6.3 PROTEIN SYNTHESIS: TRANSCRIPTION AND TRANSLATION …

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6.3 PROTEIN SYNTHESIS: TRANSCRIPTION AND

TRANSLATION

6.4 GENE REGULATION AND EXPRESSION – lac

operon

EXPRESSION OF BIOLOGICAL INFORMATION 2

6.3 Protein Synthesis

6.4 Gene Regulation & Expression-Lac Operon

LEARNING OUTCOMES

a) Explain briefly

transcription and

translation

(MQF:C1 & C2)

b) Introduce codon and

its relationship with

sequence of amino acid

using genetic code table

(MQF: C2)

b) State the

component of

operon

(MQF: C1)

3EXPRESSION OF BIOLOGICAL INFORMATION

PROTEIN SYNTHESIS

How is DNA used to make proteins?


PROTEIN SYNTHESIS : OVERVIEW OF

TRANSCRIPTION & TRANSLATION


The synthesis of mRNA

using a DNA template

Occurs in the nucleus

Single strand of DNA

act as a template

Only a part of DNA will

be copied

Catalyzed by RNA

polymerase

TRANSCRIPTION

MQF:C2


STEPS IN TRANSCRIPTION

• RNA Polymerase bind to the promoterINITIATION

• RNA polymerase makes a copy of the template strand using base pairing rules

• The bond that forms between adjacent RNA nucleotides is a phosphodiester bond.

ELONGATION

• RNA polymerase makes mRNA until it reaches the termination site where it stops

TERMINATION

MQF:C2


PROTEIN SYNTHESIS : TRANSCRIPTION

Enzyme involved : RNA polymerase

•Functions:

Select which gene to transcribe

Recognizes 1 of the 2 DNA strands it should

copy/ act as template

Identifies where it should begin and end

transcription

Unwinds DNA double helix

By breaking the hydrogen bonds

Add new RNA nucleotides5’ – 3’ direction

Does not requires a primer

Rewinds the DNA strands

MQF:C1


mRNA SPLICING

MQF:C2


OVERVIEW OF TRANSLATION


TRANSLATION

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule

Occurs in the cytoplasm

Facilitates by: tRNA & ribosome

MQF:C2


STEPS OF TRANSLATION

INITIATION

ELONGATION

TERMINATION

MQF:C1


Consists of single RNA strand

• about 80 nucleotides long.

TRANSFER RNA (tRNA) STRUCTURE

“Clover leaf” structure

• anticodon on “clover leaf” end

• amino acid attached on 3’ end

Function:

• Transfer the amino acids encoded

by codon to the ribosome. MQF:C1

MQF:C1


A nucleotide triplet at one

end of a tRNA molecule

that base pairs with a

particular complementary

codon on an mRNA

molecule.

ANTICODON

MQF:C1


CODON

A triplet of nucleotides

within mRNA that codes for

an amino acid.

MQF:C1


CHARACTERISTICS OF CODON

1. 1 codon consists of triplet

nucleotide combination

There are 64 codons in

genetic code table

Only 61 codon specify amino

acids

2. One start codon, AUG

Encodes for Methionine (Met)

3. 3 stop codons: UAA,UGA,

UAG

Termination codons

Do not specify amino acids.

4. Non-overlapping

E.g: Codon

AUGUCUAGU read

as AUG, UCU, AGU

NOT AUG, GUC,

CUA

5. 1 codon will always

code for the same

amino acid.

6. 1 amino acid can be

encode by more than

1 codon.

MQF:C1


THE CODON-ANTICODON RELATIONSHIP

During translation, codons pair with anticodons so that the

correct amino acids can be linked to a given codon.

MQF:C2


HOW ARE THE CODONS MATCHED TO AMINO

ACIDS?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

aminoacid

tRNA

anti-codon

codon

UAC

MetGCA

ArgCAU

ValMQF:C2


GENETIC CODE TABLE

19

1

PROTEIN

SYNTHESIS:

TRANSLATION

12

1

2 3

12

34

4 53

1. Initiation

2. Elongation

3. Termination

R

F

2. Elongation

MQF:C1


GENE REGULATION AND EXPRESSION –

LAC OPERON

Jacob and Monod (1961) showed that E. coli is capable

of regulating the expression of its genes.


OPERON AND GENE REGULATION

Lac operon :

• Cluster of genes consisting of operator, promoter

and structural genes (lac Z, lac Y, lac A) that codes

for enzymes used to metabolize lactose in E. coli.

MQF:C1


MECHANISM OF THE OPERON IN THE

ABSENCE OF LACTOSE

MQF:C2


MECHANISM OF THE OPERON IN THE

PRESENCE OF LACTOSE

MQF:C2

6.3 PROTEIN SYNTHESIS: TRANSCRIPTION AND TRANSLATION …

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