DNA & genetic information DNA replication Protein synthesis Gene regulation & expression DNA...
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Transcript of DNA & genetic information DNA replication Protein synthesis Gene regulation & expression DNA...
DNA & genetic
information DNA
replication
Protein synthesis
Gene regulation & expression
DNA structure
DNA as a carrier
Gene concept Definition
Models of DNA replication
DNA replication process
Enzyme involved
Transcription
Translation
Expression of Biological Information
concept
Components
Mechanism
Overview the roles of transcription and translation in the flow of genetic informationExplain transcriptionDescribe the stages involved:
i. initiation ii. elongation
iii. terminationState the formation of mRNA strand from 5’ to 3’Describe the relationship between base sequences in codons with specific amino acids using genetic code table
Overview the roles of transcription and translation
in the flow of genetic information
DNA
RNA Protein
Transcription
Translation
DNA Replication
RNA polymerase enzyme involved
Specific sequences of nucleotides along the DNA mark where the transcription begin (promoter site) and
ends (terminator site)
The stretch of DNA that is transcribed into mRNA is called a transcription unit
mRNA elongates in its 5’ to 3’ direction
1) RNA polymerase binding and initiation
RNA polymerase recognize and attaches to promoter site on DNA.
Enzyme begins to separate the DNA strand .
Segment of DNA strand unwind.
As RNA polymerase moves along the template of DNA, complementary RNA nucleotides pair with DNA nucleotides of the strand.
RNA polymerase joins the RNA nucleotides together in the 5’ to 3’ direction
3) Termination
Elongation of mRNA continues until RNA polymerase reaches a terminator site on the DNA
Terminator site causes the RNA polymerase to stop transcribing DNA and release the mRNA
mRNA will leave the nucleus through the nucleus pore to the cytoplasm
Formation of mRNA strand from 5’ to 3’
Most eukaryotic genes have interrupted coding sequence, exons and introns
- Exon : A nucleotide sequence in a gene that codes for parts or all of the gene product and is therefore expressed in mature mRNA.- Intron : A nucleotide sequence in a gene that does not
code for gene product. : It usually transcribed in eukaryotes into mRNA but subsequently removed from transcript before translation. ExonExon Intron Intron Intron
A pre-mRNA contains both exon and intron sequences
Introns must be removed and the exons spliced together to form a continuous protein-coding message
ExonExon Intron Intron Intron
Pre-mRNA mRNA
Genetic code Genetic code: Base triplet in DNA provides a
template for ordering the complementary triplet in mRNA molecule.
Every base triplet is code for ONE amino acid.(very specific, almost universal)
Three bases of an mRNA codon are designated as first, second and third bases.
A T G G C A T G G C
DNA
Genetic code
Genetic code There are only FOUR nucleotide
bases, to specify 20 amino acids; A-adenine, C-cytosine, G-guanine, T-
thymine (unique to DNA), U-uracil (unique to RNA) [pyrimidine, very similar to thymine].
Flow of information from gene to protein is based on triplet code.
Type of code Number of bases in codon
Number of Codons
Ambiguous / degenerate
Singlet code 1 4 Ambiguous
Doublet code 2 4*4=16 Ambiguous
Triplet code 3 4*4*4=64 Degenerate
1. Give ONE reason why DNA from the nucleus is not esed directly by the ribosome for the translation process.
less chances of damage to the DNA
A cell cannot directly translate a gene’s base triplets into amino acids.
1. Triplet of bases2. Almost universal3. Non-overlapping4. Commaless5. Each codon is specific for one amino
acid6. Degenerate / one amino acid can be
coded by several codons
7. Start codon AUG8. Stop codon UAG, UAA, UGA
PSPM 2007/2008
Feature of Genetic codes
A T G G C A T G G C
DNA
Genetic code
Non-overlapping Commaless
A T G G A T G G CC
A T G G C A T G G C
Genetic code
An mRNA molecule is complementary rather than identical to its DNA
template according to base-pairing rules.
A-U, T-A, C-G, G-C
mRNA base triplets are called codons.
A triplet of nucleotides within a molecule of messenger RNA that functions as a unit of genetic coding, usually by specifying a particular amino acid during the synthesis of proteins in a cell
* also refer to any corresponding nucleotide triplets of DNA that transcribed into codons
Consist of triplet bases (3 bases)
One codon code for one amino acid
Codon are complementary to anticodon
A few codons specify instructions during protein synthesis (start & stop codon)
Customarily written in 5’ to 3’ direction
Initiation codon
Codon AUG is a starter to the process of translation.
Codon AUG has dual function, as a start signal / initiation codon and it also code for amino acid methionine (Met).
Polypeptide chains begin with methionine
An enzyme may subsequently remove starter amino acid from chain.
Termination codon
Three triplet bases of STOP signal: UAA, UAG, UGA.
marking the end of a genetic code , and the completed polypeptide chain is released from the ribosome..
Genetic massages begin with the mRNA codon AUG, which signals the protein- synthesizing machinery to begin translating the mRNA at the location.
Noticed that U only can be found on mRNA strand, substitute for T (only on DNA strand).
U on mRNA pairs with A on DNA strand, while T on DNA strand pairs with A on mRNA.