CHAPTER 5 REVIEW

Multiple Choice
Choose the letter of the best answer.

1. Which of the following is not an organic molecule?
c. water

2. Which of the following terms includes all the other terms on this list?
b. carbohydrate

3. Which term is most appropriate to describe a molecule that dissolves easily in water?
c. hydrophilic

4. Cholesterol is an example of what kind of molecule?
b. lipid

5. The 20 amino acids very only in their:
c. amino groups

6. A specific reactant an enzyme acts upon is called the:
d. substrate

7. An enzyme does which of the following?
b. lowers the activation energy of a reaction

8. Besides satisfying your hunger, why else might you consume a big bowl of pasta the night before a race?
Pasta contains carbohydrates, which is an organic compound made up of sugar molecules. We need sugar for energy, and therefore I might consume a big bowl of pasta, so I would be ready to use up a lot of energy at the race.

9. How are glucose, sucrose, and starch related?
Glucose is a monosaccharide, sucrose is a disaccharide, and starch is a polysaccharide, which are all carbohydrates, linked and related to each other. Sucrose consists of a glucose molecule linked to a fructose molecule. When sucrose, a major carbohydrate in plant, is consumed, it is broken down into glucose and fructose. Starch consists entirely of glucose monomers linked in a long polymer chain.

10. What are steroids? Describe two functions they have in cells.
Steroids are lipid molecules with four fused carbon rings each. They circulate in your body as chemical signals, such as hormones, and also has a hydrophobic characteristic.

11. How are polypeptides related to proteins?
Amino acids are linked together into a polypeptide chain, by the cells, trying to create proteins.

12. How does denaturation affect the ability of a protein to function?
Denaturation unravels and loses the normal shape of the protein. It affects the polypeptide chains to become tangled up with one another, and since the protein’s function varies depending on its shape, it would also lose its ability to work properly.

14. The reaction below shows two amino acids joining together.

a. One product of this reaction is represented by a question mark. Which molecule is it?
When the two amino acids joined together, it went through a dehydration reaction, releasing a water molecule, which should be filled in as H20 in the question mark.

b. What is this kind of reaction called? Explain.
The process of a water molecule released when a monomer is added to a chain, or when two monomers join together, is called a dehydration reaction.

c. If an amino acid were added to this chain, at what two places could it attach?
It would attach on the OH (Hydrogen Oxygen) atom or the H (Hydrogen) atom on the other side.

15. Use the graph to answer the questions below.

a. At which temperature does enzyme A perform best? Enzyme B?
Enzyme A performs best in about 37 degrees, and enzyme B performs best in about 77 degrees.

b. Knowing that one of these enzymes is found in humans and the other in thermopilic (heat-loving) bacteria, hypothesize which enzyme came from which organism.
Enzyme A should be the enzymes found in humans, because its best performing temperature is the average human body temperature. Enzyme B would be the enzyme found in thermophilic bacteria, because the bacteria is heat-loving, and 77 degrees is pretty high.

c. Propose a hypothesis that explains why the rate of the reaction catalyzed by enzyme A slows down at temperatures above 40˚C.
Enzyme A is the enzyme found in humans. If the human body temperature rises above 40˚C, the person is close to death. The human body cannot perform its abilities when it reaches to that certain amount of temperature. That could be why this enzyme slows down at this point, since it is not able to perform anymore at that stage.