What you must understand | What you must be able to do | • | •• | •• ••• |
DNA Structure, Function and Replication - DNA stores and transmits genetic information; it functions in the same way in all living things.
- DNA is a helical double-stranded molecule.
- In eukaryotes, DNA is bound to proteins (histones) in linear chromosomes, which are found in the nucleus.
- DNA is unbound and circular in the cytosol of prokaryotes and in the mitochondria and chloroplasts of eukaryotes.
- Replication of DNA allows for genetic information to be inherited.
- Base-pairing rules and method of DNA replication are universal.
| - Compare chromosomes in prokaryotes and eukaryotes.
- Describe the structural properties of the DNA molecule, including:
- nucleotide composition and pairing
- the weak bonds between strands of DNA that allow for replication.
- Explain the importance of complementary base pairing (A–T and C–G).
- Describe and represent the process of semi-conservative replication of DNA.
- Recognise that DNA strands are directional and are read 5’ to 3’.
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Genes and Protein Synthesis - A gene consists of a unique sequence of nucleotides that codes for a functional protein or an RNA molecule.
- Protein synthesis involves transcription of a gene into messenger RNA (mRNA), and translation of mRNA into an amino acid sequence at the ribosomes. In eukaryotic cells, transcription occurs in the nucleus.
| - Distinguish between exons and introns as coding and non-coding segments of DNA found in genes in eukaryotes.
- Describe how both exons and introns are transcribed but only the information contained in exons is translated to form a polypeptide in eukaryotes.
- Describe and illustrate the role of DNA, mRNA, transfer RNA (tRNA), and ribosomal RNA (rRNA) in transcription and translation.
- Describe the relationship between DNA codons, RNA codons, anticodons, and amino acids.
- Distinguish between coding (gene) and template strands of DNA.
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Protein Structure and Function - The folding of a polypeptide to form a protein with a unique three-dimensional shape is determined by its sequence of amino acids.
- Proteins are essential to cell structure and function.
- Examples of proteins with specific shapes include enzymes, some hormones, receptor proteins, and antibodies.
- Enzymes are specific for their substrate and increase reaction rates by lowering activation energy.
- Enzymes have specific functions and are affected by factors including:
- temperature
- pH
- presence of inhibitors.
| - Describe the factors that determine the primary, secondary, tertiary, and quaternary structure of proteins.
- Explain why the three-dimensional shape of a protein is critical to its function.
- Describe the induced-fit model of enzyme–substrate binding.
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What you must understand | What you must be able to do | • | •• | ••• |
- The rate of an enzyme-controlled reaction is affected by:
- concentrations of reactants
- concentration of the enzyme.
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Gene Expression and Mutation - The phenotypic expression of genes depends on factors controlling transcription and translation. These include the products of other genes, such as transcription factors, and the environment.
- Cellular differentiation associated with tissue growth and development is controlled by gene expression.
- Epigenetic changes can lead to phenotypic differences between identical siblings, phenotypic differences between clones, and may cause human diseases.
- Changes in the DNA sequence are called ‘mutations’.
- Mutations in genes and chromosomes can result from errors in DNA replication or cell division, or from damage by physical or chemical factors in the environment.
- Mutation rate can be increased by:
- ionising radiation
- mutagenic chemicals
- viruses.
| - Recognise that changes in DNA methylation and histone modification can alter gene expression.
- Explain how epigenetic modifications in genes that control cell division, such as changes in DNA methylation, can lead to cancer.
- Compare the different potential consequences of mutations in germ cells and somatic cells.
- Explain how inheritable mutations can lead to changes in the characteristics of the descendants.
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Biotechnology - DNA can be extracted from cells.
- Modern techniques can be used to analyse even small amounts of DNA.
- Segments of DNA can be multiplied using the polymerase chain reaction (PCR).
- The base sequence of DNA can be determined by electrophoresis.
- The results of electrophoresis may be displayed in an electropherogram.
- DNA sequencing enables mapping of species’ genomes.
- The results of electrophoresis can be used to construct DNA profiles. They may be displayed in an electropherogram or in a table of data.
- DNA profiling identifies the unique genetic makeup of individuals.
- Biotechnology can involve the use of plasmids and viruses as vectors, bacterial enzymes, and yeasts.
- Techniques include bacterial transformations, electroporation, and microinjection.
| - Describe PCR, including the roles of
- heating and cooling
- primers
- free nucleotides
- heat-resistant enzymes.
- Describe electrophoresis.
- Interpret electrophoresis electropherograms that illustrate DNA sequences.
- Interpret DNA profiling electropherograms and tables of data that illustrate DNA profiles.
- Explain how differences in DNA fragments, identified by DNA profiling, can be used; for example, in forensic science.
- Discuss the ethical, economic, and cultural issues related to the collection of genetic information.
- Describe how particular genes can be selected using probes and removed using restriction enzymes.
- Describe how selected genes can be transferred between species.
- Describe how CRISPR such as CRISPR-Cas9 can be used to edit and/or transfer genes.
- Discuss the design of new proteins and their uses.
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