a.p. biologymr. tesoro homework reminder: do now: what does s. salivaris produce that seems to...

A.P. Biology Mr. Tesoro

Homework Reminder:

Do now: What does S. salivaris produce that seems to prevent S. mutans from destroying tooth enamel?

http://news.sciencemag.org/sciencenow/2011/04/a-bacterium-that-acts-like-a-toothbrush.html?ref=hp

A Bacterium That Acts Like a Toothbrush from ScienceNOW Daily News Researchers have identified a new ally in the war

against tooth decay: an enzyme produced by a mouth bacterium that prevents plaque formation. The finding could eventually lead to the development of toothpaste that harnesses the body's own plaque-fighting tools.

The human mouth is awash with bacteria. More than 700 species thrive in the hot, moist conditions, including Streptococcus mutans, one of the main components of plaque. Clinging to the teeth in thin layers called biofilms, S. mutans digests sugars and produces acids that can eat into enamel and cause cavities. Other bacteria are more gracious guests. In 2009, for example, scientists found that S. salivarius, a type of bacterium found on the tongue and other soft tissues in the mouth, decreases the buildup of S. mutans biofilms.

Hidenobu Senpuku, a biologist at the National Institute of Infectious Diseases in Tokyo, and colleagues wanted to know what substance conferred S. salivarius's cavity-fighting powers. Using chromatography, a method that divides the molecules in a mixture based on charge or size, they separated out individual proteins from samples of the microbe. The scientists then mixed each kind of protein with S. mutans cells and measured which cultures grew the smallest amount of biofilm on plates in the lab. The protein FruA, an enzyme that breaks apart complex sugars, was the most powerful biofilm blocker.

Aim: What are enzymes and how do they function?

What are enzymes?

Enzymes are organic catalysts required to maintain the proper metabolism of the cell.

A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction. An enzyme is a catalytic protein.

Why are enzymes required for metabolic reactions to occur?

1) A biochemical reaction can proceed spontaneously if it releases free energy. –ΔG bond breaking and bond forming. To hydrolyze sucrose, the bond between glucose and

fructose must be broken and then new bonds formed with a hydrogen ion and hydroxyl group from water.


2) Most biochemical reactions have activation energies too high to occur without a catalyst.

Activation energy is the amount of energy necessary to push the reactants over an energy barrier.


3) Catalysts, such as enzymes, lower the activation energy enough to allow reactions to proceed quickly at normal body temperatures.

Enzymes do not change the ΔG of the reaction.

What are some facts about enzymes?

1) Enzymes are highly selective. Maltase hydrolyzes maltose but not sucrose.

2) The name of most enzymes ends with a ‘ase’ suffix.


3) Enzymes usually are globular proteins. They work specifically with chemicals called substrates.

Enzyme Substrate Product

Maltase Maltose Glucose

Sucrase Sucrose Glucose and fructose


4) Most enzymes make use of the Induced Fit Model.

The place on the enzyme where the catalysis occurs is called the ‘active site’.

It is typically a pocket or groove on the surface of the protein into which the substrate fits.

Induced Fit Model

The active site is made up of specific R groups. Substrates that are compatible are attracted to the

active site and bond temporarily. This is called the enzyme-substrate complex.

The same enzyme that is used to synthesize macromolecules can also hydrolyze them. H2O + maltose 2 glucose (hydrolysis using maltase) 2 glucose H2O + maltose (synthesis using maltase)

Induced Fit Model

As the substrate binds, the enzyme changes shape leading to a tighter induced fit, bringing chemical groups in position to catalyze the reaction.

Induced Fit Model


5) Many enzymes require the binding of a prosthetic group in order to activate them.

Minerals (inorganic cofactors) such as zinc and iron are necessary.

Many vitamins are coenzymes or coenzyme precursors.

6) Both the enzyme and coenzyme are reusable and needed in small amounts. A single enzyme molecule can catalyze thousands or more reactions a second.


8) Enzymes cease to function if they are denatured. Denaturing alters the three dimensional contour of globular proteins and changes the active site. Substrates can no longer enter these sites. Sickness and death may result.


9) Enzymes are greatly affected by temperature, pH, substrate concentration or enzyme concentration.

As temperature increases, collisions between substrates and active sites occur more frequently as molecules move faster.

Each enzyme has an optimal temperature.

Temperature increases above the optimal temperature lead to the denaturing of the enzyme.


Because pH also influences shape and therefore reaction rate, each enzyme has an optimal pH too.

This falls between pH 6 - 8 for most enzymes.

However, digestive enzymes in the stomach are designed to work best at pH 2 while those in the intestine are optimal at pH 8, both matching their working environments.

What are some methods of controlling enzyme activity?

1) Competitive inhibition: A chemical similar in structure to the substrate

binds to the active site. This chemical, an inhibitor, competes for the enzyme and makes less enzymes available.

Most competitive inhibitions are reversible. However, an example of a nonreversible competitive inhibition is carbon monoxide poisoning of hemoglobin molecules.


2) Noncompetitive inhibition: Certain enzymes have more than one active

site. They are allosteric. One active site is for the substrate while another may be occupied by an inhibitor.

Such enzymes exist in two forms: an active form and an inactive form.


2) Noncompetitive inhibition: (continued) In the active form, the enzyme is freely catalyzing the

substrate. In the inactive form, the inhibitor binds to the

inhibitor site and alters the configuration (shape) of the substrate active site.

Such inhibitors are called ‘modulators’. Reversible inhibition of enzymes is a natural part of

the regulation of metabolism.


Negative modulators (inhibitors) – turn off enzymes

Positive modulators (activators) – turn enzymes on

Sometimes the substrate product acts as its own allosteric inhibitor and turns off the very enzyme that created it!!!

This is called feedback inhibition.

a.p. biologymr. tesoro homework reminder: do now: what does s. salivaris produce that seems to...

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