NAS2 Part 7 Review

Which four major classes of organic compounds are essential to human structure and function?

Carbohydrates, lipids, proteins, and nucleotides/nucleic acids.

Why are carbohydrates, lipids, proteins, and nucleic acids classified as organic compounds?

They contain carbon bonded with hydrogen.

Why can carbon form so many different stable biological molecules?

Carbon has four valence electrons and can form four covalent bonds with carbon, hydrogen, oxygen, nitrogen, and other atoms.

True or false: Carbon normally completes its valence shell by gaining or losing four electrons.

False. Carbon usually completes its valence shell by sharing electrons in covalent bonds.

What is a carbon skeleton?

A chain or framework of covalently bonded carbon atoms that forms the core of an organic molecule.

What is a hydrocarbon?

A grouping or region made only of carbon and hydrogen.

How does a hydrocarbon-rich region usually affect a molecule’s interaction with water?

It tends to make that region nonpolar and hydrophobic.

What is a functional group?

A covalently bonded group of atoms that tends to act as a single unit in chemical reactions.

Name the five functional groups emphasized in Section 2.5.

Hydroxyl, carboxyl, amino, methyl, and phosphate.

Which functional group is written as —OH?

The hydroxyl group.

Why are hydroxyl groups important in biological molecules?

They are polar, occur in all four major organic-compound classes, and participate in dehydration synthesis and hydrolysis.

Which functional group contains a carbon double-bonded to oxygen and single-bonded to hydroxyl?

The carboxyl group (—COOH).

Where are carboxyl groups commonly found?

In fatty acids, amino acids, and many other acids.

Which functional group is written as —NH2?

The amino group.

What major biological monomers contain amino groups?

Amino acids, the monomers of proteins.

Which functional group is written as —CH3?

The methyl group.

Which functional group is found in phospholipids and nucleotides?

The phosphate group.

Which two functional groups give amino acids both acidic and basic properties?

The acidic carboxyl group and the basic amino group.

What is a macromolecule?

A large molecule.

What is a monomer?

A single molecular subunit that can join with similar units.

What is a polymer?

A large molecule made of many covalently linked monomers.

During dehydration synthesis, what does each of two joining monomers contribute?

One contributes hydrogen and the other contributes hydroxyl; these form water as the covalent bond forms.

How do dehydration synthesis and hydrolysis differ?

Dehydration synthesis removes water to join monomers; hydrolysis adds water to split polymers or larger molecules.

True or false: Hydrolysis produces a polymer and releases water.

False. Hydrolysis uses water to break a larger molecule into smaller units.

What elements make up carbohydrates?

Carbon, hydrogen, and oxygen.

What is the general formula for many carbohydrates?

(CH2O)n.

What does the term saccharide mean?

Sugar.

Distinguish monosaccharides, disaccharides, and polysaccharides.

Monosaccharides are single sugar monomers; disaccharides contain two monosaccharides; polysaccharides contain many monosaccharides.

What is a monosaccharide?

A single sugar unit and the monomer of carbohydrates.

Which three important monosaccharides are hexoses?

Glucose, fructose, and galactose.

Which two important monosaccharides are pentoses?

Ribose and deoxyribose.

How do hexose and pentose sugars differ?

Hexoses contain six carbon atoms; pentoses contain five.

A diagram shows glucose, fructose, galactose, ribose, and deoxyribose. Which are the six-carbon sugars?

Glucose, fructose, and galactose.

In Figure 2.18, which sugars are directly associated with nucleotides?

Ribose and deoxyribose.

What is a disaccharide?

A carbohydrate made of two monosaccharides.

What is a glycosidic bond?

The covalent bond linking sugar monomers.

How is a disaccharide formed?

Two monosaccharides join by dehydration synthesis, creating a glycosidic bond and releasing water.

What is the common name for sucrose?

Table sugar.

What is the common name for lactose?

Milk sugar.

What is the common name for maltose?

Malt sugar.

Why must dietary disaccharides be digested before body cells can use them?

They must be hydrolyzed into absorbable monosaccharides.

What common process forms sucrose, lactose, and maltose in Figure 2.19?

Dehydration synthesis.

What happens when water encounters a glycosidic bond during digestion?

Hydrolysis breaks the bond and separates the monosaccharides.

What is a polysaccharide?

A carbohydrate polymer containing many monosaccharides.

What are the three polysaccharides emphasized in this section?

Starch, glycogen, and cellulose/fiber.

What is starch?

A plant storage polysaccharide made of glucose.

How do amylose and amylopectin differ?

Amylose forms long unbranched chains; amylopectin forms branched chains.

What is glycogen?

The highly branched animal storage polymer of glucose.

Where is glycogen stored in the human body?

Primarily in the liver and skeletal muscles.

True or false: Glycogen is a major dietary carbohydrate obtained from meat.

False. Little glycogen remains in animal tissues after slaughter; the body makes and stores its own glycogen.

What is cellulose?

A glucose polysaccharide that forms the primary structural component of plant cell walls.

What common dietary term refers to cellulose in plant foods?

Fiber.

Why does cellulose supply little or no usable glucose to humans?

