DNA & RNA for MBBS course

1. DNA & RNA
Dr. Farhana Atia
Assistant Professor
Department of Biochemistry
Nilphamari Medical College, Nilphamari
Email: farhana.atia@gmail.com

2. Traits DNA RNA
Denote Deoxyribonucleic acid Ribonucleic acid
Location Nucleus & mitochondria Nucleus & cytoplasm
Pentose
sugar
Deoxyribose sugar Ribose sugar
Base AGCT AGUC
Double stranded
deoxyribosephosphate
backbone
Strands are antiparallel
Single strand
No backbone
Complementary base No

3. DNA RNA
Can not be hydrolyzed due to
absence of 2’ hydroxyl group
Can be hydrolyzed by alkali due
to presence of 2’ OH group.
Alkali liability of RNA is used in
diagnostic & analytic purpose.
Molecular size- Large Smaller
Function- Chemical basis of
heredity & fundamental unit of
genetic information.
Protein synthesis.

4. FUNCTIONS OF DNA
Chemical basis of heredity & fundamental unit of
genetic information.
Genetic information stored in nucleotide sequence
of DNA serve two purpose
Source of information for synthesis of all protein
molecule of cells & organism. DNA molecule
serve as a template for transcription of
information of RNA.
Provide information inherit by daughter cell/
offspring. Replicate information into daughter
DNA molecule.

5. Watson & Crick Model of DNA
Structure
Introduction:
DNA is a poly deoxyribonucleotide that
contains many mono deoxyRNT.
Covalently linked by 3′ 5′ phosphodiester
bond.
Double stranded molecule
Two strands wind around anti-parallelly each
other forming a double helix.

6. Salient features
Right handed double helix
3′ 5′ phosphodiester bond
Base pairing rule
H bonding
Anti parallel
Other feature

7. Right handed double helix
The two strands are twisted around a central
axis in the form of right handed double helix
similar to a spiral staircase.
Right handed : as one looks down the double
helix- clockwise direction
Hand rail : Sugar & Phosphate group
Steps : Bases jutting inside
Base : perpendicular to helix axis
Sugar : Right angle to the axis

8. Right handed double helix

9. 3′, 5′- phosphodiester bond
Join the 5’ OH group
of on the d-pentose of
one nucleotide to 3’
OH group on d-
pentose of another
nucleotide through a P
bond.
Possesses a polarity;
one end has a 5’ OH
or P terminal while the
other has a 3’ OH or P
terminal.

10. Base pairing rule
The 2 strands are always complementary to
each other
A of one strand are in pair with T of
opposite strand, while G with C.
The base pairing is called Chargaff’s rule.
Chargaff’s rule : no of purine is equal to the
no of pyrimidine.
Stabilize the structure of double helix.

11. H Bonding
Strands are held
together mainly by H
bond between purine
& pyrimidine bases.
A-T : 2 H bonds
G-C : 3 H bonds,
stronger [more
resistant to melting]
Stabilize structure of
double helix.

12. Anti-parallel
The two strands run anti-parallel.
One strand runs in 5’ to 3’ direction
Another runs in 3’ to 5’ direction.
Other
Each strand act as a template for the synthesis
of opposite strand during replication process.

13. Template strand : genetic information
resides in sequence of NT of one
strand. It copied during RNA
synthesis. So called non-coding
strand.
Coding strand : Opposite strand
which matches the sequence of RNA
transcript that encode protein
[contain U instead of T]
A single turn of double helix :
10 bp [34 A]
WIDTH- 20 A

14. Denaturation of DNA
Separation
The loss of helical structure is called denaturation.
The double strand of DNA may be denatured &
separated by heat. This is called melting of DNA.
Melting temperature [Tm] is the temperature
when half of the helical structure is denatured.
Annealing : Melted structures are re-associated at
lowering of temperature.

15. Denaturation & Annealing

16. DNA
Transcription Translation
TraitRNA Protein
The “Central
Dogma” of
Genetics
RNA processing

17. RNA
Unbranched polymeric molecule composed of
mono-nucleotide joined together by
phospho-di-ester bond
Contain ribose sugar & pyrimidine base uracil
instead of deoxy-ribose & thymine in DNA
Different types of RNA differs from each other
in terms of size, function & special structural
modification

18. Classes of eukaryotic RNA
RNA Abundance Function in Function
Ribosomal
(rRNA)
80% of total Cytoplasm Structural framework for
ribosome
Machinery for protein
synthesis
Messenger
(mRNA)
2-5% of
total
Nucleus,
migrates to
ribosome in
Cytoplasm
Transfer of genetic information
from nucleus to cytoplasm or
from gene to ribosome
Transfer
(tRNA)
15% of total Cytoplasm Transfer of amino acid to
ribosome & correct sequence
insertion
Small RNAs
Small nuclear
(snRNA)
<1% of total Processing of rRNA & mRNA
Involved in gene regulation
Micro (miRNA) <1% of total Inhibition of gene expression

19. hn RNA [heterogeneous nuclear RNA]
Precursor RNA
sc RNA [small cytosolic RNA]
Selection of protein for export
Other small RNA [important role in gene
regulation]
Micro RNA [mi- RNA]
Small interfering RNA [ si RNA]

20. rRNA
Found in association of a number of
different protein as a component of
ribosome
The complex structure served as the site of
protein synthesis
Size species of RNA
Prokaryotic cell- 23s, 16s, 5s
Eukaryotic cytosol- 28s, 18s, 5.8s, 5s
Eukaryotic mitochondria- 23s, 16s, 5s

21. rRNA

22. tRNA
Smallest of 3 major species (molecular wt-4s)
Length 74-95 NTs
Allow extensive folding & intrastrand
complementarity to generate a secondary
structure
Each tRNA molecule carries a specific aa to the site
of protein synthesis
At least 1 specific type of tRNA for each of 20
amino acid that commonly found in protein
So minimum 20 RNA present in every cell

23. 4 main arm
Acceptor arm
Terminates in CCA-OH (added post-
transcriptionally)
Amino acid attached/ charged (onto 3΄OH
of A)
Anticodon arm- Recognize triplet codone of
mRNA
D arm (dihydrouracil)
TψC arm- Contain sequence of T, C,
pseudouridine

24. tRNA

25. mRNA
Most heterogenous type in terms of size (500-
6000NT) & base sequence
Carry genetic information from DNA to cytosol
where it used as a template for protein synthesis
PolyA tail: a long sequence of adenine nucleotide
of 3΄ end of RNA chain
A cap on 5΄end consists 7-methyl guanosine
attached backward (5΄- 5΄) to a tri-phosphate
linkage

26. mRNA