Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest DNA Function Lecture PPT
DNA
DNA and RNA collectively called as nucleic acid.
DNA genetic information in all species except some virus.
DNA encode protein and RNA in a cell , RNA crucial role in
transmission of genetic information in all species.
CHEMICAL COMOSITION.
DNA IS COMPLEX POLYMERS 0F MONOMERS called
Deoxyribonucleotides.
DNA- a Polymer of Deoxyribonucleotides.
Four types of Deoxyribonucleotides are found in DNA as shown
2' dAMP- 2' deoxyadenosine monophosphate.
2' d GMP- 2 'deoxyguanosine monophosphate
2' d CMP - cytidine
2' d TMP- thymidine
These deoxyribonucleotide differ in purine or pyrimidine base
attached to deoxyribose by a N-glycosidic linkage.
BASES FOUND IN DNA.
Purine-
Adenine and guanine---Fused ring of
nitrogen and carbon atom.
Pyrimidine-
cytosine and thymine? only a single ring.
DNA contain thymine pyrimidine while RNA contain
Uracil.
Structure of Pyrimidine and Purine.
Components of nucleotides.
Base.(Nitrogen base.)-A, G, C or T.
Sugar.(Pentose sugar)
Phosphate.
NUCLEOTIDE
Basic unit of nucleic acid composed of three component,
These are sugar, phosphate group, and a ring of
carbon and nitrogen atom known as a Base.
NUCLEOSIDE = Base + Sugar
NUCLEOTIDE= Nucleoside + phosphate.
A cyclic five carbon sugar(D- ribose or D 2-
deoxyribose)
A heterocyclic nitrogenous base( Purine or Pyrimidine)
Phosphoric acid or phosphate.
NUCLEOTIDE--- is monomer of DNA.
NUCLEOTIDE STRUCTURE.
PHOSPHATE
Phosphoric acid is-H3PO4.
Contain 3 monovalent hydroxyl group and a
divalent oxygen atom, all linked to the pentavalent
phosphorous atom.
PENTOSE SUGAR
DNA contain--2-deoxy-D - ribose
Pentose sugar has capacity to form ester with
phosphoric acid. OH- group of pentose , especially
3rd and 5th involved forming 3'-5 `? phosphodiester
bond between adjacent pentose residue.
NITROGENOUS BASE
PURINE and PYRIMIDINE.
BASE is linked to the sugar moiety by the same
carbon (c1) used in sugar sugar bond.
PURINE Bases--Adenine and Guanine.
PYRIMIDINE-- Uracil, Thymine and cytosine.
DNA NUCLEOTIDE.
PHOSPHODIESTER LINKAGE.
Watson-Crick Model of DNA Structure.
> Helical structure-Double stranded helix.
Polarity----5' to 3' direction strand or 3' to 5 `direction
strand.
Backbone of the strand up of alternative phosphate
and deoxyribose molecule, and lies exterior while
bases lies inside....
Two strand of DNA are placed antiparallel to each
other.
Right Handed Double Helix -
DNA consists of two
polydeoxyribonucleotide chains twisted around one
another in a right handed double helix similar to a
spiral stair case.
BASE PAIRING RULES.
Always two strand are complementary to each
other.
Adenine of one strand will pair with thymine of
opposite strand, while guanine will pair with
cytosine.
The base pairing (A with T, G with C ) is called
chargaff's rule.
Which states that number of the number of purines is
equal to the number of pyrimidines.
HYDROGEN BONDING.
The DNA strands are held together mainly by
hydrogen bonds between the purine and pyrimidine
bases.
Two hydrogen bond between A and T while there
are three hydrogen bonds between
C and G .
GC bond is stronger than AT bond.
ANTIPARALLEL.
One strand in 5' to 3' direction, while the other is in
the 3' to 5' direction.
OTHER FEATURES.
Denaturation of DNA strands-----
MELTING- Double stranded DNA may be
denatured and separated by heat.
At lower temperature the melted strand are re-
associated, this is called annealing.
Higher organisation of DNA
NUCLEOSOMES--
Double stranded DNA is wound
round histones to form nucleosomes.
CHROMATIN--Long stretch of DNA in association with
histones.
CHROMOSOMES--Chromatin further condensed to
form chromosomes.
Histones.
Protein with higher concentration of basic amino
acids.
Acetylation of histones leads to activation of
transcription.
Deacetylation of histones causes depression of
transcription.
NUCLEOSOME.
DNA is very long molecules.
Human diploid genome consists of about 7x 10'9
base pairs.
INTRONS, EXONS, CISTRONS.
EXONS-The segment of the gene coding for proteins
are called exons.(expressed regions).
INTRONS-Interspaced silent areas in the
DNA(intervening areas ). Introns are not translated.
