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

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

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.