Enzymes Section 3.2. Metabolism How quickly or how slowly your body can break down food is metabolism. Metabolism describes all the chemical reactions.

EnzymesSection 3.2

Metabolism • How quickly or how slowly your body can break down food is

metabolism. • Metabolism describes all the chemical reactions in your body.

Enzymes • Enzymes are special proteins that speed up, or catalyze, the rate of

reactions. • Enzymes help break down food in your body to get the energy from it.• Enzymes are names for the reaction that catalyze and end in the suffix

-ase. Example: sucrase is needed to break down sucrose.

• Enzymes lower the activation energy for a chemical reaction so that the reaction can occur quickly.

Activation Energy

Induced Fit• The chemicals that are metabolized

by an enzyme catalyzed reaction are the enzyme's substrate. • The place the enzyme binds to the

substrate is the enzyme's active site. • The shape change by the enzyme in

response to substrate binding is called induced fit.• Enzymes have specificity.

Lactose Intolerance • This is a common dietary problem. • People with lactose intolerance cannot digest a large amount of lactose

(the most common sugar in milk).• They do not have the enzyme, lactase.• Lactase breaks down lactose into glucose and galactose, which can be

absorbed into the bloodstream.• Is there is no lactase, bacteria in the intestine will metabolize lactose and

produce lactic acid.• When there is a lot of lactic acid in the body the person feels bloated, has

gas, has cramps, and diarrhea.

Lactose Intolerance • Most babies can digest lactose efficiently, but as they grow older they

have less lactase in their bodies. • A long time ago, lactase wasn't necessary and most adults were

lactose intolerant. • But now, the human diet has a lot of dairy products , so you need

the enzyme in adulthood.• Lactose intolerance can be treated by taking the lactase enzyme as a

pill.

Questions 71. What is metabolism?2. What do enzymes do?3. What is a substrate?4. What is an active site?5. What is induced fit?6. What enzyme breaks down lactose?7. What is made when there is no lactase in the body?

Calories & Metabolic Rate

Section 3.2

Calories • A calorie is the amount of energy needed to raise the temperature of

1 gram of water by 1 degree Celsius. • In scientific literature, energy is usually reported in kilocalories but in

physiology we use calories. • Calories are eaten to give the body energy to do work, which includes

maintaining body temperature.• When the input of calories is greater than the output of calories then

the excess calories are stored as fat.

Metabolic Rate• A person's metabolic rate shows how much energy he or she is using.• A person's metabolic rate depends on the person activity level. • For example, we use less energy when sleeping than we do exercising.• The basal metabolic rate is the resting energy of an awake, alert

person.• The average basal metabolic rate is 70 calories per hour, or 1680

calories per day. But this rate depends on exercise, body weight, sex, age, and genetics. It can also depend on nutrition: for example, if you are missing a vitamin, metabolism can be affected.

Calorie Facts• You can lose calories by exercising. • A heavier person will lose more calories during exercise than a thin person. • Men need more calories per day than women because of testosterone and

muscle. Testosterone increases the rate at which fat breaks down. And more energy is needed to maintain muscle.• Less calorie loss because of age: Metabolic rate slows down as you become

older. • Less calorie loss because of genetics: Some people are born with a low

metabolic rate.• To lose one pound of fat, you need to burn 3,500 more calories than you eat.

Some Calorie Calculations To calculate how much calories you should eat per day: • Multiply the weight you want to be maintain

by 11 and add the number of calories you burn during exercise. • To calculate the number of calories you are

burning for hour, look at the picture.

The End of Metabolism • To be fully metabolized, food is

broken down by the digestive system and then transported to cells via the bloodstream. • In the mitochondria of cells,

food energy is changed into chemical energy in the form of adenosine triphosphate or ATP.

Questions 8

1. What is a calorie?2. Define basal metabolic rate.3. What does the basal metabolic rate depend on?4. Why do men need more calories per day than women?5. How is food fully metabolized?