Ch.8 Section 4

What is meant by induced fit?

this model proposes that the initial interaction between enzyme and substrate is relatively weak, but that these weak interactions rapidly induce conformational/shape changes in the both that strengthen binding.

Define allosteric regulation

Any case in which a protein's function at one site is affected by the binding of a regulatory molecule at a different site. It can function as an inhibitor or an activator.

How is activation energy usually supplied to a reaction? leave the reaction?

As thermal energy from inter-molecular collisions or bond stretching vibrations. As products are formed the activation energy is quickly degraded to heat

How does an enzyme speed up a reaction?

By lowering the activation energy required to being the reaction.

Magnesium, an essential trace element for most organisms, is present in the enzyme DNA polymerase and necessary for its function. The magnesium most likely functions as _____.

a cofactor necessary for enzyme activity

True or False: By regulating enzyme activity the cell can control it's metabolism.

True: Allosteric regulation and Inhibition feedback are both ways

The active site of an enzyme is the region that _____.

is involved in the catalytic reaction of the enzyme

Activation energy

(Ea or ΔG✳) The minimum energy required or the thermodynamic barrier that must be overcome for a reaction to take place ex: 2 atp required to breakdown glucose into pyruvic acid in respiration.

How do mutations or changes in the genes affect enzymes?

...

How do cells regulate enzyme activity?

1. Control of Enzyme Activity Level (allosteric, and feedback inhibition, phosphorylation) 2. Control the Amount of the Enzyme (Biosynthesis of the enzyme protein can be controlled at the level of the gene via regulation of transcription (ie synthesis of the enzyme's mRNA).

Coenzyme

an organic cofactor. Ex: vitamins

Define cooperativity.

the effect the binding of one substrate has on the binding of the second. It means that an enzyme has multiple active sites. If the first binds and increases the affinity of the second, this is called positive . If the first inhibits the binding of the second, it is called negative.

Define Feedback Inhibition.

A cellular control mechanism in which a catalyzing enzyme of a particular substance in the cell is inhibited when that substance has accumulated to a certain level, thereby balancing the amount provided with the amount needed. Ex: A lack of feedback inhibition for insulin results in diabetes

Describe competitive and non competitive inhibitors

Competitive inhibitors binds to the active site of the enzyme mimicking the substrate and directly "competes" with the substrate for occupation of the active site Noncompetitive inhibitors bind to the enzyme somewhere other than the active site altering the shape of the enzyme and making it either impossible for substrate to bind or function efficiently.

Why is cooperativity considered allosteric?

Considered allosteric regulation because binding of the substrate to one active site affects the catalysis of another active site.

How can the active site lower the activation energy?

During induced fit the active site can cause stress on other parts of the enzyme, creating more potential energy

Define enzyme

Enzymes are protein molecules that catalyze (i.e., increase the rates of) chemical reactions.

True or False: Enzymes lower the free energy of a reaction.

False: Enzymes do not affect the free energy change of a reaction, only the speed at which is occurs and the activation energy

Describe the substrate specificity of enzymes.

The active site of an enzyme is very specific to its substrates as it has a very precise shape. This results in enzymes being able to catalyze only certain reactions as only a small number of substrates fit in the active site. This is called enzyme-substrate specificity. For a substrate to bind to the active site of an enzyme it must fit in the active site and be chemically attracted to it. "LOCK and KEY"

What theory supports the broad specificity of an enzyme?

The induced fit model explains how an enzyme may be able to bind to, and catalyse, several different substrates (broad specificity)

Define cofactor

non protein helper required by the enzyme for catalytic activity. These may be bound permanently or loosely and reversible like the substrate.

What local conditions effect enzyme activity?

pH (optimal 6-8), temperature (optimal 30-40 C) and denaturing. cofactors and inhibitors