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.

Concept 5.3) Lipids include fats and steroids

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KEY TERMS

Lipid: is one of a class of water-avoiding compounds.
Hydrophobic: avoids water molecules.
Fat: is an organic compound consisting of a three-carbon back-bone (glycerol) attached to three fatty acids (: contains long hydrocarbon chains).
Saturated fat: is fat in which all three fatty acid chains contain he maximum possible number of hydrogen atoms.
Unsaturated fat: is fat with less than the maximum number of hydrogen in one or more of its fatty acid chains. This is because some of its carbon atoms are double-bonded to each other.
Steroid: is a lipid molecule with four fused carbon rings.
Cholesterol: is a steroid molecule present in the plasma membranes of animal and human cells. It can be the starting point from which your body produces other steroids.
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Lipids and Fats

• Compounds, that have characteristic of being unable to mix with the class of water, like oil, all called lipids, and they are said to be hydrophobic.
• Lipids have functions of acting as a boundary that surrounds and contains the aqueous, or watery, contents of your cells.
• Other types of lipid circulate in your body as chemical signals to cells.
• The other type of lipids is – fat, which stores energy in your body, as well as cushions your organs and provides your body with insulation.
• All the carbon atoms in the fatty acid chains form single bonds with each other, and the rest of their bonds are with hydrogen atoms.
• Saturated fat- most animal fats, such as butter.
• Unsaturated fat- generally fats in fruits, vegetables, and fish, such as corn oil, olive oil, and other vegetable oils.
• Having diets of consuming much rich saturated fats can be unhealthy, building up lipid-containing deposits within the walls of blood vessels, called plaques. Plaques can reduce blood flow, and may lead to heart diseases.
• It has hydrophillic head and hydrophobic tails.

Steroids

• Are classified as lipids because of its hydrophobic characteristics, but they are different from fats in structure and function.
• They circulate in your body as chemical signals, such as hormones.
• Cholesterol is best-known for an example of a steroid. But substances with high levels of cholesterol in the blood can link to the risk for cardiovascular (heart and blood vessel) disease.

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Concept Check
1. What is the difference between saturated and unsaturated fat?
2. What are lipids, and what are its characteristics?
3. What are steroids?