Download MBBS DNA Function Lecture PPT

DNA

DNA and RNA collectively called as nucleic acid.

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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.

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CHEMICAL COMOSITION.

DNA IS COMPLEX POLYMERS 0F MONOMERS called

Deoxyribonucleotides.

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DNA- a Polymer of Deoxyribonucleotides.

Four types of Deoxyribonucleotides are found in DNA as shown
2' dAMP- 2' deoxyadenosine monophosphate.

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2' d GMP- 2 'deoxyguanosine monophosphate
2' d CMP - cytidine
2' d TMP- thymidine

These deoxyribonucleotide differ in purine or pyrimidine base

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attached to deoxyribose by a N-glycosidic linkage.
BASES FOUND IN DNA.

Purine-

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Adenine and guanine---Fused ring of

nitrogen and carbon atom.

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Pyrimidine-
cytosine and thymine? only a single ring.

DNA contain thymine pyrimidine while RNA contain

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Uracil.
Structure of Pyrimidine and Purine.
Components of nucleotides.

Base.(Nitrogen base.)-A, G, C or T.

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Sugar.(Pentose sugar)

Phosphate.
NUCLEOTIDE

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Basic unit of nucleic acid composed of three component,

These are sugar, phosphate group, and a ring of

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carbon and nitrogen atom known as a Base.

NUCLEOSIDE = Base + Sugar

NUCLEOTIDE= Nucleoside + phosphate.

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A cyclic five carbon sugar(D- ribose or D 2-

deoxyribose)

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A heterocyclic nitrogenous base( Purine or Pyrimidine)

Phosphoric acid or phosphate.

NUCLEOTIDE--- is monomer of DNA.

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NUCLEOTIDE STRUCTURE.
PHOSPHATE

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Phosphoric acid is-H3PO4.

Contain 3 monovalent hydroxyl group and a

divalent oxygen atom, all linked to the pentavalent

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phosphorous atom.
PENTOSE SUGAR

DNA contain--2-deoxy-D - ribose

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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.

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NITROGENOUS BASE

PURINE and PYRIMIDINE.

BASE is linked to the sugar moiety by the same

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carbon (c1) used in sugar sugar bond.

PURINE Bases--Adenine and Guanine.

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PYRIMIDINE-- Uracil, Thymine and cytosine.
DNA NUCLEOTIDE.


PHOSPHODIESTER LINKAGE.

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Watson-Crick Model of DNA Structure.


> Helical structure-Double stranded helix.

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Polarity----5' to 3' direction strand or 3' to 5 `direction

strand.

Backbone of the strand up of alternative phosphate

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and deoxyribose molecule, and lies exterior while

bases lies inside....

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Two strand of DNA are placed antiparallel to each

other.
Right Handed Double Helix -

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DNA consists of two

polydeoxyribonucleotide chains twisted around one
another in a right handed double helix similar to a
spiral stair case.

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BASE PAIRING RULES.

Always two strand are complementary to each

other.

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Adenine of one strand will pair with thymine of

opposite strand, while guanine will pair with
cytosine.

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The base pairing (A with T, G with C ) is called

chargaff's rule.

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Which states that number of the number of purines is

equal to the number of pyrimidines.
HYDROGEN BONDING.

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The DNA strands are held together mainly by

hydrogen bonds between the purine and pyrimidine
bases.

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Two hydrogen bond between A and T while there

are three hydrogen bonds between

C and G .

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GC bond is stronger than AT bond.
ANTIPARALLEL.

One strand in 5' to 3' direction, while the other is in

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the 3' to 5' direction.
OTHER FEATURES.

Denaturation of DNA strands-----

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MELTING- Double stranded DNA may be

denatured and separated by heat.

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At lower temperature the melted strand are re-

associated, this is called annealing.
Higher organisation of DNA

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NUCLEOSOMES--

Double stranded DNA is wound

round histones to form nucleosomes.

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CHROMATIN--Long stretch of DNA in association with

histones.

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CHROMOSOMES--Chromatin further condensed to

form chromosomes.

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Histones.

Protein with higher concentration of basic amino

acids.

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Acetylation of histones leads to activation of

transcription.

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Deacetylation of histones causes depression of

transcription.
NUCLEOSOME.
DNA is very long molecules.

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Human diploid genome consists of about 7x 10'9

base pairs.
INTRONS, EXONS, CISTRONS.

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EXONS-The segment of the gene coding for proteins

are called exons.(expressed regions).

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INTRONS-Interspaced silent areas in the

DNA(intervening areas ). Introns are not translated.

