Amino acids and Proteins Flashcards
What is the general formula for an α-amino acid?
They have an -NH2 group bonded to a carbon atom which is next to the carboxylic acid group.
Apart from aminoethanoic acid, what do all α-amino acids contain?
One or more chiral centres, so they can display optical isomerism.
What is the state of α-amino acids at room temperature?
Solids, because of their high melting point.
Why is the melting temperature of α-amino acids much higher than expected?
Because they exist as zwitterions, where there are strong ionic forces between positive and negative ions and more energy is needed to overcome these forces.
What is a zwitterion?
A dipolar form of an amino acid where the carboxylic acid group loses a proton, becoming COO-, and the amino group gains the proton, becoming +NH3.
Why is aminoethanoic acid described as a neutral amino acid?
As the positive and negative charges are balanced out.
What is the solubility of aminoethanoic acid at 25C?
25g in 100cm3 of water.
What is the solubility of 2-amino-3-phenylpropanoic acid at 25C?
3g in 100cm3 of water.
What is the isoelectric point?
The pH that aqueous zwitterions can exist in solution (different for each amino acid).
What happens if the pH is below the isoelectric point?
The amino acid acts as a base, accepting a H+.
What happens if the pH is above the isoelectric point?
The amino acid acts as an acid, losing a H+.
How is a dipeptide formed?
When two amino acid molecules join together in a condensation reaction.
What happens when two different amino acids are used in a condensation reaction?
Two different dipeptides can be formed as the product.
What does the formation of a dipeptide introduce?
A peptide linkage is formed (peptide bond, amide linkage).
How is aspartame (artificial sweetener) formed?
It is the methyl ester of the condensation product between phenylalanine and aspartic acid.
What is a polypeptide?
A long chain of condensed amino acids joined together by peptide linkages.
What is the primary structure of proteins?
The order of amino acids in the chain.
How many amino acids are there, and how are they categorised?
Twenty can make up the polypeptide chain. Twelve can be obtained or made in the body, but eight are essential amino acids.
What are essential amino acids?
α-Amino acids that cannot be synthesised in the body and must be supplied through the diet.
What is the secondary structure of proteins?
How the amino acid chains are arranged. This can be alpha helixes or beta pleated sheets.
What is the structure of an alpha helix?
The polypeptide chain is coiled into a spiral, which is maintained through hydrogen bonds between the N-H hydrogen of the amide group and the C=O carbonyl oxygen atom of another amide group.
What is the structure of a beta pleated sheet?
The structure is maintained by hydrogen bonds, but the C=O and N-H groups are in different chains. Van der Waals forces are responsible for producing a pleated sheet rather than a flat arrangement.
What is the tertiary structure of proteins?
The way in which the protein chain is folded. Proteins can be globular or fibrous.
Describe fibrous proteins
They have a chain length many times its diameter and tend to be insoluble in water.
Describe globular proteins
Roughly spherical in shape and tend to be soluble in water.
How are globular proteins water soluble?
In water, they take up a shape where the polar groups are on the surface of the protein and lipophillic groups are towards the interior of the structure.
Describe the function of enzymes
Macromolecular biological catalysts that lower the activation energy that is necessary for a reaction to take place.
What are some commercial application of enzymes?
In laundry, brewing and dairy.
In what state can enzymes operate?
Enzymes can operate in aqueous conditions of mild acidity or alkalinity.
How can enzymes be used in laundry?
Removing stains from proteins, starch or fats from clothes. Amylases degrade starches to water-soluble sugars, lipases hydrolyse fats and proteases digest proteins.
How can enzymes be used in the dairy industry?
Rennin is used to hydrolyse the protein in cheese making. The hydrophobic product from this degradation is the main component of curd from which cheese is made.
How can enzymes be used in the brewing industry?
Enzymes hydrolyse polysaccharides and proteins to smaller molecules.
