Biochemistry practice Questions part 1
1. Prokaryotic cells, but not eukaryotic cells, have:
(a) endoplasmic reticulum. (b) histones.(c) nucleoid. (d) a nucleus.
2. Factors responsible for a water molecule being a dipole include:
(a) the tetrahedral structure of liquid water.(b) the magnitude of the H-O-H bond angle.
(c) the ability of water to hydrogen bond to various chemical structures.
(d) the difference in bond strength between hydrogen bonds and covalent bonds.
3. Hydrogen bonds can be expected to form only between electronegative atoms such asoxygen or nitrogen and a hydrogen atom bonded to:
(a) carbon. (b) an electronegative atom.(c) hydrogen. (d) iodine.
4. The ion product of water:
(a) is independent of temperature.(b) has a numerical value of 1 × 10–14 at 25°C.
(c) is the equilibrium constant for the reaction H3O+ and OH–.
(d) requires that [H+] and [OH–] always be identical.
5. Lysosomal enzymes:
(a) are hydrolases.(b) usually operate at acidic pH.
(c) are normally isolated from their substrates by the impermeable lysosomal
membrane.
(d) All of the above are correct.
6. In a DNA double helix:
(a) the individual strands are not helical.(b) hydrogen bonds form between a purine and a pyrimidine base on the same strand.
(c) adenine on one strand is hydrogen bonded to thymine on the opposite strand.
(d) phospho diester bonds are oriented toward the interior of the helix.
7. The A helix of DNA differs from the B helix in all of the following EXCEPT:
(a) appearance of the major and minor grooves.(b) pitch of the base pairs relative to the helix axis.
(c) thickness of the helix.
(d) polarity of the strands.
8. The Z-DNA helix:
(a) has fewer base pairs per turn than the B-DNA.(b) is favored by an alternating GC sequence.
(c) tends to be found at the 3'-end of genes.
(d) is inhibited by methylation of the bases.
9. RNA:
(a) incorporates both modified and unmodified purine and pyrimidine bases during transcription.(b) does not exhibit any double-helical structure.
(c) structures exhibit base stacking and hydrogen-bonded base pairing.
(d) usually contains about 65-100 nucleotides.
10. Bent DNA:
(a) occurs only in the presence of external agents like the antitumor drugs.(b) may be a fundamental element in the interaction between DNA sequences and
proteins for such processes as transcription and site-specific recombination.
(c) occurs primarily in the presence of triple-stranded DNA.
(d) requires the presence of inverted repeats.
11. Chaperone proteins:
(a) all require ATP to exert their effect.(b) cleave incorrect disulfide bonds, allowing correct ones to subsequently form.
(c) guide the folding of polypeptide chains into patterns that would be thermo-
dynamically unstable without the presence of chaperones.
(d) of the hsp70 class are involved in transport of proteins across mitochondrial and endoplasmic reticulum membranes.
12. Proteins may be separated according to size by:
(a) isoelectric focusing.(b) polyacrylamide gel electrophoresis.
(c) ion-exchange chromatography
(d) molecular exclusion chromatography.
13. Changes in protein conformation can be detected rapidly by:
(a) ultraviolet absorbance spectroscopy.(b) fluorescence emission spectroscopy
(c) optical rotatory dispersion.
(d) all of above.
14. Which of the following statements about E. coli DNA polymerases is correct?
(a) All polymerases have both 3' to 5' and 5' to 3' exonuclease activity.(b) The primary role of polymerase III is in DNA repair.
(c) Polymerases I and III require both a primer and a template.
(d) Polymerase I tends to remain bound to the template until a large number of
nucleotides have been added.
15. Both strands of DNA serve as templates concurrently in:
(a) replication. (b) excision repair.(c) mismatch repair. (d) transcription-coupled repair.
16. All of the following statements about telomerase are correct EXCEPT:
(a) the RNA component acts as a template for the synthesis of a segment of DNA.(b) it adds telomeres to the 5' ends of the DNA strands.
(c) it provides a mechanism for replicating the ends of linear chromosomes in most
eukaryotes.
(d) it is a reverse transcriptase.
17. A transition mutation:
(a) occurs when a purine is substituted for a pyrimidine, or vice versa.(b) results from the insertion of one or two bases or base analogs into the DNA
chain.
(c) decreases in frequency in the presence of base analogs such as 2-amino purine.
(d) results from the substitution of one purine for another or of one pyrimidine for
another.
18. Homologous recombination:
(a) occurs only between two segments from the same DNA molecule.(b) requires that a specific DNA sequence be present.
(c) requires that one of the duplexes undergoing recombination be nicked in both strands.
(d) may result in strand exchange by branch migration.
19. Of the following are true about transpositions EXCEPT:
(a) transposons move from one location to a different one within a chromosome.(b) both the donor and target sites must be homologous.
(c) transposons have insertion sequences that are recognized by transposases.
(d) the transposon may either be excised and moved or be replicated with the
replicated piece moving.
20. All of the following are true about nucleotide excision repair EXCEPT:
(a) removal of the damaged bases occurs on only one strand of the DNA.(b) it removes thymine dimers generated by UV light.
(c) it involves the activity of an excision nuclease, which is an endonuclease.
(d) only the damaged nucleotides are removed.
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