The document outlines key concepts related to genes and gene expression, including replication, transcription, and translation. It explains the regulation of gene expression in prokaryotes and eukaryotes, with a focus on operons, particularly the lactose operon in E. coli. The content also differentiates between constitutive and inducible genes, highlighting their roles in metabolic pathways.

1. Presented by
Moh.Uzair
M.Pharm(Pharmacology) Ist Semester Student
SPER, Jamia Hamdard New Delhi

2. Contents
1. Gene. 1
2. Gene Expression. 2
a)Replication 5-6
b) Transcription 7-8
c) Translation 9-10
3. Regulation of Gene Expression. 11
4. Types of Gene Regulation. 12-13
a)Positive Regulation
b) Negative Regulation

3. Contents
5. Types of Genes. 14-15
a) Constitutive Genes
b) Inducible Genes
6.Regulation of Gene Expression in
Prokaryotes. 16-24
Operon
. Lac Operon
7.References. 25

4. 1.Gene
 Gene is a small piece of genetic material
written in a code and called DNA.
 Gene is passed from parents to child.
 Genes determines the child’s
characteristics - like hair,eye,skin color,
height and whether the child will have an
inherited disease.
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5. 2.Gene Expression
 Gene expression refers to multistep
process that results in production of
structural & functional unit of cell called
protein.
 Gene Expression is the combined process
of the transcription of a gene into mRNA &
its translation into protein.
 The first step is
DNARNAmRNAProtein.
 Gene Expression = Transcription+
Translation
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6. Gene Expression
 Genetic mutation alters the regulation or
expression of gene and results in dysfunctional
and non functional protein synthesis.
 Non protein coding genes are not translated.
 Multistep process is also called Central Dogma.
 Central Dogma is the flow of information from
DNA to RNA & then to Protein.
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7. Gene Expression is a multistep
process which involves
a) Replication
b) Transcription
c) Translation
4
Moh.Uzair

8. a) Replication(DNA Synthesis)
 The duplication or synthesis of DNA is
called replication.
 It is occurs in S-phase of cell cycle.
 All over the body replication process found
in same way, but Transcription process
have different cell to cell.
 Replication process is semi-conservative
means the mechanism of DNA replication
that leads to a daughter molecule with one
old strand and one new strand.
5

9. Replicating fork
6

10. b) Transcription
 It is synthesis of RNA from DNA that
results in the transfer of the information
stored in double stranded DNA to Single
stranded RNA.
 Enzyme involved is RNA Polymerase.
 During transcription, only one strand of
DNA is usually copied. This is called the
template strand, and the RNA molecules
produced are single-
stranded messenger RNA (mRNAs).
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11. Transcription
8

12. c) Translation(Protein
biosynthesis)
 Protein biosynthesis is called translation.
 It is found in Ribosomes(free/ cytosolic)
 mRNA is translated in 5’ to 3’direction.
 Protein is synthesized from amino
terminal(N-terminal ) to carboxy terminal(c-
terminal).
 All amino acids should be present at the
time of translation otherwise translation will
stop at codons.
 tRNA is required for translation & accept
the amino acid in protein synthesis
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13. 10

