ENERGY & ENZYMES

Chemical reactions that occur in the cell need to occur quickly, accurately and precisely. There are four factors that affect the rate of a chemical reaction:

1) TemperatureUsually an increase in temperature will increase the reaction rate.

2) Concentration of the reactantsAn increase in the concentration of reactants will cause an increase in the reaction rate.

  3) State

The state in which the reactants are in will determine the rate of the reaction. Molecules in a solid state move slower than molecules in a gaseous state.

4) Enzymes and Catalysts A catalyst is a chemical that controls the rate of

the reaction. A catalyst DOES NOT alter or change the

products of the reaction. The catalyst remains unchanged after the

reaction. A catalyst does not add energy to the reaction; it

lowers the EA barrier.

Enzymes are protein catalysts that serve in biological reactions

REACTIONS AND REACTION RATES

Activation Energy (EA)The energy required to initiate a reaction.

http://www.youtube.com/watch?v=VbIaK6PLrRM&feature=related  

HOW DO ENZYMES WORK? Enzymes have distinct three-dimensional

shapes. It is this shape that determines which reaction the enzyme will catalyze.

A substrate is the substance that the enzyme acts on. It is the reactant. Each enzyme recognizes a specific substrate.

 

Catalyzing a Reaction: 1) The enzyme will bind to the substrate(s) 2) The substrate binds to the active site of the enzyme. The

active site is a groove or pocket on the enzyme. The active site only fits one type of substrate.

3) When the substrate attaches to the active site, the active site slightly changes so that the site is tightly wrapped around the substrate.

4) Once the substrate is in the proper position, the enzyme can catalyze the reaction.

5) While attached to the active site, the reaction occurs; the substrate turns into the product(s).

6) After the completion of the reaction, the enzyme releases the product(s).

This model is called the induced fit model because of the slight change in the active site once the substrate binds.

 

An enzyme can act on thousands or millions of substrate molecules per second.

http://www.youtube.com/watch?v=V4OPO6JQLOE&feature=related

WHAT AFFECTS THE ACTIVITY OF ENZYMES? 

Temperature High temperatures denature enzymes.

pH Most enzymes work best at a neutral pH (6-8).

However, stomach enzymes will only function at the pH of the stomach.

Concentration of substrate The greater the number of substrate molecules,

the greater the number of collisions, and therefore the greater the rate of the reaction.

Co-factors Some enzymes will not work unless they have a

co-factor. A co-factor is generally an inorganic molecule (i.e. zinc or iron, or copper). If a co-factor is an organic molecule, then it is called a coenzyme. Majority of coenzymes are vitamins or made from vitamins.

ENZYME INHIBITORS Anything that blocks the activity of an

enzyme is called an enzyme inhibitor. There are two types of inhibitors:

1) Competitive InhibitorResembles the enzyme’s normal substrate so it competes with the regular substrate to attach to the active site. If the inhibitor binds to the active site, the enzyme will not be able to act.

2) Non-competitive InhibitorThis inhibitor will not bind to the active site. However, it binds to the enzyme on another site. This binding causes the enzyme to change shape so that the substrate can no longer bind to the active site.

Some inhibition is reversible, while others are not. The reversibility depends on the strength of the bond formed between the inhibitor and the enzyme.

Inhibition can be good for cell metabolism. If the inhibition is reversible, then it can aid in regulation.

SOME INTERESTING INFORMATION ABOUT ENZYMES

Some pesticides are harmful to insects because they bind to important enzymes irreversibly in their nervous system. If the nerve cells are prevented from transmitting signals then the insect dies.

One type of pesticide, malathion, is poisonous to insects, animals, and humans. However, the dose that kills insects is not strong enough to kill humans.

 

Antibiotics Some antibiotics work by binding to the

enzymes that are essential to the bacteria. Penicillin inhibits the enzyme that is essential for the bacteria to make cell walls.

Siamese CatsSiamese cats have a heat sensitive

enzyme called tyrosinase. Tyrosinase converts tyrosine to melanine (black pigment). The enzyme will denature at normal body temperature. The black pigment is only present at the cooler parts of the body. You can test this by looking at Siamese cats that have been left outside all winter, they will be all black. Siamese cats that have been outside in hot climates will be all white.

 

Hydrogen cyanideHydrogen cyanide will bind

permanently to the active site of cytochrome c oxidase, which is essential in cellular respiration. The cell can not function properly and dies from lack of energy.

 

Alcohol BreakdownThe enzyme alcohol dehydrogenase

aids in the breakdown of alcohol that would otherwise be toxic. Young women do not express the enzyme as well as men. This is one reason why men can out-drink, or hold their alcohol better. The activity of the enzyme and expression is also different in regions of the world. It has been found that Europeans have higher activity than Asian or American countries.

ENZYMES IN THE BODY:

In the mouth amylase breaks down carbohydrates In the stomach there is the production of pepsin which

breaks down proteins. Gastric lipase breaks down lipids. Gastric amylase breaks down starch.

In the small intestine trypsin and chymotrypsin cleave proteins into amino acids. There are also enzymes that will break down disaccharides into monosaccharides such as sucrase, maltase, and lactase.

Enzymes: http://www.youtube.com/watch?v=E90D4BmaVJM   Digestion and enzymes http://www.youtube.com/watch?v=AFbPHlhI13g