CISTRONS- is the unit of genetic expression.
one cistron will code for one polypeptide.
Repeat sequences of DNA.
Only about 1-2 % of the human DNA contain genes,
the rest are silent areas.
About 90% of the DNA is made up of non coding
intervening sequences, called as introns.
About 30 % of the genome consists of repetitive
sequences.
DNA STRUCTURE.
STRUCTURE DNA
DNA STRUCTURE.
Two strand are held together by hydrogen bond,
hydrophobic interaction and vander wall forces.
Adenine bonds with thymine by two hydrogen bond.
Guanine bonds with cytosine by 3 hydrogen bond.
Double stranded molecule is coiled into a Right
handed helix.
DNA STRANDS VIEW.
TYPES OF DNA.
DNA FORM
PITCH-nm
Bases per turn
Major grouve
Minor grouve
A
2.46
11
Deep narrow
Broad and
shallow
B
3.32
10
Wide and
Narrow and
deep
deep
Z
4.56
12
Flat
Deep narrow
B- FORM OF DNA
Most common form...
Right handed double helix.
Pitch of length of each turn is approx 3.4 nm.
Pitch has approx 10 base pairs.
Wide major groove and narrow minor groove.
Z DNA----
zig- zag not true helical.
left handed helix and has 12 base pairs per turn.
No true major groove.
RNA
GENES, GENETIC INFORMATION, and CENTRAL DOGMA.
? DNA---
CENT
? REPLICATION.
? mRNA
RAL
? TRANSCRIPTION
? PROTEIN
DOGMA ? TRANSLATION.
POLYPEPTIDE SYNTHESIS.
m RNA.
RNA is polymer of ribonucleotides.
m-RNA : it has cap, coding region, and poly A tail.
Cap at the 5' end is a 7- methyl- guanosine triphosphate
molecule.
Ribosome recognise mRNA by its cap structure.
Leader region-leader sequence is immediately after the
cap region.
Coding region--codes for protein synthesis, contains
start(AUG) and stop (UAG) codon
Termination sequence-lies after coding sequence.
Poly A tail- present at 3' end, helps in stability of mRNA.
TYPES OF RNA
messenger RNA.
Transfer RNA.
Ribosomal RNA.
The others are =
small nuclear RNA
micro RNA.
small interferring RNA
heterogenous RNA.
Messenger RNA.
5% of RNA in cell.
Function as messengers carrying the information in a
gene to the protein synthesizing machinery.
5- terminal end is capped by 7- methyl guanosine
Triphosphate cap.
The cap is involved in the recognition of mRNA by the
translating machinery.
It stablise mRNA by protecting it from 5 exonuclease.
3- end of most m- RNA have a polymer of Adenylate
residues.
Structure of m-RNA.
m-RNA molecules are formed with the help of DNA
template during process of transcription.
The sequence of nucleotides in m ? RNA is
complementary to the sequence of nucleotide on
template DNA.
Sequence carried on m-RNA is read in the form of
codons.
Codon is made up of 3 nucleotides.
m-RNA is formed after processing of hn RNA.
hn RNA.
Is immediate product of gene transcription.
75 % hn RNA is degradeded in the nucleus , only
25% is processed to mature RNA.
Mature RNA is formed from primary transcript by
caping, tailing ,splicing, and base modification.
Transfer RNA.
Most t -RNA display a clover leaf like structure with
several arms and loops.
ACCEPTOR ARM-
Near the 3' end and terminate in CCA
sequence.
This arm carries specific amino acid.
Structure of t- RNA.
t- RNA.
ANTI CODON ARM --
Anticodon arm reads the
nucleotide on mRNA ---CODON.
The comlimentary triplet anticodon is present in this arm.
D-ARM--
Because it contain at least two dihydrouracil
bases.
Helps in recognition of t-RNA by the enzyme amino acyl t
- RNA synthase.
Catalyse the attachment of aminoacid to the acceptor
arm with CCA sequence.
t-RNA.
T psi C Arm--
Two unusual nucleotides ?ribothymidine and
pseudouridine...
Thymine normally present in DNA.
variable arm- not always present.
FUNCTION OF t- RNA.
15% of cellular RNA.
Read information on mRNA and then provide
specific amino acid to Ribosome.
RIBOSOMAL RNA.
Ribosomes contain RNA 65% and protein 35%.
Ribosomal RNA protein combine to form a
nucleoprotein called ribosome.
Ribosome serve as the site and carries the enzyme
necessory for protein synthesis.
r RNA
r RNA.
FUNCTION OF RNA.
PROTEIN SYNTHESIS.
GENETIC MATERIAL- eg---Retrovirus.....RNA virus.
RIBOZYME-----RNA acting as enzyme--ribizyme.
This post was last modified on 30 November 2021