Question 1

Which of the following statements best explains why L-isomers of amino acids are found in proteins, but not D-isomers?

Accepted Answer

The enzymes responsible for protein synthesis specifically recognize and incorporate L-isomers due to their stereochemistry.

Question 2

A peptide bond is formed by a condensation reaction between which two functional groups of adjacent amino acids?

Accepted Answer

The amino group of one amino acid and the carboxyl group of another amino acid.

Question 3

Which of the following interactions is primarily responsible for stabilizing the secondary structure of proteins?

Accepted Answer

Hydrogen bonds between backbone atoms of the polypeptide chain.

Question 4

If a protein contains both alpha-helices and beta-sheets, which level of protein structure does this describe?

Accepted Answer

Secondary structure

Question 5

Which of the following best describes the tertiary structure of a protein?

Accepted Answer

The overall three-dimensional shape formed by interactions between R groups.

Question 6

Which of the following bonds or interactions is NOT typically involved in stabilizing tertiary protein structure?

Accepted Answer

Peptide bonds

Question 7

A DNA nucleotide differs from an RNA nucleotide in which of the following ways?

Accepted Answer

DNA nucleotides have a deoxyribose sugar, while RNA nucleotides have a ribose sugar.

Question 8

If a sample of DNA contains 30% adenine, what percentage of guanine does it contain? (Assume Chargaff's rules apply.)

Accepted Answer

$$20\%$$

Question 9

Which of the following is the correct formula for glucose, and what is its most common isomer in nature?

Accepted Answer

$$C_6H_{12}O_6$, D-glucose

Question 10

Which type of glycosidic bond is found in cellulose, and why can't most animals digest it?

Accepted Answer

$$\beta-$$glycosidic bond; animals lack the enzyme to break it down.

Question 11

Which of the following statements about phospholipids is correct?

Accepted Answer

Phospholipids are amphipathic, containing both hydrophobic and hydrophilic regions.

Question 12

A triglyceride is formed by a condensation reaction between which molecules?

Accepted Answer

Three fatty acids and one glycerol

Question 13

Which of the following statements about saturated and unsaturated fatty acids is TRUE?

Accepted Answer

Saturated fatty acids have only single bonds between carbon atoms and higher melting points than unsaturated fatty acids.

Question 14

Which of the following is a function of cholesterol in animal cell membranes?

Accepted Answer

It increases membrane fluidity and serves as a precursor for steroid hormones.

Question 15

Which of the following best describes the directionality of nucleic acid synthesis?

Accepted Answer

Nucleic acids are synthesized in the 5' to 3' direction.

Question 16

Which of the following polysaccharides is found in animal cells and serves as a storage molecule?

Accepted Answer

Glycogen

Question 17

Which of the following is a correct statement about the structure of a nucleotide?

Accepted Answer

A nucleotide consists of a 5-carbon sugar, a phosphate group, and a nitrogen-containing base.

Question 18

Which of the following best explains why nonpolar R groups are found in the interior of folded proteins?

Accepted Answer

Nonpolar R groups are hydrophobic and avoid contact with water, so they cluster inside the protein.

Macromolecules of the Cell: Proteins, Nucleic Acids, Carbohydrates, and Lipids

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