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131.

The base sequence in one of the strands of DNA is TAGCATGAT.

(i) Give the base sequence of its complementary strand.

(ii) How are these base pairs held together in a DNA molecule?

(iii) Explain the base complementarity rules. Name the scientist who framed this rule.

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132.

What is a cistron?

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Translation is the process of polymerising amino acid to form a polypeptide chain.

The triplet sequence of base pairs in mRNA defines the order and sequence of amino acids in a polypeptide chain.

The process of translation involves the following three steps:

(i) Initiation

(ii) Elongation

(iii) Termination

During the initiation of the translation, tRNA gets charged when the amino acid binds to it using ATP.
The start (initiation) codon (AUG) present on mRNA is recognised only by the charged tRNA.
The ribosome acts as an actual site for the process of translation and contains two separate sites in a large subunit for the attachment of subsequent amino acids.
The small subunit of ribosome binds to mRNA at the start codon (AUG) followed by the large subunit. Then, it initiates the process of translation.
During the elongation process, the ribosome moves one codon downstream along with mRNA so as to leave the space for binding of another charged tRNA.
The amino acid brought by tRNA gets linked with the previous amino acid through a peptide bond and this process continues to result in the formation of a polypeptide chain.
When the ribosome reaches one or more stop codon (VAA, UAG and UGA), the process of translation gets terminated.
The polypeptide chain is released and the ribosomes get detached from mRNA.

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