* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download DNA
Non-coding RNA wikipedia , lookup
Agarose gel electrophoresis wikipedia , lookup
Expanded genetic code wikipedia , lookup
Cell-penetrating peptide wikipedia , lookup
Epitranscriptome wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Maurice Wilkins wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Genetic code wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Community fingerprinting wikipedia , lookup
Gene expression wikipedia , lookup
Gel electrophoresis of nucleic acids wikipedia , lookup
DNA vaccination wikipedia , lookup
Molecular evolution wikipedia , lookup
Biochemistry wikipedia , lookup
Non-coding DNA wikipedia , lookup
Molecular cloning wikipedia , lookup
Transformation (genetics) wikipedia , lookup
List of types of proteins wikipedia , lookup
Point mutation wikipedia , lookup
DNA supercoil wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Chapter 7: DNA And The Genetic Code 7.1 Evidence that the nucleus contains the hereditary material - Hammerling used an unusually large single-celled alga to section & isolate the nucleus and proved that the nucleus contain the hereditary material DNA. - Evidence that DNA ( DeoxyRibosenucleic Acid ) is the hereditary material: 1. Chromosome analysis 2. Metabolic stability of DNA 3. Constancy of DNA in a cell 4. Correlation between mutagens and their effects on DNA 5. Experiments on bacterial transformation (Griffith 1928) 6. Experiments to identify the transforming principle 7. Transduction experiments 7.2 Evidence that DNA is the hereditary material 7.2.1 Chromosome Analysis - Chromosomes occur only when cell division occurs proteins - Chromosomes are made of _____ DNA and _____________ - DNA analysis shows that its bases carry a genetic code for heredity 7.2.2 Metabolic stability of DNA - Unlike protein, DNA molecules show very remarkable stability, e.g. when using radioactive isotopes, their disappearance is very slow 7.2 Evidence that DNA is the hereditary material 7.2.3 Constancy of DNA within a cell - analysis showed that the amount of DNA remains constant for all cells within a species except for the gametes (why?) - prior to cell division, amount of DNA per cell doubles Gametes have only half of the chromosome number as their 7.2.4 Correlation between mutagens and their effects on DNA parents. - Mutagens are agents which cause mutations in living organisms A Mutation is an alteration to an organism's characteristics which is inherited - Examples of mutagens: X-rays, nitrous acids, dyes Mutagens alter the structure of DNA in some way, e.g.UV ray on bases (pyrimidine) 7.2.5 Experiments on bacterial transformation - Griffith, 1928 - Bacterium Pneumococcus exists in two forms: harmful form with shiny, smooth colonies (S- strain) safe form with dull, rough colonies (R-strain) Explanation: The code for the toxin was transferred from the head harmful form to the living safe variety. Living safe form can make the toxin and pneumonia results - The substance (or DNA) was able to transform one strain of pneumococcus into another: The transforming principle 7.2.6 Experiments to identify The Transforming Principle - McCarty & McCleod (1944) isolated and purified different substances from the dead & harmful types of pneumococcus and found DNA to be capable of bringing about the transforming. The ability stopped when DNAase was added. 7.2.7 Transduction experiments - Using T2 bacteriophage attacking E. Coli with radioactive substances: 35S in protein of one phage and 32P in DNA of another phage - Culture injected with radioactive DNA contained radioactive bacteria, while that injected with radioactive protein did not - DNA was the hereditary material, with further proof from electron microscope studies 7.3 Nucleic Acids 7.3.1 Structure of Nucleotides Each nucleotide consists of 3 parts: 1. Phosphoric acid 2. Pentose sugar 3. Organic base: 7.3 Nucleic Acids 7.3.1 Structure of Nucleotides Each nucleotide consists of 3 parts: 1. Phosphoric acid 2. Pentose sugar 3. Organic base: Pyrimidines - single ringed, six-sided; cytosine, thymine, uracil Purines - 5 sided & 6 sided double ringed base; adenine & guanine Purines Pyrimidines Dinucleotide: 2 nucleotides joined together Polynucleotide: > 2 nucleotides joined together Ribonucleic Acid (RNA) RNA is a single-stranded polymer of nucleotides where the pentose is ribose & the bases are adenine, guanine, cytosine and uracil. Three types of RNA: Ribosomal (rRNA), Transfer (tRNA), and Messenger (mRNA) Function: for protein synthesis Ribosomal RNA: - a large, complex molecule with single & double helices - it is manufactured by DNA but found in cytoplasm, making up of half the mass of ribosmes - base sequence is similar in all organisms Transfer RNA: - small, single stranded, manufactured by DNA - clover-leaf shape, one end with CCA to attach amino acid - at least 20 types - anticodon with 3 specific bases for specific