14. 3.Regulation of Gene Expression
 Regulation of gene expression is essential
for metabolic functions, growth and
development and differentiation of tissues.
 The rate of expression of
prokaryotic(bacteria) genes is controlled
mainly at the level of transcription, mRNA
synthesis.
 Eukaryotes however have a much larger
and more complex genome than
prokaryotes.
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15. 4.Types of Gene Regulation
a) Positive regulation
b) Negative regulation
a) Positive Regulation :
 Gene expression is increased by a
regulatory element.
 The element or molecule mediating the
positive regulation is said to
be an activator or inducer.
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16. Types of Gene Regulation
b) Negative Regulation : Gene
expression is decreased by regulatory
element is said to be a negative
regulator(repressor/inhibitor).
Double negative effect on gene
regulation results in a positive
phenomenon.
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17. 5.Types of genes
a) Constitutive / housekeeping genes:
 Always active.
 They form products(proteins/ enzymes) which is
required for basic cell function all the time.
 It is the genes whose expression is not regulated.
 These genes are expressed at a constant rate.
E.g. The enzymes of citric acid cycle.
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18. Types of genes
b) Inducible Genes :
 It is expressed only in special circumstances.
 E.g. This genes synthesize the enzymes of
gluconeogenesis which is not required in
normal situation(fed state).So these genes are
inhibited in a normal situation.
 But it required (e.g. during fasting/starvation),
these genes are activated.
 It is regulated by various molecular signals
that is why it is known as Regulated Genes.
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19. 6. REGULATION OF GENE
EXPRESSION.
operon
 In prokaryotes, the genes involved in a
metabolic pathway are often present in a
linear fashion, called an operon.
 Operon is functioning unit of DNA
containing a cluster of genes, under the
control of a single promoter.
 Transcription is the main site of
regulation of gene expression.
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20. Operons occur in prokaryotes but not in
eukaryotes. For example:
• Lactose operon (Lac operon for
regulation of lactose metabolism)
• Arabinose operon (Ara operon for
regulation of arabinose
metabolism)
• Galactose operon (Gal operon for
regulation of galactose metabolism).
17

21. Lac Operon/ Lactose Operon
 The concept of operon was introduced by
Jacob and Monod in 1961.
 It is occurs in E.coli.
 Bacterial cell normally get energy from
glucose because glucose is mostly present
in the environment of E.coli.
 There is no need for this bacterial to cell
use lactose. So these genes (synthesize
the enzymes of lactose metabolism) are
inhibited(repressed).But if required, these
genes can be activated(induced).
18

22.  It is consists of a regulatory gene(I; I for
inhibition), operator gene (O) and 3
structural genes(Z,Y,A).
 Lac Z- codes for Beta Galactosidase
breaks Lactose to Galactose and
Glucose
 Lac Y- codes for permease facilitate
permeation of Lactose into the cell.
 Lac A-Codes for Transacetylase
acetylates lactose.
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23. How Genes are Inhibited
20
 Lac I is a house keeping gene(always
active).So, this gene always produces
its protein i.e. repressor tetramer.
 This repressor tetramer goes and binds
with operator site on DNA.
 Upstream to operator, promotor is
present where RNA polymerase binds.
 Repressor tetramer gives hindrance in
the path of RNA polymerase, which has
to move downstream to transcribe these

24. 21
Genes for lactose metabolism. So these
genes are inhibited.

25. How Genes are Activated
22
 These genes are activated if glucose
decreases in the environment of E. coli and
lactose is present.
 So when glucose decreases then cAMP is
increased.
 This cAMP binds with CAP(Catabolic
Activator Protein also known as CRP i.e.
cAMP Regulatory Protein) & makes cAMP-
CAP complex.
 This complex binds to CAP site on DNA
and activates RNA polymerase.

26.  Lactose is converted to its isomer-
Allolactose, which binds to repressor
tetramer and removes repressor
tetramer from operator site.
 So, there is no hindrance of repressor
tetramer and RNA polymerase is active.
 Now genes are activated and
transcription occurs and lactose can be
used by bacterial cell.
23

27. 24

28. 7. References
1. Harper’s Illustrated Biochemistry 30th edition The
McGraw-Hill Companies, Page No. 371-431
2. Lippincott Williams & Wilkins|Wolters Kluwer 4th
edition, Page No. 437
3. Essentials of Biochemistry by Pankaja Naik 2nd
edition, Jaypee Brothers Medical Publishers, Page
No.355-356
4. Biochemistry by U.Satyanarayana 4th edition,
Elsevier Publication, Page No.566-567
5. https://www.topperlearning.com/doubts-
solutions/what-is-lac-operon-in-briefly-zimbkvgg
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