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 monophosphate2' 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 withphosphoric acid. OH- group of pentose , especially
3rd and 5th involved forming 3'-5 `? phosphodiester
bond between adjacent pentose residue.
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NITROGENOUS BASEPURINE 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 `directionstrand.
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 eachother.
Right Handed Double Helix -
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DNA consists of twopolydeoxyribonucleotide 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 isequal to the number of pyrimidines.
HYDROGEN BONDING.
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The DNA strands are held together mainly byhydrogen bonds between the purine and pyrimidine
bases.
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Two hydrogen bond between A and T while thereare 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 toform 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 oftranscription.
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 theDNA(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 Righthanded helix.
DNA STRANDS VIEW.
TYPES OF DNA.
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DNA FORM
PITCH-nm
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Bases per turnMajor grouve
Minor grouve
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A
2.46
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11Deep narrow
Broad and
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shallowB
3.32
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10
Wide and
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Narrow anddeep
deep
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Z
4.56
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12Flat
Deep narrow
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B- FORM OF DNAMost 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 enzymenecessory 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.