ENZYMESMr. Safford’s Biological Sciences

WHAT ARE ENZYMES?

All enzymes are globular proteins thus spherical in shape

Control biochemical reactions in cells

They have the suffix "-ase"

WHAT ARE ENZYMES? Intracellular enzymes are found inside the cell Extracellular enzymes act outside the cell (e.g.

digestive enzymes) Enzymes are catalysts → speed up chemical reactions

Reduce activation energy required to start a reaction between molecules

Substrate molecules (reactants) are converted into products Reaction may not take place in absence of enzymes (each

enzyme has a specific catalytic action) Enzymes catalyze a reaction at max. rate at an

optimum state

HOW DO THEY WORK? Lock and key theory

Only one substrate (key) can fit into the enzyme's active site (lock)

Both structures have a unique shape Enzyme is not used (reusable) up in the

reaction (unlike substrates)

HOW DO THEY WORK?

HOW DO THEY WORK? Let’s See it in Action!

3 THINGS THAT AFFECT ENZYME EFFECTIVENESS

1. Changes in pH Affect attraction between substrate and enzyme Ionic bonds can break and change shape →

enzyme is denatured Charges on amino acids can change → Enzyme

Substrate complex cannot form Optimum pH (enzymes work best)

pH 7 for intracellular enzymes Acidic range (pH 1-6) in the stomach for digestive

enzymes (pepsin) Alkaline range (pH 8-14) in oral cavity (amylase)

2. TemperatureIncreased Temperature Increases speed of molecular movement → increased

chances of molecular collisions → more ES complexes Enzymes have optimum temp. for their action

(usually 37°C in humans) Just above ≈42°C, enzyme is denatured due to the

breaking Hydrogen bonds and higher temps. break covalent bonds

Denaturation -the loss of appropriate structure rendering the enzyme inactive.

Shape is changed → active site can't be used, ever again

DENATURED

Decreased Temperature Enzymes become less and less active, due to

reductions in speed of molecular movement Below freezing point

Inactivated, not denatured Regain their function when returning to

normal temperature

A typical graph of rate against temperature might look like this:

3. Concentrations of Substrate and Enzyme

4.  The presence of inhibitors Enzyme inhibitors are substances which

alter the catalytic action of the enzyme and consequently slow down, or in some cases, stop catalysis.

three common types of enzyme inhibition – Competitive-compete for active site Non-competitive- bind to enzyme somewhere other

than the active site and change the active site