unit 1 test 2

Amylase is an enzyme that converts carbohydrate polymers into monomers. Glycogen synthase is one of the enzymes involved in converting carbohydrate monomers into polymers. Which of the following best explains the reactions of these enzymes?

Amylase aids in the addition of a water molecule to break covalent bonds whereas glycogen synthase aids in the removal of a water molecule to form covalent bonds.

Humans produce sweat as a cooling mechanism to maintain a stable internal temperature. Which of the following best explains how the properties of water contribute to this physiological process?

The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas.

The amino acid in Figure 1 is found in a region of a polypeptide that folds away from water. Which part of the amino acid most likely contributes to the hydrophobic behavior of this region of the polypeptide?

Methyl (CH3) group

Based on the molecular structures shown in the figure, which molecule is likely to be solid at room temperature?

Palmitic acid, because the absence of carbon-carbon double bonds allows the molecules to pack closely together

Which of the following characteristics of Figure 1 best shows that the fragment is RNA and not DNA?

The identity of each nitrogenous base

Water and ammonia interact to form hydrogen bonds, as represented in the figure.

The nitrogen has a partial negative charge, and the hydrogen attached to the oxygen has a partial positive charge.

The diagram shows how water can adhere to the xylem in the stems of plants, which contributes to water movement in the plant. Which of the following best explains how water is able to move upward from the roots of a plant, through its xylem in the stem, and out to the leaves?

Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.

Based on the results of the experiment, which of the following types of molecules did the bacteriophages most likely inject into the bacteria cells?

DNA

Which of the following best supports the researcher's claim?

Guanine-cytosine pairs denature at a higher temperature because they have more hydrogen bonds between them than adenine-thymine pairs do.

Which of the following is responsible for the cohesive property of water?

Hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

Which of the following is an accurate description of the process shown in Figure 1 ?

The formation of a covalent peptide bond in a dehydration synthesis reaction

Which of the following most likely explains how the amino acid substitution has resulted in decreased catalytic activity by the mutated enzyme?

The substitution altered the secondary and tertiary structure of the enzyme so that the mutated enzyme folds into a different shape than the normal enzyme does.

Read each question carefully. Write your response in the space provided for each part of each question. Answers must be written out in paragraph form. Outlines, bulleted lists, or diagrams alone are not acceptable and will not be scored. The stems and fruits of pineapple plants contain a group of protein-digesting enzymes collectively called bromelain and often used as an antibrowning agent for fruits and vegetables. Fruits and vegetables brown when they are bruised during transport or sliced and exposed to air. This browning is controlled by enzymatic pathways that produce brown pigments. The browning of fruits and vegetables reduces the nutritional value of the food, so antibrowning agents such as bromelain are used. (a) Identify the type of monomer of which this enzyme is composed. (b) Bromelain works by breaking the enzymes that cause browning into smaller molecules. Explain how the reaction that breaks up the enzymes occurs. (c) The pH of a solution determines the charge of certain R groups. The pH of pineapple fruit ranges from 3.5 to 5.2. Predict the effect on the activity of bromelain if it is used in a product with a pH of 11. (d) Provide reasoning to justify your prediction.

(a) This enzyme is composed of the protein monomer, amino acid. (b) The reaction that breaks up the enzymes occurs by hydrolysis, in which H20 is added to break up the peptide bond of the enzymes. (c)The activity of bromelain will decrease. The stems and fruits of pineapple plants, with a pH ranging from 3.5 to 5.3, contain bromelain. Since bromelain functions in this acidic environment, the activity of bromelain would decrease in a very basic environment. (d) Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule, positively and negatively charged amino acids will attract. This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site. Changing the pH will affect the charges on the amino acid molecules; therefore, amino acids that attracted each other may no longer be. Extremes of pH also denature enzymes, since optimum pH level for enzymes is 8.

Which of the following best explains why a cell's plasma membrane is composed of two layers of phospholipids rather than just a single layer?

Having two oppositely oriented layers of phospholipids allows only the hydrophilic heads to interact with water inside and outside of the cell.

Researchers compared similar proteins from related organisms in different habitats. They found that the proteins from organisms living in harsh environments had a greater number of cysteine amino acids than did proteins from organisms not living in harsh environments. The structure of cysteine is shown. Bonds can form between the sulfur atom of different cysteine amino acids (S-S bonds).

The change leads to increased protein stability because of an increased number of S-S bonds in the tertiary structure of the proteins.