7 characteristics of enzymes as biological catalysts

What are enzymes?

Biological catalysts that increase the rate of reactions without being consumed.

Optimal enzyme conditions?

Physiological: pH ~7, temperature < 40°C, atmospheric pressure ~1 atm.

What are enzymes?

Biological catalysts that increase the rate of reactions without being consumed.

Optimal enzyme conditions?

Physiological: pH ~7, temperature < 40°C, atmospheric pressure ~1 atm.

How do enzymes catalyze reactions?

By lowering activation energy, often via enzyme-substrate complex formation.

What does E + S → ES → EP → E + P represent?

Enzyme-substrate interaction and product formation cycle.

What are Oxidoreductases?

Enzymes that catalyze oxidation-reduction reactions (e.g., Lactate → Pyruvate).

What are Transferases?

Transfer functional groups (e.g., Glucose → Glucose-6-phosphate by hexokinase).

What are Hydrolases?

Use water to cleave bonds via hydrolysis.

What are Lyases?

Add or remove groups to form double bonds without hydrolysis or oxidation.

What are Isomerases?

Catalyze rearrangement of atoms (e.g., Malate → Fumarate).

What are Ligases?

Join molecules using energy from ATP (e.g., Pyruvate + CO₂ + ATP → Oxaloacetate).

Mechanism 1 of enzyme catalysis

Catalysis by bond strain (tension) – induces structural rearrangements.

Mechanism 2 of enzyme catalysis

Catalysis by proximity and orientation – substrate is guided to active site.

Mechanism 3 of enzyme catalysis

Catalysis by proton donors (acids) and acceptors (bases) to stabilize charges.

Mechanism 4 of enzyme catalysis

Covalent catalysis – formation of covalent bonds during catalysis.

Lock and Key Model

The enzyme’s active site and substrate have a perfect geometric fit.

Induced Fit Model

Active site adjusts shape to bind substrate upon contact.

What is the active site of an enzyme?

The 3D region where substrate binds and reaction occurs.

How is the active site formed?

From folding of the enzyme’s tertiary or quaternary structure.

Role of residues in active site

They participate in binding and reaction (catalytic, contact, conformational, assistant).

Catalytic residues

Directly involved in the chemical reaction.

Contact residues

Help bind the substrate to the active site.

Conformational residues

Help fold enzyme structure for activity.

Assistant residues

Support catalytic and contact groups.

What is enzyme specificity?

Enzymes act specifically toward a certain reaction and substrate type.

Type 1: String specificity

Enzymes like arginase, glucokinase – act on specific substrates.

Type 2: Group specificity

Monoesterase, pepsin, trypsin – act on specific groups of molecules.

Type 3: Bond specificity

Example: lipase – specific to ester bonds.

Type 4: Steric isomer specificity

L-AAO, D-AAO – differentiate between optical isomers.

Type 5: Geometric isomer specificity

Example: fumarase – acts on geometric isomers.