HL
HEINEMANN
BACCALAUREATE
H IG H E R L E V E L
Biology
DEVELOPED SPECIFICALLY FOR THE
IB DIPLOMA
ALAN DAMON RANDY McGONEGAL
PATRICIA TOSTO WILLIAM WARD
SAMPLE MATERIAL
to show the design and layout for the series
See back cover for full title list
I N T E R N AT I O N A L
DEVELOPED SPECIFICALLY FOR THE IB DIPLOMA
HEINEMANN
BACCALAUREATE
An exciting new series of textbooks for students and
teachers of the IB Diploma, written and developed by
practising IB teachers
comprehensive coverage of all the latest syllabus
requirements and all the options for each subject
differentiated for Standard and Higher levels
appropriate and accessible language, illustrated
examples and levelled exercises
clear links to TOK throughout
exam-style assessment opportunities using
questions from past papers
supported by teacher’s notes
C O N T E N TS
Introduction
1
Statistical analysis
2
Cells
3
The chemistry of life
4
Genetics 1
5
Ecology and evolution
6
Human health and physiology 1
7
Nucleic acids and proteins
8
Cell respiration and photosynthesis
9
Plant science
10
Genetics 2
11
Human health and physiology 2
12 (Option A) Human nutrition and health
13 (Option B) Physiology of exercise
14 (Option C) Cells and energy
15
(Option D) Evolution
16
(Option E) Neurobiology and behaviour
17
(Option F) Microbes and biotechnology
18
(Option G) Ecology and conservation
19
(Option H) Further human physiology
Theory of Knowledge
Advice on Internal Assessment
Advice on Extended Essay
Answers
Index
*Please note that the content in this pack is sample
material which has yet to go through final checks and
may contain minor errors.
Assessment statements are reiterated at
the start of each section, showing which
areas in the curriculum are covered.
3
DNA REPLICATION
3.4
DNA replication
Assessment statements
3.4.1
3.4.2
3.4.3
Interesting facts place
the material in reallife contexts and give
depth to students’
understanding of a
topic. They also prompt
further enquiry.
Key facts are drawn out
and highlighted in text
boxes, to help reinforce
the most important
concepts.
Interesting fact
Helicase may catalyse the
unzipping of DNA at a rate
measured in hundreds of base
pairs per second.
Key fact
DNA must replicate before any
cell divides. This means that DNA
replication precedes binary fission
for prokayotes, mitosis for many
eukaryotic cells and meiosis for
eukaryotic gamete and spore
producing cells.
Explain DNA replication in terms of unwinding the double helix and
separation of the strands by helicase, followed by formation of the
new complementary strands by DNA polymerase.
Explain the significance of complementary base pairing in the
conservation of the base sequence of DNA.
State that DNA replication is semiconservative.
DNA replication involves ‘unzipping’
Cells must prepare for a cell division by doubling the DNA content of the cell
in a process called DNA replication. This process doubles the quantity of DNA
and also ensures that there is an exact copy of each DNA molecule. You should
try to picture the environment in which the DNA is actually replicating. This
is the environment of the nucleus during interphase of the cell cycle. During
interphase, there is a nuclear membrane which separates the fluid of the nucleus
(nucleoplasm) from the cytoplasm. The DNA is in the form of chromatin (not
tightly coiled chromosomes). Among the variety of molecules present in the
nucleoplasm there are two types that are particularly important for the process of
DNA replication; they are:
enzymes needed for replication – these include helicase and a group of
enzymes collectively called DNA polymerase;
free nucleotides – these are nucleotides that are not yet bonded and are found
floating freely in the nucleoplasm, some contain adenine, some thymine,
some cytosine and some guanine. (Free nucleotides are more properly called
nucleoside triphosphates.)
One of the early events of DNA replication is the separation
of the double helix into two single strands. DNA will lose its
characteristic double helix shape when beginning this process.
You should remember that the double helix is held together
by the hydrogen bonds between complementary base pairs
(A and T, C and G). The enzyme that initiates this separation
into two single strands is called helicase. Helicase begins at
a point in or at the end of a DNA molecule and moves one
complementary base pair at a time, breaking the hydrogen
bonds so the double-stranded DNA molecule becomes two
separate strands.
Helicase (currently at about the halfway point in this image) would have
started on the left and would be moving
towards the right.
234
The unpaired nucleotides on each of these single strands can
now be used as a template to help create two double-stranded
DNA molecules identical to the original. Some people use
the analogy of a zipper for this process. When you pull on a
zipper, the slide mechanism is like helicase. The separation of
the two sides of the DNA molecule are like the two opened
sides of a zipper (see Figure 3.13).
Figure 3.13 The first step of
DNA replication is helicase
unzipping the doublestranded DNA molecule
forming a section with two
single strands.
C
A
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T
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Weblink
The experimental work which
determined that DNA replication
was semiconservative is often called
‘the most beautiful experiment
in biology’. See how this classic
experiment was conducted at
http://users.rcn.com/jkimball.
ma.ultranet/BiologyPages/M/
Meselson_Stahl.html
unzipped section
A
T
G
G
A
T
G
C
C
A
helicase moving
T
A
G
C
Formation of two complementary strands
Weblinks support
Aim 7 in encouraging
students to use ICT
skills in the study of
their subject.
