Chapter 2 Quiz Practice

Nucleic acids are polymers of

nucleotides. Note: Nucleic acids such as DNA and RNA are polymers of nucleotides. Polysaccharides are polymers of monosaccharides, triglycerides are made up of fatty acids bound to glycerol, and proteins are composed of amino acids.

What type of bond will connect the amino acids in a protein?

peptide Note: A peptide bond will connect the amino acids together to form a protein. The atoms associate with a peptide bond unevenly because the oxygen is more electronegative than nitrogen.

Which of the following types of lipids is the most abundant constituent of cell membranes?

phospholipid Note: Phospholipids are the most abundant type of lipids in cell membranes. Animal cells also have cholesterol in their membranes, but it is less abundant than phospholipids. Triglycerides, also known as neutral fats or simply fats, are energy-storage molecules, not structural molecules.

The lower the pH

the more acidic the solution. Note: The pH scale is based on hydrogen ion (H+) concentration. The higher the concentration of H+ (and the lower the concentration of OH-, hydroxide), the lower the pH, and the more acidic the solution.

Which of the following molecules is NOT a compound?

H2 Note: A compound consists of atoms of two or more different elements bound together; H2 is two molecules of the same element (hydrogen) bound together.

Potassium, a metal with one electron in the outermost shell, will react with how many chlorine atoms? (Chlorine is a nonmetal with seven electrons in the outermost shell.)

1(one) Note: Potassium will attain stability by transferring the one electron in its outermost shell to chlorine, which needs only one more electron in its outermost shell to become stable. The result will be a potassium ion (K+) and a chloride ion (Cl-). The two oppositely charged ions will be attracted to one another, thus forming an ionic compound.

One carbon atom can form covalent bonds with up to ________ other atoms to form an organic molecule.

4(four) Note: Carbon, with an atomic number of 6, has 4 electrons in its outermost shell. Thus, carbon can form 4 single covalent bonds with other atoms.

The pH of blood is slightly basic. Which of the following would therefore be an expected pH for blood?

7.4 Note: The pH scale ranges from 0 to 14, with 7 being neutral. Numbers lower than 7 are acidic, and those higher than 7 are basic. Thus, a pH of 7.4 would be slightly basic.

Which statement regarding acids and bases is correct?

Acids increase the proportion of hydrogen ions (H+), and bases reduce the proportion of H+. Note: Acids raise the hydrogen ion (H+) content of a solution, while bases reduce the proportion of H+. The lower the pH, the more acidic the solution, and the higher the pH, the more basic the solution. Strong acids and bases are both harmful. When acids combine with bases, salts result.

Which of the following is not a function of ATP within the cell?

All of the answer choices are functions of ATP within the cell.: energy currency of the cell synthesis of macromolecules conduction of nerve impulses contraction of muscle cells

________ is a polysaccharide that is found in plant cell walls and accounts for their strength.

Cellulose

Which functional groups are associated with a dehydration reaction?

H and OH Note: H and OH are associated with the dehydration reactions.

Which of the following is not a property of water that results from hydrogen bonding?

Ice melts at -100°C. Note: Due to its hydrogen bonding, water melts at 0°C instead of -100°C. All the other answer choices are accurate statements.

During the formation of a polymer, two monomers are joined by the removal of

OH and H. Note: Polymers are formed when H and OH are removed from the monomers during a dehydration reaction. COH, SH, NHH, and COOH are all functional groups.

Which of the following statements is NOT true of chemical bonds?

Table salt (NaCl) is covalently bonded. Note: Salts, such as sodium chloride (NaCl), are ionic compounds. All the other answer choices are accurate statements.

Rain falling in the northeastern U.S. has a pH between 5.0 and 4.0. Normally, rainwater has a pH of about 5.6. Which of the following statements is not correct?

The pH of the rainwater has changed from neutral to acidic. Note: The pH of rainwater is normally acidic (5.6) not neutral (7). All the other answer choices are accurate statements.

Determine what would happen to an individual's proteins if they developed a fever of 103∘ F for several days.

The proteins would denature due to the increase in body temperature and would become unable to function correctly.

Hydrogen bonding produces which of the following properties of water?

Water is less dense as ice than as liquid water. Note: Due to the increased stability of hydrogen bonding at lower temperatures, water is less dense as ice than as liquid water. Water can absorb and release heat, but with a relatively small change in temperature. Due to hydrogen bonding, water boils at 100°C; without hydrogen bonding, it would boil at -91°C.

The moon lacks life and varies dramatically in temperature. If we could keep a layer of water spread on the surface of the moon, what effect would it have?

