Enzymatics

5.1 Enzymatic Activity

Enzymes are proteins with tertiary or quaternary structures

Each one has a unique 3D configuration that is a product of its unique sequence of amino acids

Molecules that react with enzymes are called substrates

Ex. Maltose is substrate for maltase, and sucrose for sucrase

Catabolism is when an enzyme reaction involves the cleaving of a single substrate into two products

Anabolism is the opposite reaction

Homeostasis is the process of keeping the internal environment constant

Lock and Key Analogy

The activated enzyme-substrate complex is when the substrate and enzyme are attached

It is believed that when the activated ES forms, it forces the substrate into a slightly different shape. Scientists refer to this as the induced fit hypothesis

The reaction proceeds when the required energy exists

The portion of the enzyme that attaches to the substrate is called the active site

If an ES complex cannot form then no reaction takes place

It is possible for a substance to fit into an active site, with no reaction occurring because the configuration of the combination is not correct (inhibited)

The amount of ATP required for a reaction is called the activation energy

Enzymes lower the activation energy for a specific reaction

If the overall reaction results a net input of energy, it is termed endothermic

If the overall reaction results in a net output of energy, it is termed exothermic

Many enzymatic reactions exist as part of a larger metabolic pathway, where the product of one step becomes the substrate for a subsequent reaction

When enough of an end product is formed, the product begins to inhibit an enzyme from earlier on to stop the continual forming of itself. This process is called negative feedback

Some reactions need the help of co-enzymes and cofactors to create the correct shape of the enzyme substrate

Review

Which of the following is FALSE about enzymatic reactions?

a) Enzymes can be used repeatedlyb) The energy of activation required for a

reaction is increased by the presence of enzymes

c) Substrates temporarily bond onto enzymes for a reaction to occur

d) Enzymes each catalyze only one specific reaction

Which of the following is FALSE about enzymatic reactions?

a) Enzymes can be used repeatedlyb) The energy of activation required for a

reaction is increased by the presence of enzymes

c) Substrates temporarily bond onto enzymes for a reaction to occur

d) Enzymes each catalyze only one specific reaction

Where does the energy for enzymatic reactions come from?

a) ATPb) Enzymesc) Substratesd) Co-enzymes

Where does the energy for enzymatic reactions come from?

a) ATPb) Enzymesc) Substratesd) Co-enzymes

Which of the following is TRUE about a metabolic pathway

a) ATP is required at each stepb) A final end product is never producedc) The same enzyme is used each step in the

pathwayd) the products become the next substrates

Which of the following is TRUE about a metabolic pathway

a) A net loss of ATP is required at each stepb) A final end product is never producedc) The same enzyme is used each step in the

pathwayd) the products become the next substrates

Which part of a persons diet supplies them with co-enzymes?

a) Lipids

b) Proteins

c) Vitamins

d) Carbohydrates

Which part of a persons diet supplies them with co-enzymes?

a) Lipids

b) Proteins

c) Vitamins

d) Carbohydrates

Which part of a persons diet supplies them with co-factors?

a) Fats

b) Water

c) Minerals

d) Vitamins

Which part of a persons diet supplies them with co-factors?

a) Fats

b) Water

c) Minerals

d) Vitamins

TEMPERATUREPH

HEAVY METAL IONSINHIBITORS

SUBSTRATE AND ENZYME CONCENTRATION

Factors Affecting Enzymes

5.2 Temperature

H-bonds that help maintain the tertiary structure of enzymes are sensitive to temperature

Too much exposure to a temperature increase will cause the bonds to break (denature) and the enzyme to take a new set of properties

The optimum temperature of an enzyme is the temperature when the shape of the active site most exactly matches the shape of the substrate

In humans, this temperature is about 37o C

As body temperature increases, human enzymes continue to function at a decreasing rate up to about 50o C before they denature

At temperatures less than 37o C, reactions slow because of decreased kinetic energy

This event is called hypothermia

Some victims of hypothermia drop 15-20o C and have been revived

Brain damage often occurs if the body temperature is very low for very long, but the enzymes required for life can become renatured

5.3 pH

As with temperature, an enzyme functions best at an optimum pH

Deviations from this pH can result in the denaturing of the enzyme

Such is the case with the digestive system

Stomach enzymes function at a pH of about 2.5

The enzymes of the small intestine function better at a pH of 8.3

The body has a mechanism for adjusting the pH between these organs

If the pH of blood were to deviate very far from its average pH of between 7.3 and 7.4, death would be imminent

Review

A particular reaction that occurs in the mouth was proceeding in a test tube at 45oC and at a pH of 2.5. Which of the following would likely cause the greatest INCREASE in the reaction rate?

a) Raise the temperature and increase the pHb) Raise the temperature and decrease the pHc) lower the temperature and decrease the pHd) lower the temperature and increase the pH

A particular reaction that occurs in the mouth was proceeding in a test tube at 45oC and at a pH of 2.5. Which of the following would likely cause the greatest INCREASE in the reaction rate?

a) Raise the temperature and increase the pHb) Raise the temperature and decrease the pHc) lower the temperature and decrease the pHd) lower the temperature and increase the pH

Which component is temperature and pH sensitive?

a) E

b) S

c) P

d) None of them are

Which component is temperature and pH sensitive?

a) E

b) S

c) P

d) None of them are

5.4 Heavy Metals

When heavy metal ions (like Hg2+ and Pb4+) get together with enzymes, they tend to disrupt the normal distribution of electrons in the enzyme

When this happens, the shape of the enzyme is affected, lessening the chance of forming the activated ES complex

5.5 Inhibitors

The presence of inhibitors affects the ability of an enzyme to bond with its substrate

Two types:

Competitive Inhibitors

Non-competitive Inhibitors

Competitive Inhibitors

Compete with the substrate for occupancy of the active site

The greater the concentration of the inhibitors relative to the concentration of the substances, the more of an effect on the rate of enzyme activity

As long as the inhibitor is occupying the site, no ES forms

Non-competitive Inhibitors

Combine with the enzyme in a location other than the active site and affects its shape, preventing the formation of the ES complex

5.6 Substrate and Enzyme Concentrations

Reaction rate increases as substrate concentration increases until all of the enzymes are in use

At this point the rate of reactions is constant

Review

Which of the following factors will NOT denature an enzyme?

a) pH

b) Temperature

c) Concentration

d) Heavy Metals

Which of the following factors will NOT denature an enzyme?

a) pH

b) Temperature

c) Concentration

d) Heavy Metals

Which of the following is the LEAST likely to affect the rate of enzymatic activity?

a) pH

b) Temperature

c) Concentration

d) Osmotic Pressure

Which of the following is the LEAST likely to affect the rate of enzymatic activity?

a) pH

b) Temperature

c) Concentration

d) Osmotic Pressure

Generally increasing the enzyme concentration in an enzymatic reaction will cause the reaction to

a) Stop

b) Reverse

c) Speed up

d) Slow down

Generally increasing the enzyme concentration in an enzymatic reaction will cause the reaction to

a) Stop

b) Reverse

c) Speed up

d) Slow down