CHAPTER 6 LECTURE KML 2024_2025

CHAPTER 6

EXPRESSION OF BIOLOGICAL

INFORMATION

(Hours: 2L + 8T)

CHAPTER 6: EXPRESSION OF BIOLOGICAL

INFORMATION

6.1 DNA and genetic information
6.2 DNA Replication
6.3 Protein synthesis: transcription and translation

6.4 Gene regulation and expression – lac operon

UPS 1

PSPM 1

7 MCQ

14 marks

LEARNING OUTCOMES

6.1 DNA and genetic information

a) State the concept of Central Dogma (C1)

Definition:
The dogma is a framework
for understanding the flow of
genetic information between
DNA,

RNA

&

protein,

in

living organisms.

Central Dogma

Learning Outcomes :

6.1 (a) : State the concept of Central Dogma

Look at this diagram:

Central Dogma

Learning Outcomes :

6.1 (a) : State the concept of Central Dogma

• The DNA replicates its information in a process that

involves many enzymes; known as DNA replication.

• DNA information can be copied into mRNA during

transcription.

• mRNA as a template carries coded information from DNA

(nucleus) to cytoplasm & ribosomes use it for protein
synthesis. This process is called translation.

Central Dogma

Learning Outcomes :

6.1 (a) : State the concept of Central Dogma

Multiple Choice

Which of the following correctly represents the central dogma of molecular biology?

• DNA → Protein → RNA

• RNA → DNA → Protein

• DNA → RNA → Protein

• Protein → RNA → DNA

Multiple Choice

During the process of transcription, what molecule is synthesized?

• DNA

• mRNA

• Protein

• Amino acids

Multiple Choice

What is the role of mRNA in the central dogma?

• It carries genetic information from DNA to the ribosome for protein synthesis.

• It is the site of protein synthesis.

• It carries amino acids to the ribosome.

• It acts as an enzyme in protein synthesis.

LEARNING OUTCOMES

6.2 DNA Replication

​a)  Explain semi-conservative replication of DNA.

b) Explain the enzymes and proteins involved in DNA replication.

c) Explain the mechanism of DNA replication and the enzymes involved.

Multiple Choice

Which of the following enzymes is responsible for unwinding the DNA double helix during replication?

• Primase

• DNA Polymerase

• Helicase

• Ligase

Multiple Choice

What is the main function of primase in DNA replication?

• Unwinds the DNA double helix

• Adds nucleotides to the growing DNA strand

• Synthesizes a short RNA primer

• Joins Okazaki fragments together

Multiple Choice

Which enzyme adds new nucleotides to a growing DNA strand during replication?

• Helicase

• Primase

• DNA Polymerase

• Ligase

Learning Outcomes :

6.2 (b) : Explain the enzymes and proteins involved in DNA Replication

Learning Outcomes :

6.2 (c) : Explain the mechanism of DNA Replication and the enzymes involved

CONCLUSION

Learning Outcomes :

6.2 (c) : Explain the mechanism of DNA Replication and the enzymes involved

CONCLUSION

LEARNING OUTCOMES

6.3: Protein Synthesis: Transcription And Translation

a) Explain briefly transcription and translation. (C3)
b) Introduce codon and its relationship with sequence of

amino acid using genetic code table. (C2)

c) Explain transcription and the stages involved (initiation,

elongation and termination) in the formation of mRNA
strand 5’ to 3’. (C3)

d) Explain translation and the stages involved in

translation: (C3)
i.

Initiation

ii.

Elongation (codon recognition, peptide bond
formation and translocation); and

iii.

Termination

• Transcription is the synthesis (production) of RNA

using information in the DNA.

• Translation is the synthesis of a polypeptide using the

information in the mRNA.

Transcription And Translation

Learning Outcomes :

6.3 (a) : Explain briefly transcription and translation

• Information is transferred

in the form genetic code.

• A sequence of three

bases (triplet code) in
mRNA is called a codon
and they are written in the
5′ to 3′ direction

Codon and Genetic Code Table

Learning Outcomes :

6.3 (b) : Introduce codon and its relationship with sequence of amino acid using genetic code table

Learning Outcomes :

6.3 (b) : Introduce codon and its relationship with sequence of amino acid using genetic code table

1) Composed of nucleotides triplets

•3 nucleotides in mRNA is called a codon

•A sequence of 3 bases is the most possible since it
can give 64 (43) combinations of bases since there
are 20 different amino acids

2) Unambiguous (tidak kabur)

•Each codon has only one meaning that encode for
one specific amino acid

3) The code is degenerate

•Amino acids may be coded by more than one codon.
An amino acid can be specified by more than 1 triplet
codon.

