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Molecular Basis of Inheritance Test - 49

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Molecular Basis of Inheritance Test - 49
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  • Question 1
    1 / -0
    Which one of the following codons codes for the same information as UGG?
    Solution
    Triplet UGC codes for cysteine; UGA and UAG are stop codons that causes termination of protein synthesis and does not code for any amino acid; UGG codes for tryptophan. Thus, the codon that specifies same information as “UGG” is UGG itself. Correct option is D.
  • Question 2
    1 / -0
    Who discovered genetic code?
    Solution
    Correct Option: A
    Explanation:

    • The genetic code was deciphered by  Nirenberg and H.Khorana.
    • They elucidated the nature of genetic codes by using cell free systems to translate polyuracil RNA sequence. They deduced UUU type codon of amino acid phenylalanine.
  • Question 3
    1 / -0
    The bond formed between phosphate and pentose sugars of DNA is
    Solution
    DNA is a polymer of nucleotides each of which has a pentose sugar, a nitrogenous base and phosphate group. The base of a nucleotide is joined covalently (at N-1 of pyrimidines and N-9 of purines) in an N –$$\beta$$- glycosyl bond to the 1’ carbon of sugar. The phosphate is linked by a phosphodiester linkage to the 5’ carbon. Two complementary bases of two strands of DNA are paired by hydrogen bonding; adenine makes two hydrogen bonds with thymine and guanine makes three hydrogen bonds with cytosine. Two successive nucleotides of DNA are joined by phosphodiester linkage in which the 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide. Thus, phosphate and pentose sugars of DNA are joined by phosphodiester linkage; the correct answer is B.
  • Question 4
    1 / -0
    Out of 64 codons, 61 codons are for 20 types of amino acids. It is due to
    Solution
    The genetic code is universal which means that a particular codon specifies a particular amino acid in all the organisms. The mRNA codon "ACU" codes for threonine, irrespective of its source. It does not explain the presence of 61 codons for 20 amino acids. The genetic code is nonoverlapping means a base in mRNA is not shared by two different codons; if it was the case, six bases could code for four amino acids which are not true. Wobble pairing refers to loose base pairing between first base of the anticodon (5’-3’direction) and the third base of the codon on mRNA. The presence of wobble bases (inosine, I) at the first (wobble) nucleotide of an anticodon allows three different codons to be recognized by a tRNA. This is because it contains the uncommon base hypoxanthine and can pair with three different nucleotides (U, C, and A). Wobble base allows rapid dissociation of from mRNA but does not explain 61 codons for 20 amino acids. Genetic code show degeneracy which means that multiple codons specify particular amino acid; asparagine is encoded by "GAU and GAC". Degeneracy allows one amino acid to be encoded by multiple codons; thus 61 codons for 20 amino acids. The correct option is B.
  • Question 5
    1 / -0
    Which one is correctly matched with its specificity for an amino acid, start or stop in protein synthesis?
    Solution
    Codons are the nucleotide base triplets that specify a particular amino acid in proteins. The codons that do not code for any amino acid and cause termination of protein synthesis are known as stop codons. The RNA stop codons are UAG, UAA and UGA; option B is wrong. The start codon specifies the first codon of mRNA transcript that is translated by a ribosome. It codes for methionine in eukaryotes and a modified Met in prokaryotes. "AUG" is the most common start codon which makes option A wrong. The triplet UGU codes for cysteine, UAC codes for tyrosine, UCG codes for serine and UUU codes for phenylalanine. Option C is incorrect and D is correct.
  • Question 6
    1 / -0
    During transcription, holoenzyme RNA polymerase binds to DNA sequence and DNA assumes a saddle like structure at that point. The sequence is called as
    Solution
    A TATA box is a sequence of DNA that indicates where a genetic sequence can be read and decoded. It is a promoter sequence, which leads the initiation of the transcription process. The TATA box is named for its conserved DNA sequence, which is most commonly TATAAA. Many eukaryotic genes have a conserved TATA box located 25-35 base pairs before the transcription start site of a gene. The TATA box is able to define the direction of transcription and also indicates the DNA strand to be read. The TATA box is recognized by the TATA-binding protein or TBP. TBP binds the TATA box directly by folding its DNA binding domain into a semi-symmetrical saddle shape, with the DNA in between the two sides of the saddle.
    Thus, the correct answer is option B.
  • Question 7
    1 / -0
    Which of the following are termination codons?
    Solution
    Triplets UAA, UGA and UAG are stop codons that cause termination of protein synthesis and does not code for any amino acid. In option B, GUG code for valine; GCG codes for alanine and GAA codes for glutamic acid. In option C, CCU code for proline; CAA code for glutamine and CUA code for leucine. In option D, CUC, CUA and CUG code for leucine. Hence, all triplets given in option A are termination codons. 
    Thus, the correct answer is option A.
  • Question 8
    1 / -0
    Watson and Crick shared the Nobel Prize for DNA structure with
    Solution
    Watson and Crick shared the Nobel Prize with Wilkins for showing the molecular structure of DNA. Wilkins used X-ray crystallography and showed that two antiparallel polynucleotides chains of DNA are coiled around the same axis while bases are present at a right angle to the axis. Since, one complete turn of the double helix is 3.4 nm long and each of which has 10 base pairs, the distance between two consecutive base pairs 0.34 nm. Watson and Crick postulated the 3-D model of DNA using all available data. According to their model, the DNA molecule is made up of two helical DNA chains that are wound around the same axis. The hydrophilic backbones of alternating sugar and phosphate groups are present on the outside of the double helix facing the surrounding water. The nitrogenous bases, purine and pyrimidine, are stacked inside the double helix. Each nucleotide base of one strand is paired in the same plane with a base of the other strand.
  • Question 9
    1 / -0
    In the DNA molecule
    Solution
    According to Chargaff’s rule, in all cellular DNAs, regardless of the species, a number of adenosine residues is equal to the number of thymidine residues which means that A = T; and the number of guanosine residues is equal to the number of cytidine residues; G = C which makes option A incorrect. Hence, that the sum of the purine residues equals the sum of the pyrimidine residues, i.e., A + G = T + C; this means that purine to pyrimidine (A+G/T+C) or pyrimidine to purine ratio (T+C/A+G) is constant for a species; which makes option C incorrect. The same orientation of all phosphodiester linkages along the DNA chain imparts each linear nucleic acid strand a specific polarity and distinct 5’ and 3’ ends. The 5’ end lacks a nucleotide at the 5’ position thereby, having free phosphate group and the 3’ end lacks a nucleotide at the 3’ position thereby, having a free hydroxyl group. The 5’ phosphate of one strand faces 3’ hydroxyl group of other strand and that the 5’ phosphate groups of two strands are present in opposite position; two DNA strands are antiparallel, i.e., not parallel; option D is incorrect and B is correct.
    Thus, the correct answer is option B.
  • Question 10
    1 / -0
    The one aspect, which is not a salient feature of genetic code, is its being
    Solution
    Genetic code is specific and this character is maintained by first two bases of codons; the first two bases make strong bonding with corresponding tRNA and determines the coding specificity. An amino acid encoded by several different codons and the codons differ in either of the first two bases, each codon requires different tRNAs. Genetic code is universal which means that a particular codon specify a particular amino acid in all the organisms. The mRNA codon "ACU" codes for threonine, irrespective of its source. Genetic code show degeneracy which means that multiple codon specifies particular amino acid; asparagine is encoded by "GAU and GAC". Genetic code is unambiguous, and not ambiguous, which means that one codon for one amino acid only; GAA codes for glutamine only. Correct answer is A.
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