2.2.10 Amino Acids & Peptide Bonds

Question 1

Proteins

Answer 1

Proteins are polypeptides (and macromolecules) made up of monomers called animo acids
The sequence, type and number of the amino acids with a protein determines its shape and therefore its function
Proteins are extremely important for cell growth, cell repair and structure
They form all of the following:
- enzymes
- cell membranes proteins (e.g. carrier)
- hormones
- immunoproteins (e.g. immunoglobulins)
- transport proteins (e.g. haemoglobin)
- structural proteins (e.g. Keaton, collagen)
- contractile proteins (e.g. myosin)

Question 2

Amino Acids

Answer 2

Amino acids are the monomers of polypeptides
There are 20 amino acids found in proteins common to all living organisms
The general structure of all amino acids is a central carbon atom bonded to:
- an amine group - NH2
- a carboxyl acid group - COOH
- a hydrogen atom
- an R group (which is how each amino acid differs and why amino acid properties differ e.g. whether they are acidic or based or whether they bare polar or non-polar)

Question 3

The Peptide Bond

Answer 3

Peptide bonds form between amino acids
- peptide bonds are covalent bonds and so involve the sharing of electrons
In order to form a peptide bond, a hydroxyl (-OH) is lost from the carboxyl group of one of the amino acid and a hydrogen atom is lost from the amine group of another amino acid
The remaining carbon atom (with the double-bonded oxygen) from the first amino acid bonds to the nitrogen atom of the second amino acid
This is a condensation reaction so water is released
Dipeptides are formed by the condensation to 2 amino acids
Polypeptides are formed by the condensation of many (3 or more) amino acids
A protein may have only one polypeptide chain or it may have multiple chains interacting withy each other
During hydrolysis reactions, the addition of water breaks the peptide bonds resulting in polypeptides being broken down to amino acids