Protein synthesis in cell

BIOCHEMISTRY MEDICAL

1. Protein Synthesis in Cell

2. Learning Objectives Importance of proteins Site of protein synthesis Steps of protein synthesis Regulation of protein synthesis Applied aspects 10/12/2015 Dept. of Physiology, MSRMC

3. Proteins: their importance Membrane proteins Structural proteins Enzymes Hormones Antigens 10/12/2015 Dept. of Physiology, MSRMC

4. 10/12/2015 Dept. of Physiology, MSRMC Site of Protein Synthesis

5. Site of Protein Synthesis 10/12/2015 Dept. of Physiology, MSRMC

6. DNA DNA has two functions. self-renewing data repository that maintains a constant source of genetic information for the cell. serve as a template for the translation of genetic information into proteins, which are the functional units of the cell. 10/12/2015 Dept. of Physiology, MSRMC

7. Basic building blocks of DNA Phosphoric acid Sugar Nitrogenous base 10/12/2015 Dept. of Physiology, MSRMC

8. Gene The gene consists of a segment of DNA that is transcribed into RNA. Gene expression is tissue specific. Gene expression is inducible. Central dogma of molecular biology : genetic information flows unidirectionally from DNA to proteins. 10/12/2015 Dept. of Physiology, MSRMC

9. Genetic Code The gene consists of a segment of DNA that is transcribed into RNA. The genetic code consists of successive "triplets" of bases on the DNA. Each three successive bases is a code word. The successive triplets eventually control the sequence of amino acids in a protein molecule that is to be synthesized in the cell. 10/12/2015 Dept. of Physiology, MSRMC

10. Pathway from Genes to Proteins 10/12/2015 Dept. of Physiology, MSRMC

11. Central dogma of molecular biology : genetic information flows unidirectionally from DNA to proteins. 10/12/2015 Dept. of Physiology, MSRMC

12. Steps of Protein Synthesis Transcription Translation Post translational modificaton 10/12/2015 Dept. of Physiology, MSRMC

13. Transcription Definition : Transcription is the synthesis of RNA from a DNA template, mediated by an enzyme called RNA polymerase. Site: Nucleus 10/12/2015 Dept. of Physiology, MSRMC

14. Requirements: DNA template RNA polymerase Activated ribonucleotides Transcription contd. 10/12/2015 Dept. of Physiology, MSRMC

15. Building blocks of RNA Phosphoric acid Sugar Nitrogenous base 10/12/2015 Dept. of Physiology, MSRMC

16. The basic building blocks of RNA form RNA nucleotides. RNA nucleotides are then activated by RNA Polymerase. 10/12/2015 Dept. of Physiology, MSRMC

17. "Activation" of the RNA Nucleotides This occurs by adding to each nucleotide two extra phosphate radicals to form triphosphates . These last two phosphates are combined with the nucleotide by high-energy phosphate bonds derived from ATP in the cell. 10/12/2015 Dept. of Physiology, MSRMC

18. The result of this activation process is that large quantities of ATP energy are made available to each of the nucleotides. This energy is used to promote the chemical reactions that add each new RNA nucleotide at the end of the developing RNA chain. 10/12/2015 Dept. of Physiology, MSRMC

19. RNA polymerase recognises the promoter region in DNA and binds to it. Unwinding of a segment of DNA Attachment of activated ribonucleotides to the DNA segment 10/12/2015 Dept. of Physiology, MSRMC

20. In the DNA strand immediately ahead of the initial gene is a sequence of nucleotides called the promoter . The RNA polymerase has an appropriate complementary structure that recognizes this promoter and becomes attached to it. This is the essential step for initiating formation of the RNA molecule. 10/12/2015 Dept. of Physiology, MSRMC

21. Transcription from DNA in chromatin requires partial disruption of the regular nucleosome structure and some unwinding of the DNA. During synthesis of RNA, the two strands of the DNA molecule separate temporarily; one of these strands is used as a template for synthesis of an RNA molecule. 10/12/2015 Dept. of Physiology, MSRMC

22. The polymerase causes unwinding of about two turns of the DNA helix and separation of the unwound portions of the two strands. Then the polymerase moves along the DNA strand, temporarily unwinding and separating the two DNA strands at each stage of its movement. 10/12/2015 Dept. of Physiology, MSRMC

23. As it moves along, it adds at each stage a new activated RNA nucleotide to the end of the newly forming RNA chain. First, it causes a hydrogen bond to form between the end base of the DNA strand and the base of a RNA nucleotide in the nucleoplasm . 10/12/2015 Dept. of Physiology, MSRMC

24. Polymerase moves along the DNA strand Breakage of 2 phosphate radicals from RNA nucleotides Covalent linkage of 3 rd phosphate with ribose 10/12/2015 Dept. of Physiology, MSRMC

