Chapter 5 The Structure and Function of Large Biological Molecules

Enzyme molecules require a specific shape to perform their catalytic function. Which of the following might alter the shape of an enzymatic protein?

A change in salt concentrations or pH Heating the protein Treating the protein with a chemical that breaks hydrogen bonds Denaturing the protein All of the above!

Which of the following represents a specific description of a polypeptide?

A polypeptide is a chain of amino acids that have been linked together by dehydration reactions.

What do Alzheimer's, Parkinson's, and mad cow disease have in common?

All are associated with the buildup of misfolded proteins in cells

Which of the following is true regarding complementary base pairing in DNA and RNA molecules?

Although the base pairing between two strands of DNA in a DNA molecule can be thousands to millions of base pairs long, base pairing in an RNA molecule is limited to short stretches of nucleotides in the same molecule or between two RNA molecules. Complementary base pairing provides an accurate way to synthesize a new DNA molecule from an existing one and gives RNA molecules particular three-dimensional shapes necessary for their function.

Which of the following molecules is a monosaccharide

C6H12O6 Monosaccharides have molecular formulas that are multiples of CH2O

Which of the following components of a tossed salad will pass through the human digestive tract and be digested the least?

Cellulose (in the lettuce) Cellulose contains glycosidic linkages that cannot be broken by human digestive enzymes.

High cholesterol levels are considered a major risk factor for heart disease. If it is so bad for humans, why does the body make cholesterol in the first place?

Cholesterol is the precursor for many important molecules such as sex hormones; cholesterol is important to form other hormones

The type of bond that forms to join monomers (such as sugars and amino acids) into polymers (such as starch and proteins) is a(n) __________ bond

Covalent bonds

A shortage of phosphorus in the soil would make it especially difficult for a plant to manufacture __________

DNA

When a protein is denatured, why does it lose its functionality?

Denaturation breaks the intramolecular bonds, such as hydrogen bonds and van der Waals interactions, that hold the protein in its three-dimensional shape. Without the proper shape, the protein cannot function. Denaturation disrupts secondary, tertiary, and quaternary protein structure, causing the protein to lose its form, and thus its function.

Nutritionally, saturated triacylglycerols are considered to be less healthful than unsaturated triacylglycerols. What is the difference between them?

For carbon skeletons of equal length, saturated triacylglycerols have more hydrogen atoms than unsaturated triacylglycerols do. Saturated triacylglycerols are saturated with hydrogen atoms

The sex hormones estradiol and testosterone belong to which class of molecules?

Lipids Steroids, such as estradiol and testosterone, are lipids based on their insolubility in water. The molecules are characterized by a carbon skeleton consisting of four fused rings of carbon atoms

Generally, animals cannot digest (hydrolyze) the glycosidic linkages between the glucose molecules in cellulose. How then do cows get enough nutrients from eating grass?

Microorganisms in their digestive tracts hydrolyze the cellulose to individual glucose units

Which of the following is a true statement comparing phospholipids and triacylglycerols (fats and oils)?

Phospholipid molecules have a distinctly polar "head" and a distinctly nonpolar "tail," whereas triacylglycerols are predominantly nonpolar Triacylglycerols consist of three (nonpolar) fatty acid tails attached to a glycerol molecule. Phospholipids have two fatty acid tails and a hydrophilic head containing a negatively charged phosphate group.

Which of the following describes a difference between DNA and RNA?

RNA molecules generally consist of a single polynucleotide chain, whereas DNA molecules generally consist of two polynucleotide chains organized into a double helix. Both molecules contain adenine, guanine, and cytosine, but DNA also contains thymine and RNA also contains uracil. They contain different sugars.

n what polysaccharide form do plants store glucose to be available later as an energy source?

Starch Starch is a glucose storage polymer in plants.

Amylase is an enzyme that breaks down starch. Why can the same enzyme not break down cellulose?

The monosaccharide monomers in cellulose are bonded together differently than those in starch. The glucose monomers in cellulose are bonded in a β glycosidic linkage, whereas those in starch have an α glycosidic linkage. The enzyme amylase is specific for the α glycosidic linkage

Which of the following lists ranks these molecules in the correct order by size from smallest to largest?

Water, glucose, sucrose, protein

If a small droplet of triacylglycerol molecules is suspended in water, the fat molecules form a "ball of spaghetti" with no particular orientation. But if a droplet of phospholipid molecules is put in water, all the molecules point outward, toward the water. Phospholipids are forced into this orientation because phospholipids have __________.

a charged or polar end and an uncharged or nonpolar end The nonpolar hydrocarbon tails of phospholipids are hydrophobic—that is, they are excluded from water. The negatively charged phosphate group and its attachments form a hydrophilic head that is attracted to water.

A glucose molecule is to starch as __________

a nucleotide is to a nucleic acid Nucleotides are the monomers that make nucleic acid polymers, just as glucose is the monosaccharide (monomer) from which starch (polymer) is constructed.

In a hydrolosis reaction,

a polymer is broken up into monomers, and water in consumed

Manufacturers make vegetable oils solid or semisolid at room temperature by __________

adding hydrogen atoms to the fatty acid hydrocarbon chains, thereby converting carbon-carbon double bonds to single bonds he phrase hydrogenated vegetable oils found on food labels means that unsaturated fats have been synthetically converted to saturated fats by the addition of hydrogen.

Lipids differ from other large biological molecules in that they __________

are not truly polymers Lipids are not all made of the same type of monomer. Their association as a group (fats, phospholipids, and steroids) is related to their solubility behavior

At a conference, the speaker's grand finale was sautéing mealworms (insect larvae) in butter and serving them to the audience. They were crunchy (like popcorn hulls) because their exoskeletons contain the polysaccharide __________

chitin Chitin is the structural polysaccharide found in arthropod exoskeletons.

The peptide bond is __________

covalent bond joining two amino acids to form a polypeptide

Which reaction links monomers to form polymers?

dehydration reaction

One characteristic shared by sucrose, lactose, and maltose is that __________

disaccharide a disaccharide consists of two monosaccharides joined together by a glycosidic linkage.

Carbohydrates are used in our bodies mainly for __________

energy storage and release Simple sugar molecules, stored in polysaccharides such as glycogen in animals and starch in plants, are a major energy source for cellular work.

Some lipids are formed when fatty acids are linked to glycerol. These subunits are linked together by __________

ester linkages In making a fat, each of the three fatty acid molecules is bonded to a glycerol molecule by an ester linkage type of covalent bond.

A polysaccharide that is used for storing energy in human muscle and liver cells is __________

glycogen Humans and other vertebrates store glucose as a polysaccharide called glycogen in their liver and muscles

The α helix and β pleated sheet represent which level of protein structure?

secondary structure Both the α helix and the β pleated sheet are localized regions of polypeptides held in a given structure by hydrogen bonds.

The polysaccharide that you are most likely to have eaten recently is __________

starch Starch is a storage polysaccharide found especially in certain plant tissues

Carbohydrates can function in which of the following ways?

structural support and energy storage Carbohydrates function as both storage molecules (starch, glycogen) and structural support molecules (cellulose)