Humans lack enzymes that digest its glycosidic bonds.

List three benefits associated with dietary fiber.

It promotes fullness, supports digestive-tract health, and may reduce risk of heart disease and some cancers.

A carbohydrate diagram shows a plant storage polymer, an animal storage polymer, and plant structural fiber. Identify them.

Starch, glycogen, and cellulose, respectively.

What foods provide most dietary carbohydrates?

Plant foods such as grains, fruits, legumes, and vegetables; dairy supplies lactose.

Which cells are especially dependent on glucose as fuel according to the section?

Neurons and red blood cells.

What is the principal immediate-energy product made when cells break down glucose?

ATP.

What are the major products when glucose reacts with oxygen during cellular respiration?

Carbon dioxide, water, and ATP.

How does oxygen availability affect ATP production from glucose?

Pathways using oxygen produce more ATP than pathways that do not use oxygen.

How can carbohydrates contribute to cell-membrane structure?

They attach to proteins to form glycoproteins and to lipids to form glycolipids.

What is a lipid?

A diverse organic compound composed mostly of hydrocarbons and generally hydrophobic.

Why are most lipids hydrophobic?

Their large nonpolar hydrocarbon regions do not interact favorably with water.

What is an emulsion?

A mixture of liquids or solutions that do not mix well, such as lipid droplets dispersed in water.

What is a triglyceride?

A lipid made of one glycerol molecule bonded to three fatty acids.

What forms the three-carbon backbone of a triglyceride?

Glycerol.

What is a fatty acid?

A long hydrocarbon chain with a carboxyl group at one end and a methyl group at the other.

How many water molecules are released when one triglyceride forms from glycerol and three fatty acids?

Three water molecules.

Describe triglyceride formation by dehydration synthesis.

Each of glycerol’s three hydroxyl sites reacts with a fatty acid carboxyl group, forming three covalent linkages and releasing three waters.

What is a saturated fatty acid?

A fatty acid with no carbon-carbon double bonds and the maximum number of hydrogens.

What is a monounsaturated fatty acid?

A fatty acid with one carbon-carbon double bond.

What is a polyunsaturated fatty acid?

A fatty acid with two or more carbon-carbon double bonds.

How do saturated and unsaturated fatty-acid shapes differ?

Saturated chains are relatively straight; cis unsaturated chains are kinked at double bonds.

Why are saturated fats often solid at room temperature?

Their straight chains pack tightly together.

Why are many unsaturated fats liquid at room temperature?

Double-bond kinks prevent tight packing.

In Figure 2.22, which chain would appear straight: saturated or unsaturated?

Saturated.

What defines an omega-3 fatty acid?

Its first carbon-carbon double bond occurs at the third carbon from the methyl, or omega, end.

Name a food source emphasized for omega-3 fatty acids.

Cold-water fish such as salmon.

How are many trans fats produced?

By partially hydrogenating unsaturated oils.

True or false: Trans fats are generally considered safer for the cardiovascular system than saturated fats.

False. The section describes trans fats as potentially even more harmful.

What major role do stored triglycerides play at rest or during sleep?

They provide much of the energy used to sustain life.

What type of activity relies substantially on triglycerides?

Long-duration, lower-intensity activity such as hiking or gardening.

Which vitamins depend on dietary fat for absorption and transport?

Vitamins A, D, E, and K.

Besides energy storage, what two protective roles does adipose tissue perform?

It cushions organs and bones and insulates the body to conserve heat.

What is a lipoprotein?

A particle in which hydrophobic lipids are packaged within proteins for transport through body fluids.

What is a glycolipid?

A carbohydrate-lipid compound found in cell membranes.

What is a phospholipid?

A lipid with glycerol, two fatty acids, and a phosphate-containing polar head.

How does a phospholipid differ structurally from a triglyceride?

A phospholipid has two fatty acids and a phosphate-containing head; a triglyceride has three fatty acids.

Which parts of a phospholipid are hydrophilic and hydrophobic?

The charged phosphate-containing head is hydrophilic; the fatty-acid tails are hydrophobic.

Why can phospholipids form cell-membrane bilayers?

Their hydrophilic heads interact with water while their hydrophobic tails cluster away from water.

Which lipid in Figure 2.23 has two fatty-acid tails and a phosphate-containing head?

A phospholipid.

What structural feature defines a steroid or sterol?

Four fused hydrocarbon rings.

What is the most important sterol in human structure and function?

Cholesterol.

Where is cholesterol synthesized in the human body?

Primarily in the liver.

How does cholesterol contribute to digestion?

It is used to make bile acids that emulsify dietary fats.

How does cholesterol contribute to endocrine function?

It serves as a building block for many steroid hormones.

What role does cholesterol play in cell membranes?

Its hydrophilic and hydrophobic regions help regulate membrane properties and movement of substances.

What is a prostaglandin?

A locally acting signaling molecule derived from unsaturated fatty acids.

What processes can prostaglandins help regulate?

Blood pressure, inflammation, and pain sensitivity.

How do NSAIDs reduce pain and inflammation?

They reduce the production or effects of prostaglandins.