Module 2
In the accompanying figure, hydrophobic interactions would occur between the R groups of which two amino acids?
3 and 6
The hydroxyl group is weakly acidic because of the presence of a strongly electronegative oxygen.
False
What are compounds that have the same molecular formulas but different structures and different molecules?
Isomers
What is the atomic mass of the atom identified as A in the accompanying figure?
12 amu
An example of an anion is K+.
False
Why is ATP important in living organisms?
It can transfer some of its energy to other chemicals.
Hemoglobin consists of 574 amino acids arranged in four polypeptide chains.
True
Molecular chaperones mediate the folding of other protein molecules.
True
Which element activates many enzymes and is needed in blood and other tissues of animals?
magnesium
What is the specific heat of water?
1 cal/g of water per degree Celsius
What is the approximate pH of ammonia?
11
How many molecules are present in one mole of C6H12O6?
6.02 × 1023 molecules
What is the difference between a stable isotope and a radioisotope?
A radioisotope emits radiation.
Which statement best describes an atom?
A substance that cannot be broken into a simpler substance
Which of the following solutions has a pH value of 9.0?
Bleach
Which of the following would most likely form electrolytes in water?
an inorganic compound
What is the functionality of regulatory proteins?
control the activities of proteins, genes, cells, and tissues
A chlorine atom has 17 protons and 18 neutrons. What is its atomic mass?
35 amu
Which of the following describes an amphipathic molecule?
A phospholipid with both a hydrophobic end and a hydrophilic end
Which component becomes oxidized in the following chemical reaction? 4 Fe + 3 O2 → 2 Fe2O3
iron
Which substance is an example of a very strong acid?
lemon juice
Which of the following is a covalent compound?
methane
The products of the process in the accompanying figure are:
monosaccharides
Assume that the shaded portions of the molecule in the accompanying figure each represent different polypeptide chains. What does this represent?
The quaternary structure of a protein
Which statement about van der Waal interactions is false?
They are very strong.
What is the purpose of regulatory proteins?
To control the expression of specific genes
A calorie is the amount of heat energy required to raise the temperature of 1 g of water 1 degree Celsius (C).
True
The carboxyl group can exist in either an ionized or nonionized form.
True
The tetrahedron shape of a methane molecule is the result of orbital hybridization.
True
Most animals convert carotenoids to which vitamin?
Vitamin A
When a small amount of hydrochloric acid (HCl) is added to a solution of Na2HPO4, the pH of the solution does not change markedly. The pH also does not change drastically when a small amount of sodium hydroxide (NaOH) is added to this same solution. Based on these observations, the compound Na2HPO4 is:
acting as a buffer
A salt is a compound in which the hydrogen ion of ____ is replaced by some other cation.
an acid
Which element forms the backbone of organic molecules?
carbon
You isolate a compound that is insoluble in water, has alternating single and double bonds and has a bright orange color. You correctly conclude that this compound is a:
carotenoid
Which is the main structural component of the walls that surround plant cells?
cellulose
What type of protein accelerates the thousands of different chemical reactions that take place in an organism?
enzyme
When we know what kinds of ____ are present in an organic compound, we can predict its chemical behavior.
functional groups
Which of the following is sometime referred to as animal starch?
glycogen
The covalent bond between a hydrogen atom and the oxygen atom in water is formed when:
hydrogen and oxygen share an electron pair
Consider the aquatic insects pictured in the accompanying figure. Which characteristic of water molecules directly contributes to their remarkable "water walking" success?
hydrogen bonds
The cohesiveness between water molecules is due largely to _________.
hydrogen bonds
Which of the following is responsible for the alpha-helical structure of proteins?
hydrogen bonds
Sugar dissolves readily in water because it is a(n) ____ substance.
hydrophilic
Isotopes differ from each other with respect to the number of:
neutrons only
Which pair matches the correct macromolecule with the bond that joins its subunits?
nucleic acid−phosphodiester linkage
The chemical behavior of an atom is determined most directly by the:
number of valence electrons
Which of the following is a common oxidizing agent?
oxygen
Which functional group in cysteine residues can form bridges that help stabilize a protein's tertiary structure?
sulfhydryl
Which event illustrates evaporative cooling?
sweat evaporating from the skin
Why are hydrocarbons considered hydrophobic?
the covalent bonds between hydrogen and carbon are nonpolar
What is the difference between the two atoms in the accompanying figure?
the number of neutrons
What substance is removed during a condensation reaction?
water
How many covalent bonds are formed by carbon atoms, producing a wide variety of molecular shapes and sizes?
Four
Analysis of a certain polymer shows that it contains phosphate groups, ribose groups, and pyrimidines. Based on this information, what statement best describes this compound?
It is RNA.
Which statement best describes the product of a chemical reaction?
It is the substance generated by the reaction.
Which organic compound is not only responsible for energy storage, but can also provide thermal insulation?
Lipids
The primary difference between the amino acids commonly found in proteins is in their:
R or variable groups
The molecular fragment, represented in the accompanying figure is:
RNA
When two amino acids combine in a condensation reaction, a ____________ is formed.
peptide bond
What group of molecules is represented in this structure?
phospholipids
A base is defined as a(n) _____ acceptor.
proton
Which atom would most likely be involved in an ionic bond?
sodium
It takes one calorie of heat to raise the temperature of one gram of water by one degree Celsius at sea level. This is referred to as the ____ of water.
specific heat
What is the atomic mass of the most common isotope of carbon?
12.01 amu
_______________________ are isomers that are mirror images of each other.
Enantiomers
A beta-pleated sheet is an example of a protein's tertiary structure.
False
A chemical formula shows the types and numbers of atoms in a molecule and their arrangement.
False
Condensation and hydrolysis reactions are catalyzed by the same enzymes.
False
Since a carbon atom has 4 valence electrons, it can complete its valence shell by forming a total of 4 hydrogen bonds.
False
Specific heat refers to the amount of energy required to change 1 gram of a substance from the liquid phase to the vapor phase.
False
The atomic mass determines the identity of an element.
False
The valence shell of hydrogen or helium is unstable when it contains two electrons.
False
A phosphate group is weakly acidic.
True
Cellulose is the main structural component of the walls that surround plant cells.
True
Water molecules have a strong tendency to stick to one another, a property known as ___________.
cohesion
The helical coil shape of an α-helix fibrous protein provides what type of property to that protein?
elasticity
Which of the following describes the tertiary structure of a protein molecule?
three-dimensional shape of an individual polypeptide chain