amino acid during protein synthesis Messenger RNA: - long, single-stranded helix - manufactured in nucleus, a mirror copy of part of DNA strand - immense variety - enters cytoplasm as a template for protein synthesis - easily broken down & short-lived Some important nucleotides: Molecule Abbreviation Function Some important nucleotides: Molecule Abbreviation Function deoxyribonucleic DNA contain the genetic information of acid cells Some important nucleotides: Molecule Abbreviation Function deoxyribonucleic DNA contain the genetic information of acid cells Ribonucleic acid RNA protein synthesis Some important nucleotides: Molecule Abbreviation Function deoxyribonucleic DNA contain the genetic information of acid cells Ribonucleic acid RNA protein synthesis Adenosine coenzymes for energy release Some important nucleotides: Molecule Abbreviation deoxyribonucleic DNA acid Ribonucleic acid RNA Adenosine monophosphate AMP diphosphate ADP triphosphate ATP Function contain the genetic information of cells protein synthesis coenzymes for energy release Some important nucleotides: Molecule Abbreviation Function deoxyribonucleic DNA contain the genetic information of acid cells Ribonucleic acid RNA protein synthesis Adenosine coenzymes for energy release monophosphate AMP diphosphate ADP triphosphate ATP Nicotinamide Electron carriers in transferring adenine dinucleotide NAD hydrogen atoms in respiratory Krebs Flavine adenine cycle dinucleotide FAD Some important nucleotides: Molecule Abbreviation Function deoxyribonucleic DNA contain the genetic information of acid cells Ribonucleic acid RNA protein synthesis Adenosine coenzymes for energy release monophosphate AMP diphosphate ADP triphosphate ATP Nicotinamide Electron carriers in transferring adenine dinucleotide NAD hydrogen atoms in respiratory Krebs Flavine adenine cycle dinucleotide FAD Nicotinamide Electron carrier for accepting adenine dinucleotide electrons from chlorophyll molecule phosphate NADP in photolysis of water Some important nucleotides: Molecule Abbreviation Function deoxyribonucleic DNA contain the genetic information of acid cells Ribonucleic acid RNA protein synthesis Adenosine coenzymes for energy release monophosphate AMP diphosphate ADP triphosphate ATP Nicotinamide Electron carriers in transferring adenine dinucleotide NAD hydrogen atoms in respiratory Krebs Flavine adenine cycle dinucleotide FAD Nicotinamide Electron carrier for accepting adenine dinucleotide electrons from chlorophyll molecule phosphate NADP in photolysis of water Coenzyme A CoA coenzyme for respiratory Krebs cycle 7.3.3 Deoxyribonucleic Acid (DNA) A double stranded polymer of nucleotides, with deoxyribose sugar and organic bases: adenine, guanine, cytosine, thymine (no uracil); each chain is extremely long with millions of nucleotide units Facts about DNA: 1 It is very long, made up nucleotides 2 It contains 4 organic bases: adenine, guanine, cytosine, thymine 3 Amount of guanine is equal to that of cytosine 4 Amount of adenine is equal to that of thymine 5 It is in the form of a helix maintained by hydrogen bonding Watson and Crick (1953) suggested a molecular structure for DNA: - a double helix of two nucleotide strands linked together by pairs of organic bases which are joined together by hydrogen bonds - C pairs with G by 3 hydrogen bonds; A pairs with T by 2 hydrogen bonds; consistent with the known ratio of bases in molecule and allowed for an identical separation of strands throughout the molecule Watson and Crick (1953) suggested a molecular structure for DNA: - a double helix of two nucleotide strands linked together by pairs of organic bases which are joined together by hydrogen bonds - C pairs with G by 3 hydrogen bonds; A pairs with T by 2 hydrogen bonds; consistent with the known ratio of bases in molecule and allowed for an identical separation of strands throughout the molecule - two strands twist around each other in an antiparallel direction Watson and Crick (1953) suggested a molecular structure for DNA: - a double helix of two nucleotide strands linked together by pairs of organic bases which are joined together by hydrogen bonds - C pairs with G by 3 hydrogen bonds; A pairs with T by 2 hydrogen bonds; consistent with the known ratio of bases in molecule and allowed for an identical separation of strands throughout the molecule - two strands twist around each other in an antiparallel direction - DNA's extreme length permits a long sequence of bases which can vary indefinitely for its immense store of genetic information - Double stranded structures allow its semi-conservative replication during cell division to give two identical daughter cells Differences between RNA and DNA 1 single stranded 1 double stranded Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T 6 Ratio of A, U to C, G varies 6 Ratio of A, T to C, G is 1 Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T 6 Ratio of A, U to C, G varies 6 Ratio