Water would absorb and hold heat and moderate the temperature extremes. Note: Water has a high heat capacity; this serves to moderate temperature changes. Although water does have a high heat of vaporization, this also has a moderating effect, and would prevent temperatures from rising to the highest extremes.

If an element has an atomic number of 15, then

a neutral atom has 15 electrons. Note: In an electrically neutral atom, the number of protons (the atomic number) is the same as the number of electrons. The atom would need three orbitals to accommodate 15 electrons, and there would be 5 electrons in its outermost shell. The atomic mass includes the protons and the neutrons; the number of neutrons is not specified in this question.

A covalent bond is

a sharing of electrons between two atoms. Note:A covalent bond results when two atoms share electrons in such a way that each atom has eight electrons in its outermost shell. In contrast, ionic compounds result from the complete transfer of electrons between bonded atoms.

When two glucose molecules combine they form a disaccharide molecule and

a water molecule. Note: Glucose is a monosaccharide (a carbohydrate monomer); two glucose molecules combine to form a disaccharide, not a dipeptide or a lipid. In the process, a water molecule is released, which is why this is called a dehydration reaction.

Aspirin is acetyl salicylic acid and can therefore pose a problem to people who have ulcers. Bufferin is an alternative to aspirin that uses a buffer to neutralize this effect by

adding chemicals that take up excess hydrogen (H+) ions. Note: Bufferin contains a buffering system to bind the excess H+ from the aspirin (acetyl salicylic acid). This would not be a salt; salts form when acids and bases react.

The backbone of a nucleic acid strand is composed of

alternating pentose sugars and phosphate groups. Note: The backbone of a nucleic acid such as DNA is composed of alternating pentose sugars and phosphate groups. Glycerol is the backbone of a triglyceride. Although nitrogenous bases such as adenine and thymine are part of DNA, they do not make up the backbone. R groups are part of amino acids, not nucleotides.

Organic molecules

always contain carbon (and usually hydrogen). Note: none

Since pure water is neutral in pH, it contains

an equal number of hydrogen ions (H+) and hydroxide ions (OH-). Note: Pure water is neutral, with a pH of 7 (midway between 0 and 14 on the pH scale), meaning that it has equal concentrations of hydrogen ions (H+) and hydroxide ions (OH-).

In water, a weak hydrogen bond occurs between hydrogen in one molecule and

an oxygen atom in a different molecule. Note: Because water molecules are polar, and each oxygen has slight negative charge and the hydrogen a slight positive charge, hydrogen bonding occurs between a hydrogen atom of one water molecule and the oxygen of another.

Which of these combinations would be found in a nucleotide?

base-sugar-phosphate Note: A nucleotide is composed of a nitrogenous base, a pentose sugar, and a phosphate group. Adenine, thymine, and uracil are bases. Combining an acid and a base yields a salt. Sugars, proteins, and fats are all biological organic molecules. DNA and RNA are nucleic acids composed of nucleotides. Both are made in the nucleus of a cell.

Calcium chloride, CaCl2, is an ionic compound in which

calcium has lost two electrons. Note: In the ionic compound CaCl2, calcium has transferred two electrons from its outermost shell, becoming a calcium ion (Ca2+). One of the electrons has been accepted by each chlorine atom, so they become chloride ions (Cl-).

Maltose is classified as a

carbohydrate. Note: Maltose is classified as a carbohydrate due to its carbon and hydrogen backbone.

Two molecules of glucose combine to form a disaccharide molecule during a(n) ________ reaction.

dehydration Note: The glucose molecules are monomers; forming a covalent bond between them requires a dehydration reaction. A hydrolysis reaction could be used to break the disaccharide apart into individual glucose monomers. An inert material would not react at all.

What type of reaction is necessary to produce a dipeptide from individual amino acids?

dehydration reaction Note: Two amino acids are joined during a dehydration reaction to form a dipeptide. Hydrolysis reactions will break apart a dipeptide into individual amino acids. Denaturation is the change in shape of a protein. Dipeptides are formed from amino acids.

The final shape of a protein is very important to its function. When proteins undergo an irreversible change in shape called ________ they ________ perform their usual functions.

denaturation/cannot Note: Denaturation is when a protein loses its shape and cannot function. Although dehydration reactions do join amino acids together, this represents only the most basic (primary) level of protein structure.

