Question

Question 8: Differentiate between the followings: (a) Repetitive DNA and Satellite DNA (b) mRNA and tRNA (c) Template strand and Coding strand

Class 12 - Biology - Molecular Basis of Inheritance Page 125

Answer 1

1.REPETITIVE DNA:
In some specific regions in a DNA sequence,
a small stretch of DNA is repeated many
times. This is called repetitive DNA. This
DNA is separated from bulk genomic DNA as
different peaks during density gradient
centrifugation.

2.SATELLITE DNA:
During density gradient centrifugation, the
bulk DNA forms a major peak and the other
small peaks are called satellite DNA.
Depending on the base composition, length
of segment and number of repetitive units,
these may be micro-satellites and mini-satellites. These sequences do not code for
any protein, but they form a large portion of
the human genome.

3.MRNA:
It is formed by the DNA template in the
nucleus and moves to the cytoplasm within
two subunits of ribosomes. It forms about 5-
10% of the total RNA in a cell. It carries
codons which serve as a message tape to be
decoded into a protein.

4.TRNA:
It is an adapter molecule which picks up
activated amino acid from the cytoplasm
and supplies it to m-RNA in a ribosome
according to the message expressed in the
form of a codon. It is soluble RNA and
constitutes about 10-12% of the total RNA in
the cell cytoplasm.

5.CODING STRAND:
This strand has polarity 5'-3' and the sequence is the same as RNA except with thymine at the place of uracil. This strand
which does not code for anything is referred
to as the coding strand.

6.TEMPLATE STRAND:
During the process of transcription, one of
the strands which has polarity 3'-5' acts as a
template strand.