of A, T to C, G is 1 7 made in nucleus but found throughout the cell 7 found almost entirely in nucleus Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T 6 Ratio of A, U to C, G varies 6 Ratio of A, T to C, G is 1 7 made in nucleus but found throughout the cell 7 found almost entirely in nucleus 8 Amount varies from cell to cell 8 Amt constant for cells of a species Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T 6 Ratio of A, U to C, G varies 6 Ratio of A, T to C, G is 1 7 made in nucleus but found throughout the cell 7 found almost entirely in nucleus 8 Amount varies from cell to cell 9 Chemically less stable 8 Amt constant for cells of a species 9 Chemically very stable Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T 6 Ratio of A, U to C, G varies 6 Ratio of A, T to C, G is 1 7 made in nucleus but found throughout the cell 7 found almost entirely in nucleus 8 Amount varies from cell to cell 8 Amt constant for cells of a species 9 Chemically less stable 9 Chemically very stable 10 exit temporarily 10 permanent Differences between RNA and DNA 1 single stranded 1 double stranded 2 smaller molecule mass 2 larger molecule mass 3 may be single or double helix 3 always double helix 4 Pentose: oxyribose 4 Pentose: deoxyribose 5 Organic bases: A, G, C, U 5 Organic bases: A, G, C, T 6 Ratio of A, U to C, G varies 6 Ratio of A, T to C, G is 1 7 made in nucleus but found throughout the cell 7 found almost entirely in nucleus 8 Amount varies from cell to cell 8 Amt constant for cells of a species 9 Chemically less stable 9 Chemically very stable 10 exit temporarily 10 permanent 11 3 forms: rRNA, tRNA, mRNA 11 one form but indefinite variety 7.4 DNA Replication - semi-conservative method 7.4 DNA Replication - semi-conservative method 2. Two strands of DNA separate by DNA polymerase 7.4 DNA Replication - semi-conservative method 3. Free nucleotides are attracted to their complementary bases 7.4 DNA Replication - semi-conservative method 4. New nucleotides line up and join together, with unpaired bases continue to attract their complementary bases 7.4 DNA Replication - semi-conservative method 5. Finally all the nucleotides are joined to form a complete polynucleotide chain to form two identical strands of DNA 7.4 DNA Replication - semi-conservative method 1. A representative portion of DNA about to undergo replication 2. Two strands of DNA separate by DNA polymerase 3. Free nucleotides are attracted to their complementary bases 4.New nucleotides line up and join together, with unpaired bases continue to attract their complementary bases 5.Finally all the nucleotides are joined to form a complete polynucleotide chain to form two identical strands of DNA 7.4 DNA Replication - semi-conservative method Experiments by Meselsohn and Stahl using labelled 15N: 1. DNA extracted from E. coli grown in a medium containing normal nitrogen (14N); All DNA is of the light type. 2. DNA extracted from E. coli grown in a medium containing heavy nitrogen (15N) and then transferred to a medium containing normal nitrogen (14N); The weight was intermediate between the heavy and light DNA. 3. DNA extracted from E. coli grown in a medium containing heavy nitrogen (15N) 1 2 3 7.5 The Genetic Code DNA enzymes proteins which determine an organism's characteristics triplet code: GUA, CGC, AAA, GGG, AUG, etc. Characteristics of the genetic code: degenerate code stop/nonsense code non-overlapping universal Totally: 64 combinations eg. valine (GU*) where * can be any base UAA, UAG, UGA code for no amino acids but stop/nonsense command CUGAGCUAG is read as CUG-AGC-UAG The codes are precisely the same for all organisms. 1 (a) Explain the features of the genetic code (6 marks) (98-II-3) 2. Distinguish between transcription and translation. (2 marks) 95-I-4(a) Describe how the information carried on DNA is used in protein synthesis. (If you wish, you may use labelled diagrams to answer this question.) (10 marks) 80-II-5(a) 4. (a) Briefly illustrate the structure of the DNA molecule. (5 marks) 81-II-1 Diagram to show the double helix, sugar phosphate backbone, nucleotide bases (names of bases should be mentioned). 4. (a) Briefly illustrate the structure of the DNA molecule. (5 marks) 81-II-1 (b) How does the DNA molecule function as the carrier of genetic information? (The role of the messenger RNAs should also be mentioned.) (15 marks) Order of nucleotide bases determine specificity of the gene The triplet code Involvement of messenger RNA Order of amino acids determine specificity of polypeptide chain, order is dictated by order of the codons Phenotype of organism depends on specific spectrum of proteins (e.g. enzymes) DNA molecule can duplicate itself DNA molecule carried in germ cells max 15 marks 7.6 Protein Synthesis Four main stages in the formation of a protein: 1 Synthesis of amino acids 2 Transcription (formation of mRNA) 3 Amino acid activation 4 Translation 7.6.1 Synthesis of Amino Acids In