Monomers and polymers

· Monomers = small units that build larger molecules; examples: monosaccharides, amino acids, nucleotides.
· Polymers = large molecules made of many monomers joined together.
· Condensation reaction = joins 2 molecules, forms a covalent bond, eliminates water (H₂O).
· Hydrolysis reaction = breaks a bond, uses water (H₂O) to split molecules.
· Exam tip: name the bond type formed/broken (e.g., glycosidic, peptide, ester, phosphodiester) and link to condensation vs hydrolysis.
· SPECIFICATION: Explain how condensation forms polymers from monomers and how hydrolysis breaks polymers into monomers.

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Wikimedia Commons – File: Dehydration and hydrolysis reactions.svg
Directions: On the page, the main diagram appears at the top in the file preview. Click “Original file” (SVG) to view at full size.
What it shows: A clear overview of dehydration/condensation vs hydrolysis, with water removed/added.
Visible caption/title: “Dehydration and hydrolysis reactions”.
Position: Main image at top (file preview).
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Carbohydrates

· Monosaccharides = monomers for larger carbohydrates: glucose, galactose, fructose.
· Condensation between 2 monosaccharides forms a glycosidic bond → disaccharide.
· Disaccharides (know monomers):
· Maltose = glucose + glucose
· Sucrose = glucose + fructose
· Lactose = glucose + galactose
· Glucose isomers: α-glucose vs β-glucose (different orientation of –OH on C1 → major structural consequences).
· Polysaccharides = many glucose units joined by glycosidic bonds.
· Storage polysaccharides (from α-glucose):
· Starch (plants): amylose (unbranched α-1,4) + amylopectin (branched α-1,4 and α-1,6)
· Glycogen (animals): very highly branched (more α-1,6 branches) → rapid glucose release
· Structural polysaccharide (from β-glucose):
· Cellulose (plants): β-1,4 links, alternating monomers inverted → straight chains, many H-bonds, microfibrils → high tensile strength
· Structure → function (high-yield): branching increases compactness + many ends for enzyme action (starch/glycogen); β-linking enables strong fibres (cellulose).
· Biochemical tests:
· Benedict’s test (reducing sugars): heat in water bath → green→yellow→orange→brick-red precipitate (increasing concentration)
· Non-reducing sugars: hydrolyse with dilute HCl, neutralise (e.g., NaHCO₃), then Benedict’s
· Iodine/potassium iodide test (starch): blue-black positive
· SPECIFICATION: Use and interpret qualitative tests for reducing sugars, non-reducing sugars, and starch.
· SPECIFICATION: Use chromatography (with known standards) to separate monosaccharides and identify components.
· SPECIFICATION: Produce a glucose dilution series and use colorimetry to generate a calibration curve to find an unknown concentration.

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Wikimedia Commons – File: 219 Three Important Polysaccharides-01.jpg
Directions: The main labelled diagram is at the top in the file preview; click “Original file” to open full resolution.
What it shows: Side-by-side comparison of starch (amylose/amylopectin), glycogen (highly branched), and cellulose (β-glucose, straight chains).
Visible caption/title: “Three Important Polysaccharides” (caption notes branching and cellulose inversion).
Position: Main image at top (file preview).
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Lipids
· Two key groups: triglycerides and phospholipids.
· Triglyceride structure: glycerol + 3 fatty acids formed by condensation → 3 ester bonds + 3 H₂O released.
· Fatty acids:
· Saturated = no C=C, straight chains → pack tightly → higher melting point, often solid
· Unsaturated = ≥1 C=C, causes “kink” → pack poorly → lower melting point, often liquid
· Phospholipid structure: like a triglyceride but one fatty acid replaced by a phosphate-containing group.
· Properties linked to structure:
· Triglycerides: non-polar, hydrophobic, energy storage, insoluble in water
· Phospholipids: hydrophilic phosphate head + hydrophobic fatty acid tails → form bilayers (membranes)
· Emulsion test (lipids): shake with ethanol, then add water → white/cloudy emulsion = positive.
· SPECIFICATION: Recognise saturated vs unsaturated fatty acids from diagrams.
· SPECIFICATION: Explain different properties of triglycerides vs phospholipids from structure.
· SPECIFICATION: Use and interpret results of the emulsion test for lipids.

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Wikimedia Commons – File: Formation of Triglyceride.svg
Directions: The main reaction diagram is at the top in the file preview; open the “Original file” for full-size viewing.
What it shows: Condensation of glycerol with three fatty acids, forming ester bonds and releasing water.
Visible caption/title: “Formation of Triglyceride”.
Position: Main image at top (file preview).
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Proteins (general properties)
· Amino acids = protein monomers; general structure: amine group (NH₂), carboxyl group (COOH), R-group (variable).
· Condensation between amino acids forms a peptide bond.
· Dipeptide = 2 amino acids; polypeptide = many amino acids.
· Functional proteins can contain one or more polypeptides.
· Bonds stabilising protein structure: hydrogen bonds, ionic bonds, disulfide bridges (covalent, between cysteines).
· Protein structure levels (link to function):
· Primary: amino acid sequence
· Secondary: α-helix / β-pleated sheet (H-bonds)
· Tertiary: overall 3D folding (R-group interactions)
· Quaternary: multiple polypeptides (e.g., haemoglobin)
· Biuret test: alkaline + Cu²⁺ → lilac/purple = protein present.
· SPECIFICATION: Relate protein structure to function/properties in contexts across the course.
· SPECIFICATION: Use and interpret results of the biuret test.
· SPECIFICATION: Use chromatography (with known standards) to separate amino acids and identify components.

