Inhibitors of Dna replication, transcription and translation

This ppt tells about various inhibitors of Dna replication, transcription and translation

1. INHIBITORS OF DNA REPLICATION TRANSCRIPTION ANDTRANSLATION Presenter Name : Deepak Patel Batch : MBBS 2024-25 Roll No: 31 Moderated By : Dr. Professor B.P.Mishra Sir Department Of Biochemistry MSD Autonomous State Medical College & MB Hospital, Bahraich

2. Index Inhibitors of DNA replication Inhibitors of DNA transcription Inhibitors of DNA translation Varieties of inhibitors in protein synthesis

3. INHIBITORS OF DNA Replication

4. Supercoiling and DNA gyrase When DNA is under strain due to overwinding or underwinding , it can twist upon itself to relieve the stress. This twisting is called supercoiling. TYPES OF SUPERCOILING: In negative supercoiling, the DNA is underwound , meaning it has fewer helical turns than it would naturally have. In positive supercoiling, the DNA is overwound, meaning it has more helical turns than it would naturally have. This further compacts the DNA, making it more difficult for proteins to access the genetic information. Enzymes called topoisomerases play a crucial role in regulating supercoiling by adding or removing twists in the DNA.

5. During DNA replication, helicases unwind the DNA double helix, creating positive supercoils ahead of the replication fork. DNA gyrase removes these positive supercoils and introduces negative supercoils, allowing replication to proceed smoothl y.

6. INHIBITORS OF Bacterial DNA gyrase Ciprofloxacin Nalidixic acid Mechanism of action: Ciprofloxacin an antibiotic binds to the A subunit of DNA gyrase , an enzyme that introduces negative supercoils into DNA, which is crucial for DNA replication and transcription. This blockage leads to the accumulation of DNA damage, including double-strand breaks, which are generally lethal to bacterial cell

7. 6 mercaptopurine 6-MP is a purine analog , meaning it resembles the natural purine bases adenine and guanine, which are essential components of DNA and RNA. In the cell, 6-MP is converted into 6-thioguanine nucleotides (6-TGN) , they are incorporated into DNA and RNA during replication and transcription, acting as fraudulent bases. 6-MP also inhibits the enzyme phosphoribosyl pyrophosphate amidotransferase (PRPP amidotransferase ), which is crucial for de novo purine synthesis. Effects; The fraudulent bases disrupt the normal structure of DNA, causing replication errors and potentially leading to cell death.

8. 5 Fluorouracil Metabolic Conversion : 5-FU enters cells and is converted into several active metabolites, including FdUMP. Thymidylate Synthase Inhibition : FdUMP binds to and inhibits thymidylate synthase . dTMP Depletion : TS is essential for producing dTMP, which is needed for DNA synthesis. DNA Replication Disruption: By inhibiting TS, 5-FU starves the cell of dTMP, disrupting DNA replication.

9. INHIBITORS OF TRANSCRIPTION

10. Alpha Amanitin Alpha- amanitin is a bicyclic octapeptide , meaning it's a molecule composed of eight amino acids arranged in a cyclic structure with two rings. Alpha- amanitin specifically binds to RNA polymerase II, blocking its ability to transcribe DNA into mRNA. It inhibits the polymerase activity in both initiation and elongation states.

11. Actinomycin D Actinomycin D binds to DNA, specifically targeting guanine residues, and inhibits RNA synthesis by interfering with DNA-dependent RNA polymerase. This action disrupts the ability of cancer cells to replicate and grow.

12. Rifampicin Rifampicin specifically targets the beta subunit ( rpoB ) of bacterial RNA polymerase, an enzyme crucial for transcription. It binds to a specific pocket within the RNA polymerase, This binding prevents the enzyme from effectively initiating RNA synthesis, thereby inhibiting the transcription process.

13. INHIBITORS OF TRANSLATION

14. Varieties of inhibitors INHIBITORS inhibiting protein synthesis in prokaryotes. 1. Erythromycin 2. Chloromphenicol 3. Tetracyclin INHIBITORS inhibiting protein synthesis in both eukaryotes and prokaryotes 1. Puromycin INHIBITORS inhibiting protein synthesis in eukaryotes 1. Diptheria Toxin 2. Rici n

15. Erythromycin • Erythromycin inhibits protein synthesis by binding to the 23srna molecule (in the 50S subunit) of the bacterial ribosome. • Binds to the larger subunit of ribosomes and thereby inhibits translocation of the polypeptide chain from A site to P site.

16. Chloromphenicol It is an antibiotic and its binding is reversible Chloramphenicol functions by binding to the A site of the 50S subunit of the ribosome. It affects proper binding of the aminoacyl tRNA to the A site and thus inhibits the peptidyl transferase activity.

17. Tetracyclin Semisynthetic antibiotic made by catalytic hydrogenation of chlorotetracycline . It binds to 30S ribosomal subunit. Blocking binding of aminoacyl tRNA to the A site of ribosome.

18. Puromycin It is bind to the ribosomal A site and participate in peptide bond formation, producing peptidylpuromycin . It does not engage in translocation and dissociates from the ribosome shortly after it is linked to the carboxyl terminal of the peptide. This premature dissociation terminates polypeptide synthesis

19. Diptheria Toxin Diphtheria toxin, a protei n is composed of two fragments: fragment A and fragment B . Fragment B is responsible for binding to a specific receptor on the surface of the host cell. This binding triggers the cell to engulf the toxin in a process called endocytosis, forming an endosome. Once in the cytoplasm, fragment A, also known as the catalytic domain, interacts with NAD+ and EF-2. It catalyzes the transfer of the ADP-ribose moiety from NAD+ to EF-2, This ADP- ribosylation inactivates EF-2. EF-2 is crucial for protein synthesis, and its inactivation halts the translation of mRNA

20. Ricin Ricin, a toxic protein found in castor beans, inhibits protein synthesis by inactivating ribosomes. Ricin, composed of A and B chains, enters cells through a process called endocytosis, where the cell membrane engulfs the toxin. After internalization, the ricin A chain undergoes a process of retrograde transport from the Golgi apparatus to the ER. Within the ER, the disulfide bond between the A and B chains is cleaved, The ricin A chain, now in the cytosol, acts as an enzyme, targeting and modifying the 28S rRNA of the ribosome. It specifically cleaves an adenine base from a specific site (position 4324) within the 28S rRNA

21. References Textbook of Biochemistry for Medical Student By D.M Vasudevan 9th and 10th edition.