ENZYMES

Enzymes

Most, but not all end in the suffix …ase Participate in reactions but are not used up or

changed in any way …although they can eventually “wear out” Can perform either catabolic (destructive)

reactions. eg. 1 substrate = 2 products Can perform either anabolic (constructive)

reactions. eg. 2 substrate = 1 products

Some quick facts.Enzymes …

Act at both the intra and extracellular level Act on SUBSTRATE and yield PRODUCT Reduce the ACTIVATION energy required to

start a reaction in the body Are very specific, each individual type of

substrate is acted upon by a specific enzyme Generally names are based on the specific

substrate (eg lipids acted upon by lipase)

Enzyme Structure

Enzymes have an active site and a regulatory region The active site is where substrate binds to the enzyme The regulatory region is where cofactors coenzymes or enzyme

inhibitors can alter the function of an enzyme

Substrate

Active site

Regulatory region

Products

Enzyme inhibitor

Enzymes – inhibitors / cofactors

Enzyme inhibitors can be either competitive or non-competitive

A competitive inhibitor blocks the substrate from entering the active site

A non-competitive inhibitor binds to the regulatory region, thereby changing the shape of the active site

Other enzymes will not work unless a particular cofactor occupies the regulatory region

The “Lock and Key” model of enzyme activity

The enzyme provides a perfect fit for a particular substrate

The “Induced Fit” model of enzyme activity

The substrate induces the enzyme to change shape to create a tighter fit

Factors Affecting Enzyme Activity

pH Most biological enzymes operate

at a neutral pH range of 6-8 If enzymes are at a pH outside

their optimum range, their shape will change and they will be less efficient.

Enzyme

Cells

Carbonic Anhydrase

Trypsin Pepsin

Location Blood Small Intestine

Stomach

Opt. pH 7.6 7.4 8.0 2.0

Factors Affecting Enzyme Activity

Temperature Most biological enzymes have an optimum

temperature of 37° If an enzyme is exposed to temperatures higher than

optimum, it will permanently denature. If an enzyme is exposed to temperatures lower than

optimum, it will become inactive until temperature returns to optimum.

The enzymes of other organisms have optimum temperatures suited to the environment in which they live

Effect of temperature

Factors Affecting Enzyme Activity

Enzyme Concentration An increase in enzyme conc. will cause an

increase in reaction rate but won’t increase the yield.

Substrate concentration Reaction rate will initially increase as

unoccupied enzymes take on substrate but will then plateau.

Inhibition Other molecules can block the active site or

regulatory region of an enzyme.

Increasing substrate concentration

Enzymes – advanced content

Biochemical pathways Inhibition of biochemical pathways Allosteric enzymes Biochemical processes