Topic 1- Biological Molecules

Polymer- large molecule composed of monomers

Monomer- a repeating basic unit

Monomers are joined by a condensation reaction which produces water.

Polymers are broken by a hydrolysis reaction which is the addition of water.

The basic unit of a carbohydrate is a monosaccharide

The elements found in carbohydrates are: carbon, hydrogen and oxygen

There are two main isomers of glucose, alpha and beta glucose, where the difference lies in where the OH group on carbon 1 is placed.

Alpha glucose has the OH group BELOW the carbon

Beta glucose has the OH group ABOVE the carbon

Both of these isomers are a source of energy and are a respiratory substrate.

When joined by a condensation reaction they form 1, 4 glycosysidic bonds.

Sucrose is a disaccharide formed of alpha glucose and fructose- it is a NON reducing sugar.

Maltose is a disaccharide formed of two alpha glucose molecules- it is a reducing sugar.

Lactose is a disaccharide formed of alpha glucose and galactose- it is a reducing sugar.

To test for a reducing sugar you:

Add Benedicts solution and heat it; if a reducing sugar is present then the solution will go from green, yellow, orange and then brick red forming a precipitate.

This test however is subjective (based on your own perception)

To test for Sucrose you:

Add HCl and heat before neutralising to break the glucosidic bond and then you follow the same procedure for testing for a reducing sugar by adding Benedicts solution and heating the mixture to get a precipitate.

Starch: is only found in plant cells and is made of alpha glucose only.

It comes in two forms: Amylase which is a compact grain and Amylopectin which is a branched chain.

Both form a compact grain but amylopectin is more compact which makes it ideal for storage.

Startch is insoluble which means that it does not affect the water potential of the cell and it is also inert so it is unreactive.

To test for starch you use the Iodine solution test/ Iodine in KI solution:

If positive the solution will go a blue/black colour

If negative then the solution will remain orange

Glycogen is an animal energy reserve made of alpha glucose

It is very compact with lots of branching so many 1,6 glycosidic bonds have formed, inert and insoluble.

It is found in large quantities in the liver and in the muscle

Cellulose is made of beta glucose and is found in the plant cell wall.

When the 1,4 glycosidic bonds form a beta glucose molecule alternately flips 180 degrees which creates long straight fibrils and therefore as a result has a high tensile strength.

Hydrogen bonds hold the fibrals together.

The basic unit of a protein is an amino acid. They have the basic structure of:

There are 20 different types of proteins naturally occurring which differ only in the R groups.
There are 10 essential amino acids that must be in our diet.
When joined by a condensation reaction to form a dipeptide

Primary structure: is a sequence of amino acids that are joined by peptide bonds ONLY.

Secondary structure: hydrogen bonds form not (but not between the R groups) it forms an alpha helix or a beta pleated sheet,

Tertiary structure: it is determined by the bonds between the R groups such as:
Disulfide bridges (only involving cystine [Cys] whoch are very strong
Ionic bonds between charged groups
Hydrophobic interactions and
Some hydrogen bonds

These bonds cause it to create a compact GLOBULAR 3D structure which is very specific.

Quaternary structure: where 2 or more polypeptide chains are joined together e.g. haemoglobin has 4 chains each with a prothetic group which is the haem group.

To test for a protein you use the BIURET test:

(NaOH and CuSO4) if a protein is present then the solution will turn lilac.

It makes up tendons and is made of three interwoven polypeptides.

It has no prothetic group and is inelastic.

Its function is to hold muscle to bone for movement.

Has staggered ends so there is no line of weakness in the junctions between polypeptides.

The chains are held together by hydrogen bonds and it is insoluble.

Lipids are NOT polymers and are made of glycerol attached to three fatty acids.

These fatty acids are mostly made up of hydrocarbons and they differ as to whether they are saturated or unsaturated.

The glycerol is joined to a fatty acid by a condensation reaction to form a peptide bond.

Saturated fatty acids are bonded to the maximum number of hydrogen atoms 

Unsaturated fatty acids contain a carbon to carbon double bond so the chain has a kink in it. This means that it is not bonded to the maximum number of carbon atoms and if the glycerol is attached to an unsaturated fatty acid then the lipid is liquid at room temperature.

To test for a lipid you:

Add ethanol to the sample and shake before adding water and shaking again, If a lipid is present then a cloudy emulsion will form.

 Water is a dipolar molecule as the electrons used in the covalent bond are held closer to the oxygen atom.

Due to this hydrogen bonds can form between water molecules which:

Aids cohesion- the fprce of attraction between water molecules for example up the xylem

Creates surface tension- creates a film that insects can walk on such as pond skaters

Causes a high specific heat capacity- takes a lot of heat energy (4.2 Joules of energy is needed to heat 1cm cubed of water by 1 degrees C) to become vapour which means that oceans and lake are thermally stable habitats

When solid water creates a lattice which traps air allowing it to float.
It therefore creates a habitat and insulates the water below it.

Latent heat of vapourisation- sweating acts as a coolant (cools us down)

Turgidity- water in cells of a leaf causes its broad shape which means that there is a large surface area for photosynthesis

Transport medium- in plasma, cells and xylem

Photosynthesis- water is a substrate in photosynthesis

Is involved in hydrolysis reactions so is a good solvent

Calcium- provides strength in bones and teeth, used in nerve impulse transmission, used in muscle contractions

Iron- is known as haem- binds to the oxygen in red blood cells and is an electron carrier

Nitrogen- is used in proteins

Phosphate- used in ATP, used in the phospholipid bilayer and used in DNA

Sodium- used in nerve cell impulses and co-transport in the gut

Potassium- used in nerve cell impulses and in guard cell action