B1.2 Proteins

• All amino acids have the same general structure including: a carboxyl group, an amino group, and a central R group.
• A peptide bond forms between; the carbon of the carboxylic acid group of one amino acid and the amine group of the second amino acid.
• A polypeptide is a long chain of amino acids.
• Polypeptides are formed by many condensation reactions at a ribosome during the process of translation.
• The peptide bond is always between the C and N of neighbouring amino acids.
• Proteins are part of a healthy human diet.
• Proteins are broken down to amino acids by the digestive system.
• Humans require 20 amino acids to produce all of the proteins.
• Humans can synthesize eleven amino acids, which are known as non-essential amino acids.
• The other nine amino acids that humans require are known as essential amino acids, and must be consumed in the diet.
• Meat and animal products are considered complete proteins, as they contain all nine of the essential amino acids.
• The genetic code of DNA is transcribed to mRNA.
• Denaturation is a conformational change in the shape of a molecule, such as a protein, resulting in the loss of function.
• All proteins have a specific shape which determines the function of the protein. Proteins can be denatured by extreme changes in pH and temperature.
• The 20 amino acids found in living things all have the same general structure, but they have different side chains, R groups.
• R-group properties; ●Hydrophobic - repelled by water ●Hydrophilic - attracted to water.
• The hydrophilic R groups are; ●Polar or charged ●Acidic or basic
• The chemical interactions of the R groups in polypeptides determine the shape of proteins.

  The shape of proteins determines their function.
• The primary protein structure is the number and sequence of amino acids in a polypeptide.
• The primary protein structure is determined by the nucleotide base sequence of a gene.
• Secondary protein structure is the folding of the polypeptide to form alpha helices and beta pleated sheets.
• The tertiary protein structure is the further folding of the polypeptide due to interactions between the R groups.
• Disulfide bridges are bonds that form between the R groups of two cysteine amino acids in a polypeptide.
• Cysteine is an amino acid with sulfur within its R group.

  If the R groups of two cysteine amino acids are in close proximity, a covalent bond forms between the sulfurs.
• A conjugated protein is a protein attached to a non-polypeptide group, known as a prosthetic group.
• Adult haemoglobin is an example of a globular conjugated protein.
• The function of haemoglobin is to carry oxygen within red blood cells
• Haemoglobin is composed of:

  ●Two alpha polypeptide chains ●Two beta polypeptide chains● Four haem groups (which are not polypeptides)
• Non-conjugated proteins are composed of only polypeptides.
• Insulin is a globular non-conjugated protein composed of two polypeptide chains linked by two disulfide bridges.
• Insulin is a hormone that helps to regulate blood glucose levels, by causing the liver to remove glucose from the blood.
• Collagen is a fibrous protein composed of three polypeptide chains that are tightly coiled together into a triple helix structure
• Collagen is the main structural protein found in connective tissues such as skin, cartilage, and bones.

  The fibrous nature of collagen provides strength, support, and elasticity to tissues.