Learning Outcomes :

6.3 (b) : Introduce codon and its relationship with sequence of amino acid using genetic code table

Characteristics of codon in Genetic code

4) Genetic Code is nearly universal.

• The genetic codes is nearly universal, shared by

organisms from the simplest bacteria to the most
complex plants and animals.

5) The code has start & stop signals.

• There is one start codon (AUG) & three stop codons

(UAA, UAG, UGA).

6) Non-overlapping

• Sequence of codon is read continuously from a fixed

starting point until it reaches the termination point

Learning Outcomes :

6.3 (b) : Introduce codon and its relationship with sequence of amino acid using genetic code table

Characteristics of codon in Genetic code

Learning Outcomes :

6.3 (b) : Introduce codon and its relationship with sequence of amino acid using genetic code table

Multiple Choice

Which of the following best describes the process of transcription?

• Conversion of mRNA into a polypeptide chain.

• Synthesis of a DNA strand from an RNA template.

• Synthesis of mRNA from a DNA template.

• Assembly of ribosomes in the cytoplasm.

Multiple Choice

In eukaryotic cells, where does translation occur?

• Nucleus

• Cytoplasm

• Mitochondria

• Endoplasmic reticulum

Multiple Choice

During transcription, the enzyme responsible for synthesizing mRNA is:

• DNA polymerase

• RNA polymerase

• Helicase

• Ligase

Multiple Choice

What is the role of a codon in the process of translation?

• It signals the start of transcription.

• It determines the sequence of amino acids in a protein.

• It initiates DNA replication.

• It marks the end of DNA synthesis.

Multiple Choice

Which of the following mRNA codons serves as a stop codon in protein synthesis?

• UAA

• AUG

• UUU

• GGG

LEARNING OUTCOMES

6.4 Gene regulation and expression – lac operon

a) Explain the concept of operon and gene regulation

(C3)

b) State the components of operon (C1)

c) Explain the components of lac operon and their

function in E.coli (C3)

d) Explain the mechanism of the operon in the

absence and presence of lactose (C3)

76

Operon

Learning Outcomes :

6.4 a) Explain the concept of operon and gene regulation

● A series of structural genes expressed as a group

controlled by the single operator and promoter

● Consists of promoter, operator and structural genes

● Structural genes function as a single transcription unit

transcribed into single mRNA

● Only in prokaryotes (e.g. bacteria)

Gene Regulation

Learning Outcomes :

6.4 a) Explain the concept of operon and gene regulation

● Genes

of

related

functions

are

grouped

into

one

transcription unit

● These genes are regulated such that they are all turned on

or off together

● These genes are coordinately controlled

● The on-off switch is a segment of DNA called an operator

Gene Regulation

Learning Outcomes :

6.4 a) Explain the concept of operon and gene regulation

● Operator can be switched off by repressor protein

● Repressor binds to operator and blocks the attachment

of

RNA

polymerase

to

the

promoter,

preventing

transcription of the genes

● The repressor is encoded by regulatory gene (outside

the operon, has its own promoter)

Component of Operon

Learning Outcomes :

6.4 b) State the components of operon

Operon includes the following:

1) Promoter
2) Operator
3) Structural genes; lacZ, lacY, lacA

lac operon

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

● The operon model was proposed by Francois Jacob

and Jacques Monod (1961) in E.coli

● Some of the bacterial genes will be expressed only

when it is necessary

● Lactose (lac) operon:


Regulates lactose metabolism in E.coli (contains
genes that encode for enzymes used in the
hydrolysis and metabolism of lactose)

Components of lac operon

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

● lac operon consists of:

1. Structural genes

2. Promoter

3. Operator

⮚lacZ
⮚lacY
⮚lacA

Components of lac operon

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

● lacZ : codes for /encodes β-galactosidase

● lacY : codes for /encodes permease

● lacA : codes for /encodes transacetylase

1. STRUCTURAL GENES

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

Components of lac operon

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

● Binding site for RNA polymerase

● Binding site for repressor protein

● Act as switch; which activate/ inactivate the operon

2. PROMOTER

3. OPERATOR

Learning Outcomes :

6.4 c) Explain the components of lac operon and their function in E.coli

● Encodes for repressor protein

● Located outside the operon, has its own promoter gene

REGULATORY GENE/ lacI

Learning Outcomes :

6.4 d) Explain the mechanism of the operon in the absence and presence of lactose

Mechanism of lac operon

LACTOSE ABSENT

Learning Outcomes :

