The document discusses various mechanisms of gene expression and regulation in prokaryotes and eukaryotes. It explains that gene expression involves the transcription of DNA into mRNA and the translation of mRNA into protein. In prokaryotes, genes may be organized into operons and regulated through repression and induction. The lactose and tryptophan operons are discussed as examples. Eukaryotes have additional complexities in gene expression including RNA processing, alternative splicing, and transport of mRNA. Gene expression is regulated at transcriptional, post-transcriptional, translational, and post-translational levels.

3. Synthesis of protein under the influence of gene is
called gene expression
All genes of cell are not expressed at all the time
for example any hormone ( Eg Insulin)

4. It is a combined process of the
transcription of a gene into mRNA , the
processing of that mRNA and its
translation into protein
The gene is expressed in the form of
protein
Prokaryotic gene is controlled mainly
at the level of transcription m-RNA
synthesis

6. Regulation of gene expression is
absolutely essential for the growth,
development and the very existence
of an organism
They are of two type :-
1.Positive Regulation (Inducers)
2.Negative Regulation(Repressors)

7. There are two types of genes -
1.constitutive gene-they are present in almost each
and every cell , therefore also know as housekeeping
genes
 Example- citric acid cycle
2. Inducible gene – they are synthesized when
molecular signals are given
 Example – Tryptophan pyrrolase of liver is induced
by tryptophan
Inducible genes are subject to regulated expression

8.  The chemical product of gene expression is a protein which
may be an enzyme
Each gene codes for specific enzyme-
One gene –one enzyme , where as several enzymes are
composed of more than two non-identical subunits
 The cistron is the smallest unit of genetic expression .It is
the fragment of DNA coding for the subunit of a protein
molecule.
Thus the original concept one gene-one enzyme is replaced
by one cistron-one subunit

9. Prokaryotes have a simple mechanism
for coordinating the regulation of gene
.In prokaryotes the gene are clustered
on chromosome and transcribed
together
In prokaryotes the gene involved, in
metabolic pathway are often present in
a linear fashion called an operon
Example –
Lactose operon

10. OPERON
 Operon is a functioning unit of DNA containing a cluster
of genes under the control of single promoter
 Its Unit of gene expression, which includes structural
genes, control elements, regulator/inhibitor gene,
promoter and operator area

12. Schematic Diagram of LAC
OPERON

13. Regulatory
gene(Lac
i)
• Produces a
repressor
protein
Promoter
site(P)
• CAP site
• Site for entry of
RNA polymerase
Operator
site
• LAC repressor
binds here
Structural
genes
• Z-galactosidase
• Y-galactosidase
permease
• A-Transacetylase

14. Ai P O Z Y A
RNA
polymeras
e

15. Ai P O Z Y A
RNA
polymeras
e

16. Ai P O Z Y A
RNA
polymeras
e
Galactosidase

17. Ai P O Z Y A
RNA
polymeras
e
Galactosidase

18. Ai P O Z Y A
RNA
polymeras
e
Galactosidase
Permease

19. Ai P O Z Y A
RNA
polymeras
e
Galactosidase
Permease

20. Ai P O Z Y A
RNA
polymeras
e
Galactosidase
Permease
Transacetyla
se

21. Ai P O Z Y A
RNA
polymeras
e
Galactosidase
Permease
Transacetylase

23. Type of
regulation
Regulated
by
Lactose Glucose
Negative
regulation
Lac
repressor
Absent Present
Positive
regulation
Induction of
expression
Present Absent
Positive
control
Catabolite
repression
Present Present

24. Ai P O Z Y A
active

25. Ai P O Z Y A
Repressor
protein

26. Ai P O Z Y A
Repressor
protein

27. Ai P O Z Y A
Repressor
protein

28. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase

29. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase

30. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase

31. Ai P O Z Y A
Repressor
protein

33. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase
Lactose

34. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase
Lactose

35. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase
Lactose

36. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase
Lactose

37. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase
Lactose

38. Ai P O Z Y A
Repressor
protein
RNA
polymer
ase
Lactose
Galactosidase
Permease
Transacetyla
se

40. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
glucose
glucose
glucose

41. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
glucose
glucose
glucose

42. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMP

43. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP

44. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP

45. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP

46. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP

47. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP

48. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP
Galactosidase
Permease
Transacetyla
se

49. Ai P O Z Y A
RNA
polymer
ase
Lactose
Lactose
Lactose
Lactose
Lactose
cAMPCAP
Galactosidase
Permease
Transacetyla
se

51. Lactase in human intestine is an inducible enzyme.
Clinical manifestations of lactase deficiency and lactose
intolerance are described.
Examples of derepression in human beings:
1. Induction of tryptophan pyrrolase by tryptophan
2. Transaminases by glucocorticoids
3. ALA synthase by barbiturates
4. Glucuronyl transferase by barbiturates.
Clinical Applications of Derepression

