Chapter 1
Answers
1
QUICK-CHECK questions
What are the special characteristics of the light produced by a synchrotron?
In a synchrotron, electrons are accelerated to very high speeds (almost the speed of
light). Light is created when the direction of movement of these electrons is changed
(deflected) using magnetic fields. A characteristic of this light is that it is extremely
bright.
2
a
Explain why ice is less dense than water.
Ice is less dense than liquid water because, as water solidifies, the water
molecules form a regular lattice structure in which each molecule is linked by
hydrogen bonds to four other water molecules. In liquid water, the hydrogen bonds
are less stable and the water molecules pack together more densely. Hence, the
molecular arrangement of water in solid form (ice) has more spaces within it and
takes up a greater volume than the same number of water molecules in the liquid
state. As a result, ice is less dense and so floats on water.
b
Explain how this difference in density is of vital importance to organisms
that live in water.
The fact that ice is less dense than liquid water means that ice in a body of water,
such as in a lake or in the sea, floats at the top, rather than sinking to the bottom.
So, when a body of water freezes, this takes place from the top down. The ice that
forms at the surface acts as an insulating layer so that the underlying water stays
above freezing point and organisms living in the water are protected from freezing.
3
a
What name is given to a solution that has equal numbers of hydrogen and
hydroxide ions?
A solution in which the numbers of hydrogen ions and hydroxide ions are equal is
termed a neutral solution.
b
What general name is given to solutions that have many more hydrogen
ions than hydroxide ions?
Solutions that have many more hydrogen ions than hydroxide ions are termed
acidic.
4
Name the monomers of carbohydrates, proteins, lipids and nucleic acids.
The monomers (basic building blocks) of carbohydrates are sugars.
The monomers of proteins are amino acids.
The monomers of lipids include fatty acids.
The monomers of nucleic acids are nucleotides.
5
Where is the monosaccharide glucose found in its natural state? What is its
function?
The monosaccharide glucose in its natural state is found in solution in cells. Glucose is
an energy source for cells.
6
Name two polysaccharides found:
(a) in plants
Polysaccharides found in plants include:
 starch, a storage polysaccharide
 cellulose, a polysaccharide that forms part of the structure of cell walls.
(b) in animals.
Polysaccharides found in animals include:
 glycogen, a storage saccharide
 chitin, a polysaccharide that forms part of the structure of some animals such
as the hard exoskeleton of insects, crabs and other arthropods.
7
What is the basic formula for an amino acid molecule?
The basic formula for an amino acid molecule is a carbon atom joined to a hydrogen
atom (H), a carboxyl group (COOH), an amino group (H2N) and a variable group called
R (see figure on page 14). (Note: At physiological pH in a cell, the amino group is
positively charged H3N+ and the carboxyl group is negatively charged COO–.)
8
How is a peptide bond formed?
A peptide bond forms between two amino acid molecules and involves the formation of
a covalent bond between the carboxyl group of one amino acid and the amino group of
the adjacent amino acid (see figure at bottom of page 14 and figure 1.17).
9
List the four basic structures of protein molecules and draw an example of each.
The four basic structures of protein molecules are:
 primary structure, which identifies the amino acid sequence
 secondary structure, which describes how part of the polypeptide chain is arranged
and can be an alpha helix, a random coil or a beta-pleated sheet
 tertiary structure, which describes the overall 3D shape of the polypeptide chain
 quaternary structure, which describes how those proteins that consist of more than
one polypeptide chain are arranged in 3D space.
(Note: All proteins have a primary, secondary and tertiary structure, but only proteins
with two or more polypeptide chains have a quaternary structure.)
For sample drawings of each type of structure, see figure 1.18 on page 16.
10
Give an example of
a
a structural protein
Examples include keratin (in hair and nails) and collagen (in cartilage).
b
a contractile protein
Examples include actin and myosin (in muscles).
c
a conjugated protein.
Examples include haemoglobin, with protein chains linked to haem groups.
11
Why is proteomics considered important?
Proteomics is the study of the proteome, that is, the complete array of proteins of a cell
or of an organism. This study is important because proteins play many essential roles
in biological function and structure. Different kinds of cells show different patterns and
times of production of various proteins. Identifying differences in patterns of protein
production in normal cells and in abnormal cells can provide insight to a range of
disorders.
12
Why are fats so ‘energy dense’?
Fats are more ‘energy dense’ than carbohydrates. Each unit of mass of a fat contains
about twice the amount of chemical energy as the same mass of carbohydrate.
13
Explain the meaning of the statement: ‘Fats are hydrophobic’.
The statement ‘Fats are hydrophobic’ refers to the fact that fat molecules are insoluble
in water, that is, fats have no affinity for and tend to be repelled by water. Molecules
that show this property are termed hydrophobic or ‘water hating’. This contrasts with
other kinds of molecules that are highly water soluble and are termed ‘hydrophilic’ or
‘water loving’.
14
What is a significant function of phospholipids?
One significant function of phospholipids is their role in the structure of the plasma
membrane of all cells. The plasma membrane contains a double layer of phospholipids
molecules.
15
Olive oil is liquid at room temperatures and yet margarine made from olive oil is
solid. How is this difference achieved?
Natural olive oil has a particular arrangement at the C=C double bond in its fatty acid
chains. This arrangement creates a bend in the fatty acid chains so that the oil
molecules cannot pack together tightly enough to form a solid, so that olive oil is liquid
at room temperatures.
Olive oil can be treated under conditions of high temperature and pressure so that the
geometry at this double bond is changed. The change results in the removal of the
bend in the fatty acid chains so that they become straight. As a result, the molecules
can pack more densely and form a solid at room temperatures.
16
An acronym is a word formed from the initials or other parts of several words,
for example WHO from the initial letters of World Health Organization. What do
the acronyms DNA and RNA stand for?
DNA stands for deoxyribonucleic acid.
RNA stands for ribonuncleic acid.
17
What are the four kinds of nucleotides:
a
in DNA
The four kinds of nucleotides in DNA are adenine (A), thymine (T), cytosine (C)
and guanine (G).
b
in RNA?
The four kinds of nucleotides in RNA are adenine (A), uracil (U), cytosine (C) and
guanine (G).
18
Where in a cell would you find DNA and what is its function?
DNA occurs in the nucleus of a cell. DNA is an information-containing molecule that
holds in coded form the genetic instructions that control the production of all the
proteins produced by a cell.
(Note: Very tiny amounts of DNA (as compared with the amounts of nuclear DNA) also
occur in mitochondria and in plant chloroplasts.)
19
There are three different kinds of RNA molecules. What are they and where is
each found in the cell?
Messenger RNA (mRNA) is found in the cytosol of the cell.
Ribosomal RNA (rRNA) is found in ribosomes, one of the cell organelles found in the
cytosol.
Transfer RNA (tRNA) is found the cytosol.
20
In what ways do the kinds of RNA differ from each other?
mRNA, rRNA and tRNA differ from each other in their particular function within a cell:
 Messenger RNA (mRNA) carries a copy of one genetic instruction held in DNA to
the ribosomes.
 Ribosomal RNA (rRNA) is a component of the ribosomes.
 Transfer RNA (tRNA) is linked to a specific amino acid that it carries to the
ribosomes for assembly into a polypeptide chain.