Q: Cellulose and starch are both polymers of glucose. Why can humans digest starch but not cellulose?

Humans have enzymes that can break the $oldsymbol{ ext{α}}$-glycosidic bonds in starch, but not the $eta$-glycosidic bonds in cellulose.

Question 1

Which property of carbon most directly explains its ability to form large, complex biological molecules?

Accepted Answer

Carbon can form four covalent bonds, allowing for diverse molecular structures.

Question 2

Stanley Miller's classic experiment demonstrated the abiotic synthesis of organic compounds. Why is this experiment significant for our understanding of the origin of life?

Accepted Answer

It showed that organic molecules could form under prebiotic Earth conditions, supporting the idea that life's building blocks could arise naturally.

Question 3

Which functional group is most likely to make a molecule hydrophilic?

Accepted Answer

Phosphate group ($-PO_4^{2-}$)

Question 4

A molecule with the formula $C_6H_{12}O_6$ can be a structural isomer, a geometric (cis-trans) isomer, or an enantiomer. Which of the following best describes the importance of these isomers in biology?

Accepted Answer

Isomers can have drastically different biological activities due to differences in three-dimensional shape.

Question 5

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

Accepted Answer

Unsaturated fatty acids have at least one double bond, making them liquid at room temperature.

Question 6

Which of the following best explains why phospholipids form bilayers in water?

Accepted Answer

Phospholipids have both hydrophilic heads and hydrophobic tails, causing them to arrange in bilayers with heads facing water and tails facing inward.

Question 7

Which of the following is a correct description of a dehydration reaction in the synthesis of biological polymers?

Accepted Answer

A water molecule is removed to form a new covalent bond between monomers.

Question 8

Cellulose and starch are both polymers of glucose. Why can humans digest starch but not cellulose?

Accepted Answer

Humans have enzymes that can break the $oldsymbol{	ext{α}}$-glycosidic bonds in starch, but not the $eta$-glycosidic bonds in cellulose.

Question 9

Which of the following amino acid substitutions would likely have the smallest effect on protein structure and function?

Accepted Answer

Serine (polar) for threonine (polar)

Question 10

A globular protein found in tears protects the eye from bacterial infections. Which of the following best describes the outside of this protein?

Accepted Answer

Mostly hydrophilic side chains are on the surface of the protein.

Question 11

Which level of protein structure is directly determined by the sequence of amino acids?

Accepted Answer

Primary structure

Question 12

Which type of bond is responsible for holding together the two strands of DNA?

Accepted Answer

Hydrogen bonds between nitrogenous bases

Question 13

Which of the following is a characteristic common to all lipids?

Accepted Answer

They contain long chains of C-H bonds and do not dissolve well in water.

Question 14

Which of the following best describes the role of cholesterol in animal cell membranes?

Accepted Answer

Cholesterol is a structural lipid that helps maintain membrane fluidity.

Question 15

Which of the following is NOT a polymer?

Accepted Answer

Glucose

Question 16

Which process is responsible for breaking down polymers into monomers in biological systems?

Accepted Answer

Hydrolysis

Question 17

Which of the following best explains why trans fats are considered unhealthy?

Accepted Answer

Trans fats raise LDL (bad cholesterol) and lower HDL (good cholesterol), contributing to cardiovascular disease.

Question 18

Which of the following is a correct description of a nucleotide found in DNA?

Accepted Answer

A nucleotide consists of a phosphate group, a pentose sugar, and a nitrogenous base.

Question 19

Which of the following bonds is formed during the polymerization of nucleic acids?

Accepted Answer

Phosphodiester bond

Question 20

A mutation changes one amino acid in hemoglobin from glutamic acid (negatively charged) to valine (nonpolar). What is the most likely consequence?

Accepted Answer

Altered hemoglobin structure, leading to sickle-cell disease due to hydrophobic interactions.

Carbon and Biological Molecules: Structure, Function, and Importance in Life

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