REGULATION OF GENE EXPRESSION IN PROKARYOTES & EUKARYOTES

REGULATION OF
GENE EXPRESSION
IN PROKARYOTES & EUKARYOTES .
This presentation is enriched with lots of information of gene expression with many pictures so that anyone can understand gene expression easily.

Gene expression is the process by which the information encoded in a gene is used to direct the assembly of a protein molecule.
Gene expression is explored through a study of protein structure and function, transcription and translation, differentiation and stem cells.
It is the process by which information from a gene is used in the synthesis of a functional gene product.
These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
The process of gene expression is used by all known life - eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea)
Regulation of gene expression:

Regulation of gene expression includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA).
Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed.
CLASSIFICATION OF GENE WITH RESPECT TO THEIR EXPRESSION:

Constitutive ( house keeping) genes:
Are expressed at a fixed rate, irrespective to the cell condition.
Their structure is simpler.
Controllable genes:
Are expressed only as needed. Their amount may increase or decrease with respect to their basal level in different condition.
Their structure is relatively complicated with some response elements.
TYPES OF REGULATION OF GENE:
positive & negative regulation.
Steps involving gene regulation of prokaryotes & eukaryotes.
Operon-structure,classification of mechanisms- lac operon,tryptophan operon ,
and many things related to gene expression.
This is a video slide so anyone can understand this topic easily by seeing pictures included in this slide.

1. REGULATION OF GENE EXPRESSION IN PROKARYOTES & EUKARYOTES PRESENTED BY AFSANA TAJMIM 4 TH YEAR,1 ST SEMISTER DEPT. OF PHARMACY JESSORE UNIVERSITY OF SCIENCE & TECHNOLOGY 10/25/2014 1

2. OBJECTIVES To know and explain: Regulation of Bacterial Gene Expression Constitutive ( house keeping) vs. Controllable genes OPERON structure and its role in gene regulation Regulation of Eukaryotic Gene Expression at different levels: DNA methylation Histon modifications(Chromatin Remodeling) Increasing the number of gene copies (gene amplification) Changing the rate of initiation of transcription Alternate splicing mRNA stability Changing the rate of initiation of translation 10/25/2014 2

3. Gene expression is the process by which the information encoded in a gene is used to direct the assembly of a protein molecule . Gene expression is explored through a study of protein structure and function, transcription and translation, differentiation and stem cells . It is the process by which information from a gene is used in the synthesis of a functional gene product . These products are often proteins, but in non-protein coding genes such as ribosomal RNA ( rRNA ), transfer RNA ( tRNA ) or small nuclear RNA ( snRNA ) genes, the product is a functional RNA. The process of gene expression is used by all known life - eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea ) GENE EXPRESSION 10/25/2014 3

4. Regulation of gene expression Regulation of gene expression includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA ). Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed. 10/25/2014 4

5. Although a functional gene product may be an RNA or a protein, the majority of known mechanisms regulate protein coding genes. Any step of the gene's expression may be modulated, from DNA-RNA transcription to the post-translational modification of a protein. The first discovered example of a gene regulation system was the lac operon, discovered by Jacques Monod, in which protein involved in lactose metabolism are expressed by E.coli only in the presence of lactose and absence of glucose. Gene regulation drives the processes of cellular differentiation and morphogenesis, leading to the creation of different cell types in multicellular organisms where the different types of cells may possess different gene expression profile. 10/25/2014 5

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7. GENES 10/25/2014 7 Genes are subunits of DNA, the information database of a cell that is contained inside the cell nucleus. This DNA carries the genetic blueprint that is used to make all the proteins the cell needs. Every gene contains a particular set of instructions that code for a specific protein

8. CLASSIFICATION OF GENE WITH RESPECT TO THEIR EXPRESSION Constitutive ( house keeping) genes: Are expressed at a fixed rate, irrespective to the cell condition. Their structure is simpler. Controllable genes: Are expressed only as needed. Their amount may increase or decrease with respect to their basal level in different condition . Their structure is relatively complicated with some response elements 10/25/2014 8

