Biological molecules

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Water molecules have 2 hydrogen atoms and 1 oxygen atom. The hydrogen and oxygen atoms are joined together by shared electrons. oxygen attracts the electrons more strongly than hydrogen.This makes water molecules polar.This polarity leads to the formation of H bonds between water molecules. The H bonds in water absorb a lot of energy giving it high specific heat capacity. This allows the organisms to avoid rapid changes in tempreture.It takes a lot of energy to break the H bonds in water so water has a high latent heat of evaporation. this means water is good for cooling things.Water's polarity makes it very cohesive. this helps it to flow, allowing it to transport substances. Water polarity allows it to dissolve other molecules. This allows water to act as a universal solvent so it can transport substances.

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  • Carbohydrates are long complex molecules consisting of monosaccarides
  • It stores energy in chemical bonds so it is main energy source in plants and animals
  • Carbohydrates are sweet, soluble and crysatlline
  • Glucose has six carbon atoms and is a single monosaccharide
  • Two forms of glucose : ALPHA GLUCOSE and BETA GLUCOSE(
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  • A disaccharide is formed when 2 monosaccharides join together.
  • Monosaccharides are joined together by GLYCOSIDIC BONDS.
  • During synthesis, a hydrogen atom from the monosaccharide bonds to a hydoxyl (OH) group on the other releasing a water molecule. (CONDENSATION)
  • The opposite is the water molecule reacting with the glycosidic bond breaking it apart.(HYDOLYSIS)



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  • A polysaccahride is formed when more than 2 monosaccharides join together
  • STARCH- Energy storage in plants
  • Alpha glucose: Amylose and Amylopectin
  • AMYLOSE- A long unbrached chain, coiled structure that makes it compact so its good for storage.
  • AMYLOPECTIN-A long branched chain, lots od side branches that can be broken down by an enzyme to release energy quickly.
  • INSOLUBLE- So water does not enter by osmosis.
  • GLYCOGEN- Energy storage in animals.
  • A long branched chain, lots od side branches that can be broken down by an enzyme to release energy quickly.It's also compact molecule so good for storage.
  • CELLULOSE- Main component of cell walls in plants
  • Long, unbranched chains of oppositly orientated beta glucose.The bonds between sugars are straight so chain is straight so they can fit in microfibrils. The cellulose chain is linked by H bonds to form strong microfibrils so the strong fibres can provide structural support for cell.
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  • Source of energy
  • Energy storage
  • Cell membranes
  • Waterproofing
  • Hormones
  • Insulation
  • During respiration produces 2x more energy than carbohydrates.
  • A condensation reaction occurs between the acid group of the fatty acid and one of the hydoxyl groups of the glycerol molecule forming a convalent bond. A water molecule is produced and a new bond called ESTER BOND.


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  • One molecule made of three fatty acids and glycerol group.
  • The long hydrocarbon tails contain lots of chemical energy which is released when they are broken down.
  • They bundle together as insoluble droplets with tails fcae inwards as they are hydropobic with glycerol facing outwards so they are shielded.This stops water entering by osmosis.


  • One molecule of two fatty acids, glycerol group and phosphate group.
  • Molecule of hydophobic tails and hydrophillic heads facing inwards. This forms a bilayer in cell membrane so it can act as a barrier contolling exist and entry of substances.


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  • One molecule made of one hydroxyl group, hydrocarbon rings and one hydrocarbon tail.
  • They are small sized and have a flattened shape so they can fit in between the phospholipid bilayer causing them to be packed together.This allows the membrane to be less fluid and more rigid.
  • Polar hydroxyl group makes it soluble.
  • Used to make steroids as nature of lipids means that they can pass directly through the phospholipid bilayer to reach their target receptor.This is in the nucleus so has to pass the lipid bilayer of the nuclear envelope
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  • Proteins are made up of long chains of amino acids.
  • A dipeptide is formed when two amino acids join toegther
  • A polypeptide is formed when more than two amino acids join together.
  • Proteins are made of one or more polypeptides.
  • A amino acid has a carboxyl group and amino group attached to a carbon atom. The difference between the amino acids is the variable group.(R)
  • R group can be small/large, positve/negative charged or hyrophobic/hydrphillic.
  • A condensation reaction between the acid group of one amino group and the amino groups of another forms a convalent bond between the two amino acids. A water molecule is produced and a new bond formed called PEPTIDE BOND. 
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  • PRIMARY STRUCTURE-This is the sequence of amino acids in the polypeptide chain joined by peptide bonds and linked byconvalent bonds.
  • SECONDARY STRUCTURE-The polypeptide chain doesn't remain flat and straight.H-bonds form between the amino acids in the chain making them coil into alpha helix or fold into beta pleated sheets.
  • TERTIARY STRUCTURE-The coiled or folded chain of amino acids is often coiled and folded futher.More bonds form between different parts of the polypeptide chain.For protiens made from a single polypeptide chain, the tertiary structure forms their final 3D structure
  • QUANTERNARY STRUCTURE-Some protiens are made of several different polypeptide chains held together by bonds. The quanternary structure is the way these polypeptide chains are assembled together. E.G. Haemoglobin is made of four polypeptide chains, bonded together. For protiens made from more than one polypeptide chain, the quaternary structure is the protien's final 3D structure. 
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  • PRIMARY STRUCTURE- Held together by the peptide bonds between amino acids.
  • SECONDARY STRUCTURE- Held together by H bonds that forms between nearby amino acids. These bonds create alpha helix chains or beta pleated sheets.
  • TERTIARY STRUCTURE- Different bonds:
  • IONIC INTERACTIONS-Weak attractions between negative and positive charges on different parts of the molecule.
  • DISULFIDE BONDS- When two molecules of the amino acids cysteine are close together the sulphur atoms form disulfide bonds.
  • HYDROPHOBIC and HYDRPHILLIC INTERACTIONS- When hyrophobic groups are closed together in the protien, they tend to clump together. This means that hyrophillic groups are pushed to the outside which affects the way the protiens fold up into its final structure.
  • QUATERNARY STRUCTURE- Influenced by all the bonds above.
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  • COLLAGEN- Forms supportive tissues in animals so it needs to be strong.
  • It's made up of three polypeptide chains that are tightly coiled into a strong triple helix.
  • The chains are interlinked by strong convalent bonds.
  • Minerals can bind to the triple helix to increase its rigidity.


  • HAEMOGLOBIN- It has an iron- containing heam group that binds to oxygen, carrying it around the body
  • Its structure is curled up so that hydrophillic side chains are on the outside of the molecule and hydrphobic side chains face inwards.
  • This makes the haemoglobin soluble in water, which makes it good for transport in the blood. 
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  • Add benedict's solution and to heat to 80°C in a water bath
  • Blue to orange-red


  • If reducing sugar test is negative, boil with hydrochloric acid, cool, and neutralise with sodium hydrogencarbonate solution or sodium carbonate solution, repeat benedicts test.
  • Blue to orange-red
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  • Add biuret reagent; Sodium hydroxide and Copper sulfate
  • Blue to lilac


  • Add ethanol to extract ( dissolve) lipid and por alcohol into water in another testtube.
  • White emulsion forms near top of water


  • Add few drops of iodine solution
  • Brown to blue/ black
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