Ch. 03 - The Macromolecules of the Cell (Homework Set)

Several different kinds of bonds or interactions are involved in generating and maintaining the structure of proteins. List five such bonds or interactions.

-peptide bond -hydrogen bond -hydrophobic bond -ionic bond -disulfide bond

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.

1' ... 5'

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

A; T

List the Purines

Adenine and Guanine

Many cell biologists claim that monosaccharides are older (chronologically and evolutionarily) than nucleotides. Which of the following observations supports this hypothesis? -Nucleotides have more chemically complicated structures than monosaccharides. -All nucleotides contain monosaccharides. -Monosaccharides are metabolized by cells to make nucleotides (i.e., glucose is metabolized by the enzymes of glycolysis to make ATP). -All of the other answer choices support this hypothesis.

All of the other answer choices support this hypothesis.

Trans fats -resemble saturated fatty acids in shape. -are present in small amounts in meat and dairy products. -are unsaturated fatty acids. -are associated with an increased risk of heart disease. -All of these statements are true

All of these statements are true

The primary structure of a protein -is simply the order of amino acids from one end of the protein to another. -is the linear sequence of amino acids that are linked together by peptide bonds. -is important for determining the secondary and tertiary structure of a protein. -is important both genetically and structurally. -All of these statements are true.

All of these statements are true.

Which of these illustrates the secondary structure of a protein?

Alpha helices and beta pleated sheets are characteristic of a protein's secondary structure.

What is the difference between a DNA nucleotide and an RNA nucleotide?

DNA has a sugar with two, and not three, oxygen atoms

Which of these is a difference between a DNA and an RNA molecule? -DNA contains nitrogenous bases, whereas RNA contains phosphate groups. -DNA contains five-carbon sugars, whereas RNA contains six-carbon sugars. -DNA contains uracil, whereas RNA contains thymine. -DNA is a polymer composed of nucleotides, whereas -RNA is a polymer composed of nucleic acids. -DNA is double-stranded, whereas RNA is single-stranded.

DNA is double-stranded, whereas RNA is single-stranded.

Two proteins associated with a rare neurodegenerative disorder have been sequenced. Protein A contains many polar amino acids with small regions containing nonpolar, hydrophobic amino acids. Protein B is rich in nonpolar, hydrophobic amino acids with only two small regions containing polar amino acids. What might this suggest about the two proteins?

Protein A may be a cytoplasmic protein and Protein B may be a membrane associate protein.

Which of the following is true of purines?

Purines have a double-ringed structure.

What is the difference between a purine and a pyrimidine?

Pyrimidines are single ring structures

The chemical nature of each amino acid is determined by which of the following groups?

R

Which of the following statements is the most accurate reflection of native protein tertiary structure?

Tertiary structure is the overall three-dimensional shape of a protein. It is determined by hydrogen bonds, interactions between hydrophobic R groups, ionic bonds between R groups, van der Waals interactions, and disulfide bridges.

Cellulose, chitin, and the polysaccharide that makes up the cell walls of many bacteria are the structural polysaccharides, whereas starch and glycogen are the main storage polysaccharides. What must be true about these two classes of polysaccharides?

The alpha-glycosidic bonds of storage polysaccharides are less stable than the beta-glycosidic bonds of structural polysaccharides.

Sickle-cell anemia is a striking example of the drastic effect a single amino acid substitution can have on the structure and function of a protein. Given the chemical nature of glutamate and valine, can you suggest why substitution of valine for glutamate at position 6 of the β chain would be especially deleterious?

The amino acid glutamate is hydrophilic and ionizes at cellular pH, whereas valine is hydrophobic and nonionic.

You are researching a cytoplasmic protein associated with a nerve disorder. The native form of the enzyme appears to be globular protein; however, when a sample of the purified protein is treated with a chemical that reduces disulfide bonds, the enzymatic activity decreases dramatically and multiple globular proteins can be detected in the sample. What does this tell you about the protein?

