Cell use RNA to make protein: Central dogma => genetic info resides in DNA => flow down on RNA => Converted into protein.
Transcription:
Enzyme => RNA polymerase binds to promoter => located at up stream of gene.
Transcription DNA => mRNA. Transcription RNA => protein. Enzymes moves along the strand into gene mRNA is synthesized. Stop signal => on the other end of gene => enzyme disengage itself from DNA =>release Henry assembled RNA chain. This chain is a complementary transcript of gene from which it is copied.
Translation:
Information in mRNA => direct the synthesis of polypeptide => by ribosomes. Nucleotides sequence of mRNA => translated into a.acid in polypeptide.
Transcription and Translation => gene expression.
rRNa:
• Found in ribosomes.
• During translation, rRNA provides site where polypeptide are assembled.
tRNa:
• Transport a.acids to ribosomes for use in building the polypeptide.
• Alsi position each a.acid at collect place on elongated polypeptide chain.
• 45 different tRNA in human cells.
mRNa:
• Long strands of RNA transcribed from DNA and then travel ribosomes to direct which a.acid are assembled in polypeptides.
Transcription:
DNA => mRNA => RNA polymerase enzyme. Only of the two strands are transcribed opposite strand is => Template strand coding or sense strand of antisense strands. RNA polymerase => synthesize RNA => 5 to 3. In prokaryotes => olny one type of RNA polymerase which synthesize all three types of RNAs.t,r,m. In Eukaryotes => three types of RNA polymerase.
RNA polymerase 1 => rRNA.
RNA polymerase 11 => mRNA.
RNA polymerase 111 => tRNA.
1st step:
• Transcription start => at RNA polymerase binding site => promoter on DNA template.
• In prokaryotes within promoter there are two binding sites.
TIGACA => 35 sequence (affinity).
TATAAT => 10 sequence (for RNA polymerase).
• In Eukaryotes => 75 sites and 35 sites.
2nd step:
Sigma Factor => subunits of RNA polymerase => correct initiation of transcription once transcription started => sigma factor released and remaining part of enzyme (core enzyme) move over template strand => completes transcription.
3rd step:
DNA strands open up at place where enzyme is attached to template strand => form => transcription bubble. Transcription bubble movee down DNA => leaving growing strand protradry from bubble. Stop sequence at end of gene => Termintes mRNA synthesis. Stop signal => series of 4C base pairs folled by AT base pairs. RNA formed has 4C harping followed by 4 or more U Ribonucleotides. stop synthesis.
• In Bacteria => newly synthesized mRNA is directly released into cytoplasm => converted into polypeptide chain.
• In Eukaryotes => long distance => from => inside nucleus to => ribosomes => outsides in cytoplasm. Eukaryotic => mRNA => future modified.
1-7 methyl GTP cap libked 5 to 5 => within first nucleotides polyAtail => to 3 end of RNA => 50-250 A nucleotides for stability of mRNA in ribosomes. Caps and tails save mRNA => from clesradation from variety of nucleases and phophatases help ribosomes to bind mRNA.
Genetic code:
• Combination of three nucleotides => specific a particular a.acid. Three nucleotides in a cordon => Two not enough to yield combination for 20 different a.acid coding.
Four DNA nucleotides:
(G,C,A,T) 4²16 d/f pairs of nucleotides would be formed. 4³ = 64 combinations of three enough to code for 20 a.acids.
Genetic code => Triplet code. Reading => continuesly between three nucleotides units. Marshall Nivenburg, Philip leader and Har Gobind Khorana => test all 64 codons => by making => uses than to stabilize a protein.
• Non-sense codon => UAA, UAG, UGA. Stop codon => end of gene do not code for any a.acids.
• Initiation codon => AUG => codes => methionine. Genetic code => universal from organisms. Genes can be transferred same from one organism to another successfully => Transcribed translated.
• Genetic code for mitochondrial DNA => Not universe.
Translation:
mRNA => protein
In prokaryotes => initial portion of mRNA binds to rRNA molecule in ribosomes => translation before.
mRNA molecule lies on ribosomes => one if its codon is exposed at polypeptide site at any time.
tRNA possing anticodon (Complementary and Nucleotide base pairs) => binds to ecposed condon on mRNA.
As mRNA molecule moves through ribosomes successive codons on mRNA are exposes and is tRNA molecule bond to exposed. tRNA each carries attached a.acids. Codon which is attached to end of growing polypeptide. Amino acyl - tRNA synthetic => tRNA attached to specific a.acid at mRNA through this one of which exists for each of 20 common a.acids.
Prokaryotes:
Initiation complex:
tRNA carrying methionine initiation factor positive the tRNA on ribosomal surface. A site (amino acyl site) successive a.acids bearing tRNA will bind. Site exit (emphs tRNA exist ribosomes).
Elongation facter:
After initiation => at A site => large ribosoi subunits bind tRNA with anticodon elongative factor assist in binding it to mRNA codon. Two a.acids lie close to each other which release initital methionine from tRNA => attaches it by peptide bond to 2nd a.acid. Under go a reaction catalyzed by large Ribosomal subunit.
Ribosomes now moves 3 more nucleotides along mRNA => 5 - 3 direction => guided by another elongation factor.
initial tRNA => to E site and ejects from ribosomes growing polypeptide contains and a.acid at to P site and exposes next codon on mRNA on A site. tRNA molecule binds to codon at A site process continues. When stop codon at mRNA exposed => do not tRNA => translation ends => release polypeptide from ribosomes.
Mutation:
All DNA in all cells at adult human => stretch to 100 billion km => 60 times distance from earth to Jupiter. Changes in DNA => mistakes in replication or damage to genetic code => mutations somatic mutations do not pass but genetic mutation passes to generation => Hence raw material from which natural selection produce evolution change.
Chromosomal aberation:
Megachanges Extra chromosome or loss ov chromosome => from diploid number. Deletion, insertion, invasion e.g: Down Klitter syndrome.
Point mutation:
Effect message itself.
Produces alteration in DNA nucleotide.
One or few base pairs DNA alternation in coding sequence.
Some point mutation occur dur to spontaneous pairing errors occur in DNA replication.
e.g Sickle cell anomia Phenylketonuria alkaption chemical.
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