Chapter 2 Flashcards
Regarding acids, bases, and pH, which of these statements is true?
- Substances that release protons when they dissolve in water are termed bases and result in a pH lower than 7.
- Substances that release protons when they dissolve in water are termed bases and result in a pH higher than 7.
- Substances that release protons when they dissolve in water are termed acids and result in a pH higher than 7.
- Substances that release protons when they dissolve in water are termed acids and result in a pH lower than 7.
Substances that release protons when they dissolve in water are termed acids and result in a pH lower than 7.
(Substances that release protons when they dissolve in water are termed acids and result in a pH lower than 7. These protons, once released from the acid, associate with water and generate a hydronium ion. An increase in the concentration of hydronium is what lowers the pH value. This is true because of the pH expression: pH = –log[H+]. On the other hand, bases accept protons when dissolved in water, which raises the pH. Bases react with hydronium and thereby decrease the concentration of hydronium, thus increasing the pH value.)
Which of the following atoms is most likely to participate in an ionic bond?
- chlorine, with an outer electron shell filled with 7 of a possible 8 electrons
- phosphorus, with an outer electron shell filled with 5 of a possible 8 electrons
- carbon, with an outer electron shell filled with 4 of a possible 8 electrons
Chlorine, with an outer electron shell filled with 7 of a possible 8 electrons.
(Carbon almost always forms covalent bonds. To become an ion, carbon would have to lose four electrons or gain four electrons, and neither of these scenarios is probable. Phosphorus mostly forms covalent bonds. To become an ion, phosphorus would have to lose five electrons or gain three electrons. Gaining three is possible, forming the phosphide anion; however another option in this list is far more probable—the gaining of one electron by chlorine. Chlorine can readily accept a single electron to form an ionic bond. This atom has an outer electron shell filled with seven of a possible eight electrons. Thus, gaining one electron creates the chloride anion with a –1 charge. When the halogen, in this case chlorine, accepts an electron to become a halide ion, then this anion can associate with a metal cation to form a salt.)
Which statement is true of hydrophilic molecules?
- They mix well with water.
- They are generally uncharged.
- They form few or no hydrogen bonds.
- They are typically hydrocarbons.
They mix well with water.
(Hydrophilic molecules dissolve in water. Salts that carry positive or negative charges and substances that contain polar bonds and can form hydrogen bonds also mix well with water. Hydrophobic (“water-fearing”) molecules, by contrast, are uncharged and do not dissolve in water. Examples of hydrophobic chemicals are those that are generally uncharged hydrocarbons that form very few or no hydrogen bonds.)
When sodium loses an outer electron, it becomes positively charged, and a positively charged atom is called a(n) ______.
Cation.
(When sodium loses an outer electron, it becomes positively charged (example: Na+), and a positively charged atom is called a cation. Anions are the negatively charged ions; an example is chloride (Cl–), which forms when a chlorine atom gains an electron and becomes the anion. Isotopes are different versions of the same element, but these atoms have a different number of neutrons.)
Carbon, which has four electrons in its outer shell (with a capacity of eight electrons), can form a maximum of how many covalent bonds with other atoms?
- 8
- 4
- 2
- 0
4
(To figure out how many covalent bonds carbon atoms can participate in, you must subtract the number of outer shell electrons from eight—this gives you the number of possible covalent bonds. Carbon has four vacancies in its outer shell, meaning that it can form up to four covalent bonds with other atoms, including other carbons. One example is methane, CH4, where each of the carbons’ valence electrons are involved in a single bond with each of the four hydrogen atoms. Here are some additional examples: nitrogen, with a valence of five, can form three bonds (8 – 5 = 3); oxygen, with a valence of six, can form two bonds (8 – 6 = 2); and chlorine, with a valence of seven, can form one bond (8 – 7 = 1).)
Which bond term describes a covalent bond in which electrons are shared unequally?
- nonpolar
- hydrogen
- polar
- Ionic
Polar.
(In molecules held together by polar covalent bonds, the positive charge will be concentrated toward one end of the molecule and the negative charge toward the other. This is due to an unequal sharing of electrons across the covalent bond. In nonpolar covalent bonds, on the other hand, electrons are shared equally—often because the atoms involved are the same element. Ionic bonds and hydrogen bonds are not covalent in nature; they do not involve electron sharing. A great example of the polar covalent bond is observed in water. The bonds between the oxygen atom and each hydrogen atom are polar covalent bonds.)
Which four elements make up 96% of the weight of living organisms?
- carbon, oxygen, sodium, hydrogen
- carbon, hydrogen, nitrogen, oxygen
- carbon, calcium, oxygen, nitrogen
- carbon, phosphorus, sodium, hydrogen
- carbon, sodium, chloride, oxygen
carbon, hydrogen, nitrogen, oxygen
(Carbon, hydrogen, nitrogen, and oxygen make up 96% of the weight of living organisms. When looking at the atomic composition of biomolecules, these four elements are present in significant amounts. This set differs from the most abundant elements found in geological samples, and it is evidence that a distinctive type of chemistry operates in biological systems. Phosphorus, chlorine, calcium, and sodium are indeed found in living things, but they are not among the top four most abundant elements. Many metal cations are integral to the biochemistry that occurs across the plasma membrane.)
What type of bond is formed when two atoms share electrons?
