Biological molecules

• A hydrogen bond is between a slightly negative molecule and a slightly positive molecule.

  They are weaker than covalent bonds.

  When water moves it constantly breaks and makes hydrogen bonds.
• Due to water being a liquid:

  it provides habitats, such as rivers and lakes

  its a major component of the tissues in living organisms

  it’s an effective transport medium eg. Blood
• Density-

  density of water provides an ideal habitat, if water was less dense, aquatic life wouldn’t be able to float

  Ice is less dense than water, due to its polar nature.
• Aquatic life is able to live in cold conditions due to ice being less dense.

  Ice also acts like an insulator in really extreme cold conditions.
• Water is a good solvent for many substances found in living things. Eg. Chloride and glucose.

  Due to the polarity of the water, water has both negative and positive particles, which then attract to positive and negative parts of the solute.

  The water molecules cluster around these charged parts of the solute molecules and will separate them and keep them apart.

  They dissolve and the solution if formed.
• Due to the arrangement of the molecules and the hydrogen bonds. The water molecules at the surface are all hydrogen bonded to the molecules beneath rather than the air molecules.

  They are more attracted to the molecules beneath.

  It gives the surface of water an ability to resist force applied to it, which is why humans can’t walk on water.
• Lipids are biological molecules which are only soluble in organic solvents such as alcohol.
• Saturated fats- found in animal dont contain any carbon- carbon double bonds.
• Unsaturated fats- which are found in plants- contain a double carbon- carbon bond.

  They melt at a lower temperature.
• The greater the number of unsaturated bonds, the weaker the intermolecular bonds, resulting in a lower melting point.
• Triglycerides function as a long- term storage form of energy in the human body- long chains.

  Triglycerides are non polar molecules and do not dissolve in polar solvents.

  They can be broken down into components for energy.
• Fats and oils are made up of carbon, hydrogen and oxygen.

  The building blocks of fats are glycerol and lipids.

  Three fatty acid molecules bond to each glycerol molecule by a condensation reaction.

  This bond is called an Ester bond.

  Fats are solid and room temp.

  Oils are liquids at room temp.
• Phospholipids form when two fatty acids and phosphate group bond to a glycerol molecule.

  The phosphate end of the molecule is hydrophilic and the two fatty acid tails are hydrophobic.

  Phospholipids are a major structural component of cell membranes

  Hormones such as cholesterol, oestrogen and progesterone also belong to the class of lipids
• Proteins are polymers.
• They are formed by their monomers- amino acids. More than one monomer makes up a polymer. Proteins are made up of a long chain of amino acids.
• All amino acids have the smae structuire, they each contain a carboxyl group and an amino group. However, the difference between each amino acid is the variable group know as the R group.
• Each amino acid contains : carbon, oxygen, nitrogen and some contain sulfur.
• Amino acids are joined by peptide bonds to form polymers.

  When two molecules join, a molecule of water is released meaning that it is a condensation reaction. To reverse the reaction and break the bond, water must be added. This is known as a hydrolysis reaction.
• To bond the two amino acids together, the OH from amino acid 1 bonds with the H on amino acid 2
• Proteins have four structural levels: primary, secondary, tertiary, and quaternary.
• Primary structure: The sequence of amino acids in a polypeptide chain. Different proteins have a different sequences of amino acids. A change in amino acid could change the whole protein. Its held together by peptide bonds.
• Secondary structure: The local folding of the polypeptide chain into alpha helices and beta sheets. This is due to hydrogen bonds between the amino acids. Its held together by hydrogen bonds.
• Tertiary structure: folded and coiled even more. More bonds are formed between different part of the polypeptide chain. It forms a 3D shape. It’s held together via ionic bonds, hydrogen bonds and disulphide bridges and hydrophobic and hydrphilic interactions.
• Quaternary structure: The three-dimensional structure of a protein that results from the interaction of multiple polypeptide chains. Normally determined by tertiary structure. it can be influenced by all of the bonds.
• Globular proteins: the hydrophilic R groups on the amino acids are pushed to the outside of the molecule. This makes them soluble, therefore they can be transported easily through liquid
• Examples of Globular proteins: Haemoglobin, insulin and amylase.
• Haemoglobin: A protein that carries oxygen in the blood. It’s known as a conjugated protein as it has a non- protein group attached to it. Each of the polypeptide chains in haemoglobin has a prosthetic group called haem, which carries iron.
• Insulin: A hormone that is released by the pancreas to control blood glucose levels. Solubility is important as it needs to be able to travel around the body through the blood. It is made by two polypeptide chains that are bonded together via disulfide bonds.
• Amylase: A type of enzyme that breaks down starch into glucose. It is made up of a singular chain of amino acids. Most enzymes are globular proteins.
• Fibrous proteins are made up of long chains of amino acids. They are insoluble in water. They are also strong. They are structural proteins and fairly unreactive.
• Examples of fibrous proteins: Collagen, keratin, elastin
• Collagen: A protein that makes up the fibrous connective tissue in the body. It is found in tendons, ligaments, and bones. It is very strong. Minerals can bind to the protein to increase rigidity.
• Keratin: A protein that makes up the outer layer of the epidermis and the hair shaft. It can be either flexible or hard and strong.
• Elastin: A protein that gives elasticity to the skin and blood vessels. It is elastic so allows tissues to return to their original shape after stretching.
• Monosaccharides- simple sugars: glucose, galactose, fructose.
• Glucose: hexose sugar- 6 carbons. source of energy in humans, cellular respiration- glucose helps make ATP. Alpha + Beta glucose are isomers- they have the same formula but different arrangement of molecules.
• Disaccharides= two monosaccharides. Glucose+ Glucose- maltose. Glucose + fructose- sucrose. Glucose+ galactose - lactose
• Polysaccharides- two or more monosaccharides. Joined by glycosidic bonds. They can be branched and unbranched. Examples include glycogen and starch and cellulose.
• What are the functions of starch?


  Main energy storage material in plants. Stored in seeds of plants. Starch is broken down to glucose for energy. Source of food for animals and humans.
• Starch is insoluble (doesn't dissolve in water)