Introduction to Enzymes in Physiology Flashcards
What is an enzyme?
- Enzymes are biological catalysts
- Provides a reaction surface (active site)
- Bring reactants together
- Position reactants correctly for reaction
- Weaken bonds in the reactants
- May provide acid/base catalysis
- May provide nucleophiles
- Do not change equilibrium position of reaction
Describe enzyme energetics.
- For a chemical reaction to proceed it must exhibit a negative ΔG
- ΔG = free energy of initial state - free energy of final state
- To reach final state reaction must first reach activation energy
- Enzymes decrease reaction energy = increased rate of reaction
Describe what occurs at the enzyme active site.
- Region within an enzyme that fits the shape of substrate molecules
- Amino acid side-chains align to bind the substrate through H-bonding, hydrophobic interactions etc
- Products are released when reaction is complete
Describe the Lock and Key hypothesis.
- Active site has rigid shape
- The fit between substrate and active site is exact
- Temporary structure called enzyme-substrate complex formed
- Products have different shapes from substrate and release from active site
Describe the induced fit hypothesis.
- Active site is flexible and can change its conformation
- Shape of enzyme, active site and substrate adjust to maximise fit
- Greater range of substrate specificity, reacting with substrates of similar type
What is the optimum pH for enzymes?
~7.4
- Activity is lost at low or high pH as tertiary structure is disrupted
What happens to enzymes when there are changes to pH?
- Alters the ionisation state of amino acid side chains
- Alters ionic bonding, structural stability, shape and functionality of enzyme
- Related to the overall 3D structure of all enzymes
How does temperature affect enzyme activity?
- Enzymes most active at optimum temp of 37°C
- Show little activity at low temp.
- Activity is lost at high temp as denaturation occurs
What is the function of cofactors?
Bind to enzymes to maintain correct configuration of active site - metal ions and other inorganic factors
What are coenzymes?
- An organic molecule bound to enzyme by weak interactions/hydrogen bonds
- They carry electrons or small groups
- Many have modified vitamins in their structure
State the function of oxidoreductases.
- Catalyse transfer of electrons from donors to acceptors
- Catalyse many oxidation-reduction reactions found in biochemical pathways
Give examples of oxidoreductases.
- Dehydrogenases accept and donate electrons as hydride ions (H:-)
- Hydrogen atoms often using coenzymes such as NAD+/NADH as an electron
donor or acceptor.
e.g. Lactate Dehydrogenase (LDH).
What is the function of transferases?
Catalyse transfer of a specific functional group between molecules
What are the four transferase enzymes and state their functions.
- Kinases - transfer phosphate groups usually from ATP to another molecule
- Aminotransferases - transfer amino groups; important in amino acid metabolism
- Glycosyltransferases - transfer carbohydrate residues
- Acyltransferases - transfer fatty acyl groups
State the function of hydrolases.
Catalyse cleavage of bonds by the addition of a water molecule
