All Free Biology MCQs with Answers

• A. Synthesis of complementary DNA and RNA using reverse transcriptase
• B. Silencing of specific mRNA due to complementary RNA
• C. Interference of RNA in the synthesis of DNA
• D. Synthesis of mRNA from DNA

Explanation: RNA interference (RNAi) is the phenomenon of inhibiting the activity of a gene through the production of both sense and antisense RNA. RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves specific mRNA silencing. It is due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA causing its silencing.

• A. Adenovirus
• B. Cosmid
• C. Ri plasmid
• D. Ti plasmid

Explanation: Gene therapy is a corrective therapy that is given to patients with diseases caused by some gene defects. Here, genes are inserted into a person's cells and tissues to treat the disease by replacing the defective gene. The normal gene delivered into the individual or embryo takes over the function and compensates for the normal gene. Viral vectors like adenovirus are generally used to deliver the normal gene.

• A. 'Flavr Savr' tomato
• B. Canolla
• C. Golden rice
• D. Bt­-Brinjal

Explanation: Golden rice is a transgenic variety of rice (Oryza sativa) that contains good quantities of B-carotene (provitamin A-inactive state of vitamin A). B-carotene is a principal source of vitamin A. The grains of this rice are yellow in color due to B­-carotene and are commonly called golden rice.

• A. The relative proportions of purines and pyrimidines in DNA
• B. The relative difference in the DNA occurrence in blood, skin, and saliva
• C. The relative amount of DNA in the ridges and grooves of the fingerprints
• D. Satellite DNA occurring as highly repeated, short DNA segments

Explanation: DNA fingerprinting is a technique of determining nucleotide sequences of certain areas of DNA which are unique to each individual. The difference of about 0.1% or 3 × 106 base pairs (out of 3 × 10 9 bp) provides individuality to each human being. The human genome possesses numerous small noncoding but inheritable sequences of bases that are repeated many times. These sequences occur near telomere, centromeres, Y chromosome, and heterochromatic area. The area with the same sequence of bases repeated several times is called repetitive DNA. It is separated as a satellite from the bulk DNA during density gradient centrifugation and hence called satellite DNA where repetition of the bases is in tandem. Satellite DNAs show polymorphism (the occurrence of mutations in a population at high frequency), which is the basis of genetic mapping of human genome as well as DNA fingerprinting. While mutations in genes produce alleles with different expressions, mutations in noncoding repetitive DNA have no immediate impact. These mutations which have piled up with time form the basis of polymorphism.

• A. Diabetes mellitus
• B. Chicken pox
• C. Rheumatoid arthritis
• D. Adenosine deaminase deficiency.

Explanation: Gene therapy is a collection of methods that allows the correction of a gene defect that has been diagnosed in a child/embryo. Here genes are inserted into a person's cells and tissues to treat a disease. Correction of a genetic defect involves the delivery of a normal gene into the individual or embryo to take over the function of and compensate for the non­functional gene. The first clinical gene therapy was given in 1990 to a 4- year old girl with adenosine deaminase (ADA) deficiency. This enzyme is very important for the immune system to function. SCID is caused due to defect in the gene for the enzyme adenosine deaminase. In some children, ADA deficiency can be cured by bone marrow transplantation. Here, the isolated gene from bone marrow cells producing ADA is introduced into cells at early embryonic stages; it can be a permanent cure.

• A. Nematodes
• B. Fungi
• C. Viruses
• D. Insects

Explanation: Many nematodes live in plants and animals including human beings. A nematode Meloidogyne incognita infests the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infection that was based on the process of RNA interference (RNAi). RNA interference (RNAi) is the phenomenon of inhibiting the activity of a gene by the synthesis of RNA molecules complementary to the mRNA. The normal (in vivo synthesized) mRNA of a gene is said to be "sense" because it carries the codons that are "read" during translation. Normally, the complement to the mRNA "sense" strand will not contain a sequence of codons that can be translated to produce a functional protein; thus, this complementary strand is called "anti-­sense RNA". The anti­-sense RNA and mRNA molecules will anneal to form duplex RNA molecules (or double-stranded RNA) and the duplex RNA molecules can not be translated. Thus, the presence of anti­sense RNA will block translation of the mRNA of the affected gene.

• A. Binds with epithelial cells in the midgut of the insect pest ultimately killing it
• B. Is coded by several genes including the gene cry
• C. Is activated by acid pH of the foregut of the insect pest
• D. Does not kill the carrier bacterium which is itself resistant to this toxin

Explanation: Soil bacterium Bacillus thuringiensis produces proteins that kill certain insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes). B. thuringiensis forms some protein crystals which contain a toxic insecticidal protein. This toxin does not kill the Bacillus (bacterium) because it exists as inactive protoxins in them. But, once an insect ingests it, it is converted into an active form of toxin due to the alkaline pH of the alimentary canal. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause swelling and lysis and finally cause the death of the insect.

• A. B and C
• B. C and D
• C. A and C
• D. A and B

Explanation: In 1997, the first transgenic cow, Rosie, produced human protein enriched milk. The milk contained the human alpha ­lactalbumin and was nutritionally a more balanced product for human babies than natural cow­milk. Isolation of DNA from other macromolecule is achieved by treating the bacterial cells/plant or animal tissue with enzymes such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus).

• A. Long fibre and resistance to aphids
• B. Medium yield, long fibre and resistance to beetle pests
• C. High yield and production of toxic protein crystals which kill dipteran pests
• D. High yield and resistance to bollworms.

Explanation: Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the cotton plant. The genetically modified crop is called Bt cotton. Bt cotton has the following useful characteristics: pest resistance, herbicide tolerance, high-yield, and resistance to bollworm infestation.

• A. Nicotine
• B. Morphine
• C. Quinine
• D. Insulin

Explanation: Insulin is now being commercially produced by genetic engineering. Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulfide bonds. Insulin, in mammals, is synthesized as a prohormone which contains an extra stretch called the C­-peptide.In 1988 an American company prepared functional insulin from two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of E.coli to produce insulin chains. In this way, chains A and B were produced separately which was extracted, combined by creating disulfide bonds to get human insulin.