6.4 d) Explain the mechanism of the operon in the absence and presence of lactose

Mechanism of lac operon

● Some / small amount of

lactose is converted to
allolactose (inducer)

● Allolactose binds to

repressor protein

● Repressor protein change

its conformation to become
inactive form

● Repressor protein cannot

binds to /detached from
operator

LACTOSE PRESENT

Learning Outcomes :

6.4 d) Explain the mechanism of the operon in the absence and presence of lactose

Mechanism of lac operon

● Promoter is unblocked

● RNA polymerase binds to

promoter

● lac operon switched on

● Transcription of structural

genes (lacZ, lacY and lacA)
occur

● β-galactosidase, permease

and transacetylase are
produced

● Lactose hydrolysed into

glucose and galactose

LACTOSE PRESENT

Learning Outcomes :

6.4 d) Explain the mechanism of the operon in the absence and presence of lactose

Mechanism of lac operon

LACTOSE PRESENT

Learning Outcomes :

6.4 d) Explain the mechanism of the operon in the absence and presence of lactose

One mRNA is translated into three polypeptides

Multiple Choice

What is the function of the lacZ gene in the lac operon?

• Encodes a protein that imports lactose into the cell

• Encodes the enzyme β-galactosidase, which breaks down lactose

• Encodes a protein that inhibits lactose breakdown

• Encodes the repressor protein that blocks transcription

Multiple Choice

Which molecule acts as the inducer in the lac operon?

• Glucose

• Allolactose

• Lactose permease

• Thiogalactoside transacetylase

Multiple Choice

What happens to the lac operon when there is no lactose present?

• The repressor binds to the operator, blocking transcription

• The structural genes are actively transcribed

• RNA polymerase binds to the promoter and initiates transcription

• The operon is induced, and enzymes for lactose metabolism are produced

Multiple Choice

Which of the following correctly describes the role of the lacI gene?

• Encodes β-galactosidase

• Encodes the repressor protein that regulates the lac operon

• Encodes a protein that facilitates the transport of lactose

• Encodes an enzyme that detoxifies by-products of lactose metabolism

Multiple Choice

Which gene produces the repressor protein that regulates the lac genes?

• lacZ

• lacY

• lacI

• lacA

• Campbell N.A & Reece, J.B., Biology, 12thed. (2021),

Pearson Education, Inc.

• Solomon E.P & Berg, L.R, Biology, 11thed. (2019) Thomson

Learning, Inc.

• Mason K.A & Losos J.B., Biology 12thed. (2019), McGraw-Hill

Education.

• Solomon, Martin, Martin, Berg (2018). Biology (11thed).

Cengage

• Reece, J., Urry, L., Cain, Wasserman, S. Minorsky, P., &

Jackson, R.(2018). Biology (11thed.), Pearson Benjamin
Cummings

REFERENCES

•Figure 1 –https://en.wikipedia.org/wiki/Three_prime_untranslated_region

•Figure 2 – https://byjus.com/biology/central-dogma-inheritance-mechanism/

•Figure 3 – Copyright © 2010 Pearson Education, Inc

•Figure 4 & 5 – Campbell 12thed page 372

•Figure 6 – Adapted from Campbell 12thed page 371

•Figure 7 – Campbell 12thed page 376

•Figure 8 & 9 – Campbell 12thed page 373

•Figure 10 – https://www.slideshare.net/slideshow/dna-replication-17194030/17194030#24

•Figure 11 – Solomon 11thed page 264

•Figure 12 – https://www.pinterest.com/pin/205406432982963372/

•Figure 13 – Campbell 12thed page 374

•Figure 14 – https://www.pinterest.com/pin/205406432982963372/

•Figure 15 – Solomon 11thed page 267

•Figure 16 & 17 – Campbell 12thed page 375

•Figure 18 – https://slideplayer.com/slide/14575879/

•Figure 19 & 20 – Adapted from Campbell 12thed page 375

•Figure 21 – https://slcc.pressbooks.pub/humanbiology/chapter/14-dna-structure-protein-synthesis-and-
gene-regulation-2/

•Figure 22 – https://www.slideshare.net/slideshow/the-cell-cycle-229798422/229798422#13

•Figure 23 – Raven 12thed page 292 (e-book)

•Figure 24 – Campbell 12thed page 391

•Figure 25 – Campbell 12thed page 390

•Figure 26 – Mader 12thed page 217 (e-book)

•Figure 27 – Campbell 12thed page 393

•Figure 28 – Campbell 12thed page 394

•Figure 29 – Solomon 11thed page 280

REFERENCES (FIGURE)