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  • 1. GENERAL BIOLOGY HDL 121 DNA REPLICATION & PROTEIN SYNTHESISPREPARED BY: MANEGASCHOOL OF MLTFACULTY OF HEALTH SCIENCE
  • 2. DNA REPLICATION & PROTEIN SYNTHESISLearning Outcomes After completing this lecture, students will be able to: (a) Describe basic chemical substances in cell (b) Explain physical & chemical characteristic of the substances (c) Understand & describe the physiological functions Slide 2 of 10 Topics © 2010 Cosmopoint
  • 3. DNA REPLICATION & PROTEIN SYNTHESISTopic Outlines 1.1. Basic Chemical Substances In Cell 1.1.1 Characteristics 1.1.2 Physical & chemical 1.1.3 Physiological functions Slide 3 of 10 © 2010 Cosmopoint
  • 4. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In CellNucleic acids A macromolecule composed of chains of monomeric nucleotide (linked together) Polynucleotides are formed via polymerisation of nucleotides Form polynucleotides by condensation with the formation of phosphodiester bonds Composed of (a) A base (purine or pirimidine) Purines: Adenine, guanine which are double ring structures Pirimidines: Cytosine, thymine & uracil are single ring structures (b) A sugar (ribose & deoxyribose) (c) A phosphate group 11/16/2011 4 Slide 4 of 10
  • 5. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In Cell 11/16/2011 5 Slide 5 of 10
  • 6. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In Cell In biochemistry, these molecules carry genetic information or form structures within cells The most common nucleic acids are (a) DNA (b) RNA (including mRNA, tRNA & rRNA) 11/16/2011 6 Slide 6 of 10
  • 7. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In Cell RNA  Ribonucleic acid  A close cousin of deoxyribonucleic acid (DNA)  Polymer of ribonucleoside-phosphates.  Its backbone is comprised of alternating ribose & phosphate groups  Contain ribose while DNA contains deoxyribose 11/16/2011 7 Slide 7 of 10
  • 8. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In Cell  Three major types: (a) messenger RNA (mRNA) carries information about a protein sequence to the ribosomes, the protein synthesis factories in the cell (b) transfer RNA (tRNA) is a small RNA chain that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation (c) ribosomal RNA (rRNA) & protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA & carries out protein synthesis 11/16/2011 8 Slide 8 of 10
  • 9. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In Cell 11/16/2011 9 Slide 9 of 10
  • 10. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In CellFunctions  Plays several important roles in the processes of translating genetic information from deoxyribonucleic acid (DNA) into proteins  RNA acts as a messenger between DNA & the protein synthesis complexes known as ribosomes  RNA forms vital portions of ribosomes  Serves as an essential carrier molecule for amino acids to be used in protein synthesis 11/16/2011 10 Slide 10 of 10
  • 11. DNA REPLICATION & PROTEIN SYNTHESIS1.1. Basic Chemical Substances In Cell Differences between DNA & RNA DNA RNADouble strands of polynucleotide Single strand of polynucleotideBigger molecule of more than a million Smaller molecule of less than 1000bases basesEntirely double helix strand Single &/or double helix of intra-strandPentose within is deoxyribose Pentose within is riboseBases consist of A, C, G and T Bases consist of A, C, G and UThe ratio of A + G : C + T = 1 : 1 The ratio of A + G : C + U = 1 : 1Almost all DNA is found in nucleus Found in both nucleus & cytoplasmIts amount is constant in all cells, Its amount varies among cells & it cangametes have half the amount be altered changeChemically stable Not so stableNot being broken down, it exists Can be broken down by enzymesforeverOnly one type Three types: rRNA, tRNA & mRNA 11/16/2011 11 Slide 11 of 10
  • 12. DNA REPLICATION & PROTEIN SYNTHESIS1.1. DNA Replication Introduction - DNA  Within the nucleus of every cell are long strings of DNA  The code that holds all the information needed to make & control every cell within a living organism.  Nucleic acid that contains the genetic instructions used in the development & functioning of all known living organisms.  Functionally divided into genes.  Within the molecule, it has specific sequence of bases.  This sequence of bases codes for a specific sequence of amino acids in a protein. 11/16/2011 12 Slide 12 of 10
  • 13. DNA REPLICATION & PROTEIN SYNTHESIS1.1. DNA Replication  It consists of just a few kinds of atoms: carbon, hydrogen, oxygen, nitrogen & phosphorus  Combinations of these atoms form the sugar-phosphate backbone of the DNA @ the sides of the ladder  Other combinations of these atoms form the four bases: thymine (T), adenine (A), cytosine (C) & guanine (G).  These bases are the rungs of the DNA ladder.  It takes two bases to form a rung – one for each side of the ladder DML 202 General Biology & Human 11/16/2011 Genetics (Chapter 11: DNA & 13 Slide 13 of 10 Protein Synthesis)
  • 14. DNA REPLICATION & PROTEIN SYNTHESIS1.1.1.Process InvolvedDNA Replication  Process in which a molecule of DNA forms 2 molecules of identical ones that are also identical to the original one  Takes place in the nucleus during S interphase i.e. occurs just before cell division in both mitosis & meiosis  Aim: Prepare another identical set of DNA molecules to make identical sister chromatids so that chromosome are formed before cell division can occur 11/16/2011 14 Slide 14 of 10
  • 15. DNA REPLICATION & PROTEIN SYNTHESIS1.1.1.Process Involved 11/16/2011 15 Slide 15 of 10
