Ch 3: biological macromolecules

What are the four major classes of organic molecules?

Carbohydrates, lipids, proteins, and nucleic acids.

Why is carbon important in biological molecules?

Carbon can form covalent bonds with other atoms and with other carbon atoms, allowing diverse and complex molecules to form.

What is a hydrocarbon?

A molecule consisting only of carbon and hydrogen.

Are hydrocarbons polar or nonpolar?

Nonpolar.

What happens when functional groups are added to hydrocarbons?

They confer specific chemical properties to the molecule.

How many unpaired outer electrons does carbon have?

Four.

What is the simplest hydrocarbon?

Methane (CH₄).

What are possible arrangements of carbon atoms in hydrocarbons?

Linear unbranched chains, branched chains, or rings.

What are functional groups?

Small, reactive groups of atoms that give larger molecules specific chemical properties.

What are the six major functional groups commonly involved in biological reactions?

Hydroxyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl.

What does the symbol R represent in biological molecules?

The rest of the molecule, usually attached to a functional group by a covalent bond.

What are isomers?

Molecules with the same molecular or empirical formula but different molecular structures.

What are structural isomers?

Molecules with the same chemical formula but different arrangements of atoms.

What are stereoisomers?

Molecules that differ in how their attached groups are arranged in space.

What are enantiomers?

Mirror-image molecules associated with a chiral carbon.

What are examples of enantiomers in sugars?

D-sugars and L-sugars.

How are glucose and fructose structural isomers?

They have the same formula but different structures; glucose contains an aldehyde and fructose contains a ketone.

What is a monomer?

A small, similar chemical subunit.

What is a polymer?

A large molecule built by linking monomers together.

What is dehydration synthesis?

Formation of large molecules by removing water; monomers are joined to form polymers.

What is hydrolysis?

Breakdown of large molecules by adding water; polymers are broken down into monomers.

What is the major difference between dehydration synthesis and hydrolysis?

Dehydration synthesis builds polymers by removing water, while hydrolysis breaks polymers apart by adding water.

What is the typical ratio of carbon, hydrogen, and oxygen in carbohydrates?

1:2:1.

What is the general empirical formula for carbohydrates?

(CH₂O)ₙ.

Why do carbohydrates contain significant energy?

Their C—H covalent bonds hold considerable energy.

What are the three major types of carbohydrates?

Monosaccharides, disaccharides, and polysaccharides.

What is a monosaccharide?

The simplest type of carbohydrate.

How many carbon atoms do monosaccharides contain?

Three to seven carbon atoms.

What are the three types of sugars based on carbon number?

Triose (3 carbons), pentose (5 carbons), and hexose (6 carbons).

What are examples of common hexoses?

Glucose, fructose, and galactose.

What is the molecular formula of glucose?

C₆H₁₂O₆.

What is glyceraldehyde?

A three-carbon sugar (triose).

What is ribose?

A five-carbon sugar (pentose).

What is mannose?

A six-carbon sugar (hexose).

What forms can monosaccharides exist in?

Linear and ring forms.

How do monosaccharides with five or more carbons form rings?

They fold back on themselves through a reaction between two functional groups.

What is the difference between α-glucose and β-glucose?

In α-glucose, the OH group points below the plane of the ring; in β-glucose, it points above the plane.

What is a disaccharide?

A carbohydrate made of two monosaccharides.

How are disaccharides formed?

Two monosaccharides are covalently joined through dehydration synthesis.

What type of bond joins monosaccharides?

A glycosidic bond.

What is maltose made of?

Two α-glucose molecules.

What linkage is found in maltose?

An α(1→4) glycosidic linkage.

What is sucrose made of?

Glucose + fructose.

What is lactose made of?

Glucose + galactose.

What is a polysaccharide?

A long chain of monosaccharides.

How are polysaccharides formed?

Monosaccharides are linked through dehydration synthesis.

Can polysaccharides be branched?

Yes. They may be linear, unbranched, or contain branches.

What polysaccharide do plants use for energy storage?

Starch.

What polysaccharide do animals use for energy storage?

Glycogen.

What polysaccharide provides structural support in plants?