Many proteins are enzymes
· Enzymes are biological catalysts that lower activation energy → increase reaction rate.
· Induced-fit model: active site changes shape as substrate binds → improves fit and catalytic action.
· Specificity: active site is complementary to substrate(s) → forms enzyme–substrate complex.
· Factors affecting rate (must describe shape of graphs + limiting factors):
· Enzyme concentration: rate ↑ with enzyme (if substrate in excess)
· Substrate concentration: rate ↑ then plateaus at Vmax (enzymes saturated)
· Temperature: rate ↑ to optimum, then ↓ (active site denatures)
· pH: changes ionisation of R-groups → affects active site; has an optimum pH
· Competitive inhibitors: bind active site, reduce rate; effect reduced by ↑ substrate concentration
· Non-competitive inhibitors: bind elsewhere, alter active site; effect not overcome by ↑ substrate concentration
· pH maths: pH = −log₁₀[H⁺].
· Required practical focus (high-yield skills):
· Independent, dependent, control variables (e.g., pH, temperature, volumes, enzyme/substrate concentration)
· Initial rate from graph using a tangent at time = 0
· Uncertainty in rate based on measurement uncertainty
· Appropriate graph choice (e.g., rate vs concentration; rate vs temperature)
· SPECIFICATION: Explain induced fit and how enzyme models have changed over time.
· SPECIFICATION: Calculate pH from [H⁺] using pH = −log₁₀[H⁺].
· SPECIFICATION: Plan and carry out an investigation into the effect of a named variable on enzyme-controlled rate (Required Practical 1), including controls, uncertainty, and initial rate from a tangent.

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Wikimedia Commons – File: Induced fit diagram.svg
Directions: The diagram preview is at the top; click “Original file” to view high resolution (SVG scales well).
What it shows: Induced fit—enzyme active site changes shape as the substrate binds, forming an enzyme–substrate complex.
Visible caption/title: “Induced fit diagram”.
Position: Main image at top (file preview).
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Nucleic acids (DNA & RNA structure)
· DNA stores genetic information; RNA transfers information from DNA to ribosomes (protein synthesis).
· Ribosomes are made of RNA + proteins.
· DNA and RNA are polymers of nucleotides: each nucleotide = pentose sugar + organic base + phosphate.
· DNA nucleotide: deoxyribose, phosphate, base = A, C, G, T.
· RNA nucleotide: ribose, phosphate, base = A, C, G, U.
· Condensation between nucleotides forms a phosphodiester bond → polynucleotide.
· DNA double helix: two antiparallel polynucleotide strands held by H-bonds between complementary base pairs (A–T, C–G).
· RNA: usually shorter, single-stranded polynucleotide.
· SPECIFICATION: Use base-pairing data to calculate missing base frequencies (e.g., if %A known, infer %T; if %C known, infer %G).
· SPECIFICATION: Appreciate why DNA’s apparent simplicity led some scientists to doubt it carried the genetic code.

DNA replication (semi-conservative)
· Semi-conservative replication: each new DNA molecule has one original strand + one new strand → genetic continuity.
· Key steps (exam phrasing):
· DNA unwinds; H-bonds break between complementary bases
· DNA helicase unwinds DNA and breaks H-bonds
· Free DNA nucleotides align via complementary base pairing on each template strand
· DNA polymerase catalyses condensation forming phosphodiester bonds joining nucleotides
· Spec skill: evaluate scientific evidence that validated the Watson–Crick replication model (e.g., interpreting experimental support).
· SPECIFICATION: Describe and explain semi-conservative replication, including roles of helicase and polymerase, and the formation of phosphodiester bonds.
· SPECIFICATION: Evaluate scientists’ work supporting the Watson–Crick model of replication.

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Wikimedia Commons – File: Semi-conservative replication.svg
Directions: The diagram is the main image at the top; open “Original file” for a clear, scalable view (SVG).
What it shows: Semi-conservative replication—each daughter DNA contains one parental and one newly synthesised strand.
Visible caption/title: “DNA replication generates two daughter DNAs…” (semi-conservative replication).
Position: Main image at top (file preview).
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ATP
· ATP (adenosine triphosphate) is a nucleotide derivative: ribose + adenine + 3 phosphate groups.
· ATP hydrolysis: ATP → ADP + Pi (inorganic phosphate) via ATP hydrolase; releases energy.
· Coupled reactions: energy from ATP hydrolysis drives energy-requiring cellular processes.
· Phosphorylation: released Pi can be added to other compounds → often makes them more reactive.
· ATP resynthesis: ADP + Pi → ATP (condensation), catalysed by ATP synthase during respiration or photosynthesis.
· SPECIFICATION: Explain how ATP hydrolysis is coupled to cellular work and how phosphorylation changes reactivity.

Water
· Water is a major cellular component; key properties (link property → biological significance):
· Metabolite in condensation and hydrolysis reactions
· Solvent for metabolic reactions (aqueous cytoplasm/body fluids)
· High heat capacity → buffers temperature change
· High latent heat of vaporisation → cooling via evaporation with minimal water loss
· Cohesion (H-bonding) → supports continuous water columns in xylem; creates surface tension at air–water interfaces
· SPECIFICATION: Explain how each property supports biological function (cooling, transport, temperature stability, reaction medium).

Inorganic ions
· Ions occur in cytoplasm/body fluids at varying concentrations; each has specific roles.
· High-yield roles to recognise across the course:
· Hydrogen ions (H⁺): determine pH; affect enzyme activity and protein structure
· Iron ions (Fe²⁺): component of haemoglobin (oxygen transport)
· Sodium ions (Na⁺): essential for co-transport of glucose and amino acids (e.g., ileum)
· Phosphate ions (Pi / PO₄³⁻): part of DNA nucleotides and ATP (energy transfer)
· SPECIFICATION: Recognise and apply ion roles in: pH, haemoglobin, co-transport, and as components of DNA/ATP.