Molecular Basis of Inheritance
Short Questions With Answers
One mark questions with answers
1. Termination codon is
Answer: (c) UAG
2. Anticodon occurs over
Answer: (a) tRNA
3. A substance not directly synthesized from DNA is
Answer: (a) protein
4. The gene which synthesizes repressor is
(a) operator gene
(b) regulator gene
(c) promoter gene
(d) structural gene
Answer: (b) regulator gene
5. First codon discovered by Nirenberg and Matthei is
Answer: (c) UUU
6. Enzyme that joins Okazaki fragments is
(a) DNA polymerase 1
(b) DNA polymerase III
Answer: (c) Ligase
7. Nucleotides base present in RNA but not in DNA is
Answer: (b) U
8. Number of structural genes in tryptophan operon is
Answer: (a) 5
9. Which one causes cancer?
(a) activation of oncogenes
(b) inactivation of tumor suppressor genes
(d) both a and b
Answer: (d) both a and b
10. Central dogma of molecular biology was proposed by
(b) Beadle and Tatum
(c) Watson and Crick
Answer: (d) Crick
11. RNA which functions as adaptor molecule for amino acid is
Answer: (d) tRNA
12. RNA codon for DNA codon ATG will be
Answer: (b) UTG
13. Reverse transcription was discovered by
(c) Sharp and Roberts
(d) Temin and Baltimore
Answer: (d) Temin and Baltimore
14. Segments of DNA which can shift positions are
Answer: (b) transposons
15. Khorana was awarded Nobel Prize for
(a) discovering DNA
(b) discovering RNA
(c) chemical synthesis of gene
(d) discovering DNA polymerase
Answer: (c) chemical synthesis of gene
Two marks questions with answers
1. What are tRNAs?
Answer: They are transfer or soluble RNAs which pick up particular amino acids and take the same to mRNA over particular codons corresponding to their anticodons. A tRNA can pick up only specific amino acids though an amino acid can be specified by tourist 2-6 tRNAs. Each tRNA has an area for coming in contact with ribosome and the enzyme aminoacyl tRNA synthetase.
2. Differentiate between mRNA and tRNA.
Answer: mRNA is large sized RNA whereas tRNA is small sized RNA. mRNA carries coded information whereas tRNA carries information for association with amino acid and an anticodon for its incorporation in a polypeptide. mRNA has a cap and a tail whereas tRNA possesses 3-4 loops and a limb with distant 5′ and 3′ ends.
3. Differentiate between the template strand and coding strand.
Answer: Template strand is strand of DNA which takes part in transcription whereas coding strand does not take part in transcription. The polarity is 3′ to 5′ end in case of template strand whereas in case of coding strand the polarity 5′-3 In template strand nucleotide sequence is complementary to one present in mRNA. In case of coding strand the nucleotides sequence is the same to the one present in mRNA except for presence of thymine instead of uracil.
4. Enlist two essential roles of ribosome during translation.
Answer: (a) It provides sites for attachment of mRNA and charged tRNAs for polypeptide synthesis.
(b) one of its rRNA (23S in prokaryotes) functions as peptidyl transferase ribozyme for formation of peptide bonds.
5. State any one reason to explain why RNA viruses mutate and evolve faster than other viruses.
Answer: RNA is an unstable and highly reactive molecule due to its being single stranded and exposure of its nitrogen bases. DNA is stable as its nitrogen bases are not exposed because of its double stranded nature. Therefore, RNA viruses mutate and evolve faster as compared to DNA viruses.
Three marks questions with answers
1. Explain the function of promoter, tRNA, exons.
Answer: Promoter is a change that lies near the operator which functions as binding site for RNA polymerase from where the polymerase moves over the structural gene if allowed by the operator.
tRNA functions as an adaptor molecule that picks up a particular amino acid from cellular pool and takes the same over A site mRNA for incorporation into polypeptide.
Exons are coding segments present in the primary transcript which on splicing by snRNPs get joined to form functional mRNA.
2. Why is human genome project called a mega project?
Answer: Human genome project is called mega project because it involves
(a) identification of all the genes present in human genome.
(b) identification of all the alleles of genes and their functions.
(c) huge investment
(d) Storage of data which for sequencing alone would require storage space equal to 3300 books of one thousand pages each if each page contains thousand letters.
(e) the coordinating working of several scientist from many countries for several years with first phase taking nearly 10 years.
3. Mention the application of DNA fingerprinting.
Answer: (1). DNA sequencing (fingerprinting) helps in determining the paternity of a child. The claims of being a father or mother of child can be verified.
(2). The identity of a criminal, like rapist, murderer, etc., can be established. The only material needed is a small DNA sample from blood stains, semen, urine, hairs, saliva, perspiration, etc., even if these are several years old.
(3). It can also be used to determine whether two persons are closely related.
(4). DNA sequences can also unravel the course of biological evolution by establishing relationship between different races.
(5). DNA in analysis also helps in diagnosis of inherited human diseases.
(6). By matching DNA of different persons, their relationships can be ascertained. Many aspiring migrants claim their blood relationship with a person residing in a particular country. The DNA of hopeful migrant is matched with the DNA of person, who is already an established resident of that country whom he or she claims to be a close or blood relative.
4. Briefly describe polymorphism.
Answer: Genetic polymorphism is the occurrence of more than one form of genetic material. It is of three types; allelic, SNP and RFLP.
Allelic polymorphism is an occurrence of multiple alleles of a gene. An allele is considered as a member of polymorphism if it is found at a frequency of more than one percent of population. Alleles possess different mutations which alter the structure and function of protein formed by them. It results in changes of phenotype. However, phenotypic variants are not always produced. Even in wild-type gene, an extensive polymorphism may occur due to differences in nucleotides which do not produce any visible effect.
Single nucleotide polymorphism would be useful in locating specific alleles, disease associated sequences and tracing human history.
Restriction fragment length polymorphism- Differences appear in the restriction maps of individuals. As a result different size fragments are formed by cleavage with the same restriction enzyme. Most of RFLPs have no effect on phenotypes because the commonly lie between the genes. A few would produce changes as they or parts of the genes.
5. What is DNA fingerprinting?
Answer: DNA fingerprinting also termed as DNA profiling, is a method of isolating and identifying variable elements within the base pair sequence of DNA. It is useful in identifying individuals particularly in forensic sciences. It is helpful in establishing a link between biological evidence and a suspect.
The technique for DNA fingerprinting involves a process termed as Southern blotting. The credit goes to E.M. Southern for its discovery. A very small sample of DNA is sufficient for the test. The sample includes blood, semen, urine, hair follicles, etc.