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Molecular Basis of Inheritance Test - 27

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Molecular Basis of Inheritance Test - 27
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  • Question 1
    1 / -0
    What is not true for genetic code?
    Solution
    The genetic code is a triplet code called a codon. The information in DNA must reside in the sequence of four nucleotides that constitute the DNA: A,T,G and C.
    Certain codons contain start and stop signals to initiate and terminate translation. The initiation codon is usually AUG, which specifies methionine. In few mRNA, GUG and UUG also act as initiation codon. Out of 64 codons three do not code for any amino acid and these are referred to as stop or termination codons (UAA, UAG and UGA). There are some properties of genetic code and they are as follows: 
    1. Genetic code is unambiguous, i.e., each triplet specifies only a single amino acid. 
    2. No internal punctuation is used in the code. Thus, the code is said to be commaless. Thus once the translation of mRNA begins, the code is read in a non-contiguous fashion i.e one after the other with no breaks between them. 
    3. The code is degenerate meaning that a given amino acid can be coded by more than one triplet codon. This is the case with 18 out of 21 amino acids. These different codons that code for a single amino acid are said to be synonomous. For example, UUC and UUU are synonomous codons for phenylalanine. The code is non overlapping. After translation commences, any single ribonucleotide at a specific location within the mRNA is part of only one triplet. The genetic code is nearly universal meaning thereby that same code is used throughout all life forms. Exceptions exist though. For example, UAG is a stop codon in some species while in others it may code for pyrrolysine.
  • Question 2
    1 / -0
    If the distance between two consecutive base pairs is $$0.34 nm$$ and the total number of base pairs of a DNA double helix in a typical mammalian cell is $$6.6 \times 10^9 bp$$, then the length of the DNA is approximately
    Solution
    • The distance between two consecutive base pairs - 0.34$$nm$$
     and 
    • The total number of base pairs of DNA double helix in a typical mammalian cell - $$6.6 *10^9 bp$$.
    • The length of the DNA would be - Total no. of base pairs$$\, *\,$$ distance between two consecutive base pairs.
    Length - $$6.6 *10^9 \times 0.34$$ $$*10^{-9}$$
    => $$2.24m$$
    Thus, the correct answer is (B)-2.2meters.
  • Question 3
    1 / -0
    The experimental proof for semiconservative replication of DNA was first shown in a 
    Solution

    The semiconservative nature of replication of DNA was proved by Mathew Meselson and Franklin Stahl in 1985. They performed their experiment in the bacterium Escherichia coli. So, the correct answer is option D.

  • Question 4
    1 / -0
    DNA replication in bacteria occurs
    Solution
    DNA replication is the process of multiplication of genetic material. So, before reproduction i.e., fission, genetic material increases its number and hence distributes equally in both the daughter cells.
  • Question 5
    1 / -0
    During DNA replication, Okazaki fragments are used to elongate.
    Solution

    A.Correct option

    B.Explanation for correct option:

    • The process in which the DNA is replicated and two copies are synthesized is called DNA replication. It involves the formation of a replication fork.
    • The two strands of the DNA helix separate and the new strands are formed on the original strands, known as the template strands.
    • The strand which is synthesized in 3'-5' direction is the leading strand and the strand which is synthesized in the opposite direction is the lagging strand which contains the Okazaki fragments.
    • This strand is synthesized away from the replication fork.

  • Question 6
    1 / -0
    DNA-dependent RNA polymerase catalyze transcription on one strand of the DNA which is called the
    Solution
    The template DNA strand serve in RNA synthesis during transcription is called anticoding or antisense strand while the other strand is called coding or sense strand as its base sequence is same as that of newly synthesized mRNA. 
    Therefore, the correct answer is option C.
  • Question 7
    1 / -0
    Which codon gives signal for the start of polypeptide (protein) chain synthesis?
    Solution
    The codon that gives signal for the start of polypeptide (protein) chain synthesis is AUG. The synthesis of proteins from RNA is known as translation. Translation occurs in the cytoplasm, where the ribosomes are located. Ribosomes are made of a small and large subunit that surround the mRNA. In translation, messenger RNA (mRNA) is decoded to produce a specific polypeptide according to the rules specified by the trinucleotide genetic code. This uses an mRNA sequence as a template to guide the synthesis of a chain of amino acids that form a protein. Translation proceeds in four phases: activation, initiation, elongation, and termination.
  • Question 8
    1 / -0
    Which one of the following pairs is correctly matched with regard to the codon and the amino acid coded by it?
    Solution
    A codon is a sequence of three adjacent nucleotides constituting the genetic code that determines the insertion of a specific amino acid in a polypeptide chain during protein synthesis. Lysine is coded by AAA, Valine is codded by GUC, GUA, GUU and GUG, Cysteine is coded by UGU and UGC whereas Alanine is coded by CGU, GCC, GCA and GCG. Thus, the correct answer is option B.
  • Question 9
    1 / -0
    What is the total number of nitrogenous bases in human genome estimated?
    Solution
    • The human genome project was a mega-project whose aim was to sequence the human genome with the help of bioinformatics. 
    • With the help of this project, we estimated that the human genome has 3.1 billion nitrogenous bases in its DNA. 
    • The nitrogenous bases are adenine, thymine, guanine, and cytosine. 

    Thus, the correct answer is option D.
  • Question 10
    1 / -0
    What is the function of a non-sense codon?
    Solution
    • The function of non-sense codons is to terminate the message of a gene controlled protein synthesis. The three stop codons have been given names - UAG is amber, UGA is opal, and UAA is ochre.
    • Stop codons are also called "termination" or "nonsense" codons. They signal the release of the nascent polypeptide from the ribosome because there is no cognate tRNA that has anticodons complementary to these stop signals, and so a release factor binds to the ribosome instead.

      Hence, the correct answer is C.
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