Key term
OCR GCSE Biology A J247
Cell Level Systems
Topic overviewMicroscopy, and sub-cellular structuresDNA structure: polymer, double helix and nucleotidesProtein synthesis and the triplet codeEnzyme action, and investigating enzymesCellular respiration as an exothermic processAerobic and anaerobic respiration comparedSynthesis and breakdown of carbohydrates, proteins and lipidsPhotosynthesis: producers and the processPhotosynthesis as endothermic, and investigating itLimiting factors in photosynthesis
Community Level Systems
Genes, Inheritance and Selection
Topic overviewGenetic terms, and the genomeGenome, environment and mutationsHow genetic variants influence phenotypeAsexual and sexual reproduction comparedHaploid, diploid and meiosisSingle gene inheritance and Punnett squaresSex determination, multiple genes and Mendel's workVariation within a population, and classificationNatural selection and evolutionEvidence for evolution, and the work of Darwin and Wallace
Global Challenges
Topic overviewField investigations, and human impact on ecosystemsMaintaining biodiversity, and evidence for environmental changeFood security, agricultural and biotechnological solutionsSelective breeding and genetic engineeringHealth, disease, and types of diseaseInteractions between diseases, and how they spreadReducing the spread of disease, and named examplesPhysical and chemical plant defencesDetecting plant disease; white blood cells and plateletsNon-specific defences and the immune systemMonoclonal antibodies and their usesVaccines, medicines and aseptic techniqueDeveloping new medicines, and non-communicable diseaseTreating cardiovascular disease, and lifestyle factorsCancer, and the use of stem cells in medicineGene technology in medicine, and the human genome
Organism Level Systems
Topic overviewThe nervous system and coordinated responsesThe reflex arcThe eye and its common defectsThe structure and function of the brainInvestigating and treating the brainHormonal coordination, thyroxine and adrenalineHormones in reproduction and the menstrual cycleContraception and treating infertilityPlant hormones and their commercial usesHomeostasis, and the skin in temperature controlInsulin and glucagon in blood sugar controlType 1 and type 2 diabetesOsmotic changes in body fluids, and the kidneysThe kidney tubule and the effect of ADHResponding to temperature and osmotic challenges
Scaling Up
Topic overviewDiffusion, osmosis and active transportMitosis, the cell cycle and cell differentiationStem cells in animals and meristems in plantsSurface area to volume ratio and exchange surfacesThe circulatory system, the heart and blood vesselsRed blood cells and plasmaRoot hair cells, transpiration and translocationXylem and phloemFactors affecting water uptake, and the potometer
Cell Level Systems
Protein synthesis and the triplet code
- 3 things to know
- Paper 3
Overview
How DNA unzips and a gene is transcribed into mRNA in the nucleus, why mRNA leaves instead of DNA, translation at the ribosomes with tRNA carrying amino acids, the order of events, the triplet code and how base order sets amino acid order, how a single base change can alter a protein, calculating numbers of bases and amino acids, and how amino acid order decides a protein's shape and function.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What happens during translation?
Key term
Put the main events of protein synthesis into order.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What happens to the DNA double helix at the start of making a protein?
Model answer
It unzips around the gene, separating the two strands so the bases of that gene are exposed.
- 2
What is transcription?
Model answer
Copying the base sequence of a gene from the DNA into a molecule of mRNA.
- 3
In which part of the cell is mRNA made?
Model answer
In the nucleus.
- 4
Why is a copy of the gene made instead of the DNA itself leaving the nucleus?
Model answer
The DNA molecule is far too large to leave, so the much shorter mRNA carries the coded message out.
- 5
Where in the cell does translation take place?
Model answer
In the cytoplasm, at the ribosomes.
- 6
What happens during translation?
Model answer
The nucleotide sequence of the mRNA is read and amino acids are joined together in the order it specifies.
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