• You need to know the basic molecular structure and primary functions of carbohydrates, proteins, lipids, and nucleic acids.

• You need to know the role of enzymes as catalysts that lower the activation energy of biochemical reactions.

• You need to know how factors such as pH and temperature affect enzyme activity.

As food travels through the digestive system, it is exposed to a variety of pH levels. The stomach has a pH of 2 due to the presence of hydrochloride acid (HCl), and the small intestine has a pH ranging from 7 to 9. HCl converts pepsinogen into pepsin, an enzyme that digests proteins in the stomach. Which of the following most likely happens to pepsin as it enters the small intestine?

A. It becomes inactive. 

B. It begins to replicate. 

C. It's shape changes to engulf large proteins. 

D. It's activity increases to digest more proteins.

In living cells, enzymes act as catalysts, which may reduce the amount of activation energy required for a chemical reaction to occur.  In the graphs below, pathway x is a solid line representing the uncatalyzed reaction. The dotted line shows the catalyzed reaction. Which graph best illustrates the changes in a reaction when the catalyst reduces the amount of energy required? 

The diagram below shows the general structure of an amino acid. Which type of molecule is formed from amino acids?

A. lipids

B. proteins

C. carbohydrates

D. nucleic acids

You are analyzing a compound in the laboratory. You find that it is made up of carbon, hydrogen, and oxygen in a ratio of two hydrogen atoms for each carbon atom. How will you classify the compound?

A. lipid

B. protein

C. carbohydrate

D. nucleic acid

Fats, oils and cholesterol are all types of what?

A. cell membranes

B. hormones

C. lipids

D. fatty acids

RNA and DNA are which type of macromolecules? 

A. carbohydrate

B. lipid

C. nucleic acid

D. protein

What will most likely happen if an appropriate enzyme is added to a chemical reaction? 

A. The reaction rate will increase.

B. The equilibrium of the reaction will be maintained. 

C. The reaction rate will decrease.

D. The reaction will stop. 

A sugar, a phosphate group, and a nitrogen base form the building blocks of which organic compound?

A. carbohydrates

B. lipids

C. nucleic acids

D. proteins

The human body maintains a temperature of around 98.6 degrees at all times. Enzymes are involved in almost every chemical reaction in the body. Which of the following describes the connection between these two statements? 

A. Enzymes function best at a specific temperature.

B. The body needs to be warm to prevent hypothermia.

C. The body is kept relatively warm to prevent too much enzyme action. 

D. There is no connection between the two statements. 

The enzyme lactase will break down the sugar lactose into which of the following components? 

A. monosaccharides

B. nucleic acids

C. amino acids

D. phospholipids

1. Correct answer: A. It becomes inactive.

Enzymes have an ideal pH, at which they best function. Many enzymes cannot function at all outside their ideal pH range. Pepsin functions best in the extreme acid environment of the stomach and will, therefore cease to function in the much higher pH of the small intestine.

2. Correct answer: D.

A catalyst decreases the activation energy needed for a reaction to occur. This allows the reaction to happen faster.

3. Correct answer: B. protein

Proteins are long chains of amino acids folded into specific shapes, which determine their properties and reactivity. 

4. Correct answer: C. carbohydrate

Carbohydrates are made up of Carbon, hydrogen, and oxygen. See the video for the basic carbohydrate structure.

5. Correct answers: C. lipids

See the structure of lipids in the video.

6. Correct answers: C. nucleic acids

DNA is deoxyribonucleic acid and RNA is ribonucleic acid.

7. Correct answer: A. The reaction rate will increase.

Enzymes are molecules that increase the rate of reactions.

8. Correct answer: C. nucleic acids

See the video for the basic structure of nucleic acids.

9. Correct answer: A. Enzymes function best at a specific temperature.

Enzyme activity is affected by temperature. Each enzyme has a specific temperature range in which it works most effectively. Most biological enzymes present in the human body have an ideal temperature range of around 98.6 degrees.

10. Correct answer: A. monosaccharides

Sugars are made of building blocks called monosaccharides.