Chapter 5: The Structure and Function of Large Biological Molecules

Protein

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

Fatty Acid

A carboxylic acid with a long carbon chain. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form a fat molecule, also known as a triacylglycerol or triglyceride.

Catalyst

A chemical agent that selectively increases the rate of a reaction without being consumed by the reaction.

Dehydration Reaction

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

Hydrolysis

A chemical reaction that breaks bonds between two molecules by the addition of water; functions in disassembly of polymers to monomers.

Glycosidic Linkage

A covalent bond formed between two monosaccharides by a dehydration reaction.

gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).

Disaccharide

A double sugar, consisting of two monosaccharides joined by a glycosidic linkage formed by a dehydration reaction.

Saturated Fatty Acid

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that are attached to the carbon skeleton.

Unsaturated Fatty Acid

A fatty acid that has one or more double bonds between carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.

Macromolecules

A giant molecule formed by the joining of smaller molecules, usually by a dehydration reaction. Polysaccharides, proteins, and nucleic acids are macromolecules.

Triacylglycerol

A lipid consisting of three fatty acids linked to one glycerol molecule; also called a fat or triglyceride.

Fat

A lipid consisting of three fatty acids linked to one glycerol molecule; also called a triacylglycerol or triglyceride.

Phospholipid

A lipid made up of glycerol joined to two fatty acids and a phosphate group. The hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails, while the rest of the molecule acts as a polar, hydrophilic head. Phospholipids form bilayers that function as biological membranes.

Polymer

A long molecule consisting of many similar or identical monomers linked together by covalent bonds.

Enzyme

A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed by the reaction. Most enzymes are proteins.

deoxyribonucleic acid (DNA)

A nucleic acid molecule, usually a double-stranded helix, in which each polynucleotide strand consists of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T); capable of being replicated and determining the inherited structure of a cell's proteins.

nucleic acid

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

polynucleotides

A polymer consisting of many nucleotide monomers in a chain. The nucleotides can be those of DNA or RNA.

Polypeptide

A polymer of many amino acids linked together by peptide bonds.

Polysaccharide

A polymer of many monosaccharides, formed by dehydration reactions.

Proteins are the most structurally and functionally diverse class of biological molecules. Explain the basis for this diversity.

A polypeptide, which may consist of hundreds of amino acids in a specific sequence (primary structure), has regions of coils and pleats (secondary structure), which are then folded into irregular contortions (tertiary structure) and may be noncovalently associated with other polypeptides (quaternary structure). The linear order of amino acids, with the varying properties of their side chains (R groups), determines what secondary and tertiary structures will form to produce a protein. The resulting unique three-dimensional shapes of proteins are key to their specific and diverse functions.

chaperonin

A protein complex that assists in the proper folding of other proteins.

Sickle-cell disease

A recessively inherited human blood disorder in which a single nucleotide change in the β-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals.

Cholesterol

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

Starch

A storage polysaccharide in plants, consisting entirely of glucose monomers joined by α glycosidic linkages.

disulfide bridge

A strong covalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer.

Cellulose

A structural polysaccharide of plant cell walls, consisting of glucose monomers joined by β glycosidic linkages.

Chitin

A structural polysaccharide, consisting of amino sugar monomers, found in many fungal cell walls and in the exoskeletons of all arthropods.

Carbohydrate

A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).

x-ray crystallography

A technique used to study the three-dimensional structure of molecules. It depends on the diffraction of an X-ray beam by the individual atoms of a crystallized molecule.

Steroid

A type of lipid characterized by a carbon skeleton consisting of four fused rings with various chemical groups attached.

ribonucleic acid (RNA)

A type of nucleic acid consisting of a polynucleotide made up 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, gene regulation, and as the genome of some viruses.

hydrophobic interaction

A type of weak chemical interaction caused when molecules that do not mix with water coalesce to exclude water.

Glycogen

An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.

Amino Acid

An organic molecule possessing both a carboxyl and an amino group. Amino acids serve as the monomers of polypeptides.

Trans Fat

An unsaturated fat, formed artificially during hydrogenation of oils, containing one or more trans double bonds.

Lipid

Any of a group of large biological molecules, including fats, phospholipids, and steroids, that mix poorly, if at all, with water.

Compare the structure of a fat (triglyceride) with that of a phospholipid.

Both have a glycerol molecule attached to fatty acids. The glycerol of a fat has three fatty acids attached, whereas the glycerol of a phospholipid is attached to two fatty acids and one phosphate group.

Compare the composition, structure, and function of starch and cellulose. What role do starch and cellulose play in the human body? (5.2)

Both starch and cellulose are polymers of glucose, but the glucose monomers are in the α configuration in starch and the β configuration in cellulose. The glycosidic linkages thus have different properties. Starch is an energy-storage compound in plants; cellulose is a structural component of plant cell walls. Humans can hydrolyze starch to provide energy but cannot hydrolyze cellulose. Cellulose aids in the passage of food through the digestive tract.

A dehydration reaction joins two glucose molecules to form maltose. The formula for glucose is C6H12O6. What is the formula for maltose?

