Biological molecules - PROTEINS Flashcards
What are the monomers that make up proteins?
Amino acids - hence proteins are polymers of amino acids
What are anabolic reactions?
Anabolic reactions make polymers; for example - condensation reactions join two molecules together with the formation of a chemical bond and involves the formation of a water molecule.
What are catabolic reactions?
Catabolic reactions reverse condensation reactions; for example - hydrolysis reactions break a chemical bond between two molecules and involves the use of a water molecule.
What is the primary structure of the proteins?
The amino acid sequence
Describe the structure of an amino acid
Amino group (NH2) + variable group (R) + carboxyl group (COOH)
Why are amino acids described as amphoteric?
They can act as a base or an acid
How many naturally occurring amino acids are there?
20
What are the products of a condensation reaction between two amino acids?
A peptide bond, a H2O molecule, and a new dipeptide
Why is the primary structure of a protein important?
The sequence of amino acids determines its (the proteinβs) properties and shape.
What is the secondary structure of proteins?
The secondary structure is the shape which the polypeptide chain forms as a results of hydrogen bonding. This is most often a spiral known as the Ξ±-helix, although other configurations occur.
What is an Ξ±-helix?
Hydrogen bonds can form an Ξ±-helix. This is a tight coil of amino acids held together by the hydrogen bonds.
What is a Ξ²- pleated sheet?
Polypeptide chains can also form Ξ²- pleated sheets by joining with hydrogen bonds
What type of peptidase will hydrolyse the bond between a dipeptide?
Dipeptidase
Describe a biochemical test to confirm the presence of protein in a solution
Add biuretβs solution to a liquid food sample; if proteins are present, the colour will change from blue-lilac
Describe 3 ways in which all dipeptides are similar
- All dipeptides consist of two amino acids joined
- All dipeptides will have peptide bonds
- All dipeptides will have amine and dicarboxylic acid groups
Describe one way in which dipeptides will differ from each other
They will have different βRβ groups
What is the tertiary structure of a protein?
The tertiary structure of a protein is when the secondary structures (Ξ±-helices and Ξ²- pleated sheets) fold up to form a very precise three dimensional structure.
What are London forces?
- London forces are very weak, temporary forces of attraction between some non-polar βRβ groups.
- London forces can be split by high temperatures.
What are disulphide bonds?
- Some βRβ groups contain sulphur; If 2 βRβ groups contain sulphur, they form covalent (disulphide) bonds.
- Disulphide bonds are very strong, and can resist high temperatures.
Why do polypeptides fold?
As only some βRβ groups are attracted to each other, the repulsion means the chain folds into a specific shape.
What happens to the bonds in the polypeptide if heated?
If heated, the London forces and the hydrogen bonds are more likely to break, denaturing the protein.
What are globular proteins?
Globular proteins, often enzymes, form a spherical mass with a specific 3D shape
Eg. haemoglobin
What are hydrophilic and hydrophobic groups? (in an aqueous solution)
- Hydrophilic groups dissolve in water (they are attracted by the hydrogen bonds of water, thus they are on the outside of the molecule)
- Hydrophobic groups repel water
What happens to globular proteins if they are taken out of water?
If taken out of water, the protein will unravel and change shape, as the hydrophilic groups no longer have access to water.
What is the quaternary structure of a protein?
Some proteins consist of more than one polypeptide chain held together
What are prosthetic groups?
Prosthetic groups are non organic, meaning they contain metal ions, sugars, vitamins, methyl groups, phosphate groups etc.
Describe haemoglobin
- Haemoglobin contains iron, and consists of 4 polypeptide chains - 2 Ξ²-subunits and 2 Ξ±- subunits.
- Haemoglobin contains 4 haem prosthetic groups
What are fibrous proteins?
- Fibrous protein molecules form long chains or fibres (they have primary, secondary, tertiary and quaternary structure)
- The fibres form a triple helix of polypeptide chains, held together by hydrogen bonds
How does the structure of fibrous proteins support its function, and where could we find them?
- The fibrous nature makes these proteins insoluble in water, which makes them useful for structure and support.
- Eg. Collagen; found in skin, teeth, bones, tendons, blood vessel walls
Why are collagen fibres so strong?
Collagen fibres are very strong as they have the combined strength of the individual fibrils
