Biological Molecules



Water molecules have h bonds as there is a slight negative charge on oxygen and a slight positive charge on the hydrogen. This means there is attraction between the hydrogen on one molecules with the oxygen on another. water has some special properties:

High heat capacity) The amount of heat required to raise the temperature of an object or substance one degree.Has a high heat capacity as the h bond are stable so a lot of energy is needed to increase the kinetic energy this helps organisms keep a constant body temperature.
High latent heat of evaporation) Similar to heat capacity it takes a lot of energy to change it from a liquid to a gas, this helps organisms to cool down as they use a lot of the body heat to evaporate water but the loss of water is not a lot.
Cohesion) This is when water molecules stick together it creates surface tension on ponds so insects cal walk on it, it also helps the flow of water in plants as it helps capillarity, when water molecules moves they pull others.
Solvent) Water is able to dissolve polar molecules such as ionic compound. this is due to the water being able to interact as the positive charge on hydrogen surround the anions and vice versa for the negative charge on the oxygen. This allows ions in the body to be transported.
Ice) When a liquid the waters hydrogen bonds are constantly breaking and forming allowing the molecules to be close together. When frozen the h bonds are spread out and no longer breaking. This causes ice to less dense than water causing it to float to the surface of ponds. This stop the entire pond from freezing while stopping the entire pond from freezing and providing insulation.

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Amino acids

Amino acids) Amino acids have a c at the centre, which is connected to a H, a variable group, a carboxylic acid group and amine group

Condensation reaction) A peptide bond is formed when amino acid monomers combine to form a dipeptide, this is a condensation reaction as the OH from the carboxylic acid and a H from the amine group go off to form H₂O. These condensation can be repeated to form polypeptides . the opposite of this reaction is a hydrolysis reaction when water is used to break a peptide bond.

Primary structure) This is when amino acid are joined up by peptide bond in a linear line.
Secondary structure) This is when the primary structure coils up, this structure is called the alpha helix and is held by hydrogen bonds. The hydrogen bonds are created between the C =O and the N-H.  Even though they independently are weak together they are strong enough to hold the structure. The structure ma also become a beta pleated sheet which resembles a folded piece of paper.
Tertiary structure) This structure is a precise shape, it is held in a permanent form by multiple bonds such as : hydrogen bonds, ionic bonds, disulphide bridges and hydrophilic/phobic interactions. Spherical shaped proteins are globular and are soluble, some are long chains which are fibrous proteins. These are insoluble and are usually used for structure functions.
quaternary structure) This is when multiple different polypeptides bond together to form a very specific shape, haemoglobin is 4 polypeptides formed together with a inorganic haem group, this is called a prosthetic group

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Globular And Fibrous Proteins

structure of collagen) This is a fibrous protein, it consists of 3 polypeptide chains wound around each other. H bonds are present to further strengthen these structures. These strength is then increased by the collagen forming covalent cross links with other collagens next to it. This forms a collagen fibril which can then gather to produce collagen fibres. 35% of the amino acids are glycine, They are used for structure such as for in arteries walls tendons, bones and cosmetics

  • fibres
  • insoluble
  • structural

structure of haemoglobin) Haemoglobin is a globular protein it is soluble in water and is made of 4 subunits, 2 of these are alpha chains the other 2 are beta chains. The prosthetic  group is the haem group which contains fe 2+ this is used to help bind haemoglobin to oxygen. This protein has a large range of amino acids. 

  • rolled up ball
  • soluble
  • metabolic reactions
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Monosaccharide) All carbohydrates have the formula (CH₂O)n, all monomers are soluble and so can affect the water potential in plants. Carbohydrate monomers are called a monosaccharide.

Comparing alpha and beta glucose) Glucose has the formula of is C6H12O6, the way these atoms are arranged determines if it is alpha glucose or beta glucose. Both are identical apart from the position of the OH and the H. in beta the OH is above the carbon while H is below and this is reversed for alpha.

Disaccharides) Disaccharides can be formed by a condensation reaction of two monosaccharide, this makes a glycosidic bond. There are multiple disaccharides can form from different monosaccharide:

Monosaccharide  |  Glucose + Glucose  |  Glucose + Fructose  |  Glucose + Galactose 

Disaccharide        |           Maltose            |           Sucrose            |            Lactose

A hydrolysis reaction can also break the disaccharide into two monosaccharide by using a water molecule to break the glycosidic bond.

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Polysaccharides) Amylose is a polysaccharide which is made out of alpha glucose. alpha glucose is able to make 1,4 glycosidic bonds and 1,6 glycosidic bonds.  It has 1,4 bonds this means there are no branches and the amylose ends up  forming a helix. Amylopectin is also made of alpha glucose, but it also has 1,6 glycosidic bonds allowing branches to form and be more dense and compact.                    

Starch) starch has both amylose and Amylopectin, they are used to store energy in plants. It is insoluble so it doesn’t affect the water potential. The many amylopectin branches mean that enzymes can break chains off to release energy rapidly during respiration. It is used to store energy in plants and is stored in the chloroplast.                                                                                                        

Glycogen) this is the storage molecule for animals and is stored in the liver, it releases glucose when blood sugar level is low. The structure of glycogen is similar to amylopectin but it has shorter 1,4 bongs and more branches making it more compact. Both these polysaccharides are made of alpha glucose as plants and animals only have enzymes to break alpha glucose bonds.                

Cellulose) this is made of beta glucose, due to the structure of beta glucose each alternative molecule is rotated 180 degrees making cellulose a straight chain. These chains form hydrogen bonds with each other as cross links. A bunch of these chains are called  micro fibril, a bunch of these fibrils form a macro fibril. It is insoluble and allows the plant cells to be turgid as when the water potential of the cell is low water floods in and causes the cytoplasm to push against the cell wall.

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Triglycerol) A glycerol can form with three fatty acid molecules by a condensation reaction to form a ester bond, the resulting molecule is called a triglyceride. Triglyceride is hydrophobic and therefore insoluble, it is used to store energy as fat.

Phospholipids) are similar to triglycerides however one of the fatty acid tail is replaced with a phosphorous head, the head is hydrophilic while the tails are hydrophobic. They are used to make the phospholipids' bi layer in cell membranes and they may  have molecules attached to them for cell signalling.

Cholesterol) is a lipid used in the bi layer in order to reduce fluidity, it is also used in a steroid hormone.

(               (

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Chemical tests

protein (biuret test)- dilute sodium hydroxide and dilute copper sulphate is added equal volume to the sample, if it turns violet a protein is present.

starch (iodine solution)- iodine is added to the sample, if it turns blue-black starch is present and if negative it remains orange-yellow.

lipids (emulsion test)- the sample is first shaken with ethanol and then added to water, if a white emulsion forms on top a lipid is present

reducing and non-reducing sugars (Benedict’s test)- the Benedict's solution is added in equal volume to a solution and heated in a hot water bath. If there is a reducing sugar present the solution will change from blue to brick red or yellow. If the results for this test is negative it can be tested as a non-reducing sugar, this is done by heating the solution in hydrochloric acid to create a hydrolysis reaction so glycosidic bonds are broken to form monomers. The solution is then neutralised with sodium hydrogen carbonate. The Benedict's test is done again, if the results are positive it means the sample is a non reducing sugar.

Colorimeter- The colorimeter shines alight through the sample, the more light that gets absorbed the more reducing sugar there is.

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