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Topic 7: Nucleic Acids & Proteins (15 hours) 2.7 DNA replication, transcription and translation (BCC p111) Essential idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell. Nature of science: 1. Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8) Understandings: Applications and skills: 2. The replication of DNA is semi-conservative and 10. Application: Use of Taq DNA polymerase to produce depends on complementary base pairing. multiple copies of DNA rapidly by the polymerase 3. Helicase unwinds the double helix and separates the chain reaction (PCR). two strands by breaking hydrogen bonds. 11. Application: Production of human insulin in bacteria 4. DNA polymerase links nucleotides together to form a as an example of the universality of the genetic code new strand, using the pre-existing strand as a allowing gene transfer between species. template. Guidance: The different types of DNA 12. Skill: Use a table of the genetic code to deduce which polymerase do not need to be distinguished (but see codon(s) corresponds to which amino acid. 7.1.14). 13. Skill: Analysis of Meselson and Stahl’s results to 5. Transcription is the synthesis of mRNA copied from obtain support for the theory of semi-conservative the DNA base sequences by RNA polymerase. replication of DNA. 6. Translation is the synthesis of polypeptides on 14. Skill: Use a table of mRNA codons and their ribosomes. corresponding amino acids to deduce the sequence of 7. The amino acid sequence of polypeptides is amino acids coded by a short mRNA strand of determined by mRNA according to the genetic code. known base sequence. 8. Codons of three bases on mRNA correspond to one 15. Skill: Deducing the DNA base sequence for the amino acid in a polypeptide. mRNA strand. 9. Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA. 7.1 DNA structure and replication (BCC p343) Essential idea: The structure of DNA is ideally suited to its function. Nature of science: 1. Making careful observations—Rosalind Franklin’s X-ray diffraction provided crucial evidence that DNA is a double helix. (1.8) Understandings: Applications and skills: 2. Nucleosomes help to supercoil the DNA. 8. Application: Rosalind Franklin’s and Maurice 3. DNA structure suggested a mechanism for DNA Wilkins’ investigation of DNA structure by X-ray replication. diffraction. 4. DNA polymerases can only add nucleotides to the 3’ 9. Application: Use of nucleotides containing end of a primer. Guidance: Details of DNA dideoxyribonucleic acid to stop DNA replication in replication differ between prokaryotes and preparation of samples for base sequencing. eukaryotes. Only the prokaryotic system is expected. 10. Application: Tandem repeats are used in DNA 5. DNA replication is continuous on the leading strand profiling. and discontinuous on the lagging strand. 11. Skill: Analysis of results of the Hershey and Chase 6. DNA replication is carried out by a complex system experiment providing evidence that DNA is the of enzymes. Guidance: The proteins and enzymes genetic material. involved in DNA replication should include helicase, 12. Skill: Utilization of molecular visualization software DNA gyrase, single strand binding proteins, DNA to analyse the association between protein and DNA primase and DNA polymerases I and III. within a nucleosome. 7. Some regions of DNA do not code for proteins but have other important functions. Guidance: The regions of DNA that do not code for proteins should be limited to regulators of gene expression, introns, telomeres and genes for tRNAs. Topic 7: Nucleic Acids & Proteins (15 hours) 7.2 Transcription and gene expression (BCC p355) Essential idea: Information stored as a code in DNA is copied onto mRNA. Nature of science: 1. Looking for patterns, trends and discrepancies—there is mounting evidence that the environment can trigger heritable changes in epigenetic factors. (3.1) Understandings: Applications and skills: 2. Transcription occurs in a 5’ to 3’ direction. 8. Application: The promoter as an example of nonGuidance: RNA polymerase adds the 5 ́ end of the coding DNA with a function. free RNA nucleotide to the 3 ́ end of the growing 9. Skill: Analysis of changes in the DNA methylation mRNA molecule. patterns. 3. Nucleosomes help to regulate transcription in eukaryotes. 4. Eukaryotic cells modify mRNA after transcription. 5. Splicing of mRNA increases the number of different proteins an organism can produce. 6. Gene expression is regulated by proteins that bind to specific base sequences in DNA. 7. The environment of a cell and of an organism has an impact on gene expression. 7.3 Translation (BCC p362) Essential idea: Information transferred from DNA to mRNA is translated into an amino acid sequence. Nature of science: 1. Developments in scientific research follow improvements in computing—the use of computers has enabled scientists to make advances in bioinformatics applications such as locating genes within genomes and identifying conserved sequences. (3.7) Understandings: Applications and skills: 2. Initiation of translation involves assembly of the 12. Application: tRNA-activating enzymes illustrate components that carry out the process. Guidance: enzyme–substrate specificity and the role of Examples of start and stop codons are not required. phosphorylation. 3. Synthesis of the polypeptide involves a repeated 13. Skill: Identification of polysomes in electron cycle of events. micrographs of prokaryotes and eukaryotes. 4. Disassembly of the components follows termination 14. Skill: The use of molecular visualization software to of translation. analyse the structure of eukaryotic ribosomes and a 5. Free ribosomes synthesize proteins for use primarily tRNA molecule. Guidance: Names of the tRNA within the cell. binding sites are expected as well as their roles. 6. Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes. 7. Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane. 8. The sequence and number of amino acids in the polypeptide is the primary structure. 9. The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding. 10. The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups. Guidance: Polar and non-polar amino acids are relevant to the bonds formed between R groups. 11. The quaternary structure exists in proteins with more than one polypeptide chain. Guidance: Quaternary structure may involve the binding of a prosthetic group to form a conjugated protein. Topic 7: Nucleic Acids & Proteins (15 hours) 3.5 Genetic modification and biotechnology (BCC p187) Essential idea: Biologists have developed techniques for artificial manipulation of DNA, cells and organisms. Nature of science: 1. Assessing risks associated with scientific research—scientists attempt to assess the risks associated with genetically modified crops or livestock. (4.8) Understandings: Applications and skills: 2. Gel electrophoresis is used to separate proteins or 10. Application: Use of DNA profiling in paternity and fragments of DNA according to size. forensic investigations. Guidance: Students should be 3. PCR can be used to amplify small amounts of DNA. able to deduce whether or not a man could be the 4. DNA profiling involves comparison of DNA. father of a child from the pattern of bands on a DNA 5. Genetic modification is carried out by gene transfer profile. between species. 11. Application: Gene transfer to bacteria using plasmids 6. Clones are groups of genetically identical organisms, makes use of restriction endonucleases and DNA derived from a single original parent cell. ligase. 7. Many plant species and some animal species have 12. Application: Assessment of the potential risks and natural methods of cloning. benefits associated with genetic modification of 8. Animals can be cloned at the embryo stage by crops. breaking up the embryo into more than one group of 13. Application: Production of cloned embryos produced cells. by somatic-cell nuclear transfer. Guidance: Dolly 9. Methods have been developed for cloning adult can be used as an example of somatic-cell transfer. animals using differentiated cells. 14. Skill: Design of an experiment to assess one factor affecting the rooting of stem-cuttings. Guidance: A plant species should be chosen for rooting experiments that forms roots readily in water or a solid medium. 15. Skill: Analysis of examples of DNA profiles. 16. Skill: Analysis of data on risks to monarch butterflies of Bt crops.