Biology AS AQA
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1-1-biological-molecules-carbohydrates11 主题
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1-1-1-biological-molecules-key-terms
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1-1-2-biological-molecules-reactions
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1-1-3-monosaccharides
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1-1-4-glucose
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1-1-5-the-glycosidic-bond
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1-1-6-chromatography-monosaccharides
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1-1-7-disaccharides
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1-1-8-starch-and-glycogen
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1-1-9-cellulose
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1-1-10-biochemical-tests-sugars-and-starch
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1-1-11-finding-the-concentration-of-glucose
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1-1-1-biological-molecules-key-terms
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1-2-biological-molecules-lipids3 主题
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1-3-biological-molecules-proteins5 主题
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1-4-proteins-enzymes12 主题
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1-4-1-many-proteins-are-enzymes
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1-4-2-enzyme-specificity
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1-4-3-how-enzymes-work
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1-4-4-required-practical-measuring-enzyme-activity
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1-4-5-drawing-a-graph-for-enzyme-rate-experiments
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1-4-6-using-a-tangent-to-find-initial-rate-of-reaction
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1-4-7-limiting-factors-affecting-enzymes-temperature
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1-4-8-limiting-factors-affecting-enzymes-ph
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1-4-10-limiting-factors-affecting-enzymes-enzyme-concentration
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1-4-11-limiting-factors-affecting-enzymes-substrate-concentration
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1-4-12-limiting-factors-affecting-enzymes-inhibitors
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1-4-14-control-of-variables-and-uncertainty
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1-4-1-many-proteins-are-enzymes
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1-5-nucleic-acids-structure-and-dna-replication8 主题
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1-5-2-nucleotide-structure-and-the-phosphodiester-bond
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1-5-3-dna-structure-and-function
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1-5-4-rna-structure-and-function
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1-5-5-ribosomes
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1-5-6-the-origins-of-research-on-the-genetic-code
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1-5-8-the-process-of-semi-conservative-replication
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1-5-9-calculating-the-frequency-of-nucleotide-bases
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1-5-10-the-watson-crick-model
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1-5-2-nucleotide-structure-and-the-phosphodiester-bond
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1-6-atp-water-and-inorganic-ions4 主题
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2-1-cell-structure7 主题
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2-2-the-microscope-in-cell-studies4 主题
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2-3-cell-division-in-eukaryotic-and-prokaryotic-cells8 主题
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2-4-cell-membranes-and-transport9 主题
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2-4-1-the-structure-of-cell-membranes
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2-4-3-the-cell-surface-membrane
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2-4-4-diffusion
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2-4-5-osmosis
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2-4-7-osmosis-in-animal-cells
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2-4-9-required-practical-investigating-water-potential
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2-4-10-active-transport-and-co-transport
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2-4-11-adaptations-for-rapid-transport
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2-4-13-required-practical-factors-affecting-membrane-permeability
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2-4-1-the-structure-of-cell-membranes
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2-5-cell-recognition-and-the-immune-system7 主题
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2-6-vaccines-disease-and-monoclonal-antibodies6 主题
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3-1-adaptations-for-gas-exchange6 主题
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3-2-human-gas-exchange14 主题
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3-2-5-the-alveolar-epithelium
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3-2-1-the-human-gas-exchange-system
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3-2-2-dissecting-the-gas-exchange-system
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3-2-3-microscopy-and-gas-exchange-surfaces
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3-2-4-investigating-gas-exchange
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3-5-5-investigating-heart-rate
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3-5-6-blood-vessels
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3-5-7-capillaries-and-tissue-fluid
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3-5-8-cardiovascular-disease-data
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3-2-10-risk-factor-data
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3-2-11-correlations-and-causal-relationships
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3-2-6-ventilation-and-gas-exchange
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3-2-8-the-effects-of-lung-disease
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3-2-9-pollution-and-smoking-data
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3-2-5-the-alveolar-epithelium
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3-3-digestion-and-absorption5 主题
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3-4-mass-transport-in-animals6 主题
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3-5-the-circulatory-system-in-animals4 主题
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3-6-mass-transport-in-plants6 主题
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4-1-dna-genes-and-chromosomes10 主题
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4-2-dna-and-protein-synthesis3 主题
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4-3-genetic-diversity-mutations-and-meiosis7 主题
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4-4-genetic-diversity-and-adaptation6 主题
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4-5-species-and-taxonomy4 主题
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4-6-biodiversity9 主题
1-5-3-dna-structure-and-function
Exam code:7401
DNA: structure & function
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Deoxyribonucleic acid (DNA) is a type of nucleic acid and forms a polynucleotide – it is made up of many nucleotides linked together in a chain
Nucleic acids
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DNA is a polynucleotide, this means it is made up of many nucleotides bonded together in a long chain
DNA molecule structure
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DNA consists of two polynucleotide strands that run in opposite directions — this arrangement is called antiparallel
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Each strand has a sugar-phosphate backbone, formed by alternating deoxyribose sugars and phosphate groups joined by phosphodiester bonds
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Phosphodiester bonds connect as follows:
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The 5th carbon of one deoxyribose sugar bonds to the phosphate group
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Then that phosphate group bonds to the 3rd carbon of the next sugar in the chain
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Each strand has a 3’ end and a 5’ end, based on which carbon on the sugar is free for bonding
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One DNA strand runs from 5’ to 3’, and the other runs from 3’ to 5’, making the two strands antiparallel
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The nitrogenous bases of each nucleotide project out from the backbone towards the interior of the double-stranded DNA molecule
Hydrogen bonding
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The two antiparallel DNA polynucleotide strands that make up the DNA molecule are held together by hydrogen bonds between the nitrogenous bases
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These hydrogen bonds always occur between the same pairs of bases:
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Adenine (A) always pairs with thymine (T) – two hydrogen bonds are formed between these bases
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Guanine (G) always pairs with cytosine (C) – three hydrogen bonds are formed between these bases
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This is known as complementary base pairing
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These pairs are known as DNA base pairs
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Double helix
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DNA is not two-dimensional as seen in the diagram above
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DNA is described as a double helix
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This refers to the three-dimensional shape that DNA molecules form
Examiner Tips and Tricks
Be able to identify and label the components of a DNA molecule:
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Sugar-phosphate backbone
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Nucleotides
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Complementary base pairs (A=T, C≡G)
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Phosphodiester bonds (between nucleotides)
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Hydrogen bonds (between bases)
You may be asked to calculate base numbers using base pairing rules if given the quantity of one base.
DNA function
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Deoxyribonucleic acid (DNA) is an important information-carrying molecule
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The function of DNA is to hold or store genetic information
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DNA is the molecule that contains the instructions for the growth and development of all organisms
Responses