Expression of Biological Information DNA & genetic information Gene regulation & expression DNA replication Protein synthesis • DNA structure • DNA as a carrier • Gene concept • concept • Components • Mechanism Transcription Translation • Definition • Models of DNA replication • DNA replication process • Enzyme involved
Overview the roles of transcription and translation in the flow of genetic information Explain transcription Describe the stages involved: i. initiation ii. elongation iii. termination State 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 Replication DNA Transcription RNA Protein Translation
Production of hormones Production of enzymes
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Overview the roles of transcription and translation in the flow of genetic information
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
Involeve3 steps • RNA POLYMERASE BINDING AND INITIATION • ELONGATION OF RNA STRAND • TERMINATION
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 nucleotidesof 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 codesfor • 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. Intron Exon Intron Exon Intron
A pre-mRNA contains both exon and intron sequences Intronsmust be removedand the exons splicedtogether to form a continuous protein-coding message Intron Intron Exon Intron Exon 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 ONEamino acid. (very specific, almost universal) Three bases of an mRNA codonare designated as first, second and third bases. Genetic code A T G G C A T G G C DNA
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.
A cell cannot directly translate a gene’s base triplets into amino acids. • 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
PSPM 2007/2008 Feature of Genetic codes • Triplet of bases • Almost universal • Non-overlapping • Commaless • Each codon is specific for one amino acid • Degenerate / one amino acid can be coded by several codons • Start codon AUG • Stop codon UAG, UAA, UGA
Non-overlapping • Commaless Genetic code A T G G C A T G G C DNA Genetic code A T G G C A T G G C A T G G C A T G G C
An mRNAmolecule is complementary rather than identical to its DNAtemplate 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 codoncode for one amino acid Codon are complementary to anticodon A few codonsspecify instructions during protein synthesis (start & stop codon) Customarily written in 5’ to 3’ direction
Initiation codon CodonAUGis astarterto the process of translation. CodonAUGhas dualfunction, as a start signal / initiation codonand it also code for amino acid methionine (Met). Polypeptide chains begin withmethionine 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 codonAUG, 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.