C12H22O11

Write the formula for a monosaccharide that has three carbons.

C3H6O3

Why are human sex hormones considered lipids?

Human sex hormones are steroids, a type of hydrophobic compound.

Denaturation

In proteins, a process in which a protein loses its native shape due to the disruption of weak chemical bonds and interactions, thereby becoming biologically inactive; in DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme (noncellular) conditions of pH, salt concentration, or temperature.

Why are lipids not considered to be macromolecules for polymers?

Lipids are not polymers because they do not exist as a chain linked monomers. They are not considered macromolecules because they do not reach the giant size of many polysaccharides, proteins, and nucleic acids.

How many molecules of water are needed to completely hydrolyze a polymer that is ten monomers long?

Nine, with one water molecule required to hydrolyze each connected pair of monomers.

β pleated sheet

One form of the secondary structure of proteins in which the polypeptide chain folds back and forth. Two regions of the chain lie parallel to each other and are held together by hydrogen bonds between atoms of the polypeptide backbone (not the side chains).

Purine

One of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring fused to a five-membered ring. Adenine (A) and guanine (G) are purines.

Pyrimidine

One of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring. Cytosine (C), thymine (T), and uracil (U) are pyrimidines.

antiparallel

Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5′ → 3′ directions).

Secondary Structure

Regions of repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bonding between constituents of the backbone (not the side chains).

α helix

Regions of repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bonding between constituents of the backbone (not the side chains).

What parts of a polypeptide participate in the bonds that hold together secondary structure? Tertiary structure?

Secondary structure involves hydrogen bonds between atoms of the polypeptide backbone. Tertiary structure involves interactions between atoms of the side chains of the amino acid subunits.

nucleotide

The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and one or more phosphate groups.

What role does complementary base pairing play in the functions of nucleic acids?

The complementary base pairing of the two strands of DNA makes possible the precise replication of DNA every time a cell divides, ensuring that genetic information is faithfully transmitted. In some types of RNA, complementary base pairing enables RNA molecules to assume specific three-dimensional shapes that facilitate diverse functions.

Peptide Bond

The covalent bond between the carboxyl group on one amino acid and the amino group on another, formed by a dehydration reaction.

Double helix

The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.

What are the four main classes of large biological molecules? Which class does not consist of polymers?

The four main classes are proteins, carbohydrates, lipids, and nucleic acids. Lipids are not polymers.

Why does a denatured protein no longer function normally?

The function of a protein is a consequence of its specific shape, which is lost when a protein becomes denatured.

Primary Structure

The level of protein structure referring to the specific linear sequence of amino acids.

tertiary structure

The overall shape of a protein molecule due to interactions of amino acid side chains, including hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

Quaternary structure

The particular shape of a complex, aggregate protein, defined by the characteristic three-dimensional arrangement of its constituent subunits, each a polypeptide.

What is the fundamental basis for the differences between carbohydrates proteins, and nucleic acids?

The polymers of carbohydrates, proteins, and nucleic acids are built from three different types of monomers: monosaccharides, amino acids, and nucleotides, respectively.

Monosaccharide

The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides. Also known as simple sugars, monosaccharides have molecular formulas that are generally some multiple of CH2O.

Monomer

The subunit that serves as the building block of a polymer.

Deoxyribose

The sugar component of DNA nucleotides, having one fewer hydroxyl group than ribose, the sugar component of RNA nucleotides.

Ribose

The sugar component of RNA nucleotides.

The enzyme amylase can break glycosidic linkages between glucose monomers only if the monomers are in the α form. Which of the following could amylase break down? a. glycogen, starch, and amylopectin b. glycogen and cellulose c. cellulose and chitin d. starch and chitin e. starch, amylopectin, and cellulose

a

The structural level of a protein least affected by a disruption in hydrogen bonding is the a. primary level. b. secondary level. c. tertiary level. d. quaternary level. e. All structural levels are equally affected.

a

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes? a. The two strands of the double helix would separate. b. The phosphodiester linkages of the polynucleotide backbone would be broken. e. All bases would be separated from dexyribose sugars.

b

Which of the following statements concerning unsaturated fats is true? a. They are more common in animals than in plants. b. They have double bonds in the carbon chains of their fatty acids. c. They generally solidify at room temperature. d. They contain more hydrogen than do saturated fats having the same number of carbon atoms. e. They have fewer fatty acid molecules per fat molecule.

b

The molecular formula for glucose is C6H12O6. What would be the molecular formula for a polymer made by linking ten glucose molecules together by dehydration reactions? a. C60H120O60 b. C6H12O6 c. C60H102051 d. C60H100O50 e. C60H111O51

c

Which of the following categories includes all others in the list? a. monosaccharide b. disaccharide c. starch d. carbohydrate e. polysaccharide

d

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA? a. 5'-purine-pyrimidine-purine-pyrimidine-3' with 3'-purine-pyrimidine-purine-pyrimidine-5' b. 5'-AGCT-3' with 5'-TCGA-3' c. 5'-GCGC-3' with 5'-TATA-3' d. 5'-GCGC-3 with 5'-GCAT-3' e. All of these pairs are correct.

d