2.2 Review Questions
If xenon has an atomic number of 54 and a mass number of 108, how many neutrons does it have?
Atoms that vary in the number of neutrons found in their nuclei are called ________.
- neutral atoms
Potassium has an atomic number of 19. What is its electron configuration?
- shells 1 and 2 are full, and shell 3 has nine electrons
- shells 1, 2 and 3 are full and shell 4 has three electrons
- shells 1, 2 and 3 are full and shell 4 has one electron
- shells 1, 2 and 3 are full and no other electrons are present
Which type of bond represents a weak chemical bond?
- hydrogen bond
- atomic bond
- covalent bond
- nonpolar covalent bond
What makes ionic bonds different from covalent bonds?
Ionic bonds are created between ions. The electrons are not shared between the atoms, but rather are associated more with one ion than the other. Ionic bonds are strong bonds, but are weaker than covalent bonds, meaning it takes less energy to break an ionic bond compared with a covalent one.
Why are hydrogen bonds and van der Waals interactions necessary for cells?
Hydrogen bonds and van der Waals interactions form weak associations between different molecules or within different regions of the same molecule. They provide the structure and shape necessary for proteins and DNA within cells so that they function properly.
2.3 Review Questions
Which of the following statements is not true?
- Water is polar.
- Water stabilizes temperature.
- Water is essential for life.
- Water is the most abundant molecule in the Earth’s atmosphere.
When acids are added to a solution, the pH should ________.
- stay the same
- cannot tell without testing
A molecule that binds up excess hydrogen ions in a solution is called a(n) ________.
Which of the following statements is true?
- Acids and bases cannot mix together.
- Acids and bases will neutralize each other.
- Acids, but not bases, can change the pH of a solution.
- Acids donate hydroxide ions (OH–); bases donate hydrogen ions (H+).
Discuss how buffers help prevent drastic swings in pH.
Buffers absorb the free hydrogen ions and hydroxide ions that result from chemical reactions. Because they can bond these ions, they prevent increases or decreases in pH. An example of a buffer system is the bicarbonate system in the human body. This system is able to absorb hydrogen and hydroxide ions to prevent changes in pH and keep cells functioning properly.
Why can some insects walk on water?
Some insects can walk on water, although they are heavier (denser) than water, because of the surface tension of water. Surface tension results from cohesion, or the attraction between water molecules at the surface of the body of water (the liquid-air/gas interface).
2.4 Review Questions
Each carbon molecule can bond with as many as________ other atom(s) or molecule(s).
Which of the following is not a functional group that can bond with carbon?
What property of carbon makes it essential for organic life?
Carbon is unique and found in all living things because it can form up to four covalent bonds between atoms or molecules. These can be nonpolar or polar covalent bonds, and they allow for the formation of long chains of carbon molecules that combine to form proteins and DNA.
Compare and contrast saturated and unsaturated triglycerides.
Saturated triglycerides contain no double bonds between carbon atoms; they are usually solid at room temperature. Unsaturated triglycerides contain at least one double bond between carbon atoms and are usually liquid at room temperature.
Which of these elements is not a micronutrient?
Which of the following is the name for molecules whose structures are nonsuperimposable mirror images?
A. structural isomers
Aldehydes, amides, carboxylic acids, esters, and ketones all contain carbonyl groups.
Two molecules containing the same types and numbers of atoms but different bonding sequences are called enantiomers.
Why are carbon, nitrogen, oxygen, and hydrogen the most abundant elements in living matter and, therefore, considered macronutrients?
Identify the functional group in each of the depicted structural formulas.
The structural formula shown corresponds to penicillin G, a narrow-spectrum antibiotic that is given intravenously or intramuscularly as a treatment for several bacterial diseases. The antibiotic is produced by fungi of the genus Penicillium. (a) Identify three major functional groups in this molecule that each comprise two simpler functional groups. (b) Name the two simpler functional groups composing each of the major functional groups identified in (a).
Dehydration synthesis leads to formation of
- water and polymers
- none of the above
During the breakdown of polymers, which of the following reactions takes place?
- covalent bond
Why are biological macromolecules considered organic?
Biological macromolecules are organic because they contain carbon.
What role do electrons play in dehydration synthesis and hydrolysis?
In a dehydration synthesis reaction, the hydrogen of one monomer combines with the hydroxyl group of another monomer, releasing a molecule of water. This creates an opening in the outer shells of atoms in the monomers, which can share electrons and form covalent bonds.
2.5 Review Questions
By definition, carbohydrates contain which elements?
A. carbon and hydrogen
B. carbon, hydrogen, and nitrogen
C. carbon, hydrogen, and oxygen
D. carbon and oxygen
Monosaccharides may link together to form polysaccharides by forming which type of bond?