plants, synthesis of amino acids occurs in mitochondria & chloroplasts: a. Absorption of nitrates from soil b. Reduction of nitrate to amino group (NH2) c. Combination of amino groups with a carbohydrate skeleton d. Transfer amino groups from one carbohydrate skeleton to another non-essential amino acids In animals, most of the amino acids _______________________ can be synthesized in their bodies; essential amino acids about 9 amino acids _____________________ must be supplied from the diet. 7.6.2 Transcription (formation of messenger RNA) - Transcription is the process by which a complementary mRNA cistron/gene of the DNA copy is made of the specific region (=___________) molecule which codes for a polypeptide chain: 1. Unwinding of a portion of a cistron - by breaking of H-bonds 2. One strand acts as a template for the formation of mRNA: each base along one strand attracts its complementary RNA uracil instead of ________ thymine nucleotide, C - G ; but A - _______ 3. Enzyme RNA polymerase moves along the DNA adding complementary RNA nucleotide at a time to the newly unwind portion of DNA. A number of mRNA molecules may be formed before RNA polymerase leaves the DNA which then closes up reforming its double helix structure. 4. Each mRNA contains a sequence of triplet codes that have been determined by the DNA. mRNA goes to the ribosomes in the cytoplasm through the nuclear pore. 7.6.3Amino Acid Activation Activation is the process by which amino acids combine with tRNA using energy from ATP Each type of tRNA binds with a specific amino acid, therefore there are at least 20 ____kinds of tRNA Each tRNA possesses a specific anticodon (triplet of bases) for a particular amino acid AND a free end which terminates in the triplet CCA for the attachment of individual a.a. to form a polypeptide chain 7.6.4 Translation Translation is the means by which a specific sequence of amino acids is formed in accordance with the codons on the mRNA. Polysome is a group of ribosomes which becomes attached to the mRNA 7.6.4 Translation Complementary anticodon of a tRNAamino acid complex is attached to the 1st codon on the mRNA; 2nd codon likewise attracts its complementary anticodon Ribosome thus holds mRNA and tRNA a.a. complex until the 2 a.a. form a peptide bond between them; then ribosome moves along to a 3rd codonanticodon complex until the 3rd a.a. is formed with the 2nd, and so on to form a complete polypeptide chain 7.6.4 Translation Second and subsequent ribosomes may pass along mRNA immediately behind the 1st so that many identical polypeptide chains can be produced simultaneously Free tRNA moves back to cytoplasm & combine with another a.a. A non-sense code orders the casting of the complete polypeptide chain; polypeptide chain may undergo *spiral configuration to give its secondary structure, *folding to give a tertiary structure, or combine with other polypeptide chains to give a quaternary structure. *by H-bonding or disulphide bonds One gene specifies one polypeptide 1 (b) Describe in detail the cellular processes that are necessary in the transfer and decoding of genetic information for polypeptide synthesis. (12 marks) (98-II-3) Transcription (8M) Translation (4M) 1 (b) Describe in detail the cellular processes that are necessary in the transfer and decoding of genetic information for polypeptide synthesis. (12 marks) (98-II-3) (c) In general, what additional processes are necessary for the formation of the three-dimensional structure of proteins after polypeptide synthesis? (2 marks) 7.7 Genetic Engineering Technology which allows genes to be manipulated, altered and transferred from organism to organism, even to transform DNA itself Use of rapidly reproducing organisms (bacteria) as chemical factories producing useful, often life-saving, substances, e.g. hormones, antibodies, vitamins Use of plasmid vector in gene cloning Use of plasmid vector in gene cloning 7.7.1 Recombinant DNA Technology Methods for isolating portion of human DNA responsible for producing insulin and combining with bacterial DNA in such a way that the micro-organism will continually produce insulin because of the recombinant DNA present Traditional methods of obtaining insulin: Extracts from animals Disadvantages of traditional methods: Too expensive Other extracts from animals or humans, e.g. thyroxine, may cause antibody production, and risks of infectious disease, e.g. human HIV in haemophiliacs 7.7.2 Techniques used to manipulate DNA 1. Cutting of DNA into small sections using restriction endonucleases 2. Production of copies of DNA using either plasmids or reverse transcriptase 3. Joining together portions of DNA using DNA ligase 7.7.2 Techniques used to manipulate DNA 1. Cutting of DNA into small sections using restriction endonucleases 2. Production of copies of DNA using either plasmids or reverse transcriptase 3. Joining together portions of DNA using DNA ligase 7.7.2 Techniques used to manipulate