Expression of Biological Information
DNA &
genetic
information
DNA structure
DNA as a carrier
DNA
replication
Protein
synthesis
Transcription
Models of DNA replication
DNA replication process
Enzyme involved
concept
Components
Gene concept
Definition
Gene
regulation &
expression
Mechanism
Translation
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
DNA Replication
DNA
Overview the roles of
transcription and translation
in the flow of genetic
information
Transcription
RNA
Translation
Protein
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.
Intron
Exon
Intron
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
Intron
Exon
Intron
Exon
Pre-mRNA
Intron
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.
Genetic code
A
T
G
G
C
A
DNA
T
G
G
C
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.
Number of
Type of code 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

A cell cannot directly translate a
gene’s base triplets into amino
acids.
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
PSPM 2007/2008
Feature of Genetic codes
1.
2.
3.
4.
5.
Triplet of bases
Almost universal
Non-overlapping
Commaless
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
 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 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.