9. TYPES OF REGULATION OF GENE When the expression of genetic information is quantitatively increased by the presence of specific regulatory element is known as positive regulation. Element modulating positive regulation is known as activator or positive regulator. POSITIVE REGULATION : NEGATIVE REGUATION: When the expression of genetic information is diminished by the presence of specific regulatory element is known as negative regulation. The element or molecule mediating the negative regulation is said to be repressor. 10/25/2014 9

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12. Biological systems exhibits 3 types of temporal responses: Increased extent of gene expression is continued in presence of inducing signal. This is commonly observed in prokaryotes in response to intracellular conc. of nutrient . Increased amount of gene expression Is transient even in presence of regulatory signal. This is seen in commonly during development of organism. Type C response: Increased gene expression that persists even after termination of signal. It is seen in development of tissur or organ. Type A response: Type B response: 10/25/2014 12

13. Principles of Gene Regulation RNA polymerase binds to DNA at promoters. 2)Transcription initiation is regulated by proteins that bind to or near promoters. 10/25/2014 13

14. Synthesis of the primary RNA transcript (transcription) Posttranscriptional modification of mRNA Messenger RNA degradation Protein synthesis ( translation ) Posttranslational modification of proteins Protein targeting & transport Protein degradation STEPS INVOLVING REGULATION OF GENE EXPRESSION 10/25/2014 14

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17. In prokaryotes the primary control point is the process of transcription initiation . Different ways for regulation of gene expression in bacteria : Regulation of gene expression can be done by some operon pathways such as 1.lac operon. 2.tryptophan operon. . 10/25/2014 17

18. Step of regulation in prokaRyotes Transcriptional control Translational control Post translational control 10/25/2014 18

19. In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter. Operons occur primarily in prokaryotes but also in some eukaryotes. Operons are related to regulons , stimulons and modulons . An operon is made up of several structural genes arranged under a common promoter and regulated by a common operator . It is defined as a set of adjacent structural genes, plus the adjacent regulatory signals that affect transcription of the structural genes. OPERON 10/25/2014 19

20. General structure of an operon An operon is made up of 4 basic DNA components: Promoter – a nucleotide sequence that enables a gene to be transcribed. The promoter is recognized by RNA polymerase, which then initiates transcription. Regulator – These genes control the operator gene in cooperation with certain compounds called inducers and corepressors present in the cytoplasm. Operator – a segment of DNA that a repressor binds to. It is classically defined in the lac operon as a segment between the promoter and the genes of the operon. Structural genes – the genes that are co-regulated by the operon. 10/25/2014 20

21. General structure of an OPERON 10/25/2014 21

22. OPERON REGULATION Operon regulation can be either negative or positive by induction or repression . Negative control involves the binding of a repressor to the operator to prevent transcription . In negative inducible operons, a regulatory repressor protein is normally bound to the operator, which prevents the transcription of the genes on the operon . If an inducer molecule is present , it binds to the repressor and changes its conformation so that it is unable to bind to the operator. This allows for expression of the operon. The lac operon is a negatively controlled inducible operon, where the inducer molecule is allolactose . In negative repressible operons, transcription of the operon normally takes place. The trp operon, involved in the synthesis of tryptophan (which itself acts as the corepressor ), is a negatively controlled repressible operon . 10/25/2014 22

23. With positive control, an activator protein stimulates transcription by binding to DNA. In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA. When an inducer is bound by the activator protein, it undergoes a change in conformation so that it can bind to the DNA and activate transcription. In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment . However , when an inhibitor is bound by the activator, it is prevented from binding the DNA. This stops activation and transcription of the system . 10/25/2014 23

24. The activity of an Operon in the presence or the absence of repressor 10/25/2014 24

25. The lac operon The lac operon of the model bacterium Escherichia coli was the first operon to be discovered and provides a typical example of operon function . It consists of three adjacent structural genes, a promoter, a terminator, and an operator. The lac operon is regulated by several factors including the availability of glucose and lactose. 10/25/2014 25

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27. Absence of lac operon: 10/25/2014 27

