All Free Biology MCQs with Answers

• A. Bacterial artificial chromosome
• B. Yeast artificial chromosome
• C. Plasmid
• D. Cosmid

Explanation: Plasmids have been modified to be used as vectors. They can clone DNA fragments of about 10 kbp size while cosmid can carry up to 45 kbp. Yeast artificial chromosome can carry up to 1000-­2500 kbp. Bacterial artificial chromosome can carry around 300 - 350 kbp long DNA fragments. A kilobase pair (kbp) is a unit of length of nucleic acids, equal to 1000 base pairs

• A. T­-DNA
• B. Bacterial artificial chromosome & Yeast artificial chromosome
• C. Expression vectors
• D. TA cloning vectors

Explanation: Bacterial artificial chromosome (BAC) vectors are based on the natural, extra­-chromosomal plasmid of E. coli. BAC vector contains genes for replication and maintenance of the F-factor, a selectable marker and cloning site. These vectors can accommodate up to 300­-350 kb(kilo base) of foreign DNA and are also being used in genome sequencing project. Yeast artificial chromosome (YAC) vectors are used to clone DNA fragments of more than 1Mb in size. Therefore, they have been exploited extensively in mapping the large genomes, e.g., in the Human Genome Project. These vectors contain the telomeric sequence, the centromere and the autonomously replicating sequence from yeast chromosomes.

• A. Insertional inactivation of alpha galactosidase in recombinant bacteria
• B. Inactivation of glycosidase enzyme in recombinant bacteria
• C. Non-­recombinant bacteria containing beta galactosidase
• D. Insertional inactivation of alpha galactosidase in non­recombinant bacteria.

Explanation: The presence of restriction sites within the markers tet r and amp r of plasmid permits an easy selection for cells transformed with recombinant plasmid. Insertion of the DNA fragment into the plasmid makes antibiotic resistance genes nonfunctional, for example, insertion of the DNA fragment into the plasmid (pBR322) using Pst I or Pvu I makes amp r nonfunctional. Bacterial cells containing such a recombinant pBR322 will be unable to grow in the presence of ampicillin but will grow on tetracycline. This process, however, becomes burdensome because it requires simultaneous plating on two plates having different antibiotics. Thus, an alternative selectable marker is developed to differentiate recombinants and non­ recombinants on the basis of their ability to produce colour in the presence of a chromogenic substance. Here, a recombinant DNA is inserted in the coding sequence of an enzyme B­-galactosidase. pUC 18 plasmid contains this gene which allows it to produce B-galactosidase which degrades certain sugars and produces a blue pigment when exposed to a specific substrate analog. If the plasmid in the bacterium does not have an insert, i.e., is non­ recombinant, the presence of chromogenic substrate gives blue coloured colonies. Presence of insert in the plasmid in recombinant bacterium does not produce any colour, such bacterial colonies are marked as recombinant colonies.

• A. Electrophoresis
• B. Restriction mapping
• C. Centrifugation
• D. Polymerase chain reaction

Explanation: Electrophoresis is a technique used for the separation of substances of different ionic properties. Since the DNA fragments are negatively charged molecules, they can be separated by allowing them to move towards the anode. DNA fragments move towards the anode according to the size of their molecules through the pores of agarose gel. Thus, the smaller fragments move farther away as compared to larger fragments.

• A. Algae-Methylase
• B. Fungi-Chitinase
• C. Bacteria-Lysozyme
• D. Plant cells-Cellulase

Explanation: Cell wall of algae is made up of cellulose, pectin and mucilage. These substances cannot be degraded by methylase. Methylase is a type of transferase enzyme that transfers a methyl group from a donor to an acceptor.

• A. Precipitate DNA.
• B. Break open the cell to release DNA.
• C. Facilitate action of restriction enzymes.
• D. Remove proteins such as histones.

Explanation: Ethanol is much less polar than water. Adding it to the solution disrupts the screening charges exerted by water. The electrical attraction between phosphate and any positive ions (Na+) present in the solution becomes strong enough to form a stable ionic bond and DNA precipitates. Ethanol precipitation is a widely used technique to purify or concentrate nucleic acid.

• A. Original restriction enzyme
• B. Rop-­reduced osmotic pressure
• C. HindIII, EcoRI selectable markers
• D. AmpR, tetR -antibiotic resistance genes

Explanation: In pBR322, ori­-represents site or origin of replication rop­ codes for proteins take part in the replication of plasmid. Hind III, Eco RI­ -recognition sites of restriction endonucleases. amp R and tet R ­- antibiotic resistance genes.

• A. Study of enzymes
• B. Genetic transformation
• C. DNA sequencing
• D. Genetic fingerprinting

Explanation: Polymerase chain reaction (PCR) is used to amplify a small DNA fragment to obtain its large quantity. PCR is very helpful in DNA fingerprinting in such cases where the culprit has to be identified from a very small blood, semen or another cell sample from a crime scene. Restriction fragment length polymorphism(RFLP) is used to determine or confirm the source of DNA sample such as in paretnity tests or criminal investigtaions In genetic mapping to determine recombination rates that show the genetic distance between the loci. To identify a carrier of a disease-causing mutation in a family.

• A. Vector
• B. Selectable marker
• C. Plasmid
• D. Probe

Explanation: Probes are single-stranded, radiolabelled molecules of nucleic acids with known sequence. The probes having sequence complementary to the gene to be identified are supplied. They bind with the particular gene segment. Radiation imaging identifies the location of that particular segment that binds with the probe. Probes are used as an identification tool in gene sequencing.

• A. It is used to ligate introduced DNA in recipient cells.
• B. It serves as a selectable marker.
• C. It is isolated from a virus.
• D. It remains active at high temperature.

Explanation: In PCR, Taq polymerase is used which is obtained from Thermus aquaticus bacteria. It is a relatively thermostable enzyme thus used in PCR as during the process the step involving denaturation of DNA strands requires high temperature.