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3rd lecture Principles of Biotechnology Nucleic acids (DNA & RNA) and Biotechnology Introduction: 1) Nucleic acids are organic molecules (biomolecules) that allow organisms to transfer genetic information from one generation to the next. 2) There are two types of nucleic acids: deoxyribonucleic acid, known as DNA and ribonucleic acid, known as RNA. Why should study DNA and RNA in Biotechnology 1) One of the most important process in biotechnology is the ability to manipulate the genetic material of an organism. 2) DNA represent as a genetic material in all organism except in some viruses which have RNA as a genetic material. 3) So we need to study their structure, functions, replication, transcription and translation in order to understand these molecules and to know the mechanism that enable us to manipulate them. Why DNA is better than RNA as a genetic material 1) DNA is chemically more stable than RNA. 2) DNA has the ability to replicate itself. 3) DNA has the ability to evolve and change itself. 4) DNA is able to express the information when needed. Experiments to prove that DNA as genetic material Frederick Griffith’s Experiments (1928) 1) Griffith was studying two strains of the bacteria Streptococcus pneumoniae, which causes pneumonia and other infections. 2) Smooth strain (S): Produced a polysaccharide capsule that gave its colonies a smooth appearance. 3) Because of the capsule, the bacteria can evade the immune system and cause disease (so called pathogenic strain) 1 Dr. Mohanad J.K. Al-Dawah 3rd lecture Principles of Biotechnology 4) Rough strain (R): Does not produce a capsule, rough appearance, not pathogenic and doesn’t cause disease (so called non-pathogenic strain) 5) Griffith treated his mice with the following bacterial preparations: Treatment Outcome Live rough Mice lives Live smooth Mice dies Heat killed smooth (HKS) Mice lives HKS + live rough Mice dies Griffith conclusions 1) Griffith concluded that the genetic instructions to make capsules had been transferred to the rough bacteria, from the dead smooth bacteria. 2) He called this phenomenon transformation. 3) However, he was unable to identify what type of molecule was responsible for transformation. Figure 1: Griffith experiment (Transformation experiment) 2 Dr. Mohanad J.K. Al-Dawah 3rd lecture Principles of Biotechnology Oswald Avery’s Experiments (1944) 1) Avery repeated Griffith’s experiments using purified DNA, protein, and other substances. 2) He showed that the chemical substance responsible for transformation was DNA and not protein. 3) While many biologists were convinced, others remained doubtful. Hershey and Chase Experiments (1952): 1) They performed the definitive proof that DNA rather than protein carries the hereditary information of life 2) E. Coli bacteriophage: A virus that infects bacteria. 3) Bacteriophages only contain a protein coat (capsid) and DNA. 4) They wanted to find out whether the protein or DNA carried the genetic instructions to make more viruses. 5) They labeled either the viral proteins or DNA: 6) Protein capsid: Labeled with radioactive sulfur (35S) 7) DNA: Labeled with radioactive phosphorus (32P) 8) Radioactive labeled viruses were used to infect cells. 9) Bacterial cells that were infected with the two types of bacteriophage, were then centrifuged and examined. Results: 1) Labeled viral proteins did not enter infected bacteria (found in supernatant). 2) Labeled viral DNA did enter bacteria during viral infection (found in cell pellet). Conclusion: 1) Protein is not necessary to make new viruses. 2) DNA is the molecule that carries the genetic information to make new viruses. 3 Dr. Mohanad J.K. Al-Dawah 3rd lecture Principles of Biotechnology Nucleic acids structure: 1) Both DNA and RNA structure composed of three parts: a) Five carbon sugar b) Nitrogen bases c) Phosphate group 2) Five carbon sugar + nitrogen base is called nucleoside. 3) Nucleoside + phosphate group is called nucleotide. 4) Nucleotides are the building blocks of DNA and RNA. 5) Each nucleotide binds with another nucleotide by phosphodiester bond and form the final structure of DNA and RNA. 6) Five carbon sugar is called pentose carbon sugar. 7) Nitrogen bases have two type a) Purines which include Adenine (A) and Guanine (G). b) Pyrimidines which include Thymine (T), Cytosine (C) and Uracil (U). 8) Phosphate group gives the acidic property to DNA and RNA. DNA structure 1) The five carbon sugar that found in DNA is called deoxyribose because the absence of oxygen in the position 2'. 2) The nitrogen bases that found in DNA are A, T, G and C. 3) binds with (T) by two hydrogen bonds (A=T), while (G) binds with (C) by three hydrogen bonds (G≡C). 4) DNA usually found as a double strand. 5) DNA is found in the nucleus of the cell and in the mitochondria. RNA structure 1) The five carbon sugar that found in RNA is called ribose. 2) The nitrogen bases that found in RNA are A, U, G and C. 4 Dr. Mohanad J.K. Al-Dawah 3rd lecture Principles of Biotechnology 3) binds with (U) by two hydrogen bonds (A=U), while (G) binds with (C) by three hydrogen bonds (G≡C). 4) RNA usually found as single strand. 5) RNA found in cell nucleus, cytoplasm and ribosome depending on the its type. Functions of DNA 1) DNA stores the heredity information of an individual. 2) DNA directs the machinery of a cell to make specific proteins 3) DNA indirectly controls all of the functioning of all living organisms. 4) DNA is responsible of the evolution of organisms. 5) DNA is responsible of transferring the genetic information from parents to offspring. Functions of RNA 1) mRNA - messenger RNA, acts as a messenger that carries information from DNA to ribosomes. 2) rRNA - ribosomal RNA, combines with proteins in the cytoplasm to form the ribosomes. 3) tRNA - transfer RNA, reads the genetic code on the messenger RNA in the cytoplasm to translate it into protein. 5 Dr. Mohanad J.K. Al-Dawah 3rd lecture Principles of Biotechnology Figure 2: Components of nucleic acids: bases, sugars, and phosphate. Figure 3: The structure of DNA and RNA 6 Dr. Mohanad J.K. Al-Dawah