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 TranscriptionTranslation Expression of Biological Information concept Components Mechanism

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 RNA Protein Transcription Translation DNA Replication

Production of hormones Production of enzymes

transcribed into translated to

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

 Involeve 3 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 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

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. Exon 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 Exon Intron Pre-mRNAmRNA

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. ATGGCATGGC 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.

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 bases 2.Almost universal 3.Non-overlapping 4.Commaless 5.Each codon is specific for one amino acid 6.Degenerate / one amino acid can be coded by several codons 7.Start codon AUG 8.Stop codon UAG, UAA, UGA PSPM 2007/2008 Feature of Genetic codes

ATGGCATGGC DNA Genetic code  Non-overlapping  Commaless ATGG ATGGC C ATGGCATGGC 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.