Biology AS - Biological Molecules

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Hydrogen bond- A weak interaction that can occur wherever molecules contain a slightly negatively charged atom bonded to a slightly positively charged hydrogen.

- Density: At colder temperatures, hydrogen bonds form a crystaline structure (Ice) which is less dense and floats - insulates water underneath and protects organisms during winter - Laten Heat of Fusion

- Stable Habitat: Relative amount of energy needed to increase temperature - keeps temperature in rivers and lakes stable for life - Specific Heat Capacity

- Universal Solvent: Allows lots of solutes to dissolve in it - useful in bodily function and for reactions (e.g. blood) - Surface Tension (equal amount throughout bodies)

- Reactions: Water takes place in many important reations in the body and outer world

Adhesion: Water sticks to polar substances

Capillarity: water molecules attracted together and Adhesion - water travels against Gravity

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Proteins Part 1


  • Structural components (Muscle & bone)
  • Membrane carriers & pores (Active transport & facilitated diffusion)
  • Enzymes are proteins
  • Hormones can be proteins and antibodies are proteins too

Bond between Amino Acids is a Peptide Bond

Secondary Structure- Refers to coiling and pleating of parts of the polypeptide molecule (Alpha Helix or Beta Plate)

Tertiary Structure- The overall 3D structure of the final polypeptide/protein molecule - stabilised by coils/pleats and held together by hydrogen bonds. 

- Heating increases kinetic energy of the molecule - causing it to vibrate and break some bonds that hold the tertiary structure in place - denaturing the Protein

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Proteins Part 2

- Globular Proteins - Ball shaped structure and are usually soluble in water. They usually have metabolic roles (Enzymes) - Hydrophobic R groups are turned inwards towards the centre of the structure and hydrophillic R groups are usually on the outside so they're soluble

- Fibrous- Form fibres, usually have regular repetitive sequences of amino acids. Usually insoluble in water and have structural roles - e.g. Collagen


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Fatty acid molecules have tails of hydrocarbons and are hydrophobic (water repellent)

 - Make lipids insoluble in water

  • Saturated Fatty Acids: no double bonds between carbon and tails – saturated with hydrogen
  • Unsaturated fatty Acids: double bonds between tail and hydrogen

Ester Bond – created in condensation reaction and broken in a hydrolysis reaction

Cholesterol: help strength the cell membrane – small size allow it to fit between phospholipids and pack closer together (less fluid and more rigid)

Phospholipids: Found in the cell membrane and make up Phospholipid bilayer – the centre (due to the tails) is Hydrophobic so water-soluble substances cannot pass through easily - acts as a cell barrier

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Carbohydrates Part 1

- Macromolecules are complex molecules – e.g. Proteins, Lipids and some carbohydrates

- Polymers are large, complex molecules made out of long chains of monomers - broken down in hydrolysis reactions, breaks chemical bond with water molecule

- Biological polymers are formed through condensation reactions – releases water molecules

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Carbohydrates Part 2

Alpha & Beta Glucose:

  • Has a soluble structure – easily transported
  • Chemical bonds contain lots of energy
  • Carbohydrates are made up of carbon, hydrogen and oxygen
  • Monosaccharides are monomers that make up carbohydrates
  • Monosaccharides are bonded together with glyosidic bonds
  • Two monosaccharides make up a disaccharide
  • More than two monosaccharides make up a polysaccharide
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Inorganic Molecules - Cations

  • Calcium – e.g. transmission of nerve impulses and release of insulin
  • Sodium – e.g. generating nerve impulses, muscle contraction and regulating fluid balance
  • Potassium – e.g. generating nerve impulses, muscle contraction and regulating fluid balance
  • Hydrogen – e.g. affects pH, helps photosynthesis and respiration reactions
  • Ammonium – e.g.  Absorbed from soil by plants and source of Nitrogen
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Inorganic Molecule - Anions

  • Nitrate – e.g. Absorbed from soil by plants -  Nitrogen
  • Hydrogencarbonate – e.g. buffer and maintain pH
  • Chloride - e.g. maintain pH in blood during gas exchange - acts as cofactor
  • Phosphate – e.g. photosynthesis and respiration reactions – synthesis of many biological molecules
  • Hydroxide - e.g. affects pH substances
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