Module 2.4

Proteins play vital roles in organisms and understanding their function allows analysis of malfunctions (e.g., type one diabetes).

Proteins are polymers of amino acids with a complex structure.
- Complex structure arises from interactions between R groups and surrounding water.

Enzymes are a specific type of protein designed to accelerate chemical reactions.
- Chemical Reaction Definition: A process in which molecules interact to form new molecules with different compositions.
- Example of a reaction breaking a bond: The conversion of proinsulin to insulin involves breaking bonds in proinsulin to produce insulin and peptide C.
- Reactants: Molecules that participate in the reaction.
- Products: Molecules created as a result of the reaction.

Trillions of reactions occur in the body every second, facilitated by proteins.
Enzymes like trypsin exemplify this role, breaking bonds in proinsulin to create insulin and peptide C.
Enzymes accelerate reactions by lowering the energy needed for the reaction, functioning as catalysts.

Catalyst Definition: A substance that increases the rate of a reaction without being consumed.
Most chemical reactions in organisms are catalyzed by enzymes.
- Trypsin, an enzyme, breaks larger peptides into smaller peptides, aiding in food digestion.
- Converts proinsulin (86 amino acids) into insulin and peptide C, with specificity based on substrate.

|Substrate Definition|: A molecule that participates in a chemical reaction involving an enzyme.
- An enzyme must bond with substrates to catalyze reactions.
- Initial weak bonds formed between the enzyme's R groups and the substrate result in a conformational change in the enzyme.
- This change positions the R groups and substrates for the reaction—breaking or forming covalent bonds.
- The product is released after the reaction.
Analogy for enzyme-substrate interaction: A baseball glove catching a ball.
- The glove's design facilitates catching and releasing the ball, similar to an enzyme's active site.

Active Site Definition: Region of an enzyme where substrate binds, promoting a specific reaction.
- Active site possesses a shape and charge necessary to attract specific substrates.
- Example: Substrates with different charge arrangements interact based on the charge of the R groups in the active site.
Enzyme specificity and affinity:
- Chemical Specificity: The ability of a protein to bind a specific type of molecule.
- Higher specificity means fewer types of molecules can bind.
- Affinity Definition: Likelihood that two molecules will interact based on electrical properties.
- Greater affinity correlates with stronger interactions between molecules.

Experiment measuring enzyme activity involves a constant number of enzymes and varying substrate amounts.
- Graph representation:
- Horizontal axis: Concentration of substrate (from low to high).
- Vertical axis: Rate of enzyme activity (amount of product formed per minute).
- Two regions on the curve:
- Blue region: Rate of activity increases with substrate concentration (few enzymes bound).
- Red region: Rate of activity plateau (all enzymes bound).
Michaelis-Menten Curves: Graphical representation of the relationship between substrate concentration and enzyme activity.
- Valuable for comparing affinity of different enzyme forms.
- Different forms may catalyze the same reaction but differ in their affinity for substrates.
- High affinity: Active sites are occupied even at low substrate levels.
- Low affinity: Active sites unbound unless substrate levels are high.

Ligand Definition: Any molecule that binds to a protein.
- All substrates are ligands, but not all ligands are substrates.
- Competitive inhibitors: Ligands that bind to active sites, reducing enzyme activity, as they prevent substrate binding.
- Allosteric site: Another binding site on the enzyme.
- Ligand binding at the allosteric site alters enzyme conformation, which can either inhibit or enhance activity.
Diagrams illustrate how binding to allosteric sites affects enzyme function.
- Inhibitory ligands prevent substrate binding, lowering maximum enzyme activity regardless of substrate concentration.

Study of enzymes reveals interactions with substrates, facilitating reactions vital for biological processes.
Next lesson: Analyze trypsin's function in converting proinsulin to insulin and implications for diseases like type one diabetes.