  • 16. DNA REPLICATION & PROTEIN SYNTHESIS1.1.1.Process Involved  Occurs in semi-conservative way as proved by the experiment of Meselson & Stahl  An uncoiling enzyme helicase initially catalyses the uncoiling of small parts of DNA & then proceeds to the whole DNA  Can proceed simultaneously in several spots of a DNA molecule 11/16/2011 16 Slide 16 of 10
  • 17. DNA REPLICATION & PROTEIN SYNTHESIS1.1.1.Process Involved 11/16/2011 17 Slide 17 of 10
  • 18. DNA REPLICATION & PROTEIN SYNTHESIS1.2 Protein Definition Protein Large organic compounds made of amino acids arranged in a linear chain & joined together by peptide bonds between the carboxyl & amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by a gene & encoded in the genetic code. Genetic code: a system of representation in which a code of 3 bases in the DNA or RNA codes for an amino acid in the protein. 11/16/2011 18 Slide 18 of 10
  • 19. DNA REPLICATION & PROTEIN SYNTHESIS1.2 Protein Definition A primer RNA strand is added to the side of one DNA strand that acts as a template by the addition of nucleotide triphosphates forming the new DNA strand called leading strand It is catalysed by the enzyme DNA polymerase that adds nucleotides to the 3’ end of DNA, so replication proceeds in 5’ to 3’ fashion in the growing new DNA strand The bases on these nucleotides are very particular about what they connect to. Cytosine (C) will pair to guanine (G); adenine (A) will pair to thymine (T) 11/16/2011 19 Slide 19 of 10
  • 20. DNA REPLICATION & PROTEIN SYNTHESIS1.2 Protein Definition However, the process is different in the other complementary strand called lagging strand of DNA that is bent by the enzyme polymerase & short strands called Okazaki fragments are formed also in 5’ to 3’ way DNA ligase: enzyme to join the fragments formed to become continuous long complementary strand Finally when the primer is removed by DNA polymerase, 2 identical strands of DNA are formed Each contains one side of the original DNA & one side made of ‘new’ nucleotide 11/16/2011 20 Slide 20 of 10
  • 21. DNA REPLICATION & PROTEIN SYNTHESIS1.2 Protein Definition 11/16/2011 21 Slide 21 of 10
  • 22. DNA REPLICATION & PROTEIN SYNTHESIS1.2 Protein DefinitionProtein Large organic compounds made of amino acids arranged in a linear chain & joined together by peptide bonds between the carboxyl & amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by a gene & encoded in the genetic code. Genetic code: a system of representation in which a code of 3 bases in the DNA or RNA codes for an amino acid in the protein. 11/16/2011 22 Slide 22 of 10
  • 23. DNA REPLICATION & PROTEIN SYNTHESIS1.2 Protein Definition 11/16/2011 23 Slide 23 of 10
  • 24. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) Can be divided into Protein Synthesis (a) transcription (b) activation of amino acids (c) translation (d) formation of functional protein 24 Slide 24 of 10
  • 25. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) 25 Slide 25 of 10
  • 26. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) 26 Slide 26 of 10
  • 27. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation)Translation  The sequence of bases in mRNA is translated to become a sequence of amino acids in a polypeptide  Initially, mRNA forms a complex with the subunits of ribosome  Two sites, P and A are created on the surface of the ribosome with the first & second codes of the mRNA in them respectively  The ribosome binds to the mRNA at the start codon (AUG)  Two suitable amino-acyl tRNAs are then attached to the P site & the A site respectively each with its anti-codon complementary to that of the mRNA. 27 Slide 27 of 10
  • 28. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) 28 Slide 28 of 10
  • 29. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) 29 Slide 29 of 10
  • 30. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) A peptide bond is formed between the two amino acids, which are brought close together. The process is catalysed by a ligase A relative movement occurs in which the 3rd code of the mRNA is shifted to the A site & its 1st code is shifted out liberating the 1st tRNA & the 2nd code sits on the P site 30 ) Slide 30 of 10
  • 31. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation)Protein Synthesis Purpose: create a polypeptide – a protein made out of a chain of amino acids In a hair follicle cell, a protein called keratin is made. Many ribosomes can be working on a single strand of mRNA at once. Is not a slow process A protein chain with 400 amino acids long can be assembled in 20 seconds. 31 Slide 31 of 10
  • 32. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) A peptide bond is formed between the 2nd & 3rd amino acid lengthening the polypeptide Another relative movement occurs & the process is repeated with further lengthening of the polypeptide until the last code gets into A site 32 Slide 32 of 10
  • 33. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) The last codon is a ‘nonsence’ codon (UAG, UAA & UGA) indicating a ‘full stop’. No amino acyl-tRNA can get into the A site. The final relative movement would liberate the completed polypeptide, mRNA, tRNA & the subunits of the ribosomes 33 Slide 33 of 10
  • 34. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) 34 Slide 34 of 10
  • 35. DNA REPLICATION & PROTEIN SYNTHESIS1.2.1 Protein Synthesis (transcription and translation) DML 202 General Biology & Human 11/16/2011 Genetics (Chapter 11: DNA & 35 Slide 35 of 10 Protein Synthesis)
  • 36. DNA REPLICATION & PROTEIN SYNTHESIS Slide 36 of 10 Topics