Amino acids and peptide bonds

What are proteins made of?

Proteins are polymers made of monomers called amino acids.
They are polypeptides, which are macromolecules formed by the condensation of amino acids joined by peptide bonds.

What determines the structure and function of a protein?

The sequence, type, and number of amino acids in a polypeptide determine how it folds and therefore its shape and function.
A change in amino acid sequence (mutation) can alter the protein’s structure and cause loss or change of function.

List some of the biological roles of proteins.

Proteins perform a wide range of functions, including:

• Enzymes – biological catalysts (e.g. amylase).

• Transport proteins – e.g. haemoglobin.

• Structural proteins – e.g. collagen, keratin.

• Contractile proteins – e.g. actin, myosin.

• Hormones – e.g. insulin.

• Immunoproteins – e.g. antibodies (immunoglobulins).

• Membrane proteins – e.g. carriers, channels, receptors.

What is the general structure of an amino acid?

Each amino acid has a central carbon atom (α-carbon) bonded to:

• an amine group (-NH₂)

• a carboxyl group (-COOH)

• a hydrogen atom (H)

• an R group (side chain) that differs for each amino acid and determines its chemical properties (e.g. polar, non-polar, acidic, basic).

How many amino acids are found in proteins, and what is special about them?

There are 20 amino acids common to all living organisms.
They are universal, meaning they are used by all species and coded for by the same genetic code.

What is a peptide bond, and how does it form?

A peptide bond is a strong covalent bond between the carboxyl group of one amino acid and the amine group of another.

It forms during a condensation reaction, where a molecule of water (H₂O) is released:

• The -OH from the carboxyl group and an H from the amine group combine to form water.

• The C from the carboxyl group bonds to the N of the amine group.

What type of reaction forms a peptide bond, and what type breaks it?

• Condensation reaction → forms a peptide bond (releases water).

• Hydrolysis reaction → breaks a peptide bond (adds water), converting polypeptides back into amino acids.

What are dipeptides and polypeptides?

• Dipeptide: formed when two amino acids join via one peptide bond.

• Polypeptide: formed when three or more amino acids join via multiple peptide bonds.
  A protein can consist of one or more polypeptide chains folded into a functional 3D shape.

What type of bond holds amino acids together, and what type of reaction is involved?

• Bond type: peptide bond (a covalent bond).

• Reaction type: condensation reaction (removal of water).

Why is the R group of an amino acid important?

The R group determines the chemical behaviour and interactions of each amino acid, affecting how the polypeptide folds.
This influences the protein’s tertiary structure and ultimately its function.