Pearson Edexcel GCSE (9-1) Biology revision notes
Genetics Revision Notes
Review revision notes for Genetics in Edexcel Biology.
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Genetics
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Understanding the Genome and Genes Revision Notes
The Genome: An Organism's Complete DNA Set
Your genome, and indeed every living organism's genome, is the full set of all the genetic information (DNA) that an organism possesses. It contains all the instructions needed to build and maintain that organism, from its earliest developmental stages through to adulthood. For humans, the genome is organised into 23 pairs of chromosomes found within the nucleus of most cells, along with a small amount of mitochondrial DNA.
What is a Gene?
A gene is a specific, functional segment of a larger DNA molecule. Its primary role is to provide the 'recipe' or code for synthesising a particular protein. These proteins are diverse in their functions, acting as enzymes, structural components, transporters, or signalling molecules, and are fundamental to cell and organism function. The sequence of nucleotide bases within a gene determines the sequence of amino acids in the protein it codes for.
Relationship between Genome, Genes, and DNA
Think of DNA as a very long instruction manual. The genome is the entire manual itself. Within that manual, a gene is like a specific chapter or page that contains instructions for making one particular component (a protein). Therefore, the genome is composed of all the DNA, and genes are specific working units or sections located along that DNA.
Extracting DNA from Fruit Revision Notes
Purpose of each step in DNA extraction
Mashing or blending fruit physically breaks down cell walls. Adding detergent breaks down cell membranes. Salt helps neutralise DNA charges, causing DNA to clump. Filtering removes large debris. Cold alcohol precipitates DNA, making it visible.
The Chemistry of DNA Extraction
Detergent dissolves lipid cell membranes. Salt (e.g., sodium chloride) provides positive ions (Na+) that bind to the negatively charged phosphate groups on DNA, reducing repulsion between DNA strands and allowing them to aggregate. DNA is soluble in water but insoluble in cold alcohol, causing it to separate from the water layer and become visible.
Why use cold alcohol?
Using cold alcohol (ethanol or propan-2-ol) further reduces the solubility of DNA, enhancing its precipitation. This makes the DNA more visible as it forms a distinct layer or stringy mass, allowing for easier collection.
DNA, Amino Acids, and Protein Folding Revision Notes
Genetic Code and Amino Acid Sequence
The order of bases (A, T, C, G) in a DNA sequence determines the order of amino acids in a protein. This information flow goes from DNA to mRNA (transcription) and then to protein (translation). Each set of three bases on mRNA, called a codon, specifies one particular amino acid. The accuracy of this sequence is fundamental for proper protein structure.
Protein Folding and Function
After amino acids are linked into a polypeptide chain, they spontaneously fold into a specific three-dimensional (3D) shape. This folding is dictated by the unique sequence of amino acids and the chemical interactions (e.g., hydrogen bonds, hydrophobic interactions) between them. The specific 3D shape, particularly for enzymes, is essential for its biological function, as it forms the active site for substrate binding.
The Central Dogma
The process of genetic information transfer from DNA to RNA to protein is often referred to as the central dogma of molecular biology. This fundamental concept explains how genetic instructions are converted into functional products within a cell. Any alteration in the DNA base sequence can lead to a change in the amino acid sequence, potentially affecting the final protein's shape and thus its function.
Genetics diagram
Specification Link
This genetics diagram is used for: Give a clear account of the inheritance of the ABO blood groups with reference to codominance and multiple alleles.
What To Explain
DNA is organised into genes and chromosomes, so the diagram should be linked to inherited information.
Exam Answer Move
This is aligned to: Give a clear account of the inheritance of the ABO blood groups with reference to codominance and multiple alleles. The learner should connect the visual to genetic information, inheritance or variation as required by the objective.
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