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
1-5-2-nucleotide-structure-and-the-phosphodiester-bond
Exam code:7401
Nucleotide structure & the phosphodiester bond
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Both DNA and RNA are polymers that are made up of many repeating units called nucleotides
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Each nucleotide is formed from:
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A pentose sugar
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The carbon atoms in the sugar are numbered as 1′, 2′, 3′, 4′, and 5′
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A nitrogen-containing organic base
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A phosphate group
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DNA nucleotides
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The components of a DNA nucleotide are:
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A deoxyribose sugar with hydrogen at the 2′ position
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A phosphate group
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One of four nitrogenous bases – adenine (A), cytosine(C), guanine(G) or thymine(T)
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RNA nucleotides
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The components of an RNA nucleotide are:
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A ribose sugar with a hydroxyl (OH) group at the 2′ position
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A phosphate group
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One of four nitrogenous bases – adenine (A), cytosine(C), guanine(G) or uracil (U)
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The presence of the 2′ hydroxyl group makes RNA more susceptible to hydrolysis
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This is why DNA is the storage molecule and RNA is the transport molecule with a shorter molecular lifespan
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|
Property |
DNA |
RNA |
|---|---|---|
|
Pentose sugar |
Deoxyribose |
Ribose |
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Bases |
Adenine (A) Thymine (T) Cytosine (C) Guanine (G) |
Adenine (A) Uracil (U) Cytosine (C) Guanine (G) |
|
Structure |
Double-stranded (double helix) |
Single-stranded |
Phosphodiester bonds
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DNA and RNA are polymers (polynucleotides), meaning that they are made up of many nucleotides joined together in long chains
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Separate nucleotides are joined via condensation reactions
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These condensation reactions occur between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide
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A condensation reaction between two nucleotides forms a phosphodiester bond
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It is called a phosphodiester bond because it consists of a phosphate group and two ester bonds (phosphate with double bond oxygen attached – oxygen – carbon)
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The chain of alternating phosphate groups and pentose sugars produced as a result of many phosphodiester bonds is known as the sugar-phosphate backbone (of the DNA or RNA molecule)
Examiner Tips and Tricks
Although DNA and RNA nucleotides are very similar, make sure you know the key differences between them: unlike DNA, RNA nucleotides never contain the nitrogenous base thymine (in place of this, they contain the nitrogenous base uracil) and unlike DNA, RNA nucleotides contain the pentose sugar ribose (instead of deoxyribose).
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