CISTRONS- is the unit of genetic expression.

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one cistron will code for one polypeptide.

Repeat sequences of DNA.

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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

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intervening sequences, called as introns.

About 30 % of the genome consists of repetitive

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sequences.
DNA STRUCTURE.


STRUCTURE DNA

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DNA STRUCTURE.

Two strand are held together by hydrogen bond,

hydrophobic interaction and vander wall forces.

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Adenine bonds with thymine by two hydrogen bond.

Guanine bonds with cytosine by 3 hydrogen bond.

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Double stranded molecule is coiled into a Right

handed helix.
DNA STRANDS VIEW.
TYPES OF DNA.

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DNA FORM

PITCH-nm

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Bases per turn

Major grouve

Minor grouve

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A

2.46

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11

Deep narrow

Broad and

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shallow

B

3.32

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10

Wide and

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Narrow and

deep

deep

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Z

4.56

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12

Flat

Deep narrow

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B- FORM OF DNA

Most common form...

Right handed double helix.

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Pitch of length of each turn is approx 3.4 nm.

Pitch has approx 10 base pairs.

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Wide major groove and narrow minor groove.

Z DNA----

zig- zag not true helical.

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left handed helix and has 12 base pairs per turn.

No true major groove.
RNA

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GENES, GENETIC INFORMATION, and CENTRAL DOGMA.

? DNA---

CENT

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? REPLICATION.

? mRNA

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RAL

? TRANSCRIPTION

? PROTEIN

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DOGMA ? TRANSLATION.
POLYPEPTIDE SYNTHESIS.
m RNA.

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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.

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Ribosome recognise mRNA by its cap structure.
Leader region-leader sequence is immediately after the

cap region.

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Coding region--codes for protein synthesis, contains

start(AUG) and stop (UAG) codon

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Termination sequence-lies after coding sequence.
Poly A tail- present at 3' end, helps in stability of mRNA.
TYPES OF RNA

messenger RNA.

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Transfer RNA.

Ribosomal RNA.

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The others are =
small nuclear RNA
micro RNA.
small interferring RNA
heterogenous RNA.

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Messenger RNA.

5% of RNA in cell.

Function as messengers carrying the information in a

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gene to the protein synthesizing machinery.

5- terminal end is capped by 7- methyl guanosine

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Triphosphate cap.

The cap is involved in the recognition of mRNA by the

translating machinery.

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It stablise mRNA by protecting it from 5 exonuclease.

3- end of most m- RNA have a polymer of Adenylate

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residues.
Structure of m-RNA.

m-RNA molecules are formed with the help of DNA

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template during process of transcription.

The sequence of nucleotides in m ? RNA is

complementary to the sequence of nucleotide on

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template DNA.

Sequence carried on m-RNA is read in the form of

codons.

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Codon is made up of 3 nucleotides.
m-RNA is formed after processing of hn RNA.
hn RNA.

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Is immediate product of gene transcription.

75 % hn RNA is degradeded in the nucleus , only

25% is processed to mature RNA.

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Mature RNA is formed from primary transcript by

caping, tailing ,splicing, and base modification.
Transfer RNA.

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Most t -RNA display a clover leaf like structure with

several arms and loops.

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ACCEPTOR ARM-

Near the 3' end and terminate in CCA

sequence.

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This arm carries specific amino acid.


Structure of t- RNA.

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t- RNA.

ANTI CODON ARM --
Anticodon arm reads the

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nucleotide on mRNA ---CODON.

The comlimentary triplet anticodon is present in this arm.
D-ARM--
Because it contain at least two dihydrouracil

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bases.

Helps in recognition of t-RNA by the enzyme amino acyl t

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- RNA synthase.

Catalyse the attachment of aminoacid to the acceptor

arm with CCA sequence.

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t-RNA.

T psi C Arm--

Two unusual nucleotides ?ribothymidine and

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pseudouridine...

Thymine normally present in DNA.
variable arm- not always present.

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FUNCTION OF t- RNA.

15% of cellular RNA.

Read information on mRNA and then provide

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specific amino acid to Ribosome.
RIBOSOMAL RNA.

Ribosomes contain RNA 65% and protein 35%.

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Ribosomal RNA protein combine to form a

nucleoprotein called ribosome.

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Ribosome serve as the site and carries the enzyme

necessory for protein synthesis.
r RNA
r RNA.

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FUNCTION OF RNA.

PROTEIN SYNTHESIS.

GENETIC MATERIAL- eg---Retrovirus.....RNA virus.

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RIBOZYME-----RNA acting as enzyme--ribizyme.