Biochem exam 1

1. 1a hydronium ion

   1. Ahas the structure H3O+
   2. Bis a hydrated hydrogen ion
   3. Cis the usual form of one of the dissociation products of water in solution
   4. Dall of the above
2. 2an average protein will be denatured by the compounds below, except:

   1. Aa detergent such as sodium dodecyl sulfate
   2. BpH 10
   3. Ciodoacetic acid
   4. Durea
   5. Eheating to 90 degrees C
3. 3at pH 7.0, converting a glutamic acid to γ-carboxyglutamate will have what effect on the overall charge of the protein containing it

   1. Ait will become more negative
   2. Bit will become more positive
   3. Cit will stay the same
   4. Dthere is not enough information to answer the question
   5. Ethe answer depends on the salt concentration
4. 4at pH 7.0 converting a proline to hydroxyproline will have what effect on the overall charge of the protein containing it

   1. Ait will become more negative
   2. Bit will become more positive
   3. Cthere is not enough information to answer the question
   4. Dit will stay the same
   5. Ethe answer depends on the salt concentration
5. 5by adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to

   1. Aseparate proteins exclusively on the basis of molecular weight
   2. Bdetermine the amino acid composition of the protein
   3. Cdetermine the proteins isoelectric point
   4. Ddetermine an enzymes specific activity
   5. Epreserve a proteins native structure and biological activity
6. 6Consider an acetate buffer, initially at the same pH as its pKa (4.76). When sodium hydroxide (NaOH) is mixed with this buffer, the:

   1. ApH remains constant
   2. Bratio of acetic acid to sodium acetate in the buffer falls
   3. CpH rises more than if an equal amount of NaOH is added to an acetate buffer initially at pH 6.76
   4. DpH rises more than if an equal amount of NaOH is added to unbuffered water at pH 4.76.
   5. Esodium acetate formed precipitates because it is less soluble than acetic acid.
7. 7Experiments on denaturation and renaturation after the reduction and reoxidation of the —S—S— bonds in the enzyme ribonuclease (RNase) have shown that

   1. Afolding of denatured RNase into the native, active conformation requires the input of energy in the form of heat.
   2. Bthe primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure.
   3. Cnative ribonuclease does not have a unique secondary and tertiary structure
   4. Dthe enzyme, dissolved in water, is thermodynamically stable relative to the mixture of amino acids whose residues are contained in RNase
   5. Ethe completely unfolded enzyme, with all —S—S— bonds broken, is still enzymatically active
8. 8For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have:

   1. Aa net negative charge
   2. Bno charged groups
   3. Ca net positive charge
   4. Dno net charge
   5. Epositive and negative charges in equal concentration
9. 9Humans usually wish each other happy birthday, happy holiday, or nice weekend, but some of them wish to their colleagues to have the lowest entropy. This wish usually means that they want their colleagues to

   1. Ahave a dynamic steady state
   2. Bhave a great activation energy
   3. Chave a lower metabolism
   4. Dbe disorganized
   5. Ehave more free energy
   6. Fbe organized
10. 10If the free energy change ΔG for a reaction is -46.11 kJ/mol, the reaction is

    1. Aat equilibrium
    2. Bexergonic
    3. Cendergonic
    4. Dendothermic
    5. Eexothermic

11. 11In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel- filtration) chromatography under reducing conditions

    1. Acytochrome c Mr = 13,000
    2. Bimmunoglobulin G Mr = 145,000
    3. Cribonuclease A Mr = 13,700
    4. DRNA polymerase Mr = 450,000
    5. Eserum albumin Mr = 68,500
12. 12In an α helix, the R groups on the amino acid residues

    1. Aalternate between the outside and the inside of the helix
    2. Bcause only right-handed helices to form
    3. Cgenerate the hydrogen bonds that form the helix
    4. Dstack within the interior of the helix
    5. Eare found on the outside of the helix spiral
13. 13In the α helix the hydrogen bonds

    1. Aare roughly perpendicular to the axis of the helix.
    2. Bare roughly parallel to the axis of the helix
    3. Coccur mainly between electronegative atoms of the R groups
    4. Doccur only between some of the amino acids of the helix
    5. Eoccur only near the amino and carboxyl termini of the helix
14. 14Major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which of the following problems

    1. AMacromolecules were insoluble in the solvents used in mass spectrometry
    2. BMass spectrometric analyses of macromolecules were too complex to interpret
    3. CMass spectrometric analysis involved molecules in the gas phase.
    4. DMost macromolecules could not be purified to the degree required for mass spectrometric analysis
    5. EThe specialized instruments required were prohibitively expensive
15. 15Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________

