Topic 1-A. Biolgical Molecules

Sugars

Lipids

Proteins

Enzymes

There are 3 main monosaccharides that need to be known. They are;

  • Glucose (The structure needs to be also known)
  • Fructose
  • Galactose

Carbohydrates

Monosaccharides form with each other to produce disaccharides (2 monomers) more than this and it becomes a polysaccharide.

The -OH groups on each monosaccharide join to form water with and oxygen left over. This produces a glycosidic bond -O- between the molecules. This is known as a condensation reaction.

The combinations for disaccharides are;

  • Glucose + Glucose ---> Maltose
  • Glucose + Galactose ---> Lactose
  • Glucose + Fructose ---> Sucrose

Benedicts Test for sugars

Heat sample with benedicts reagent and 90 degrees

Sample stays blue

Sample forms green, yellow, orange, brick red precipitate

Reducing Sugar present

No reducing sugar present

Heat solution with HCl then neutralise with NaCOOH. Heat with benedicts reagent

Sample stays blue

Sample forms green, yellow, orange, brick red precipitate

Non-reducing sugar present

No non-reducing or reducing sugar present

Starch

Glycogen

Cellulose

Starch is made up of two different polysaccharides of alpha glucose, amylose and amylopectin.

Amylose is a long unbranched chain of glucose forming a helix. This makes it compact and good for storage.

Amylopectin is a long branched chain of glucose. The side branches mean the surface area is increased and the enzymes can break it down rapidly back into glucose.

Glycogen is similar in structure to amylopectin. It's a long branched chain of glucose. The only difference is that it contains more branches than amylopectin.

Cellulose is made of B-glucose rather than A-glucose. It is made of long straight chains of glucose in which each glucose is reversed orientation by 180. The chains run parallel and pack close together where the hydrogens form crosslinks between the chains called microfibrils.

There are 2 main types of lipids;

  • Triglycerides
  • Phospholipids

The bonds in all carbohydrates is called a glycosidic bond.

The bonds between glycerols and fatty acids is called an ester bond.

Triglycerides

These contain a glycerol backbone bonded to three fatty acid tails. The two -OH groups on the glycerol and fatty acid join together to form an -O- bond and water.

The structure is very good for storing energy. The fatty acid hydrocarbon tails contain very large amounts of energy that can be released when the structure is broken down. For this reason triglycerides are used as a storage molecule.

Phospolipids

Phospholipids differ in that they only contain two fatty acid tails. Instead of the third they have a phosphate head. The fatty acid tails have no charge and are non-polar. The phosphate head has a slight negative charge and therefore is polar. This is very important for their function.

Phospholipids play an important role in the structure of our cell membrane. Because the phosphate head is polar, this makes it hydrophilic, because the fatty acid tails are non-polar, they are hydrophobic. This results in phospholipids pairing up with the heads facing outwards and the tails facing inwards. The cell membrane is mainly made up of these phospholipids arranged in a spherical shape

Models of Enzymes

Induced Fit Theory

Lock and Key

Definitions/Theory

  • The substrate enters the active site
    • The substrate fits exactly into the active site, they're complementary.
    • This forms an enzyme substrate complex
    • Products are formed and no longer fit into the active site
    • The enzyme is free to take part in another reaction

Definitions

Enzymes are proteins, they have an active site which is the area of the enzyme in which the substrate binds to. Enzymes are highly specific due to their tertiary structure

Enzymes are biological catalysts. They speed up reactions without being used up.

How do they work-
For a reaction to take place, there needs to be energy supplied to the reactants called the activation energy, enzymes lower the activation energy required for a reaction to take place. This lowers the temperature required for such reactions

If two substrate's are joining together, the enzyme holds them together overcoming repulsive forces making bonding easier
If the substrate is breaking down, fitting into the active site places strain on the bonds making breaking it easier

  • The substrate enters the active site
  • The binding of the substrates induces the change in the shape of the active site of the enzyme
  • When the substrate leaves the active site it then returns to its original shape