Regulation of Gene Expression ppt
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The document discusses gene expression, detailing the processes of transcription and translation, and factors influencing these processes such as environmental elements and hormonal signaling. It highlights the roles of promoters, enhancers, and transcription factors in regulating gene expression, along with the significance of chromatin structure modifications for transcription accessibility. Additionally, it covers the interaction of siRNA and miRNA with mRNA, affecting gene regulation through cleavage and translation inhibition.
Regulation of Gene Expression ppt
- 3. By: Khaled El Masry Assistant Lecturer of Human Anatomy & Embryology Mansoura Faculty of Medicine
- 4. A gene is the sequence of nucleotides in DNA encoding one polypeptide chain or one mRNA molecule. Gene expression is carried out in 2 steps: 1. transcription. 2. translation.
- 5. 1. Environmental factors as heat and light. 2. Signaling molecules as hormones and growth factors.
- 6. HEAT: Exposure to high temperature Transcription of heat shock genes Synthesis of heat shock proteins Stabilize the internal cellular environment
- 7. LIGHT: In plants exposure to light Activate transcription of the gene for Ribulose Carboxylase The enzyme that plays a critical role in PHOTOSYNTHESIS
- 8. HORMONES ”STEROID HORMONES” Hormone receptor complex Act as a transcription factor “PEPTIDE HORMONES” Activate a signaling system
- 10. 1. Regulatory elements: Promoters & Enhancers 2. Transcription factors: Basal & Special
- 11. Promoters The region necessary to initiate transcription. Consists of short nucleotide sequence that serve as the recognition point for binding of RNA polymerase. Located immediately adjacent to the genes they regulate, upstream from the transcription startpoint.
- 12. There are significant differences in number , orientation and distance between promoters in different genes. Promoters for RNA polymerase II include: TATA box, CAAT box, GC box, & Octamer box. Promoters for RNA polymerase & I III have a different sequence and bind different transcription factors.
- 13. Site Structure Importance TATA box 25-30 bp upstream 8 bp sequences Mutations in this (from the initial composed only of sequence greatly point of T=A pairs. reduce transcription transcription (Loosing the ability to bind to transcription factors) CAAT box 70-80 bp upstream CAAT or CCAAT Mutations in this (from the initial sequence. sequence greatly point of reduce transcription transcription GC box 110 bp upstream GGGCGG Documented by (from the initial sequence, often mutational analysis point of present in multiple transcription copies. Octamer box 120-130 bp ATTTGCAT Affects the upstream sequence. efficiency of (from the initial promoter in point of initiating transcription transcription.
- 14. DNA sequences interact with regulatory proteins increase the efficiency of initiation of transcription increase its rate.
- 15. Enhancers: Large >>>> up to several hundred bp long). Tissue- specific >>>> ( stimulate transcription only in certain tissues).
- 16. 1. The proteins that bind to enhancers affect the activity of proteins that bind to promoters.??? 2. Enhancers may allow RNA polymerase to bind to DNA and move along the chromosome till it reaches a promoter site. 3. May respond to molecules outside the cell ( e.g : steroid hormones). 4. May respond to molecules inside the cell ( e.g : during development thus the gene participates in cell differentiation).
- 17. Enhancers bind to transcription factors by at Least 20 different proteins Form a complex change the configuration of the chromatin folding, bending or looping of DNA.
- 19. DNA looping will bring the distal enhancers close to the promoter site to form activated transcription complexes, then the transcription is activated, increasing the overall rate of RNA synthesis.
- 21. 1. The enhancers affect the gene expression independent of their position or orientation. 2. The enhancers operate from a distance away from their target genes.
- 22. Def. : “ they are proteins essential for initiation of the transcription, but they are not part of RNA polymerase molecule that carry out the transcription process”.
- 23. Function: Each RNA polymerase requires a number of transcription factors which help in: 1. Binding of the enzyme to DNA template. 2. Initiation and maintenance of transcription. 3. Control the rate of gene expression.
- 24. These proteins contain 2 functional domains (a.as that perform specific function). 1. DNA binding domain: binds to DNA sequences present in regulatory regions (e.g : TATA binding protein). 2. Transcriptional activating domain: activate transcription via protein-protein interaction
- 26. 1. Basal transcription factors: The initiation of transcription by RNA polymerase II requires the assistance of several basal transcription factors. Each of these proteins binds to a sequence within the promoter to facilitate the proper alignment of RNA polymerase on the template strand of DNA.
- 27. The basal TFs must interact with the promoters in the correct sequence to initiate transcription effectively. TFIID is the 1st basal TF that interact with the promoter ; it contains TATA- Binding Protein. Followed by TFII B, F, E, H & J.
- 29. 2. Special TFs: Involved in regulation of heat, light, and hormone inducible genes. They bind to: a. enhancers. b. Basal TFs. c. RNA polymerase that bind to the gene promoter. Thus, special TFs can regulate the transcriptional activity of the gene.
- 30. The normal structure of the chromatin suppresses the gene activity, making the DNA relatively inaccessible to transcription factors, and thus active transcription complex can’t occur. Thus chromatin remodeling is needed ( it is a change in chromatin conformation in which proteins of nucleosomes are released from DNA , allowing DNA to be accessible for TFs and RNA polymerase).
- 31. Inactive chromatin remodeled into active chromatin by 2 biochemical modifications: 1. Acetylation of histone proteins by histone acetyl transferases which loosen the association between DNA and histone. 2. Specialised protein complexes disrupt the nucleosome structure near the gene’s promoter site. ( this protein complex slides histone along DNA transfer the histone to other location on DNA molecule.
- 32. Active chromatin can be deactivated by 3 biochemical reactions: 1. Histone deacetylation ( catalysed by histone deacetylase). 2. Histone methylation ( catalysed by histone methyl transferases). 3. Methylation of some DNA nucleotides by DNA methyl transferases. (Chromatin subjected to these modifications tends to be transcriptionaly silent)
- 34. siRNA & miRNA These molecules 21-28 bp long. Able to interact with specific mRNA molecules. This interaction occurs by base pairing ( ) a single strand of iRNA and a complementary sequence in the mRNA molecule.
- 35. siRNA miRNA Base pair perfectly with Base pair imperfectly the target sequence in with the target mRNA sequence in mRNA mRNA cleavage and mRNA inhibition of degradation translation