The protein is most likely composed of multiple polypeptide chains that are held together by disulfide bonds.

What nitrogenous base is found in DNA but not RNA

Thymine

The term amphipathic describes the characteristic of some molecules that have ________.

both a polar and a nonpolar region

Cellulose belongs to which of the following groups of macromolecules?

carbohydrates

Which of the following is not a major functional class of proteins? -structural proteins -motility proteins -regulatory proteins -enzymes -hereditary proteins

hereditary proteins

To which of the following classes of sugars does glucose belong?

hexose

The secondary structure of a protein results from _____.

hydrogen bonds

The two strands of DNA are held together by ________; thus ________.

hydrogen bonds; double-stranded DNA separates into two separate strands at high temperatures

Which of the following contributes to the stability of the DNA double helix?

hydrophobic interactions between aromatic bases at the center of the double helix

What are the three general types of amino acids?

hydrophobic, polar (noncharged), polar (charged)

RNA and DNA differ

in that RNA contains ribose and uracil, and DNA contains deoxyribose and thymine.

A peptide bond

is a covalent bond between the carboxyl carbon of one amino acid and the amino nitrogen of a second amino acid.

What kind of sugar is in RNA

ribose

Hydrogen bonding is most important in stabilizing the ________ structure of many proteins.

secondary

Choose amino acids that would be much less likely than valine to cause impairment of hemoglobin function if substituted for the glutamate at position 6 of the β chain.

serine, threonine, tyrosine, cysteine, aspartate

Cholesterol is a ________, which ________.

steroid; is a component of eukaryotic membranes and is the basis for many animal and plant hormones

Disulfide bonds are often found to stabilize which of the following levels of protein structure?

tertiary

A general trend in the structure of many biomolecules is

that the order and bonding of monomers form the basis for the secondary and tertiary structure of the polymer.

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine

The function of triglycerides is

to store energy.

Which of the following is found exclusively in RNA?

uracil

The "permanent" wave that your local beauty parlor offers depends critically on rearrangements in the extensive disulfide bonds of keratin that give your hair its characteristic shape. To change the shape of your hair (that is, to give it a wave or curl), the beautician first treats your hair with a sulfhydryl reducing agent, then uses curlers or rollers to impose the desired artificial shape, and follows this by treatment with an oxidizing agent. Why do you suppose a permanent isn't permanent?

-Disulfide bonds occasionally break and re-form spontaneously, allowing the hair proteins to return gradually to their original, thermodynamically more favorable shape. -Hair continues to grow, and the new α-keratin molecules will have the natural (correct) disulfide bonds.

List Pyrimadines

-Thymine -Uracil -Cytosine

Nucleic acids are assembled in the _____ direction.

5' to 3'

Which of the following accurately describes the structure of fibrous proteins?

Fibrous proteins are usually composed of either α helices or β sheets throughout the molecule, giving them a highly ordered, repetitive structure.

The "permanent" wave that your local beauty parlor offers depends critically on rearrangements in the extensive disulfide bonds of keratin that give your hair its characteristic shape. To change the shape of your hair (that is, to give it a wave or curl), the beautician first treats your hair with a sulfhydryl reducing agent, then uses curlers or rollers to impose the desired artificial shape, and follows this by treatment with an oxidizing agent. What is the chemical basis of a permanent?

Hair proteins are first treated with a sulfhydryl reducing agent to break disulfide bonds and thereby destroy much of the natural tertiary structure and shape of the hair. After being set in the desired shape, the hair is treated with an oxidizing agent to allow the bonds to re-form between different cysteine groups, as determined by the positioning imposed by the curlers.

You are investigating the structure of the seeds of a newly discovered tropical plant. There is storage material inside the seed. You treat the seed with peptidase (an enzyme that breaks peptide bonds), glycoside hydrolases (an enzyme that breaks β glycosidic bonds), and amylase (an enzyme that breaks α glycosidic bonds). Only the amylase appears to dissolve the storage material in the seed. What does this tell you about the identity of the storage material?

