 |
| Fig: DNA |
Nucleic acid are present mainly within the nucleus in every living cell. These are complex molecules having very high molecular weight. These are two distinct types of nucleic acid which is called DNA or deoxy ribonucleic acid which is exclusively found in the nucleus. The other is ribonucleic acid or RNA. Some RNA is also found in nucleus but most of them are present in cell cytoplasm
Salient features of DNA and RNA:-
Except
in mitochondrial DNA occurs mainly within the nucleus. It is usually double
stranded except some viral DNA with single stranded DNA is found. It consists
of two polynucleotide chains where the sugar and phosphate group form the
backbone and the nitrogenous bases project inside the helix. Generally it
contains a large number of nucleaotides up to 4.5 million and the pentose sugar
is deoxyribose. The two polynucleotide chains have anti-parallel polarity i.e.
if one strand has 5′ → 3′ polarity, the other strand has 3′ → 5′ polarity.
The bases on the opposite strands are connected through hydrogen bonds
forming base pairs (bp). These nitrogenous based are Adenine, Guanine, Thymine
& Cytosine. Adenine always forms two hydrogen bonds with thymine from the
opposite strand and vice-versa. Guanine forms three hydrogen bonds with
cytosine from the opposite strand and vice-versa. Therefore, a purine always
pairs with a pyrimidine on the other strand, giving rise to a uniform distance
between the two strands of the helix. The helix is stable because of the base
pairs that stack over one another and hydrogen bonds that hold the bases
together.
On replication, DNA forms daughter DNA and transcription it from RNA.
The genetic messages are usually encoded in DNA and except in some viruses it
is the main genetic material of all organism.
 |
| Fig: RNA |
Click this link for Molecular Biology other notes: Click Here
Salient Feature of RNA:-
it is present mainly within the cytoplasm. mRNA is also found in
nucleus .RNA molecules are mainly single-stranded some viral mRNA may have told
to give its clover leaf like appearance. The RNA consist fewer nucleotides upto
12000. Generally in RNA, the pentose sugar is ribose. The nitrogenous bases are
some with DNA except that thymine is replace by uracil. There are generally
three types of RNA ie. messenger RNA, ribosomal RNA and transfer RNA. The RNA
does not replicate. It synthesize from DNA. It is the genetic material in some
viruses and it takes part in protein synthesis and the specific messages for
protein synthesis is usually encoded in RNA
*Additional Point: The two strands coil in
a right-handed fashion. Each turn of the helix is 3.4nm (or 34 Angstrom units)
consisting of 10 nucleotides. These nucleotides are at a distance of 0.34nm (or
3.4 Angstrom units).
