Biological molecules

• Water is a reactant in many chemical reactions, including hydrolysis reaction
• Water is a solvent which means substances dissolve in it, most biological reactions take place in solution so water is pretty essential
• Water transports substances, because it is a liquid and solvent it means it can easily transport all sort of materials like glucose and oxygen around plants and animals
• Water helps with temperature control because it has a high specific heat capacity and a high latent heat of evaporation
• A molecule of water is one atom of oxygen joined to two atoms of hydrogen by shared electrons
• Because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge
• The unshared negative electrons on the oxygen atom give it a slight negative charge
• This makes water a polar molecule because it has a partial negative charge on one side and a slight positive charge on the other
• The slightly negatively-charged oxygen atoms attract the slightly positively-charged hydrogen atoms of other water molecules. This attraction is called hydrogen bonding and it gives water some of its useful properties
• Hydrogen bonds give water a high specific heat capacity, this is the energy needed to raise the temperature of 1g of a substance by 1 degree. The hydrogen bonds between water molecules can absorb a lot of energy so water has a high specific heat capacity. It takes a lot of energy to heat up. Water does not experience rapid temperature changes
• Hydrogen bonds also give water a high latent heat of evaporation, it takes a lot of energy to break the hydrogen bonds between water molecules so alot of energy is used up when water evaporates. Water is great for cooling things
• Waters polarity makes it very cohesive . Cohesion is the attraction between molecules of the same type. Water molecules are very cohesive, they stick together, because they are polar. This helps water flow which helps transport substances.
• Waters polarity also makes it a very good solvent, the slightly positive end of a water molecule will be attracted to the negative ion and the slightly negative end of a water molecule will be attracted to the positive ion. This means the ions will be totally surrounded by water molecules and they will dissolve
• Water is less dense when it is solid because at low temperature water freezes and it turns from a liquid into a solid. Water molecules are held further apart in ice than they are in liquid water because each water molecule forms four hydrogen bonds to other water molecules making a lattice shape. This makes ice less dense than water
• Carbohydrates are made from Monosaccharides
• Most carbohydrates are polymers and a polymer is a molocules made up of many similar, smaller molecules (monomer) bonded together. The monomers that make up carbohydrates are called monosaccharides.
• Glucose is a monosaccharide with six carbon atoms, meaning it is a hexose monosaccharide. There are two forms of glucose - alpha and beta, both have a ring structure
• Ribose is a monosaccharide with five carbon atoms meaning it is a pentose monosaccharide
• Monosaccharides join together to form disaccharides and polysaccharides. Monosaccharides are joined together by glycosidic bonds.
• During synthesis, a hydrogen atom on one monosaccharide bonds to a hyrdoxyl group on the other, releasing a molecule of water. This is a condensation reaction.
• The reverse of this synthesis reaction is hydrolysis, a molecule of water reacts with the glycosidic bond, breaking it apart.
• Starch is the main energy storage material in plants, cells get energy from glucose and plants store excess glucose as starch and when it needs more glucose for energy it breaks down starch to release the glucose
• Starch is a mixture of two polysaccharides of alpha-glucose: amylose and amylopectin.
• Amylose is a long, unbranched chain of a-glucose. The angles of the glycosidic bond give it a coiled structure almost like a cylinder, this makes it compact so it is really good for storage because you can fit more into a small space
• Amylopectin is a long, branched chain of a-glucose. Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily. Meaning the glucose can be released quickly
• Starch is insoluble in water so it does not cause water to enter the cells by osmosis which would make them swell. This makes it good for storage.
• Glycogen is the main energy storage material in animals, animal cells get energy from glucose too but animals store excess glucose as glycogen. This is another polysaccharide of alpha-glucose.
• Glycogen's structure is very similar to amylopectin except it has loads more side branches coming off it. Loads of branches means that stored glucose can be released quickly, which is important for energy release in animals. It is also a very compact molecule which is good for storage.
• Cellulose is the major component of cell walls in plants. Cellulose is made of long, unbranched chains of beta-glucose.
• When beta-glucose molecules bond, they form straight cellulose chains. The cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres mean cellulose provides structural support for cell.
• Triglycerides are a kind of lipid. Triglycerides are macromolecules, they are complex molecules with a relatively large molecular mass. Like all lipids they contain the elements carbon, hyrdrogen and oxygen.
• Triglycerides have one molecule of glycerol with three fatty acids attached to it
• Fatty acid molecules have long 'tails' made of hydrocarbons. The tails are hydrophobic and the tails make lipids insoluble in water. All fatty acids have the same basic structure but the hydrocarbon tail varies.
• Triglycerides contain ester bonds, they are synthesised by the formation of an ester bond between each fatty acid and the glycerol molecule. Each ester bond is formed by a condensation reaction.
• The process in which triglycerides are synthesised is called esterification. Triglycerides break down when the ester bonds are broken. Each ester bond is broken in a hydrolysis reaction
• There are two kinds of fatty acids: saturated and unsaturated. The difference is in their hydrocarbon tails.
• Saturated fatty acid tails do not have any double bonds between their carbon atoms. The fatty acid is saturated with hydrogen.
• Unsaturated fatty acids have at least one double bond between carbon atoms, which cause the chain to kink
• Phospholipids are similar to Triglycerides. Phospholipids are also macromolecules, they are pretty similar to triglycerides except one of the fatty acid molecules is replaced by a phosphate group
• The phosphate group is hydrophilic and the fatty acid tails are hydrophobic