Question 1

Hydrogenated vegetable oil is the primary ingredient in margarine.How does hydrogenated vegetable oil differ from nonhydrogenated vegetable oil?

Accepted Answer

Hydrogenated vegetable oil is solid at room temperature due to the process of hydrogenation, which adds hydrogen atoms to unsaturated fatty acids and converts them into saturated fatty acids. Nonhydrogenated vegetable oil remains liquid at room temperature because it contains unsaturated fatty acids with double bonds.

Question 2

Which of the following is the smallest carbohydrate?

Accepted Answer

Sucrose is the smallest carbohydrate among the options given. It is a disaccharide, consisting of glucose and fructose, whereas the other options (glycogen, chitin, cellulose, and starch) are polysaccharides, which are much larger molecules composed of many sugar units.

Question 3

Which two functional groups are always found in amino acids?

Accepted Answer

Amino acids always contain a carboxyl group (COOH) and an amino group (NH2). Option A is incorrect because hydroxyl group (OH) is not present in amino acids. Option B is incorrect because carbonyl group (C=O) is not present in all amino acids. Option C is incorrect because ketone functional group (C=O) is not present in amino acids.

Question 4

Which of the following large biological molecules will self-assemble into a bilayer when mixed with water?

Accepted Answer

Phospholipids have both hydrophilic and hydrophobic regions, allowing them to self-assemble into a bilayer with the hydrophilic heads facing outward and the hydrophobic tails facing inward, when mixed with water. Steroids, triacylglycerols, and cellulose do not have this property and will not form bilayers.

Question 5

Humans can digest starch but not cellulose because

Accepted Answer

Humans have enzymes, such as amylase, that can hydrolyze the α glycosidic linkages of starch. However, humans lack the enzyme needed to break the β glycosidic linkages in cellulose. Therefore, humans cannot digest cellulose.

Question 6

Which of the following statements regarding lipids is true?

Accepted Answer

Lipids are non-polar molecules, which means they do not have a charge and cannot form hydrogen bonds with water molecules. Therefore, they are not soluble in water, but are soluble in non-polar solvents like alcohol and ether.

Question 7

A molecule with the chemical formula C₆H₁₂O₆ is most likely a

Accepted Answer

This molecule is a monosaccharide, as indicated by the chemical formula which suggests a composition typical of simple sugars (carbon, hydrogen, and oxygen in ratios that suggest a carbohydrate).

Question 8

Which of the following statements is true regarding cellulose?

Accepted Answer

Cellulose is a primary structural component of plant cell walls.

Answer: E 
 Cellulose is a polymer of glucose joined by α glycosidic linkages.

A is incorrect because cellulose is not composed of enantiomers of glucose, but rather glucose monomers that are all in the same orientation.

C is incorrect because humans lack the specific enzymes needed to digest cellulose, although some bacteria in the gut of ruminants (such as cows) are able to break it down.

D is incorrect because glycogen and starch are the storage polysaccharides in plant cells, not cellulose.

Question 9

Why are hydrocarbons insoluble in water?

Accepted Answer

Hydrocarbons are composed of nonpolar covalent bonds between carbon and hydrogen atoms. This nonpolar nature makes them insoluble in water which is a polar solvent. The polar nature of water molecules causes them to form strong hydrogen bonds with each other which attracts other polar or charged substances, but repels nonpolar substances like hydrocarbons.

Question 10

Which of the following statements regarding saturated fatty acids is true?

Accepted Answer

Saturated fatty acids are solid at room temperature and are commonly found in animal products, such as lard and butter. They do not contain any double bonds in their hydrocarbon tails. Corn oil, on the other hand, contains mostly unsaturated fatty acids. Plants can produce both saturated and unsaturated fatty acids.

Question 11

Which of the following statements concerning saturated fats is true?