    1. Aalanine; is a simple methyl group
    2. Bglycine; is a hydrogen atom
    3. Cglycine; is unbranched
    4. Dlysine; contains only nitrogen
    5. Eproline; forms a covalent bond with the amino group
16. 16one method used to prevent disulfide bond interference with protein sequencing procedures is

    1. Acleaving proteins with proteases that specifically recognize disulfide bonds
    2. Bprotecting the disulfide bridge against spontaneous reduction to cysteinyl sulfhydryl groups
    3. Cremoving cystines from protein sequences by proteolytic cleavage
    4. Dsequencing proteins that do not contain cysteinyl residues
    5. Ereducing disulfide bridges and preventing their re-formation by further modifying the —SH groups
17. 17Phosphoric acid is tribasic, with pKa’s of 2.14, 6.86, and 12.4. The ionic form that predominates at pH 3.2 is

    1. AH3PO4
    2. BHPO42-
    3. CPO43-
    4. DH2PO4-
    5. ENone of the above
18. 18Roughly how many amino acids are there in one turn of an α helix

    1. A1.9
    2. B3.8
    3. C4.2
    4. D3.6
    5. E10
19. 19Stereoisomers that are nonsuperimposable mirror images of each other are known as

    1. Aanomers
    2. Bcis-trans isomers
    3. Cdiastereoisomers
    4. Denantiomers
    5. Egeometric isomers
20. 20The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why?

    1. AThe number 110 is based on the fact that the average molecular weight of a protein is 110,000 with an average of 1,000 amino acids.
    2. BThe number 110 reflects the number of amino acids found in the typical small protein, and only small proteins have their molecular weight estimated this way.
    3. CThe number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms
    4. DThe number 110 takes into account the relatively small size of nonstandard amino acids.
    5. EThe number 138 represents the molecular weight of conjugated amino acids.
21. 21The bacterium E. coli requires simple organic molecules for growth and energy—it is therefore a:

    1. Achemoautotroph
    2. Bchemoheterotroph
    3. Clithotroph
    4. Dlithograph.
    5. Ephotoautotroph
    6. Fphototraph
22. 22The enzyme fumarase catalyzes the reversible hydration of fumaric acid to l-malate, but it will not catalyze the hydration of maleic acid, the cis isomer of fumaric acid. This is an example of:

    1. Abiological activity
    2. Bchiral activity
    3. Cracemization
    4. Dstereospecificity.
    5. Estereoisomerization
23. 23The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step:

    1. Athe individual bands become stained so that the isoelectric focus pattern can be visualized.
    2. Bproteins with similar isoelectric points can become free of charge.
    3. Cproteins with similar isoelectric points become further separated according to their molecular weights.
    4. Dthe individual bands undergo a second, more intense isoelectric focusing
    5. Ethe proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current.
24. 24The Henderson-Hasselbalch equation

    1. Aallows the graphic determination of the molecular weight of a weak acid from its pH alone.
    2. Bdoes not explain the behavior of di- or tri-basic weak acids
    3. Cemploys the same value for pKa for all weak acids.
    4. Drelates the pH of a solution to the pKa and the concentrations of acid and conjugate base
    5. Eis equally useful with solutions of acetic acid and of hydrochloric acid
25. 25The major carrier of chemical energy in all cells is:

    1. Aacetyl triphosphate
    2. Badenosine monophosphate
    3. Cadenosine triphosphate
    4. DFedEx
    5. Ecytosine tetraphosphate.
    6. Furidine diphosphate.
26. 26The most important contribution to the stability of a proteins conformation appears to be the

    1. Astabilizing effect of hydrogen bonding between the carbonyl group of one peptide bond and the amino group of another
    2. Bmaximum entropy increase from ionic interactions between the ionized amino acids in a protein.
    3. Centropy increase from the decrease in ordered water molecules forming a solvent shell around it
    4. Dsum of free energies of formation of many weak interactions between its polar amino acids and surrounding water.
    5. Enone of the above
27. 27The pH of a sample of blood is 7.4, while gastric juice is pH 2.4. The blood sample has

    1. A0.189 times the [H+] as the gastric juice.
    2. B5.29 times lower [H+] than the gastric juice.
    3. C6 times lower [H+] than the gastric juice.
    4. D100,000 times lower [H+] than the gastric juice.
    5. Ea million times lower [H+] than the gastric juice.
28. 28The pH of a solution of 1 M HCl is

    1. A0
    2. B0.1
    3. C1
    4. D10
    5. E-1
29. 29The positive charge on proteins in electrospray ionization mass spectrometry is the result of

    1. Aprotons fired at the gas-phase protein molecules.
    2. Belectrons fired at the gas-phase protein molecules.
    3. Cprotonated Asp and Glu residues.
    4. Da low pH
    5. Eprotonated Arg and Lys residues.
30. 30The three-dimensional structure of macromolecules is formed and maintained primarily through noncovalent interactions. Which one of the following is not considered a noncovalent interaction?

