Chapter 3: The Molecules of Cells

Question 1

alpha helix

Answer 1

The spiral shape resulting from the coiling of a polypeptide in a protein’s secondary structure.

Question 2

amino acid

Answer 2

An organic molecule containing a carboxyl group and an amino group; serves as the monomer of proteins.

Question 3

amino group

Answer 3

In an organic molecule, a functional group consisting of a nitrogen atom bonded to two hydrogen atoms.

Question 4

anabolic steroid

Answer 4

A synthetic variant of the male hormone testosterone that mimics some of its effects.

Question 5

carbohydrate

Answer 5

Member of the class of biological molecules consisting of simple single-monomer sugars (monosaccharides), two-monomer sugars (disaccharides), and other multiunit sugars (polysaccharides).

Question 6

carbon skeleton

Answer 6

The chain of carbon atoms that forms the structural backbone of an organic molecule.

Question 7

carbonyl group

Answer 7

In an organic molecule, a functional group consisting of a carbon atom linked by a double bond to an oxygen atom.

Question 8

carboxyl group

Answer 8

In an organic molecule, a functional group consisting of an oxygen atom double-bonded to a carbon atom that is also bonded to a hydroxyl group.

Question 9

cellulose

Answer 9

A large polysaccharide composed of many glucose monomers linked into cable-like fibrils that provide structural support in plant cell walls.

Question 10

chitin

Answer 10

A structural polysaccharide found in many fungal cell walls and in the exoskeletons of arthropods.

Question 11

cholesterol

Answer 11

A steroid that is an important component of animal cell membranes and that acts as a precursor molecule for the synthesis of other steroids such as hormones.

Question 12

dehydration reaction

Answer 12

A chemical process in which two molecules become covalently bonded to each other with the removal of a water molecule. Also called condensation.

Question 13

denaturation

Answer 13

A process in which a protein unravels, losing its specific structure and hence function; can be caused by changes in pH or salt concentration or by high temperature. Also refers to the separation of the two strands of the DNA double helix, caused by similar factors.

Question 14

deoxyribonucelic acid (DNA)

Answer 14

A double-stranded helical nucleic acid molecule consisting of nucleotide monomers with deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T). Capable of replicating, is an organism’s genetic material. See also gene.

Question 15

disaccharide

Answer 15

A sugar molecule consisting of two monosaccharides linked by a dehydration reaction.

Question 16

double helix

Answer 16

The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.

Question 17

enzyme

Answer 17

A protein (or RNA molecule) that serves as a biological catalyst, changing the rate of a chemical reaction without itself being changed into a different molecule in the process.

Question 18

fat

Answer 18

A large lipid molecule made from an alcohol called glycerol and three fatty acids; a triglyceride. Most fats function as energy-storage molecules.

Question 19

functional group

Answer 19

An assemblage of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions.

Question 20

gene

Answer 20

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses). Most of the genes of a eukaryote are located in its chromosomal DNA; a few are carried by the DNA of mitochondria and chloroplasts.

Question 21

glycogen

Answer 21

An extensively branched polysaccharide of many glucose monomers; serves as an energy-storage molecule in liver and muscle cells; the animal equivalent of starch.

Question 22

hydrocarbon

Answer 22

A chemical compound composed only of the elements carbon and hydrogen.

Question 23

hydrolysis

Answer 23

A chemical process in which polymers are broken down by the chemical addition of water molecules to the bonds linking their monomers; an essential part of digestion.

Question 24

hydrophilic

Answer 24

“Water-loving”; pertaining to polar, or charged, molecules (or parts of molecules) that are soluble in water.

Question 25

hydrophobic

Answer 25

“Water-fearing”; pertaining to nonpolar molecules (or parts of molecules) that do not dissolve in water.

Question 26

hydroxyl group

Answer 26

In an organic molecule, a functional group consisting of a hydrogen atom bonded to an oxygen atom.

Question 27

isomer

Answer 27

Organic compounds with the same molecular formula but different structures and, therefore, different properties.

Question 28

lipid

Answer 28

An organic compound consisting mainly of carbon and hydrogen atoms linked by nonpolar convalent bonds, making the compound mostly hydrophobic. Lipids include fats, phospholipids, and steroids and are insoluble in water.

Question 29

methyl group

Answer 29

In an organic molecule, a carbon bonded to three hydrogens.

Question 30

monomer

Answer 30

A chemical subunit that serves as a building block of a polymer.

Question 31

monosaccharide

Answer 31

The simplest carbohydrate; a simple sugar with a molecular formula that is generally some multiple of CH2O. Monosaccharides are the building blocks of disaccharides and polysaccharides.

Question 32

nucleic acid

Answer 32

A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular structures and activities. The two types of nucleic acids are DNA and RNA.

Question 33

nucleotide

Answer 33

An organic monomer consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group. Nucleotides are the building blocks of nucleic acids.

Question 34

organic compound

Answer 34

A chemical compound containing the element carbon and usually synthesized by cells.

Question 35

peptide bond

Answer 35

The covalent linkage between two amino acid units in a polypeptide; formed by a dehydration reaction.

Question 36

phosphate group

Answer 36

A functional group consisting of a phosphorus atom covalently bonded to four oxygen atoms.

Question 37

phospholipid

Answer 37

A lipid made up of glycerol joined to two fatty acids and a phosphate group, giving the molecule a nonpolar hydrophobic tail and a polar hydrophilic head. Phospholipids form bilayers that function as biological membranes.

Question 38

polymer

Answer 38

A large molecule consisting of many identical or similar molecular units, called monomers, covalently joined together in a chain.

Question 39

polypeptide

Answer 39

A polymer (chain) of amino acids linked by peptide bonds.

Question 40

polysaccharide

Answer 40

A carbohydrate polymer consisting of hundreds to thousands of monosaccharides (sugars) linked by dehydration synthesis.

Question 41

primary structure

Answer 41

The first level of protein structure; the specific sequence of amino acids making up a polypeptide chain.

Question 42

protein

Answer 42

A functional biological molecule consisting of one or more polypeptides folded into a specific three-dimensional structure.

Question 43

quaternary structure

Answer 43

The fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits.

Question 44

ribonucleic acid (RNA)

Answer 44

A type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.

Question 45

saturated

Answer 45

Pertaining to fats and fatty acids whose hydrocarbon chains contain the maximum number of hydrogens and therefore have no double covalent bonds. Saturated fats and fatty acids solidify at room temperature.

Question 46

secondary structure

Answer 46

The second level of protein structure; the regular local patterns of coils or folds of a polypeptide chain.

Question 47

starch

Answer 47

A storage polysaccharide found in the roots of plants and certain other cells; a polymer of glucose.

Question 48

steroid

Answer 48

A type of lipid whose carbon skeleton is in the form of four fused rings with various chemical groups attached; examples are cholesterol, testosterone, and estrogen.

Question 49

tertiary structure

Answer 49

The third level of protein structure; the overall, three-dimensional shape of a polypeptide due to interactions of the R groups of the amino acids making up the chain.

Question 50

unsaturated

Answer 50

Pertaining to fats and fatty acids whose hydrocarbon chains lack the maximum number of hydrogen atoms and therefore have one or more double covalent bonds. Unsaturated fats and fatty acids do not solidify at room temperature.