Expression of Genetic Information explain .pdf

Central dogma.

1. Expression of Genetic
Information (The Central
Dogma)
(Lecture # 4)
Ms. Saba Saeed
Lecturer
M.Phil.(Biochemistry)

2. Central Dogma-AnInheritanceMechanism
•Inmolecular biology,centraldogmadescribesthe flowof
geneticinformationfromDNAtoRNAtoprotein.
•It is defined as a process in which the information in DNA is
convertedintoa functionalproduct(protein).
•“Central dogma is the process in which the genetic
informationflowsfromDNAtoRNA,tomakeafunctional
productprotein.“

3. Central Dogma -
An Inheritance
Mechanism
•The information present in
a DNA is essential to make
up all proteins.
•RNA acts as a messenger
that carries information to
ribosomes.

4. Transcription
•Process by which the information is transferred from one
strandof theDNAtoRNAbytheenzymeRNAPolymerase.
•TheDNAstrandwhichundergoesthisprocessconsistsof
threepartsnamely
a)Promoter
b)Structuralgene
c)Terminator

5. Cont…
•TheDNAstrandthatsynthesizestheRNAiscalled the
templatestrand andtheother strandiscalledthecoding
strand (DNA strand whose base sequence is identical to
the base sequence of the RNA transcript produced)
•TheDNA-dependentRNApolymerasebindstothe
promoterandcatalyzesthepolymerizationinthe5′to3′
direction.

7. Cont…
•Theterminatorsequenceterminatesandreleasesthenewly
synthesizedRNAstrand.
•The newlyreleasedRNAstrandfurtherundergoespost-
transcriptionalmodifications.

8. Steps

10. Post Transcriptional modifications
1.Addition of adenine bases (the poly-A tail) to the 3' end of
the RNA primary transcript. The poly-A tail is important in
export, stability, and translation of the transcript.
2.The capping of pre-mRNA is carried out by theaddition of
7-methylguanosine to the 5'end. It prevents mRNA from
nucleases.
3. RNA splicing isthe process by which introns, regions of
RNA that do not code for proteins, are removed from the
pre-mRNA and the remaining exons connected to re-form
a single continuous molecule.

12. GeneticCode
•Geneticcodecontainstheinformationoftheprotein
manufacturedfromRNA.
•There arebasicallythree nucleotidesandfournitrogenous
bases,which collectivelyformatriplet codonthatcodesfor
oneaminoacid.
•Therefore,the numberofpossibleaminoacidsrangeto4 x4
x4 = 64 aminoacids.
•Thereare20naturallyexistingaminoacids.

14. Cont…
•Thegeneticcodecanbedegeneratedanditisduetothat
fewaminoacidsarecodedbymorethanonecodonthus
causingthemtodegenerate.
•Each codon codes for only one specific amino acid and the
codesareuniversal.
•Outof the64 codons,3 arestopcodonswhichstopthe
processoftranscriptionandoneofthe codonsisaninitiator
codon.
•Forexample,AUG codingforMethionine.

15. Translation
•Translationisthe processbywhichtheRNA codesfor
specificfunctional proteins.
•It is an active process which requires energy,and this
energy isprovided bythe chargedtRNAmolecules.
•Ribosomesinitiatethetranslationprocessand
the ribosomes consist of a larger subunit and a smaller
subunit.

16. Steps in Translation
•Initiation: The ribosome binds to the mRNA at the start codon (AUG).
•Elongation: tRNA molecules bring amino acids to the ribosome, matching
their anticodons to the mRNA codons.
•Peptide Bond Formation: Amino acids are linked together by peptide
bonds, forming a growing polypeptide chain.
•Translocation: The ribosome moves along the mRNA, reading each codon.
•Termination: When a stop codon is reached, the ribosome releases the
completed polypeptide chain.
•Folding: The polypeptide chain folds into its functional protein shape.