1. The most precise modern definition of a gene is a segment of genetic material that:
A) codes for one polypeptide.
B) codes for one polypeptide or
... [Show More] RNA product.
C) determines one phenotype.
D) determines one trait.
E) that codes for one protein.
B. codes for one polypeptide or RNA product
2. The DNA in a bacterial (prokaryotic) chromosome is best described as:
A) a single circular double-helical molecule.
B) a single linear double-helical molecule.
C) a single linear single-stranded molecule.
D) multiple linear double-helical molecules.
E) multiple linear single-stranded molecules
A. a single circular double-helical molecule
3. Bacterial plasmids:
A) are always covalently joined to the bacterial chromosome.
B) are composed of RNA.
C) are never circular.
D) cannot replicate when cells divide.
E) often encode proteins not normally essential to the bacterium's survival.
E. often encode proteins not normally essential to the bacterium's survival
4. Which of these statements about nucleic acids is false?
A) Mitochondria and chloroplasts contain DNA.
B) Plasmids are genes that encode plasma proteins in mammals.
C) The chromosome of E. coli is a closed-circular, double-helical DNA.
D) The DNA of viruses is usually much longer than the viral particle itself.
E) The genome of many plant viruses is RNA.
B. plasmids are genes that encode plasma proteins in mammals
5. Functional DNA is not found in:
A) bacterial nucleoids.
B) chloroplasts.
C) lysosomes.
D) mitochondria.
E) nuclei.
C. lysosomes
6. The DNA in a eukaryotic chromosome is best described as:
A) a single circular double-helical molecule.
B) a single linear double-helical molecule.
C) a single linear single-stranded molecule.
D) multiple linear double-helical molecules.
E) multiple linear single-stranded molecules
B. a single linear double-helical molecule
7. Introns:
A) are frequently present in prokaryotic genes but are rare in eukaryotic genes.
B) are spliced out before transcription.
C) are translated but not transcribed.
D) can occur many times within a single gene.
E) encode unusual amino acids in proteins.
D. can occur many times within a single gene
8. Approximately what fraction of the human genome is transposable elements?
A) 1.5%
B) 5%
C) 10%
D) 45%
E) 80%
D. 45%
9. The chromosomal region that is the point of attachment of the mitotic spindle is the:
A) centromere.
B) endomere.
C) exon.
D) intron.
E) telomere.
A. centromere
10. DNA in a closed-circular, double-stranded molecule with no net bending of the DNA axis on itself is:
A) a left-handed helix.
B) a mixed right- and left-handed helix.
C) relaxed.
D) supercoiled.
E) underwound.
C. relaxed
11. It is correct to say that DNA supercoiling cannot:
A) be induced by strand separation.
B) be induced by underwinding of the double helix.
C) form if there is Z-DNA structure present.
D) occur if a closed circular double-stranded DNA molecule has a nick.
E) result in compaction of the DNA structure.
D. occur if a closed circular double-stranded DNA molecule has a nick
12. The linking number (Lk) of a closed-circular, double-stranded DNA molecule is changed by:
A) breaking a strand, then rejoining it.
B) breaking a strand, unwinding or rewinding the DNA, then rejoining it.
C) breaking all hydrogen bonds in the DNA.
D) supercoiling without the breaking of any phosphodiester bonds.
E) underwinding without the breaking of any phosphodiester bonds.
B. breaking a strand, unwinding or rewinding the DNA, then rejoining it
13. For a closed-circular DNA molecule of 10,000 base pairs in the fully relaxed form, the linking number (Lk) is about:
A) 10,000.
B) 950.
C) 100.
D) 9.5.
E) 2.
B. 950
14. If the structure of a fully relaxed, closed-circular DNA molecule is changed so that the specific linking difference () is -0.05, the number of:
A) bases is decreased by 5%.
B) bases is increased by 5%.
C) helical turns is decreased by 5%.
D) helical turns is increased by 5%.
E) helical turns is unchanged.
C. helical turns is decreased by 5%
15. Topoisomerases can:
A) change the linking number (Lk) of a DNA molecule.
B) change the number of base pairs in a DNA molecule.
C) change the number of nucleotides in a DNA molecule.
D) convert D isomers of nucleotides to L isomers.
E) interconvert DNA and RNA.
A. change the linking number (Lk) of a DNA molecule
16. Topoisomerases:
A) can change the linking number in increments of 1 or 2.
B) can act on single-stranded DNA circles.
C) change the degree of supercoiling of a DNA molecule but not its linking number of DNA.
D) occur in bacteria, but not in eukaryotes.
E) always require energy from ATP.
A. can change the linking number in increments of 1 or 2
17. A commonality between type I and type II topoisomerases is that they both:
A) change the linking number in increments of 1 or 2.
B) require ATP.
C) go through a mechanism using a covalent enzyme-substrate intermediate.
D) are inhibited by quinoline antibiotics.
E) All of the above
C. go through a mechanism using a covalent enzyme-substrate intermediate
18. Plectonemic supercoils in a negatively supercoiled DNA molecule:
A) are always left-handed.
B) are always right-handed.
C) are balanced by solenoidal supercoils
D) can be either right- or left-handed.
E) never occur.
B. are always right-handed
19. Histones are _______ that are usually associated with _________.
A) acidic proteins; DNA
B) acidic proteins; RNA
C) basic proteins; DNA
D) basic proteins; RNA
E) coenzymes derived from histidine; enzymes
C. basic proteins; DNA
20. Which of the following does not contribute to the octameric histone core?
A) H1
B) H2A
C) H2B
D) H3
E) H4
C. H2B
21. The fundamental repeating unit of organization in a eukaryotic chromosome is the:
A) centrosome.
B) lysosome.
C) microsome.
D) nucleosome.
E) polysome.
D. nucleosome
22. Which of the following contributes to the structure of nucleosomes?
A) Plectonemic supercoiled DNA
B) Relaxed closed-circular DNA
C) Solenoidal supercoiled DNA
D) Spacer DNA
E) Z (left-handed) DNA
C. solenoidal supercoiled DNA
23. Nucleosomes:
A) are important features of chromosome organization in eukaryotes and bacteria.
B) are composed of proteins rich in acidic amino acids, such as Asp and Glu.
C) are composed of protein and RNA.
D) bind DNA and alter its supercoiling.
E) occur in chromatin at irregular intervals along the DNA molecule.
D. bind DNA and alter its supercoiling
24. A condensed eukaryotic chromosome is known to be associated with all of the following proteins, except for:
A) core histones H2A, H2B, H3, and H4.
B) histone H1.
C) SMC proteins.
D) topoisomerase I.
E) topoisomerase II
D. topoisomerase I
25. The SMC proteins (for structural maintenance of chromosomes) include cohesins and condensins, and are known to have all of the following properties except:
A) a complete ATP binding site.
B) a hinge region.
C) topoisomerase activity to produce positive supercoils.
D) the ability to condense DNA.
E) two coiled-coil domains.
C. topoisomerase activity to produce positive supercoils
26. Bacterial chromosomes:
A) are highly compacted into structures called nucleoids.
B) are seen in electron microscopy as "beads on a string."
C) are surrounded by a nuclear membrane.
D) contain large numbers of nucleosomes.
E) when fully extended are as long as the bacterial cell.
A. are highly compacted into structures called nucleoids
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