25. Then, one at a time, the RNA polymerase breaks two of the three phosphate radicals away from each of these RNA nucleotides, liberating large amounts of energy from the broken high-energy phosphate bonds. This energy is used to cause covalent linkage of the remaining phosphate on the nucleotide with the ribose on the end of the growing RNA chain. 10/12/2015 Dept. of Physiology, MSRMC

26. RNA polymerase reaches end of DNA gene (chain terminating sequence) Breaking away of polymerase & RNA chain Formation of RNA transcript 10/12/2015 Dept. of Physiology, MSRMC

27. When the RNA polymerase reaches the end of the DNA gene, it encounters a new sequence of DNA nucleotides called the chain-terminating sequence. This causes the polymerase and the newly formed RNA chain to break away from the DNA strand. The polymerase can be used again and again to form still more new RNA chains. 10/12/2015 Dept. of Physiology, MSRMC

28. The code that is present in the DNA strand is eventually transmitted in complementary form to the RNA chain. The ribose nucleotide bases always combine with the deoxyribose bases in a fixed combination. 10/12/2015 Dept. of Physiology, MSRMC

29. DNA Base RNA Base Guanine…………………………….……Cytosine Cytosine ………………………..…….… Guanine Adenine …………………………………… Uracil Thymine ………………………………… Adenine 10/12/2015 Dept. of Physiology, MSRMC

30. 10/12/2015 Dept. of Physiology, MSRMC

31. The RNA that is initially transcribed from a gene is called the primary transcript. Most eukaryotic genes contain exons , DNA sequences that are present in the mature mRNA, alternating with introns , which are not present in the mRNA. 10/12/2015 Dept. of Physiology, MSRMC

32. Splicing Addition of 5’ methyl cap Cleavage of RNA transcript downstream from polyadenylation signal Addition of poly A tail 10/12/2015 Dept. of Physiology, MSRMC Processing of The Primary Transcript

33. Processing of The Primary Transcript First, the cell removes the sequences of the introns from the primary transcript by a process called pre-mRNA splicing. Splicing involves the joining of the sequences of the exons in the RNA transcript and the removal of the intervening introns. 10/12/2015 Dept. of Physiology, MSRMC

34. 10/12/2015 Dept. of Physiology, MSRMC

35. Second, the cell adds an unusual guanosine base, which is methylated at the 7 position, through a 5′-5′ phosphodiester bond to the 5′ end of the transcript. The result is a 5′ methyl cap. The presence of the 5′ methyl cap is required for export of the mRNA from the nucleus to the cytoplasm as well as for translation of the mRNA. Processing of The Primary Transcript 10/12/2015 Dept. of Physiology, MSRMC

36. The third processing step is cleavage of the RNA transcript about 20 nucleotides downstream from the polyadenylation signal, near the 3′ end of the transcript. Processing of The Primary Transcript 10/12/2015 Dept. of Physiology, MSRMC

37. The fourth step is the addition of a string of 100 to 200 adenine bases at the site of the cleavage to form a poly(A)tail. This tail contributes to mRNA stability. Processing of The Primary Transcript 10/12/2015 Dept. of Physiology, MSRMC

38. Types of RNA mRNA tRNA rRNA miRNA 10/12/2015 Dept. of Physiology, MSRMC

39. mRNA mRNA molecules are long, single RNA strands that are suspended in the cytoplasm. They contain codons that are exactly complementary to the code triplets of the DNA genes. 10/12/2015 Dept. of Physiology, MSRMC

40. Carrier for specific amino acids from cytoplasm to mRNA Has sites for binding amino acid & mRNA 10/12/2015 Dept. of Physiology, MSRMC tRNA

41. tRNA It acts as a carrier to transport its specific type of amino acid to the ribosomes , where protein molecules are forming. In the ribosomes , each specific type of tRNA recognizes a particular codon on the mRNA and thereby delivers the appropriate amino acid to the appropriate place in the chain of the newly forming protein molecule. 10/12/2015 Dept. of Physiology, MSRMC

42. The specific code in the tRNA that allows it to recognize a specific codon is a triplet of nucleotide bases called an anticodon . During formation of the protein molecule, the anticodon bases combine loosely by hydrogen bonding with the codon bases of the mRNA. In this way, the respective amino acids are lined up one after another along the mRNA chain 10/12/2015 Dept. of Physiology, MSRMC

43. rRNA Functions in association with tRNA & mRNA Present in ribosomes 10/12/2015 Dept. of Physiology, MSRMC

44. rRNA Functions in association with tRNA & mRNA tRNA transports amino acids to the ribosome for incorporation into the developing protein molecule mRNA provides the information necessary for sequencing the amino acids in proper order for each specific type of protein to be manufactured. 10/12/2015 Dept. of Physiology, MSRMC

45. miRNA Non-coding RNA Regulate gene expression 10/12/2015 Dept. of Physiology, MSRMC