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OUTLINE

ATP AND CELLULAR WORK.

ATP STRUCTURE
REGENERATION OF ATP

ACTIVATION ENERGY
SUBSTRATE
ACTIVE SITE
COFACTORS
ENZYME INHIBITORS
ALLOSTERIC REGULATION

Significance of free energy (G) is that it is the maximum amount of energy available to do work in a cell.

CELLULAR WORK (3 main types):

1) Mechanical (e.g. beating of cilia or flagella)

2) Transport (pumping ions across membranes)

3) Chemical (pushing of endergonic reactions)

ATP = Adenosine triphosphate (= a nucleoside with 3 phosphates.

Has unstable bonds that release energy to do cellular work.

(STRUCTURE - Fig. 6.6)

How does ATP perform work?

Usually by transferring a Phosphate to another molecule thus making the other molecule more reactive.

(e.g Fig. 6.7)

Conversion of glutamic acid to glutamine.

REGENERATION OF ATP (107 molecules/sec./muscle cell) is an endergonic reaction that is driven by the exergonic reactions of cellular respiration.

(Fig. 6.8)

..

ENZYMES:

CATALYST = Chemical agent that accelerates a reaction

ENZYMES = Biological catalysts (usually proteins)

Enzymes and the lowering of activation energy.

ACTIVATION ENERGY: Amount of energy reactants must absorb to become reactive. (= free energy of activation)

SEE Figure 6.9 ("over the hump")

ENZYMES lower the energy of activation so that biological reactions can occur at low temperatures.

Fig. 6.10 ("lowering the hump")

Enzymes are very specific for what reaction they catalyze

SUBSTRATE = the substance an enzyme acts on.

substrate _____enzyme____> product

e.g.

sucrose + H2O ____sucrase___> glucose + fructose

MORE DETAILS ABOUT HOW ENZYMES WORK:

Substrate binds to the enzyme ACTIVE SITE

substrate + enzyme --> substrate-enzyme complex --> product + enzyme

(enzyme can be used again)

ACTIVE SITE = pocket or groove in the surface of enzyme that can bind the substrate via H-bonds etc.

Induced Fit = Enzyme wraps around substrate

Reaction occurs while attached to active site and the product(s) is released.

(Play Fig. 6.12)

Enzymes work in many ways:

1) warping the substrate

2) holding 2 reactants close so they will react with each other

3) micro-environment that is conducive for the reaction

..

FACTORS AFFECTING ENZYME ACTIVITY.

1) Temperature 35-40 oC for enzymes in our bodies

(Fig. 6.13)

2) pH

(Fig. 6.13b)

Trypsin (pH of intestines)

Pepsin (pH of stomach)

COFACTORS = enzyme helpers

Can be metals

Many vitamins are organic cofactors called COENZYMES

..

Competitive - bind and block the active site

Noncompetitive - bind elsewhere causing a change in the active site (also called allosteric inhibitors).

(Fig. 6.14)

..

Allosteric site = Receptor site away from the active site.

(see Fig. 6.15)

..

METABOLIC ORDER is maintained via enzyme regulation and compartmentalization of metabolic pathways.

Feedback inhibition as a method of metabolic control.

(Fig. 6.16)