Cellulose.

What polysaccharide provides structural support in arthropods and fungi?

Chitin.

What is amylose?

A plant starch formed from α-glucose units joined by α(1→4) linkages.

What linkages form the main chains of glycogen?

α(1→4) linkages.

What linkages form glycogen branches?

α(1→6) linkages.

What is chitin?

A structural polysaccharide found in arthropod exoskeletons and fungal cell walls.

What are lipids?

Water-insoluble, primarily nonpolar biological molecules composed mostly of hydrocarbons.

Why are lipids generally insoluble in water?

They are primarily nonpolar.

What are the three common types of lipids?

Neutral lipids, phospholipids, and steroids.

What is the primary function of neutral lipids?

Energy storage.

What is the primary function of phospholipids?

Forming cell membranes.

What is the primary function of many steroids?

Acting as hormones that regulate cellular activities.

What are neutral lipids?

Nonpolar energy-storage molecules that have no charged groups.

What are the two types of neutral lipids?

Oils and fats.

What is the difference between oils and fats?

Oils are liquid at biological temperatures, while fats are semisolid.

What is a fatty acid?

A molecule containing a hydrocarbon chain and a carboxyl group (—COOH) at one end.

What happens to fatty acids as chain length increases?

They become less water-soluble and more oily.

What are triglycerides made of?

One glycerol molecule and three fatty acid side chains.

How are triglycerides formed?

By dehydration synthesis between glycerol and three fatty acids.

What type of bond joins glycerol and fatty acids?

An ester linkage.

Which groups participate in triglyceride formation?

The —COOH group of a fatty acid and the —OH group of glycerol.

Why is a triglyceride nonpolar?

The polar groups of glycerol are eliminated during its formation.

What is the primary function of triglycerides in animals?

Energy storage.

How does the energy content of triglycerides compare to carbohydrates?

Triglycerides store more than twice the calories per gram.

How do triglycerides help mammals and birds?

They provide insulation.

How do triglycerides help bird feathers?

They help make feathers waterproof.

What is a saturated fatty acid?

A fatty acid with the maximum number of hydrogen atoms and only single bonds between carbon atoms.

Where are saturated fats commonly found?

Solid animal fats, such as butter.

What is a monounsaturated fatty acid?

A fatty acid with one double bond.

What is a polyunsaturated fatty acid?

A fatty acid with more than one double bond.

Why are unsaturated fatty acids more fluid?

Double bonds cause bends in the hydrocarbon chains.

At biological temperatures, how do unsaturated fats compare to saturated fats?

Unsaturated fats are generally more fluid.

What are phospholipids composed of?

Glycerol, two fatty acids, and a phosphate group.

What part of a phospholipid is nonpolar?

The two fatty acid tails.

What part of a phospholipid is polar?

The phosphate-containing head.

What do phospholipids form?

Biological membranes.

What is a phospholipid bilayer?

A film of phospholipids two molecules thick that forms the structural basis of membranes.

In a phospholipid bilayer, where do the hydrophilic heads face?

Toward the surrounding water.

In a phospholipid bilayer, where do the hydrophobic tails face?

Inward toward each other, away from water.

What is a micelle?

A structure in which lipid molecules have hydrophilic heads facing water and hydrophobic tails pointing away from water.

How are waxes formed?

Fatty acids combine with long-chain alcohols or hydrocarbon structures.

What is a function of waxes in animals?

They protect, lubricate, and keep skin, hair, or feathers pliable.

What is a function of waxes in plants?

They form a protective exterior layer that reduces water loss and resists infective agents.

What is the basic structure of steroids?

A framework of four carbon rings.

What are sterols?

Common steroids with a single polar OH group and a nonpolar hydrocarbon region.

What is cholesterol's role?

It is an important component of animal cell membranes.

What are phytosterols?

Sterols found in plant cell membranes.

What do steroid hormones regulate?

Development, behavior, and many internal biochemical processes.

What are the two major nucleic acids?

DNA and RNA.

What is the monomer of nucleic acids?

A nucleotide.

What type of bond links nucleotides together?

A phosphodiester bond.