28. Presence of lac operon 10/25/2014 28

29. Activity of an lac operon in the presence or absence of inducer 10/25/2014 29

30. Tryptophan operon Discovered in 1953 by Jacques Monod and colleagues, the trp operon in E. coli was the first repressible operon to be discovered. This operon contains five structural genes : trp E, trp D, trp C , trp B, and trp A, which encodes tryptophan synthetase . It also contains a promoter which binds to RNA polymerase and an operator which blocks transcription when bound to the protein synthesized by the repressor gene ( trp R) that binds to the operator 10/25/2014 30

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32. 10/25/2014 32 Amount of trp operon affect transcription

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34. GENE REGULATION IN EUKARYOTES 10/25/2014 34

35. Eukaryotic cells have a much larger genome Eukaryotes have much greater cell specialization Thus eukaryotic cells contain an enormous amount of DNA that does not program the synthesis of RNA or protein This requires complex organization In eukaryotes expression of gene into proteins can be controlled at various locations 10/25/2014 35

36. Check Points for Gene Expression in Eukaryotes Synthesis of proteins is controlled right from the chromatin stage. Expression of gene is controlled at many steps during the process of transcription and translation. Description of the control points is dealt in detail in the subsequent slides . SEVERAL STEPS OF EUKARYOTIC GENE REGULATION 1.Transcriptional control. 2.RNAprocessing control. 3.RNA transport & localisation control. 4.Translation control. 5.mRNAdegradation control. 6.Protein activator control. 10/25/2014 36

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38. 1.Chromatin Structure Two forms of chromatin Euchromatin – A lesser coiled transcriptionally active region which can be easily accessed by the RNA polymerases. Heterochromatin – A highly condensed transcriptionally inactive region. The genes in this region cannot be accessed by the RNA polymerases for active transcription. Ubiquitination : Ubiquitination of H2A – Transcriptional inactivation Ubiquitination of H2B - Transcriptional activation 10/25/2014 38

39. Mechanisms which affect the chromatin structure and hence the expression of gene are: Histone modifications – These modifications make a region of gene either transcriptionally active or inactive. Acetylation ↑Acetylation ----↓ Condensation of DNA ----- ↑ Transcription of genes in that region Ubiquitination Ubiquitination of H2A – Transcriptional inactivation Ubiquitination of H2B - Transcriptional activation 10/25/2014 39

40. DNA methylation:is the addition or removal of a methyl group predominantely where cytosine bases occur consecutively. bases occur consecutively. DNA methylation:is the addition or removal of a methyl group predominantely where cytosine bases occur consecutively. bases occur consecutively. Methylation occurs most often in symmetrical CG sequences. METHYLATION 10/25/2014 40

41. Acetylation : Methylation: by HDACs and corepressors leads to heterochromatin formation by HATs and coactivators leads to euchromatin formation 10/25/2014 41

42. 2.Regulation of Transcription Eukaryotes – There are two types of promoters which are: Basal promoters Upstream promoters Basal promoter or core promoter - These promoters reside within 40bp upstream of the start site. These promoters are seen in all protein coding genes . Upstream promoters - These promoters may lie up to 200bp upstream of the transcriptional initiation site. The structure of this promoter and the associated binding factors keeps varying from gene to gene. 10/25/2014 42

43. Transcriptional control: … controlling when and how often a given gene is Transcribed Figure 6. Genes can be expressed with different efficiencies. Gene A is transcribed and translated much more efficiently than gene B. This allows the amount of protein A in the cell to bemuch greater than that of protein B. 10/25/2014 43

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45. Enhancers Enhancers can be located upstream, downstream or within the gene that is transcribed The binding of these enhancers with enhancer binding proteins (transcription factors) increases the rate of transcription of that gene to a greater extent. Promoters are capable of initiating lower levels of transcription. Enhancers are responsible for the cell or tissue specific transcription. Each enhancer has its own transcription factor that it binds to . 10/25/2014 45

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62. Reference www.wikipedia.com www.slideshare.com www.webmed.com www.ncbl.com Some articles from internet Some journals 10/25/2014 62

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