Accepted Answer

Saturated fats are generally solid at room temperature, whereas unsaturated fats are usually liquid. The other choices are incorrect: A) Unsaturated fats are more common in plants than in animals, not saturated fats. B) Unsaturated fats have one or more double bonds in the carbon chains of their fatty acids, not saturated fats. D) Saturated fats have all of their carbon atoms fully saturated with hydrogen atoms, whereas unsaturated fats have one or more double bonds in their carbon chains, resulting in fewer hydrogen atoms per molecule.

Question 12

The molecular formula for glucose is C₆H₁₂O₆.What would be the molecular formula for a molecule made by linking three glucose molecules together by dehydration reactions?

Accepted Answer

Each glucose molecule contains 6 carbons, 12 hydrogens, and 6 oxygens. When three glucose molecules are linked together by dehydration reactions, two hydrogens and one oxygen are lost for each new glycosidic bond formed. Therefore, the molecular formula for the resulting molecule would be: (6x3)C + (12x3-6x2)H + (6x3-1x2)O = 18C + 30H + 16O which can be simplified to C₁₈H₃₂O₁₆.

Question 13

Which of the following polymers are assembled with monomers containing nitrogen?

Accepted Answer

Chitin is the only polymer listed that is assembled with monomers containing nitrogen. Its monomer is N-acetylglucosamine.  Starch, glycogen, and cellulose are all composed of glucose monomers, which do not contain nitrogen.

Question 14

Lactose,a sugar in milk,is composed of one glucose molecule joined by a glycosidic linkage to one galactose molecule.How is lactose classified?

Accepted Answer

Lactose is composed of two monosaccharides (glucose and galactose) joined by a glycosidic linkage, thus it is a disaccharide.

Question 15

Why are the vertebrate sex hormones estrogen and testosterone considered to be lipids?

Accepted Answer

Estrogen and testosterone are considered to be lipids because their carbon skeletons are composed of primarily C-C and C-H bonds, which are features of lipids. Although they are not made of fatty acids and are not essential components of cell membranes, they are hydrophobic compounds that are insoluble in water and soluble in organic solvents.

Question 16

Which of the following statements is true of both starch and cellulose?

Accepted Answer

Both starch and cellulose are polymers of glucose, but they differ in the glycosidic linkages between the glucose units.

Question 17

The biochemical reaction that joins two amino acids to form a dipeptide is accompanied by

Accepted Answer

The process of joining two amino acids to form a dipeptide is called dehydration synthesis or condensation reaction. This reaction involves the removal of a water molecule as the peptide bond is formed between the carboxyl group of one amino acid and the amino group of another amino acid. Therefore, the correct answer is D, which states that the reaction is accompanied by the release of a water molecule.

Question 18

The term insoluble fiber on food packaging generally refers to which of the following carbohydrates?

Accepted Answer

Insoluble fiber refers to fiber that cannot be dissolved in water and is not broken down by the digestive system. Cellulose is a type of insoluble fiber found in plant cell walls that provides bulk to the diet and promotes regularity in bowel movements. Sucrose, starch, and glycogen are all types of soluble carbohydrates that are broken down by the body for energy.

Question 19

A molecule with the formula C₁₈H₃₆O₂ is most likely a

Accepted Answer

The molecule contains several instances of the "S1U1B" unit, which likely represents a fatty acid chain with a variable length of carbon and hydrogen atoms (represented by the "S" and "B" respectively). The "HS" likely represents a hydroxyl group (-OH) commonly found in fatty acids. The "O" likely represents a carbonyl group (-C=O) found at the end of a fatty acid chain. The other elements present in the molecule, such as oxygen (O) and sulfur (S), are also commonly found in fatty acids. Therefore, the most likely option is A) fatty acid. The other options (B, C, and D) do not have structures which incorporate the "S1U1B" units.

Question 20

Amylase is an enzyme that hydrolyzes glycosidic linkages between glucose monomers only if the monomers are the α form.Which of the following macromolecules can be broken down by amylase?

Accepted Answer

Amylase can break down starch because it is made up of glucose monomers in the α form. Cellulose and chitin are made up of glucose monomers in the β form and therefore cannot be broken down by amylase.

Quiz 3: Carbon and the Molecular Diversity of Life