EnzymesChapter 8

Learning Targets

I can explain how the change in the structure of a molecular system may result in a change of the function of the system.

Structure

Protein› Recall 4 levels of structure and bonds that

hold them in place Substrate-specific: the active site is

specifically shaped so only certain molecules fit on it

Learning Targets

I can explain how the shape of enzymes, active sites and interaction with specific molecules are essential for basic functioning of the enzyme.› I can explain how for an enzyme-

mediated chemical reaction to occur, the substrate must be complementary to the surface properties (shape and charge of the active site). In other words, the substrate must fit into the enzyme’s active site.

Induced Fit Shape of active site can change

slightly as substrate binds The active site is then molded into a

precise conformation--sort of like a hand in a glove

So, some enzymes can act on similar molecules, not just specific ones

Enzyme-Substrate Interaction

How do the following relate to enzymes?› active site› substrate› induced fit› energy of

activation

Activation Energy

How reactions work

How reactions work with enzymes

Enzyme-Substrate Concentration

Enzymes act on one molecule at a time

Reach a saturation point when all enzymes are engaged in reaction› Reaction rate will

not change

pH, Temperature, Salinity All enzymes have a specific range for

optimal performance Outside of that range denature

don’t function

Denaturation Disruption of R-groups

at each level of structure› H-bonds at 2°› Disulfide bridges, ionic

bonds, hydrophobic interactions at 3°

› Disassociation of subunits at 4°

When structure changes, function changes

Sometimes reversible, sometimes not

Learning Target

› I can explain how cofactors and coenzymes affect enzyme function; this interaction relates to a structural change that alters the activity rate of the enzyme. The enzyme may only become active when all the appropriate cofactors or coenzymes are present and bind to the appropriate sites on the enzyme.

› I can explain how other molecules and the environment in which the enzyme acts can enhance or inhibit enzyme activity. Molecules can bind reversibly or irreversibly to the active or allosteric sites, changing the activity of the enzyme.

Enhancing Factors

Help/Increase Enzyme Function

Cofactors & Coenzymes Co-factors assist with

catalytic activities of enzyme› Can activate active

site, assist with substrate bonding

› Ex: iron, zinc, copper, magnesium, potassium

Co-enzyme is an organic co-factor› Ex: vitamins (ie: B, C)

Allosteric Cooperativity

One substrate molecule primes an enzyme to receive more substrates readily

Ex: hemoglobin

Inhibiting Factors

Prevent/Interfere with Enzyme Function

Competitive Inhibition

Competitive inhibitor has same shape as substrate

(competes for active site)

Prevents substrate from binding to active site by binding to active site itself

Allosteric Inhibition

Inhibitor binds to allosteric site of enzyme

Active site changes shape, no substrate binds

Allosteric Activation

Change in the enzyme’s shape due to binding of activator at allosteric site

Enzyme is stabilized by activator

Feedback Inhibition

The switching off of a biochemical pathway by the product of the pathway› Negative feedback› Conserve energy!

Bozeman Enzymes Video

Learning Targets

I can explain that the change in function of an enzyme can be interpreted from data regarding the concentrations of product or substrate as a function of time. These representations demonstrate the relationship between an enzyme’s activity, the disappearance of substrate, and/or presence of a competitive inhibitor.

AP Lab 13

Bozeman video