Proteins and enzymes

Nature of science:

Collaboration and peer review—several different experiments on several continents led to the conclusion that DNA, and not protein as originally thought, carried the information for inheritance. (4.4)

• Proteins are polymers of 2-amino acids, joined by amide links (also known as peptide bonds).
• Amino acids are amphoteric and can exist as zwitterions, cations and anions.
• Protein structures are diverse and are described at the primary, secondary, tertiary and quaternary levels.
• A protein’s three-dimensional shape determines its role in structural components or in metabolic processes.
• Most enzymes are proteins that act as catalysts by binding specifically to a substrate at the active site.
• As enzyme activity depends on the conformation, it is sensitive to changes in temperature and pH and the presence of heavy metal ions.
• Chromatography separation is based on different physical and chemical principles.

Applications and skills:

• Deduction of the structural formulas of reactants and products in condensation reactions of amino acids, and hydrolysis reactions of peptides.
• Explanation of the solubilities and melting points of amino acids in terms of zwitterions.
• Application of the relationships between charge, pH and isoelectric point for amino acids and proteins.
• Description of the four levels of protein structure, including the origin and types of bonds and interactions involved.
• Deduction and interpretation of graphs of enzyme activity involving changes in substrate concentration, pH and temperature.
• Explanation of the processes of paper chromatography and gel electrophoresis in amino acid and protein separation and identification.

• The Universal Protein Resource (UniProt) is a consortium of bioinformatics institutes. Its mission is to act as a resource for the scientific community by providing comprehensive, high-quality and freely accessible data on protein sequence and functional information.

Utilization:

• Many synthetic materials are polyamides. Examples include nylon and Kevlar®.
• Electrophoresis is used in some medical diagnostics to identify patterns of unusual protein content in blood serum or urine.
• The first protein to be sequenced was insulin by Frederick Sanger in 1951, in a process that took over ten years. Today, protein sequencing is a routine and very efficient process, and is a major part of the study known as proteomics.

Syllabus and cross-curricular links:
Topics 8.3 and 18.2—pH and pKa and pKb values
Topic 20.3—stereoisomerism
Option A.9—condensation polymers
Option B.9—chromatography
Biology topics 2.4, 2.5 and 8.1—proteins and enzymes
Aims:

• Aim 6: Experiments could involve hydrolysis of a protein, separation and identification of amino acid mixtures by paper chromatography, or gel electrophoresis of proteins and DNA.
• Aim 7: Data logging experiments involving absorption/concentration studies for protein content using the Biuret reagent.
• Aim 7: Simulations can be used for gel electrophoresis.

• The names and structural formulas of the amino acids are given in the data booklet in section 33.
• Reference should be made to alpha helix and beta pleated sheet, and to fibrous and globular proteins with examples of each.
• In paper chromatography the use of Rf values and locating agents should be covered.
• In enzyme kinetics K_m and V_max are not required.