Match each polysaccharide with its description.
|___chitin||A. energy storage polymer in plants|
|___glycogen||B. structural polymer found in plants|
|___starch||C. structural polymer found in cell walls of fungi and exoskeletons of some animals|
|___cellulose||D. energy storage polymer found in animal cells and bacteria|
What are monosaccharides, disaccharides, and polysaccharides?
The figure depicts the structural formulas of glucose, galactose, and fructose. (a) Circle the functional groups that classify the sugars either an aldose or a ketose, and identify each sugar as one or the other. (b) The chemical formula of these compounds is the same, although the structural formula is different. What are such compounds called?
Structural diagrams for the linear and cyclic forms of a monosaccharide are shown. (a) What is the molecular formula for this monosaccharide? (Count the C, H and O atoms in each to confirm that these two molecules have the same formula, and report this formula.) (b) Identify which hydroxyl group in the linear structure undergoes the ring-forming reaction with the carbonyl group.
The term “dextrose” is commonly used in medical settings when referring to the biologically relevant isomer of the monosaccharide glucose. Explain the logic of this alternative name.
2.6 Review Questions
Which of the following describes lipids?
A. a source of nutrients for organisms
B. energy-storage molecules
C. molecules having structural role in membranes
D. molecules that are part of hormones and pigments
E. all of the above
Molecules bearing both polar and nonpolar groups are said to be which of the following?
Lipids are a naturally occurring group of substances that are not soluble in water but are freely soluble in organic solvents.
Fatty acids having no double bonds are called “unsaturated.”
A triglyceride is formed by joining three glycerol molecules to a fatty acid backbone in a dehydration reaction.
Fill in the Blank
Waxes contain esters formed from long-chain __________ and saturated __________, and they may also contain substituted hydrocarbons.
alcohols; fatty acids
Cholesterol is the most common member of the __________ group, found in animal tissues; it has a tetracyclic carbon ring system with a __________ bond in one of the rings and one free __________group.
steroid; double; hydroxyl
Microorganisms can thrive under many different conditions, including high-temperature environments such as hot springs. To function properly, cell membranes have to be in a fluid state. How do you expect the fatty acid content (saturated versus unsaturated) of bacteria living in high-temperature environments might compare with that of bacteria living in more moderate temperatures?
Describe the structure of a typical phospholipid. Are these molecules polar or nonpolar?
2.7 Review Questions
Which of the following groups varies among different amino acids?
A. hydrogen atom
B. carboxyl group
C. R group
D. amino group
The amino acids present in proteins differ in which of the following?
C. side groups
D. all of the above
Which of the following bonds are not involved in tertiary structure?
A. peptide bonds
B. ionic bonds
C. hydrophobic interactions
D. hydrogen bonds
Fill in the Blank
The sequence of amino acids in a protein is called its __________.
Denaturation implies the loss of the __________ and __________ structures without the loss of the __________ structure.
A change in one amino acid in a protein sequence always results in a loss of function.
Heating a protein sufficiently may cause it to denature. Considering the definition of denaturation, what does this statement say about the strengths of peptide bonds in comparison to hydrogen bonds?
The image shown represents a tetrapeptide. (a) How many peptide bonds are in this molecule? (b) Identify the side groups of the four amino acids composing this peptide.
2.8 Review Questions
A nucleotide of DNA may contain ________.
- ribose, uracil, and a phosphate group
- deoxyribose, uracil, and a phosphate group
- deoxyribose, thymine, and a phosphate group
- ribose, thymine, and a phosphate group
The building blocks of nucleic acids are ________.
- nitrogenous bases
Which of the following molecules is likely to have the most potential energy?
What are the structural differences between RNA and DNA?
DNA has a double-helix structure. The sugar and the phosphate are on the outside of the helix and the nitrogenous bases are in the interior. The monomers of DNA are nucleotides containing deoxyribose, one of the four nitrogenous bases (A, T, G and C), and a phosphate group. RNA is usually single-stranded and is made of ribonucleotides that are linked by phosphodiester linkages. A ribonucleotide contains ribose (the pentose sugar), one of the four nitrogenous bases (A,U, G, and C), and the phosphate group.
What are the four types of RNA and how do they function?
The four types of RNA are messenger RNA, ribosomal RNA, transfer RNA, and microRNA. Messenger RNA carries the information from the DNA that controls all cellular activities. The mRNA binds to the ribosomes that are constructed of proteins and rRNA, and tRNA transfers the correct amino acid to the site of protein synthesis. microRNA regulates the availability of mRNA for translation.