- Ionic bond
- hydrogen bond
- electronic bond
- electrostatic bond
- covalent bond
Covalent bond
(Covalent bonds hold together the atoms within molecules. That is, the atoms that are participating in the covalent bond are sharing electrons with one another. The sharing of electrons stabilizes the atoms’ outer shells. Examples include carbon-to-carbon bonds and carbon-to-oxygen bonds, among many others. Ionic bonds form when one atom donates electrons to another. Hydrogen bonds are a type of noncovalent interaction where a partially positively charged atom interacts with a partially negatively charged atom. The shared electrons of a covalent bond complete the outer shells of the interacting atoms. In the simplest possible molecule—a molecule of hydrogen (H2)—two H atoms, each with a single electron, share their electrons, thus filling their outermost shells and imparting chemical stability on the molecule.)
Determine whether the following statement is true or false: Adenosine triphosphate (ATP) is a crucially important energy carrier in cells.
True.
(Adenosine triphosphate (ATP) is a crucially important energy carrier in cells. Nucleoside di- and triphosphates can act as short-term carriers of chemical energy. Above all others, the ribonucleoside triphosphate known as adenosine triphosphate, or ATP, participates in the transfer of energy in hundreds of metabolic reactions. ATP is formed through reactions that are driven by the energy released from the breakdown of foodstuffs. Its three phosphates are linked in series by two phosphoanhydride bonds. Breaking of these phosphate bonds by hydrolysis releases large amounts of useful energy, also known as free energy.)
What is not true of RNA?
- It cannot base-pair with other nucleic acids
- It is usually single stranded
- It contains a different sugar than DNA
- It contains a different base than DNA
It cannot base-pair with other nucleic acids
(Although RNA is usually single stranded, it can form base pairs with other nucleic acids that have a complementary sequence, either DNA or RNA. During transcription, the single-stranded RNA is associating in a complementary way with the template DNA strand. RNA contains a different sugar than DNA; RNA contains ribose and DNA contains deoxyribose. RNA contains a different base than DNA too; RNA contains uracil and DNA contains thymine. These represent two important chemical differences between the two main types of nucleic acid.)
What type of bond links two polynucleotide chains to each other in a double helix of DNA?
- phosphodiester bonds
- phosphoanhydride bonds
- hydrogen bonds
- disulfide bonds
- glycosidic bonds
Hydrogen bonds
(Hydrogen bonds link the two polynucleotide chains to each other in a double helix of DNA. These noncovalent bonds allow double-stranded nucleic acid molecules to be separated, for example, when an RNA molecule is produced using a single strand of DNA as a template. Phosphodiester bonds join the sugar and phosphate groups in the backbone of a single nucleic acid chain, and phosphoanhydride bonds link together the phosphate groups in a nucleotide di- or triphosphate. Nucleotide chains do not contain sulfur, so there are no disulfide bonds in DNA, and glycosidic bonds form between sugar subunits.)
What chemical group is found in a nucleotide but not in a nucleoside?
- phosphate
- hydroxyl group
- pentose
- sugar
- nitrogen-containing base
Phosphate
(A nucleotide contains at least one phosphate group in addition to the base and sugar found in a nucleoside. The phosphate group is attached to the pentose sugar at carbon position #5. Stated a different way, the nucleotide phosphate group is attached the the 5’ carbon of the nucleotide sugar. Both nucleotides and nucleosides include a pentose sugar, both nucleotides and nucleosides include a nitrogen-containing base, and both nucleotides and nucleosides include at least one hydroxyl group in their sugar. Nucleotides are the subunits of DNA and RNA, the two main forms of nucleic acid that the cell relies on very heavily.)
What reaction involving ATP releases a large amount of energy?
- the release of adenine
- the release of the base
- the release of the hydroxyl group
- the release of the sugar group
- the release of the terminal phosphate group
The release of the terminal phosphate group.
(The release of the terminal phosphate group from ATP releases a large amount of energy. The breaking of the phosphoanhydride bonds releases a large amount of useful energy for the cell. The sugar, base, hydroxyl, and adenine groups do not detach from the base to provide energy. Rather, this part of the chemical remains completely intact. Once the reaction is over, ATP breaks apart and ADP + P are left over as cleaved products.)
Which chemical group is found on all amino acids?
- methyl group
- phosphate group
- aromatic ring
- carboxylic acid group
- thiol group
Carboxylic acid group
(Every amino acid includes a carboxyl group and an amino group. These functional groups are part of all amino acids and they are directly involved in the creation of the peptide bond. Some amino acid side chains include a hydroxyl group and/or a methyl group, two amino acid side chains include sulfur, and some amino acid side chains include an aromatic ring. However, methyl, thiol, and aromatic groups are not part of all amino acids, and phosphorus is not included in the natural structures of any of the 20 individual amino acids. The common structure of the amino acids includes the amino nitrogen atom (along with its hydrogen atoms), the central alpha carbon (along with a hydrogen and the variable side-chain group), and the carboxylic acid carbon atom (along with its oxygen atoms).
What type of reaction is the reverse of a condensation reaction?
- oxidation
- decondensation
- hydrolysis
- reduction
Hydrolysis
(Water is released during a condensation reaction. In hydrolysis reactions, a bond is broken and a water molecule is consumed.
Biochemists do not refer to the reverse of a condensation reaction as a decondensation reaction, and oxidation/reduction reactions involve the loss and gain of electrons. When a hydrolysis reaction takes place, larger polymers are commonly broken down into smaller constituent parts. An example would be the conversion of a polysaccharide into monosaccharide subunits. Each monomer is released from the polymer by a hydrolysis reaction.)
