1.14 Amino acids have the fundamental unit of a carbonyl group and an
amino group bonded to a carbon atom.1.15 There are 20 different amino acid side chains found in proteins and
these differ in structure, size, and charge.
1.16 Each atom of an amino acid is identified uniquely by the atoms of
the side chain being designated by the Greek letters β, γ, δ, and ε,
proceeding from the αcarbon (the oxygen, nitrogen, and other
carbon do not have letters assigned).1.17 Only L-enantiomers of amino acids are found in proteins.
1.18(a) Arginine, lysine, and histidine. (b) Aspartic acid and glutamic acid.1.19 Proline.1.20 Tyrosine, tryptophan, and phenylalanine.1.21This residue can make a disulfide bridge with another cysteine residue.
1.22 In DNA the sugar is deoxyribose and the bases are the purines
adenine (A) and guanine (G), and the pyrimidines thymine (T) and
cytosine (C).1.23 DNA has two chains running in opposite directions down a central
axis forming a double helix with a diameter of 20 Å.
1.24 Thymine is always paired with adenine as both of these bases can
form two hydrogen bonds. Cytosine is always paired with guanine,
forming three hydrogen bonds.1.25 The backbone of RNA is formed by phosphodiester linkages as for
DNA, but the connections are to riboses, not deoxyriboses.CHAPTER 2
2.1 The internal energy will increase more if the system is at constant
volume because, at constant pressure, some of the energy input as
heat goes into work done on the surroundings instead of all going
into the kinetic energy of the gas molecules.
2.2 Since the expansion is isothermal and of an ideal gas, the change in
internal energy is zero. This means q=−wand for a compression,
wis positive. Therefore qmust be negative.2.3 The change in internal energy of any closed adiabatic system at
constant volume is zero, assuming that only pressure/volume work
is possible.2.4 The internal energy is a constant.ANSWERS TO PROBLEMS 441
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