Essential Cell Biology 5th edition

Questions
65
KEY TERMS
acid electrostatic attraction molecule
amino acid fatty acid monomer
atom hydrogen bond noncovalent bond
atomic weight hydrolysis nucleotide
ATP hydronium ion organic molecule
Avogadro’s number hydrophilic pH scale
base hydrophobic polar
buffer hydrophobic force polymer
chemical bond inorganic protein
chemical group ion proton
condensation reaction ionic bond RNA
conformation lipid sequence
covalent bond lipid bilayer subunit
DNA macromolecule sugar
electron molecular weight van der Waals attraction
electronegativity
QUESTIONS
QUESTION 2–10
Which of the following statements are correct? Explain your
answers.
A. An atomic nucleus contains protons and neutrons.
B. An atom has more electrons than protons.
C. The nucleus is surrounded by a double membrane.
D. All atoms of the same element have the same number of
neutrons.
E. The number of neutrons determines whether the nucleus
of an atom is stable or radioactive.
F. Both fatty acids and polysaccharides can be important
energy stores in the cell.
G. Hydrogen bonds are weak and can be broken by thermal
energy, yet they contribute significantly to the specificity of
interactions between macromolecules.
QUESTION 2–11
To gain a better feeling for atomic dimensions, assume that
the page on which this question is printed is made entirely of
the polysaccharide cellulose, whose molecules are described
by the formula (C n H 2n O n ), where n can be a quite large
number and is variable from one molecule to another. The
atomic weights of carbon, hydrogen, and oxygen are 12, 1,
and 16, respectively, and this page weighs 5 g.
A. How many carbon atoms are there in this page?
B. In cellulose, how many carbon atoms would be stacked
on top of each other to span the thickness of this page (the
size of the page is 21.2 cm × 27.6 cm, and it is 0.07 mm
thick)?
C. Now consider the problem from a different angle.
Assume that the page is composed only of carbon atoms.
A carbon atom has a diameter of 2 × 10 –10 m (0.2 nm); how
many carbon atoms of 0.2 nm diameter would it take to span
the thickness of the page?
D. Compare your answers from parts B and C and explain
any differences.
QUESTION 2–12
A. How many electrons can be accommodated in the first,
second, and third electron shells of an atom?
B. How many electrons would atoms of the elements listed
below have to gain or lose to obtain a completely filled outer
shell?
helium
oxygen
carbon
sodium
chlorine
gain __ lose __
gain __ lose __
gain __ lose __
gain __ lose __
gain __ lose __
C. What do the answers tell you about the reactivity of
helium and the bonds that can form between sodium and
chlorine?
QUESTION 2–13
The elements oxygen and sulfur have similar chemical
properties because they both have six electrons in their
outermost electron shells. Indeed, both elements form
molecules with two hydrogen atoms, water (H 2 O) and
hydrogen sulfide (H 2 S). Surprisingly, at room temperature,
water is a liquid, yet H 2 S is a gas, despite sulfur being much
larger and heavier than oxygen. Explain why this might be
the case.
QUESTION 2–14
Write the chemical formula for a condensation reaction of
two amino acids to form a peptide bond. Write the formula
for its hydrolysis.