AS Biology CCEA Unit 1 Bio Molecules

Biological Molecules

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  • Hydrogen Bonds - weak interaction (negatively charged atom bonded to a lightly postively charged hydrogen)
  • Covalent Bond- Shared pair of electrons
  • Dipolar - the shared electrons aren't shared evenly and the oxygen atom is capable of pulling the shared electrons towards itself and away from the hydrogen atoms. Oxygen = electronegative.
  • Solvent - medium in which all metabolic reactions take place.
  • High Heat Capacity - (the amount of heat required to raise the temperature of 1kg by 1°C - preserves life
  • High heat of fusion - (measure of heat required to melt solid) contents of cell less likely to freeze
  • Ice has higher density than liquid - ice floats, layer of insulation for marine life, density decreases below 4°C
  • Useful Structural Agent - (difficult to compress) good for hydrostatic skeleton in worms, supports a plant so it is turgid
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Solvent - The liquid in which the solute dissolves
Solute - The solid which dissolves in the solvent

A Buffer solution resists change to pH.


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Inorganic Ions

Inorganic Ions 

Nitrate - Nitrogen in the amino group of amino acids produced in plants

Sulphate - Sulphur in the R Group of the amino acid cysteine

Phosphate - ATP, bucleotides, phospholipids

Calcium - calcium phosphate, bone

Magneisum - chlorophyll

Iron - Haemoglobin

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  • Cn(H20)n
  • Energy source- released from glucose in respiration
  • Energy store -starch
  • Structural agent - cellulose

Monosaccharides (contain between 3 and 6 C atoms)(Soluble in water, Sweet Tasting, Able to form crystals)

Alpha glucose and Beta glucose - Isomers (same chemical formula but a different structural formula)

Two monosaccharides can be joinged in a condensation reaction to make a disaccharide. Glycosidic bond. Water is removed. Hydrolosis reverses this.

Alpha glucose + Alpha glucose = Maltose

Alpha glucose + Fructose = Sucrose

Alpha glucose + Galactose = Lacose

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Carbohydrates (continued)

Starch- energy storage for plants. Branched (1-4, 1-6)amylopectin and straight chain amylose (1-4) molecules. Stored in chlorplasts and in starch grains. Starch can be broken down to glucose molecules that can be respired to release energy for ATP.

Glycogen- energy storage for animals. (Animal starch) Large molecule and made up of alpha glucose. The 1-4 glucose chains in glycogen are shorter than starch ones and glycogen has more branches extending from the chain. Glycogen is more compact than starch and makes glycogen granules in animal cells, e.g. liver and muscle cells.

  • They are insoluble so they don't affect water potential of cells.
  • They also hold glucose molecules in chains so they can be broken off from ends to provide glucose for energy when needed. Hydrolysis.

Cellulose - Beta glucose, structual agent in cell walls. long straight chain (1-4)

60-70 cellulose molecules are cross linked by hydrogen bonds to form bundles called microfibrils, these microfibrils are held by more hydrogen bonds to form even larger bundles called macrofibrils which have great mechanical strength. Close to that of steel. They are embedded in a polysaccharide glue of substances called pectins to make cell walls. (can be further supported by cholesterol)

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Starch --> iodine in potassium iodide, starch is present a colour change from yellow/brown to blue/black

Reducing sugars--> Heated with benedicts solution colour change from blue to orange/red. Precipitate. (blue--green--yellow--orange--red)

Non reducing sugars--> Don't react with benedicts solution. Negative. No colour change. So make sure there are no reducing sugars, then boil with HCl <-- hydrolysing sucrose present, splitting sucrose molecules to make glucose + fructose. Cool and neutralise the solution. Do the reducing sugars test again and the test should be positive because monosaccharides glucose and fructose are present.

Proteins--> Biuret test. [Biuret re. is pale blue] The chemicals react with peptide bonds in protein resulting in a colour change to lilac.

Lipids--> Ethanol emulsion test. Positive test results in a cloudly white emulsion near the top of water. There is a band.

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  • Triglycerides (glycerol and three fatty acids, condensation reaction, ester bond)
  • Phospholipids (two hydrophobic fatty acid tails and a hydrophillic phosphate group head - forms bilayer in aqueous environment)

Saturated - Contains no double bond in the hydrocarbon chain (solid fats)

Unsaturated - Contains a double bond in the hydrocarbon chain (liquid, oils)


  • Energy (release and storage)
  • Biological Membranes
  • Insulation
  • Protection
  • Hormones
  • Buoyancy in marine animals
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  • Proteins are chains of amino acids
  • Huge variety of proteins possible
  • The overall shape is precise and integral to the function of the protein in the cell
  • It is the "R" group that differs to form the 20 different naturally occurring amino acids
  • Amino acids bond together to form a dipeptide
  • Peptide bond, condensation reaction
  • Amino acids act as buffers in solutions
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Protein Structure

The primary structure of a polypeptide is the sequence of amino acids in the chain

The secondary structure is either an alpha helix or a beta-pleated sheet, Held in place by hydrogen bonds between peptide links

Tertiary structures affect globular proteins. The chain folds over on itself in a precise way to produce a specific three dimensional shape. Maintained by hydrogen bonds, ionic bonds, disulphide bonds and hydrophobic interactions.

Futhermore some proteins consist of two or more polypeptide chains bonded together and this is the quaternary structure.

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Proteins (continued)

Haemoglobin is a globular protein found in red blood cells.Each molecule has 4 polypeptides : two alpha chains and two beta chains.Each polypeptide had an iron containing haem group attached. Important in transport of oxygen in animals as an oxygen molecule can associate with each haem to form oxyhaemoglobin

Collagen is a fibrous protein. Each molecule consists of three idenitcal polupeptides coiled round each other and held together by hydrogen bonds. Collagen molecules are bonded together to form the strong fibres found in the skins, tendons and ligaments.

Conjugated Proteins have a non-protein part attached. Called a prosthetic group.

Glycoprotein- carbohydrate- mucin; cell surface membrane

Lipoprotein - lipid - membrane strucutre

Nucleoprotein - nucleic acid - chromosome structure; ribosome structure

Haemoglobin - Haem - Red Blood Cells

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