DNA 1. Cutting of DNA into small sections using restriction endonucleases 2. Production of copies of DNA using either plasmids or reverse transcriptase 3. Joining together portions of DNA using DNA ligase 7.7.3 Gene Cloning multiple copies of a specific gene are produced which may then be used to manufacture large quantities of valuable products - involves the following stages: 1. Identification of that gene 2. Isolation of that gene 3. Insertion of the gene into a vector 4. Insertion of the vector into a host cell 5. Multiplication of the host cell 6. Synthesis of the required product by the host cell 7. Separation of the product from the host cell 8. Purification of the product 7.7.3 Gene Cloning The bacteria produced can be grown in industrial fermenters using a specific nutrient medium under strictly controlled conditions. The bacteria can then be collected and the insulin is extracted from them by suitable methods. 7.7.4 Insertion of vector into a host cell The final destination of a particular gene may be a crop plant and the bacterium chosen has the ability to infect plants. For example, Agrobacterium tumefaciens invades plant cells by incorporating its large tumourinducing plasmid into the genome of the host cells. Agrobacterium tumefaciens has a number of different strains which can infect a wide variety of plants. The bacterium is very useful in transferring genes into new organisms. 7.7.4 Insertion of vector into a host cell The desired gene is not transferred on its own, but along with a second gene (the gene marker). For example, an antibiotic resistant gene could be cultured by growing Agrobacterium on a media containing an antibiotic. Those Agrobacterium with the desired gene will survive because they also possess the marker gene (antibiotic resistant). The Agrobacterium with the new gene can now be cultured to provide a large population. They may then be used to infect host plants, which will incorporate the new gene into their own genome. 7.7.5 Application of genetic engineering This techniques can make a range of materials used to treat diseases and disorders. Other examples include: In medicine • Growth hormone Erythropoietin (controls red blood cell production) • Calcitonin (regulates calcium level in blood) Transferring a normal gene for thalassamia (a disease with abnormal haemoglobin) into patients suffering by the disease In agriculture Transfer genes which produce toxins with insecticidal properties to higher plants (potato & cotton): “built-in’ resistance to certain insect species to save time & money on insecticides and avoid killing harmless or beneficial insect species on the field Transfer genes nitrogen-fixing bacteria to cereal crops: less need to apply expensive nitrogen fertilizers and reduces the pollution problems of ‘leaching’ Other possibilities Ø Transfer genes providing resistance to all diseases, Ø Develop plants with more efficient rates of photosynthesis Ø Control weeds Ø Develops oil-digesting bacteria to clear up oil spillages • Other possibilities • Transfer genes providing resistance to all diseases, • Develop plants with more efficient rates of photosynthesis • Control weeds • Develops oil-digesting bacteria to clear up oil spillages 7.7.6 Implications of genetic engineering But there are ethical as well as practical problems to be overcome before many of these ideas can be brought to reality! Practical issues: 1. It is impossible to predict with complete accuracy what will happen if genetically engineered organisms are released into the environment. Our natural habitats might be damaged. 2. Organisms designed for use in one environment may escape to other environments with harmful consequences. 3. Advantageous genes added to domestic animals or cops may be transferred to their competitors, making them even greater potential dangers. 4. The escape of a pathogenic bacterium into a susceptible population could end in considerable damage to the species. 5. Human characteristics and behaviour could be modified but in the wrong hands this could be used by individuals, groups or governments to achieve certain goals, control opposition or gain ultimate power. Ethical issues: 1. Is it right to replace a defective gene with a normal one? 2. Is the answer the same which causes the bearer pain as it is where the gene has a merely cosmetic effect? 3. Who decides what is normal and what is defective? 4. A defective gene actually may give advantage, e.g. sickle-cell anaemia in Africa. 5. Reducing the variety of genes (unwanted genes): hindering evolution? 6. Increasing the variety of genes (beneficial genes): favouring evolution? 7. Fetal abnormality: What criteria, if any, should be applied before deciding ‘abortion’? The challenge is to develop regulations and safeguards within normal boundaries which permit genetic engineering to be used in a safe and effective way to the benefit of both individuals in particular and humans in general.