A long chain of carbon atoms with hydrogen atoms attached, ending in the acidic carboxyl group would be a(n)

fatty acid. Note: A fatty acid is a hydrocarbon chain ending with a -COOH group, which is acidic; a triglyceride is composed of three fatty acids bound to glycerol. Amino acids are the monomers of proteins, and monosaccharides are carbohydrates. Nucleic acids are polymers of nucleotides such as DNA and RNA.

Which nutrient source is the easiest one for humans to break down and form ATP?

glucose Note: Glucose is the easiest substance to break down into ATP. Proteins, cellulose, phospholipids, and chitin are not easily broken down into ATP.

An ion is an atom that

has a net charge. Note: An ion has more or less electrons than a neutral atom of the same element, so it has a net positive or negative charge.

Which type of bond formation is responsible for the properties of water?

hydrogen Note: Hydrogen bonds are the attraction between the hydrogen of one water molecule and the oxygen of a second water molecule. This attraction sets up the properties of water. A polar covalent bond forms between the hydrogen and oxygen of a particular water molecule. Water doesn't form ionic or nonpolar covalent bonds.

Water is a liquid at room temperature. This is due to

hydrogen bonding between water molecules. Note: Hydrogen bonding between water molecules keeps water in a liquid state at temperatures typically found on the Earth's surface, including room temperature. Water molecules do not covalently bond to one another, and the water molecule is too small to permit intramolecular hydrogen bonds to form. Water molecules do ionize, but this does not influence the fluid nature of water.

The water strider is an insect that skates across the water without sinking. The tips of its feet must be coated with molecules that are

hydrophobic. Note: The water strider's feet should be coated with hydrophobic molecules to repel water; a hydrophilic coating would cause the insect to stick to the surface of the water and sink. Ions, acids, and bases are hydrophilic.

The atomic mass of an element

is determined by the number of protons and neutrons it contains. Note: The atomic mass is essentially the sum of protons and neutrons in the nucleus; it is not changed by chemical reactions. The mass of electrons is negligible.

If neutral atoms become positive ions, they

lose electrons. Note: The electron transfer is what will determine if an atom becomes a positive or negative ion. To become a positive ion an atom will need to lose electrons so there are more protons than electrons.

Which group of lipids will contain a barrier formed by hydrophilic heads that face outwards and hydrophobic tails that face inwards?

phospholipids Note: Phospholipids have hydrophilic heads and hydrophobic tails that will form a barrier. Steroids have a backbone of four fused carbon rings. Triglycerides is formed from three fatty acids and a glycerol. Saturated acids and trans-fatty acids are both made from hydrocarbon chains with an acidic group on the end.

The ________ structure of a protein consists of the sequence of the amino acids joined together by peptide bonds.

primary Note: Amino acids joined together by peptide bonds constitute the primary level of protein structure. In secondary structure, hydrogen bonding between amino acids causes the polypeptide to form an alpha helix or a beta pleated sheet. In tertiary structure, interactions such as covalent bonds between R groups cause the polypeptide to fold and twist. When two or more polypeptides join together, this represents a quaternary level of structure. There is no level of protein structure termed the molecular level.

A genetic mutation can cause a change in the sequence of the 20 amino acids used to build proteins. Such a change is a change to the protein's

primary structure, but this will likely alter higher levels of structure as well. Note: A mutation (a change in a DNA sequence) may directly alter the primary structure of a protein, since this is the sequence of amino acids in the chain. However, the primary level of structure dictates the higher levels of structure—secondary, tertiary, and even quaternary—so these may be indirectly affected as a result of the mutation.

In the search to discover the agents that cause mad cow disease, scrapie in sheep, and CJD and kuru in humans, diseased brain tissues were passed through a fine filter to remove bacteria. The filtrate was still infectious, indicating that something smaller than bacteria, either viruses or organic molecules, must be the causative agent. If a virus was responsible for these brain diseases, then the infectious agent would contain either RNA or DNA. Other possibilities were that the agent was a carbohydrate, fat, or protein. Tissue filtrates were treated with agents that destroyed just one of these chemicals and then injected into a healthy animal, with the results as follows. What is the infectious agent? •Amylase digests carbohydrates; tissue filtrate still infects healthy test animal. •Lipase digests fats; tissue filtrate still infects healthy test animal. •Formaldehyde and/or heat denatures DNA and RNA; tissue filtrate still infects healthy test animal. •Trypsin digests protein; tissue filtrate does not infect healthy test animal.

protein Note: CJD, kuru, mad cow disease, and scrapie are caused by prions—infectious proteins. This was supported by the finding that only trypsin, which digests proteins, was able to deactivate the infectious agent.

