11. What is What ?
What are Nucleic Acids?
They are polymers of several Nucleotide
units held together by covalently
linkage.DNA, RNA.
What are Nucleotides ?
Structural units of Nucleic acids
consisting of a Nitrogenous base +
Pentose sugar + Phosphate group.
@ Dr MBCRNAIDU
13. What is What ?
What are Nucleosides?
Nitrogenous base + Pentose sugar only.
Nucleoside = Nucleotide – Phosphate
group
Let us Know the basic Structure of
Nucleic Acids………
32. DNA DOUBLE HELIX
Right-handed helix.
Antiparallel double helix.
Base-pairs are perpendicular to the axis of
the helix.
Axis of the helix passes through the center
of the base pairs.
Each base pair is rotated by 36 degrees from
the adjacent base pair.
Base-pairs are stacked 0.34 nm apart from
one another.
Double helix repeats every 3.4 nm, i.e. the
pitch of the double helix is 3.4 nm.
33. DOUBLE HELIX STRUCTURE
The outer parts are made of sugars.
Inner parts are made of pairs of nitrogen bases
Phosphodiester linkage between the 3’ and 5’ positions
of successive sugar residues.
Double helix explains Chargraff’s rules.
Hydrogen bonding and base stacking holds the strands
together.
10 base pairs are needed to complete a single turn of the
double helix.
34. Double helix creates a
minor and a major groove
on DNA.
The two strands are
antiparallel to each other.
5’ 3’
3’ 5’
35. CHARGAFF’S BASE PAIRING
RULE
Discovered by Erwin
Chargaff (late 1940s).
Number of Purines is
equal to number of
Pyrimidines.
Two strands are always
complementary to each
other.
A always binds with T;
G always binds with C.
36. DIFFERENT FORMS OF DNA
NO A B Z
1 Shape Broadest Intermediate Narrowest
2 Screw sense RT- Handed RT- Handed LT- Handed
3 Helix
diameter
25.5 A 23.7 A 18.4 A
4 Base pairs/
turn
11 10.4 12
5 Rise per base
pair
2.3 A 3.4 A 3.8 A
6 Major groove Narrow and very
deep
Wide & quite
deep
Flat
7 Minor groove Very broad &
shallow
Narrow and
quite deep
Very narrow and
deep
37. RNA
Messenger RNA codes template for
protein synthesis;
Ribosomal RNA constitute the catalytic
core of the ribosome.
Transfer RNA is the adaptor between
nucleic acids and proteins.
Small nuclear RNA are essential
component of splicesome.
microRNA regulates gene expression.
RNA is single stranded but it can fold
back upon itself to form secondary
structure.
38. Messenger RNA [mRNA]
- the template
Ribosomal RNA [rRNA]
- structural component of the
ribosome
Transfer RNA [tRNA]
- the adapter
RNA INVOLVED IN PROTEIN
SYNTHESIS
39. mRNA
Comprises about 5% of the RNA
in cell.
Most heterogeneous class of
RNA in terms of size and
stability.
Eukaryotic mRNA have unique
chemical characteristics such as
5’- capping and 3’- poly a tail.
Transfers genetic information
from the nucleus to the
cytoplasm.
Acts as template for protein
synthesis.
40. tRNA
Comprise about 15% of the RNA in cell.
At least one specific tRNA molecule for
each of the 20 amino acids.
Acceptor arm : consist of base paired stem
terminating in sequence CCA“ site of amino
acid attachment ”
Anticodon arm : Recognizes the triplet
nucleotide or codon of the template mRNA.
The nucleotide sequence complimentary to
the codon and is responsible for the
specificity of tRNA.
D- arm : presence of the base
dihydrouridine.
TUC- arm : presence of sequence thymine,
pseudouridine, and cytosine.
Extra arm : Most variable feature of
tRNA.
41. rRNA
Around 80 % of RNA in the cell is of Rrna.
rRNA is found in association with a
number of different proteins as
components of the ribosome.
In prokaryotes and eukaryotic
mitochondria 3 distinct speceies of rRNA
exist : 23S, 16S, 5S.
In eukaryotes 4 rRNA exist : 28S, 18S,
5.8S, & 5S
All rRNA molecules except 5S are
processed from a single 46S precursor
rRNA molecule. The 5S rRNA has its own
precursor that is independently transcribed.
FUNCTIONS: Necessary for ribosomal
assembly, binding of mRNA to ribosomes
and its translation.
