This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Genome Structure”.
1. Circular DNAs are negatively supercoiled.
Explanation: Circular DNAs extant in nature include mitochondrial, bacterial and viral DNA. These are invariably negatively supercoiled i.e. underwound. An underwound DNA has greater number of basepairs per turn of the helix.
2. Etoposide and doxorubicin, the drugs used in Cancer treatment target the enzyme ___________
a) topoisomerase I
b) topoisomerase II
Explanation: Both these drugs are target DNA in Cancer cells. They bind to topoisomerase II enzyme which prevents the DNA stands from re-ligating and thus causes it to break.
3. The three-dimensional structure of DNA can be described by _________
a) Vacuum filtration
b) X-ray crystallography
c) Gel electrophoresis
d) Mass spectroscopy
Explanation: DNA is a macromolecular formed by the assembly of a large number of atoms. The three-dimensional structure of a DNA can be described by X-Ray diffraction technique.
4. The haploid set of human chromosomes consist of __________ chromosomes
Explanation: The human genome is essentially equivalent to all the genetic information contained in the haploid set of chromosomes, which contains 23 chromosomes.
5. The process of DNA melting can be monitored by a change in ___________
Explanation: DNA melting is the process where DNA is dissolved in saline solution and the temperature is increased to initiate the process of separation. When DNA separates into its component strands, the absorbance of dissolved DNA increases and this serves as a parameter for monitoring the process.
6. The temperature at which the shift in absorbance is half completed is termed as ___________
a) melting temperature
b) denaturation temperature
c) shifting temperature
d) absorbance temperature
Explanation: When the DNA separates into two of its constituent strands. The hydrophobic interactions that result from base stacking are greatly reduced, which changes the electronic nature of the bases and increases their absorbance of ultraviolet radiation. The temperature at which the shift in absorbance is half completed is termed as the melting temperature Tm.
7. Higher the concentration of GC content, lower the Tm.
Explanation: There are three hydrogen bonds between GC pairs and two between the AT pairs. The extra hydrogen bond present leads to increase stability and an overall increase in Tm when the GC (%G + %C) content is higher.
8. DNA renaturation was first realized in the year ___________
Explanation: In the year 1960 Julius Marmur and co-workers at the Harvard University found that slowly cooling the solution of bacterial DNA that had been thermally denatured, the DNA renatures and the properties of a double helix are restored.
9. Reannealing or renaturation of the DNA is the basis of the technique ___________
a) paper chromatography
b) ultraviolet spectroscopy
c) nucleic acid hybridization
d) gel electrophoresis
Explanation: Reannealing is the process of restoration of DNA helical structure after they have been denatured. This characteristic of the genetic material forms the basis of nucleic acid hybdridization.
10. For three different samples of DNA with same concentration, the rate of annealing will depend on __________
d) genome size
Explanation: The rate of annealing will depend upon the size of genome. Smaller the genome, greater will be the rate of annealing.
11. Percentage of highly repeated DNA sequences in a genome is __________
a) 1-10 %
Explanation: The highly repeated fraction consists of sequences that are present in at least 105 copies per genome. Such sequences make up about 1 to 10% of the total DNA.
12. Which of the following type of DNA sequences for the basis of DNA fingerprinting?
a) Satellite DNA
b) Minisatellite DNA
c) Microsatellite DNA
d) Tandem sequences
Explanation: Minisatellite DNA range from 10 to 100 base pairs in length and are found in clusters containing 3000 repeats. Because of unequal crossing over, these sequences are highly unstable and polymorphic. Because the minisatellite DNA can vary from person to person, it forms the basis of technique used for criminal or paternity cases, DNA fingerprinting.
13. Which type of DNA have been used to analyze relationship between different human populations?
a) Circular DNA
b) Mitochondrial DNA
c) Minisatellite DNA
d) Microsatellite DNA
Explanation: Also called short tandem repeats, Microsatellites are short repeats of 2-6 bp of DNA that are present throughout the genome and have variability among populations. They are therefore used in DNA fingerprinting.
14. In situ hybridization was aimed at determining the location of _______
a) satellite DNA
Explanation: In 1969 Mary Lou Pardue and Joseph Gall of Yale University developed the technique of in situ hybridization to determine the location of satellite DNA.
15. Moderately repeated DNA sequences can vary from _______ percent of the total DNA.
Explanation: Moderately repeated DNA sequences can vary from 20 to more than 80 percent of the total DNA. They included sequences that code for known gene products like RNAs and proteins.
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