52. Repression is the mechanism by which the presence of excess
product of a pathway shuts off the synthesis of the key
enzyme of that pathway.
Heme synthesis is an example. It is regulated by repression of
ALA synthase, the key enzyme of the pathway.
Regulation of Genes by Repression

53. Repression of heme synthesis by heme.
(ALA: aminolevulinic acid; RNAP: RNA polymerase)

54. 5 structural genes
2 polycistronic
mRNAs
3 enzymes

55. TRP Operon is a group of genes encode
biosynthetic enzyme for amino acid Trp
Found in E Coli.
Repressible Operon
Eg of Feedback Inhibition
Trp Operon expressed on- when trp level
is low
Repressed when- trp level is high

56. Tryptophan
repressor
2
Molecules
of
tryptophan
Repressor

57. content
 TRP operon consists of:
1. 5 structural genes:
 Trp e
 Trp d
 Trp C
 Trp B
 Trp a
2. Regulatory Gene
3. Promoter
4. Operator
5. Terminator

58. Turning on and turning off
 Trp operon is normally ON.
 If surrounding medium contains Large amount of Trp:
Switched OFF.
 Trp repressor regulates Synthesis of Trp

59. Mechanism of on and off
 Trp repressor is bind with DNA of operator and block the
transcription of structural gene.
 Trp repressor doesn’t always bind to DNA instead it bind and block
Transcription only when Trp is present
 When Trp is around it, attaches to the repressor molecule and
change their structural Configuration
 Small Molecule like Trp Which Switches a repressor into its Active
state is called Co-represser
 Trp repressor(inactive) + Co-represser = Active repressor.
 Active repressor bind with Operator to block Transcription

61. Attenuation
 Mechanism based on Coupling of Transcription and
Translation.
 Trp operon is a classical example of Attenuation.
 Attenuator Region: Additional control site for regulation
of transcription

62. Continued…
 If any of RNA polymerase escape repression at the
operator, transcription begins at the Promoter.
 But, due to presence of TRP a region, transcription is
prematurely terminated at Attenuter region
 In absence of TRP, attenuter has no effect on
transcription and Transcription proceed as usual

64. GENE EXPRESSION IN EUKARYOTES
 The important features of eukaryotic gene expression
along with the regulatory aspects are described in the
eukaryotic cells also employ variety of other mechanisms
to regulate gene expression. The most important ones
are listed below , and briefly described next

65. Continued…
 1. Gene Amplification
 2.Gene Rearrangment
 3.Processing of RNA
 4. Alternate mRNA splicing
 5.Transport of mRNA from nucleus to cytoplasm
 6.Degradation of mRNA

67. Gene Amplification
 Methotrexate resistance by cancer cells
 Methotrexate inhibits the enzyme dihydrofolate
reductase.
 The malignant cells develop drug resistance to long
term administration of methotrexate by amplifying the
genes coding for dihydrofolatereductase
 Result for active folate more replication

68. Gene rearrangement

71. Processing of mRNA
 Splicing
 Capping
 Poly (A) Tail

72. Alternate mRNA splicing
For example, tropomyosin (TM) is an actin filament-binding
protein that regulates the functions of actin in both muscle
and nonmuscle cells.

73. Degradation of mRNA
 Prevented by Capping and poly (A) Tail
 Also by Stem loop in Non coding region
 Certain hormone acts by acting on protein that
regulates formation of above factors

74. Co and Post transcriptional
regulation-mRNA Editing
 apoprotein (apo) B—an essential protein component of
chylomicrons and very low density lipoproteins.
 Apo B mRNA is made in the liver and the small intes- tine;
however, in the intestine only, the C residue in the codon
(CAA) for glutamine is deaminated to U, changing the sense
codon to a nonsense or stop codon (UAA)
 This results in a shorter protein (apo B-48, representing 48%
of the message) being made in the intestine (and
incorporated into chylomicrons) than is made in the liver
(apo B-100, full-length, incorporated into VLDL)

75. ApoB48

76. Trans acting regulation –
locally such as TFs

77. Cis Acting regulation-
Hormone ( Not localised)

78. Cis Acting regulation-
Hormone ( Not localised)

79. Impacting mRNA stability

80. Impacting mRNA stability

81. At translation level
Phosphorylation of eIF-2 inhibits
its function and so inhibits
translation at the initiation step

82. Post Translationally
Hypermethylation inhibits
gene expression