ANSWERS TO REVIEW QUESTIONS – CHAPTER 02
1.
What are the characteristic atoms found in:
(a) D-galactose? This is a monosaccharide with an aldehyde functional group. The main atoms
are carbon, hydrogen and oxygen in the ratio of 1 carbon: 2 hydrogen: 1 oxygen. (p. 31)
(b) RNA? RNA is a nucleic acid consisting of long chains of nucleotides joined through
phosphodiester linkages. All nucleotides have a nitrogen-containing base, a monosaccharide and a
phosphate group. (pp. 50–51)
(c) keratin? Keratin is a structural protein containing nitrogen atoms as well as carbon, hydrogen
and oxygen. (p. 48)
(d) wax? Waxes are long-chain apolar lipids. At the molecular level they contain many hydrogen
and carbon atoms, but few oxygen atoms. The energy storing C–H bonds make lipids very
effective stores of chemical energy, ideal for long-term reserves of energy. They are also good
insulators, maintaining body warmth for a range of animals in cold environments. Lipids are also
insoluble in water, so both animals and plants use lipid layers in the form of wax to reduce or
prevent evaporative water loss. (pp. 38–39)
2.
Construct a table summarising the properties of the three types of macromolecules that are
found in all organisms. Name their building units, describe how the units are joined and list
their biological functions. (pp. 29–49)
Name
Building units
Joins
Functions
Proteins
C, H, O, N
Amino acid
chains, peptide
bonds
Enzymes, hormones, structural, transport,
defence, storage
Carbohydrates
C, H, O
Polyhydroxyl
chains
Energy storage, energy currency, structural role
Lipids
C, H, O, P
Hydrocarbon
chains, ester
linkages
Membranes, energy storage, transport,
insulation
3.
What are the physical and chemical attributes of an amphipathic molecule? Draw the
structures of three amphipathic molecules. Where in the cell would you find these molecules
and what are their functions? (pp. 41–42)
Amphipathic molecules have different properties in different parts of their structure. They often take
the form of a long rod with one end having polar groups giving that end a hydrophilic (water-loving)
nature. The other end of the rod will have hydrophobic properties making it fat-soluble. Detergents are
classic amphipathic molecules.
Amphipathic molecules in a membrane
Amphipathic molecule
Hydrophilic end
Hydrophobic end
Two kinds of amphipathic lipids are found in biological membranes. Phospholipids and glycolipids
both have hydrophobic ‘ends’ composed of hydrocarbon chains. The hydrophilic end of phospholipids
has a polar phosphate group attached. In glycolipids, the hydrophilic end is composed of sugars
(carbohydrates).
4. (a) What is the R-group of an amino acid? (pp. 43–47)
The R-group of an amino acid is one of its most important distinguishing features. All amino acids
have an amine and a carboxylic acid group but the R-group provides the distinctive properties of
acidity, polarity, shape and pattern of electron density.
(b) Draw an example of one amino acid with a simple R-group and one with a complex Rgroup. Identify the functional groups on the two amino acids. (pp. 43–47)
Carboxylic acid group
Amino group
O
H2N
CH
O
H2N
CH
C
C
OH
CH 2
OH
H
R-groups
Tryptophan
HN
Glycine
5.
Distinguish between the structures and functions of fibrous proteins and globular proteins.
(pp. 43–47)
Fibrous and globular proteins can be distinguished by their structures. The primary and secondary
structures of proteins refer respectively to (1) the sequence of amino acid monomers and (2) the bending
and folding of the amino acid chain. The tertiary structure of a protein refers to the overall shape of the
protein molecule and this is generally described as fibrous (rod shaped) or globular (spherical). The shape
of globular proteins is determined by the folding of the amino acid chain arranged such that hydrophobic
side (or R-group) chains are buried within the centre of the glob and away from interactions with water
molecules.
The function of fibrous proteins is mainly structural. Keratins are a protein family, which comprises a
significant proportion of hair, nail, horn and feathers. Another fibrous protein family is the collagens
that make up a major part of connective tissue. The function of globular proteins is mainly enzymatic
(catalytic) and comes about through folding of the surface into distinctive shapes complementary to the
substrates upon which the protein acts.
6. Compare the structure and functions of DNA and RNA. (pp. 50–51)
DNA is a double helix. It has two ‘strands’ of a sugar phosphate backbone bent into a helical shape.
Attached to the strands are the nitrogenous bases. These bases interact by hydrogen bonding with those
on the other strand, which hold the two strands together. RNA is a single strand helix with a different
class of sugar molecule in the strand.
The order of the different bases along the sugar phosphate strand in DNA is a code that controls the
morphology and functions of the cell. Transcriptions of that code are made by the cell synthesising
RNA as a complementary copy of the DNA strand.