrofolate reductase
Ribonucleotide reductase
Xanthine oxidase
Hypoxanthine-guanine phosphoribosyltransferase
Dihydropteridine reductase
9
40.
Which of the following reactions requires S-adenosylmethionine as a methyl donor?
A.
B.
C.
D.
E.
41.
Cystic fibrosis is a common inherited disease in the Caucasian population. The product
of this gene (CFTR) exhibits all of the following properties EXCEPT:
A.
B.
C.
D.
E.
42.
D.
E.
Tyrosine is iodinated before it is incorporated into thyroglobulin
Iodination occurs in a colloid extracellular space
Active hormone is released by proteolysis of a precursor stored in intracellular
vesicles
Active hormone contains either three or four iodine residues per molecule
Iodide is actively accumulated by the thyroid gland
Diacylglycerol is a necessary intermediate on the biosynthetic path to all of the
following EXCEPT:
A.
B.
C.
D.
E.
44.
It is a member of a large superfamily of ATP-binding proteins
It is an integral membrane protein with 2 ATP-binding sites
It is a chloride channel
It derives energy from a Na+ gradient
It is insensitive to cardiac glycosides such as digitalis
All of the following statements concerning synthesis of thyroid hormones are true
EXCEPT:
A.
B.
C.
43.
Formation of 5, 10-methylene-FH4 from serine
Methylation of homocysteine to form methionine
Formation of epinephrine from norepinephrine
Methylation of dUMP to form dTMP
Formation of creatinine from creatine phosphate
Phosphatidylcholine
Triacylglycerol
Phosphatidylethanolamine
CDP-diacylglycerol
Phosphatidylserine
All the following statements about cyclooxygenase activity are true EXCEPT:
A.
B.
C.
D.
E.
Forms a precursor of leukotrienes
Can be inhibited by aspirin
Catalyzed by two distinct isoenzymes
Forms a precursor of prostacyclin
Important in inflammation and hemostasis
10
45.
All of the following statements regarding polyamines are true EXCEPT:
A.
B.
C.
D.
E.
46.
They obtain carbons from glutamate
Their synthesis involves the decarboxylation of ornithine
They obtain carbons and nitrogen from serine
They are highly cationic molecules
They play important roles in cell growth and differentiation
All of the following are characteristic of facilitated diffusion EXCEPT:
A.
B.
C.
D.
E.
Saturation kinetics as a function of substrate concentration
Inhibition by structural analogs of substrate
Stereospecificity
Movement of substrate against its concentration gradient
Can be lost by genetic mutation
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Answers
1. A
2. B
3. A
4. B
5. B
6. D
7. C
8. A
9. D
10. E
11. B
12. C
13. D
14. A
15. C
16. C
17. E
18. A
19. E
20. D
21. B
22. B
23. B
24. D
25. C
26. D
27. E
28. D
29. B
30. E
31. B
32. C
33. A
34. C
35. C
36. B
37. B
38. E
39. B
40. C
41. D
42. A
43. D
44. A
45. C
46. D
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