    1. Ahydrogen-carbon bonds
    2. Bhydrogen bonds
    3. Chydrophobic interactions
    4. Dionic interactions
    5. Evan der Waals interactions
31. 31Titration of valine by a strong base, for example NaOH, reveals two pK’s. The titration reaction occurring at pK2 (pK2 = 9.62) is:

    1. A—COOH + OH- → —COO- + H2O
    2. B—COOH + —NH2 → —COO- + —NH2+
    3. C—COO- + —NH2+ → —COOH + —NH2
    4. D—NH2 + OH- → —NH- + H2O
    5. E—NH3+ + OH- → —NH2 + H2O
32. 32Which of the following is correct with respect to the amino acid composition of proteins?

    1. ALarger proteins have a more uniform distribution of amino acids than smaller proteins.
    2. BProteins contain at least one each of the 20 different standard amino acids
    3. CProteins with different functions usually differ significantly in their amino acid composition.
    4. DProteins with the same molecular weight have the same amino acid composition.
    5. EThe average molecular weight of an amino acid in a protein increases with the size of the protein.
33. 33Which of the following is not known to be involved in the process of assisted folding of proteins

    1. AChaperonins
    2. BDisulfide interchange
    3. CHeat shock proteins
    4. DPeptide bond hydrolysis
    5. EPeptide bond isomerization
34. 34Which of the following statements about aromatic amino acids is correct?

    1. AAll are strongly hydrophilic
    2. BThe major contribution to the characteristic absorption of light at 280 nm by proteins is the phenylalanine R group.
    3. COn a molar basis, tryptophan absorbs more ultraviolet light than tyrosine
    4. DThe presence of a ring structure in its R group determines whether or not an amino acid is aromatic.
    5. EHistidine’s ring structure results in its being categorized as aromatic or basic, depending on pH.
35. 35Which of the following statements about buffers is true

    1. AA buffer composed of a weak acid of pKa = 5 is stronger at pH 4 than at pH 6.
    2. BAt pH values lower than the pKa, the salt concentration is higher than that of the acid.
    3. CWhen pH = pKa, the weak acid and salt concentrations in a buffer are equal.
    4. DThe pH of a buffered solution remains constant no matter how much acid or base is added to the solution.
    5. EThe strongest buffers are those composed of strong acids and strong bases.
36. 36Which of the following statements about cystine is correct?

    1. ACystine is an example of a nonstandard amino acid, derived by linking two standard amino acids.
    2. BCystine is formed by the oxidation of the carboxylic acid group on cysteine
    3. CCystine is formed through a peptide linkage between two cysteines.
    4. DCystine forms when the —CH2—SH R group is oxidized to form a —CH2—S—S—CH2— disulfide bridge between two cysteines.
    5. ETwo cystines are released when a —CH2—S—S—CH2— disulfide bridge is reduced to —CH2—SH.
37. 37Which of the following statements concerning protein domains is true?
    Select one:

    1. AThey are a form of secondary structure.
    2. BThey may retain their correct shape even when separated from the rest of the protein.
    3. CThey are examples of structural motifs.
    4. DThey consist of separate polypeptide chains (subunits).
    5. EThey have been found only in prokaryotic proteins.
38. 38Which of the following statements concerning the process of spontaneous folding of proteins is false?

    1. AIt may be an essentially random process.
    2. BIt may be defective in some human diseases.
    3. CIt may involve a gradually decreasing range of conformational species
    4. DIt may involve initial formation of a highly compact state.
    5. EIt may involve initial formation of local secondary structure.
39. 39Which of the following statements is false?

    1. ADisulfide linkages are important for keratin structure.
    2. BGly residues are particularly abundant in collagen.
    3. CCollagen is a protein in which the polypeptides are mainly in the α-helix conformation
    4. DSilk fibroin is a protein in which the polypeptide is almost entirely in the β-helix conformation.
    5. Eα-keratin is a protein in which the polypeptides are mainly in the α-helix conformation.

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Quiz sobre Biochem exam 1, criado por Ashley Flick em 25-09-2016.

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Ashley Flick

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