Enzymes are organic compounds classified as

proteins. Note: Enzymes are proteins that speed chemical reactions in living things. Their function is very dependent upon their structure. Steroids and other lipids do not function as enzymes, nor do carbohydrates. With a very few exceptions, neither do nucleic acids.

Which of the following subatomic particles will be found within the nucleus of the atom?

protons and neutrons Note: The nucleus of an atom will contain the protons and neutrons. Electrons are found in the electron orbitals that circle the nucleus.

The nucleus of an atom contains

protons and neutrons. Note The nucleus contains protons and neutrons; electrons orbit the nucleus.

Hemoglobin is a protein composed of two pairs of polypeptide chains. What is the highest level of protein structure represented by hemoglobin?

quaternary Note: Amino acids joined together by peptide bonds constitute the primary level of protein structure. In secondary structure, hydrogen bonding between amino acids causes the polypeptide to form an alpha helix or a beta pleated sheet. In tertiary structure, interactions such as covalent bonds between R groups cause the polypeptide to fold and twist. When two or more polypeptides join together, this represents a quaternary level of structure. There is no level of protein structure termed the molecular level.

The proposed cause of CJD and kuru in humans, mad cow disease, and scrapie in sheep is a change in a brain protein. Disease victims appear to have a protein that should normally contain alpha helices but instead they have changed into a protein made of beta pleated sheets. The disease appears to spread when the abnormal protein comes into contact with the normal protein, causing it to become deformed. Which level of protein structure is associated with these diseases?

secondary Note: Amino acids joined together by peptide bonds constitute the primary level of protein structure. In secondary structure, hydrogen bonding between amino acids causes the polypeptide to form an alpha helix or a beta pleated sheet—this is the level affected in CJD and similar brain diseases. In tertiary structure, interactions such as covalent bonds between R groups cause the polypeptide to fold and twist. When two or more polypeptides join together, this represents a quaternary level of structure. There is no level of protein structure termed the "molecular level."

Which type of lipid molecule is characterized by a backbone of four fused rings?

steroid Note: Only steroids are characterized by their backbone of four fused rings. Phospholipids and triglycerides are lipids, but they do not share the same structure as steroids. Amino acids and DNA are not lipids.

Cholesterol is a component of cell membranes and is an example of which type of lipid?

steroids Note: Due to the structure of cholesterol it is classified as a steroid within the body.

Potassium hydroxide (KOH) almost completely dissociates in aqueous solution into K+ and OH-, which means it is a

strong base. Note: Because potassium hydroxide dissociates completely and adds hydroxide ions (OH-) to an aqueous solution, it is a strong base. A weak base would not dissociate so completely. An acid would contribute hydrogen ions (H+) to an aqueous solution. Potassium hydroxide is an ionic compound; a nonpolar covalent molecule would not dissociate or dissolve in an aqueous solution.

To produce images of the body in order to help medical professionals examine and diagnose, patients may undergo an MRI scan, a mammogram, or an X-ray (among other procedures). MRI imaging works by

subjecting hydrogen nuclei to fluctuating magnetic fields. Note: none

How elements interact with each other is dependent on

the number of openings for electrons in the outermost shell. Note:It is the outermost shell of an atom that can potentially react with electrons in the outermost shells of other atoms. The protons and neutrons remain in the nucleus and do not engage in chemical reactions.

Isotopes of a given element have

the same number of protons but differ in atomic mass. Note: Isotopes are atoms of the same element that differ in the number of neutrons only; thus, they have the same atomic number but different atomic masses.

When an ionic bond forms, electrons are

transferred from one atom to another. Note: Ionic compounds form when one atom gives up an electron, which is accepted by the other member of the pair. Now that one atom is a positively charged ion and the other is a negatively charged ion, the two atoms are attracted to one another.

Polar covalent bonds result from

unequal sharing of electrons in a covalent bond. Note: Covalent bonds result from the sharing of electrons between bound atoms; when the sharing is unequal, it is a polar bond, and when the sharing is equal, it is a nonpolar bond. Ionic bonds are a different type of chemical bond from covalent bonds; in an ionic bond, one or more electrons are completely transferred from one member of the compound to the other(s). Hydrogen bonding is a relatively weak attraction between hydrogen in one molecule and a highly electronegative atom (such as O or N) in an adjacent molecule.

Which of the following radiation uses is the one that is most likely to have both beneficial and harmful consequences?

using radiation to treat a cancer patient Note: When using radiation on a person for cancer treatment, there is the possibility of destroying healthy cells along with the cancer cells. Sterilizing mail, surgical equipment, and fruits and vegetables tends not to have any type of consequence on people.