The seed contains starch to store carbon and energy.

A cotton fiber consists almost exclusively of cellulose, whereas a potato tuber contains mainly starch. Cotton is tough, fibrous, and virtually insoluble in water. The starch present in a potato tuber, on the other hand, is neither tough nor fibrous and can be dispersed in hot water to form a turbid solution. Yet both the cotton fiber and the potato tuber consist primarily of polymers of D-glucose in (1→4) linkage. How can two polymers consisting of the same repeating subunit have such different properties?

The two polymers have very different properties because they differ in structure as a result of differing 1→4 linkages between glucose monomers. The β(1→4) linkage of cellulose gives it a rigid, fibrous structure not seen in starch, which has an α(1→4) linkage between glucose monomers.

Can you suggest an explanation for naturally curly hair?

There is probably a genetic difference in the positioning of cysteine groups and hence in the formation of disulfide bonds.

For each of the following features of nucleic acids, indicate whether it is true of DNA only, of RNA only, of both DNA and RNA, or of neither. -Contains the nucleotide deoxythymidine monophosphate. -Contains the base adenine. -Occurs only in single-stranded form. -Is involved in the process of protein synthesis in the cytoplasm of the cells in the liver. -Is an inherently directional molecule, with an N-terminus on one end and a C-terminus on the other end.Is an inherently directional molecule, with an N-terminus on one end and a C-terminus on the other end. -Is synthesized by a process that involves base pairing.

True of DNA only: -Contains the nucleotide deoxythymidine monophosphate. True of RNA only: -Is involved in the process of protein synthesis in the cytoplasm of the cells in the liver. True of both DNA and RNA -Contains the base adenine. -Is synthesized by a process that involves base pairing. True of Neither -Occurs only in single-stranded form.*** (is true of RNA but the system has this marked as correct) -Is an inherently directional molecule, with an N-terminus on one end and a C-terminus on the other end.Is an inherently directional molecule, with an N-terminus on one end and a C-terminus on the other end.

Is it possible that two proteins could differ at several points in their amino acid sequence and still be very similar in structure and function?

Yes, if the substitutions are always of like-for-like amino acids in terms of chemical properties.

A discrete, locally folded unit of protein tertiary structure usually having a specific function best describes __________.

a domain

The components of a nucleotide are

a five-carbon sugar, a phosphate group, and a nitrogen-containing aromatic base.

Which of the following is not a polymer of numerous monomer units? -cellulose -starch -a phospholipid -an RNA molecule -a polypeptide

a phospholipid

Proteins are polymers of _____.

amino acids

Which of the following has the greatest number of glycosidic bonds?

amylose

The rigid, fibrous structure of _________________________ and its virtual ________________________ in water makes this polymer a suitable ___________________________________________________, and the __________ flexible structure of __________________ and its __________________ solubility in water makes this polymer a suitable ___________________________________________.

cellulose; insolubility; component of the plant cell wall; more; starch; greater; storage macromolecule.

What kind of sugar is in DNA

deoxyribose

In eukaryotic cells DNA has the appearance of a _____.

double helix

Fatty acids are ________; they function in the cell as ________.

long, unbranched hydrocarbon chains with a carboxyl group at one end; building blocks for other lipids

DNA is composed of building blocks called _____.

nucleotides

Which of the following pairs correctly matches the monomer with its polymer?

nucleotides; nucleic acids

What are the components of a nucleotide?

pentose sugar, a nitrogenous base, and a phosphate group

What type of bond joins the monomers in a protein's primary structure?

peptide

Tertiary structure is NOT directly dependent on _____.

peptide bonds

Which of the following is not a steroid?

phenylalanine

The nucleoside triphosphate molecules in DNA are linked together in the 5'→3' by a(n) ________ bridge

phosphodiester