Chapter 5: structure and function of large biological molecules

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.

Carbohydrates can function in which of the following ways?

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

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.

Which of the following is the major energy storage compound of plant seeds?

Correct Answer: oils No. Cellulose is a polysaccharide.

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.

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.

What is a distinguishing feature of most naturally occurring unsaturated fats?

Nearly all naturally occurring unsaturated fats have cis double bonds. Unsaturated fats with trans double bonds are formed in the industrial process of hydrogenating unsaturated plant oils.

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 non polar. 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.

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

The monosaccharide monomers in cellulose are bonded together differently than those in starch. Correct. 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.

what is the tertiary structure determined by

The tertiary structure is determined by hydrogen bonds, hydrophobic R groups, ionic bonds between R groups, van der Waals interactions, and disulfide bridges.

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 peptide bond is __________.

a covalent bond joining amino acids together to form a polypeptide

Which of the following lists represents the chemical components of a nucleotide?

a nitrogenous base, a phosphate group, and a pentose sugar No. Nucleotides do not contain amino acids.

Based on complementary base pairing, you would expect the percentage of __________ to be equal to the percentage of __________.

adenine ... thymine

Lipids differ from other large biological molecules in that they __________.

are not truly polymers

which of the following is a polymer

cellulose, a plant cell wall component

Which type of protein shields a newly forming protein from cytoplasmic influences while it is folding into its functional form?

chaperonins

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

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

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

ester linkages

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

glycogen

The subunits (monomers) in cellulose are linked together by __________.

glycosidic linkages

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

lipids

The lipids that form the main structural component of cell membranes are __________.

phospholipids

Cellulose is a __________ made of many __________.

polymer ... glucose molecules

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

secondary structure

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

starch

In a 1-4 glycosidic linkage, __________.

the number 1 carbon in one monosaccharide is bound to the number 4 carbon in another monosaccharide

The "primary structure" of a protein refers to __________.

the sequence of amino acids along a polypeptide chain

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

they are all disaccharides

Which of the following are pyrimidines found in the nucleic acid DNA?

thymine and cytosine