As shown in Figure 3.13, once DNA has become ‘unzipped’, the nitrogenous
bases on each of the single strands are unpaired. In the environment of the
nucleoplasm, there are many free-floating nucleotides. These nucleotides
are available to form complementary pairs with the single-stranded
nucleotides of the unzipped molecule. This does not happen in a random
fashion. A free nucleotide locates on one opened strand at one end and
then a second nucleotide can come in to join the first. This will require
that these two nucleotides become covalently bonded together as they are
the beginning of a new strand. The formation of a covalent bond between
two adjoining nucleotides is catalysed by one of the DNA polymerase
enzymes that is important in this process.
A third nucleotide then joins the first two and the process continues in
a repetitive way for many nucleotides. The other unzipped strand also
acts as a template for the formation of another new strand. This strand
forms in a similar fashion, but in the opposite direction to the first strand.
Notice that one strand is replicating in the same direction as helicase is
moving and the other strand is replicating in the opposite direction.
A small section of DNA (shown in the
centre) is seen in a DNA polymerase
enzyme.
3IGNIüCANCEOFCOMPLEMENTARYBASEPAIRING
The pattern of DNA replication ensures that two identical copies of DNA are
produced from one. Figure 3.14 illustrates a very small section of DNA replicating.
Notice that in the area where replication has already
taken place, the two strands are absolutely identical
to each other. This is because the original double–
stranded molecule had complementary pairs of
nucleotides and it was the complementary nucleotides
that used the unzipped single-stranded areas as
templates.
This also means that no DNA molecule is ever
completely new. Every DNA molecule after replication
consists of a strand that was ‘old’ now paired with a
strand that is ‘new’. DNA replication is described as a
semiconservative process because half of a pre-existing
DNA molecule is always conserved (saved).
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%XERCISE
DNA polymerase
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Figure 3.14 DNA replication
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RNA
Who should decide how fast and
how far humans should go with our
study of DNA and the technology
that is rapidly emerging?
8 Most DNA mutations occur during DNA replication. Suggest how a mutation called a
deletion could occur. Suggest how a mutation called a substitution could occur.
235
Revision exercises are provided at key points in the text, to test
the students’ understanding of the material being taught, and aid
them in applying it to problem-solving situations. The answers
to all exercises are provided in the back of the book. In addition,
past IB exam paper questions are given at the end of each
chapter, to provide the student with exam practice.
A
th
TOK
7 The concept of semiconservative DNA replication has some interesting repercussions. For
example, one can argue that there never is such a thing as a ‘new’ DNA molecule. How long
has your DNA been in you? In your family lineage?
the gene
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3
DNA REPLICATION
3.5
Transcription and translation
Assessment statements
3.5.1
3.5.2
3.5.3
3.5.4
3.5.5
Compare the structure of RNA and DNA.
Outline DNA transcription in terms of the formation of an RNA strand
complementary to the DNA strand by RNA polymerase.
Describe the genetic code in terms of codons composed of triplets of
bases.
Explain the process of translation, leading to polypeptide formation.
Discuss the relationship between one gene and one polypeptide.
Protein synthesis introduction
Examiner’s hints give
the student an insight
into commonly used
exam terms, pitfalls
to avoid, and ways to
maximise their score
when it comes to the
exam.
This computer graphic shows an insulin
molecule. Insulin is a protein (peptide)
hormone and is produced by protein
synthesis.
Hint: ‘compare’ requires both similarities and differences. Answers may be
given in the form of a table. In the table
shown here, there are five comparisons
(not ten).
You probably took your first life science class several years ago. In that class, you
probably learned that the nucleus of the cell was the ‘control centre’ and that the
nucleus contained DNA. This information is not wrong – it is just incomplete.
The control that DNA has over a cell is by a process called protein synthesis.
In simplest terms, DNA controls the proteins produced in a cell. Some of the
proteins produced are enzymes. The production (or lack of production) of a
particular enzyme can have a dramatic effect on the overall biochemistry of the
cell. Thus, DNA indirectly controls the biochemistry of carbohydrates, lipids, and
nucleic acids by the production of enzymes.
Protein synthesis has two major sets of reactions called transcription and
P
DNA polymerase
C
T A
translation. Both either produce or require a type ofG nucleic helicase
acid called RNA
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C C
A T
G A
G G
A G
T
T
io
(ribonucleic acid).
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This table compares DNA and RNA.
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DNA
contains a 5-carbon sugar
5-carbon sugar is deoxyribose
each nucleotide has one of four
nitrogenous bases
the nitrogenous bases are cytosine,
guanine, adenine, and thymine
double-stranded molecule
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G
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direc
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Transcription produces RNA molecules
TOK
Is there significance to the fact that
the structure of DNA is universal
among all living things?
Is there further significance that
all living organisms use the same
genetic code?
The sections of DNA that code for polypeptides are called genes. Any one gene
is a specific sequence of nitrogenous bases found in a specific location in a DNA
molecule. Molecules of DNA are found within the confines of the nucleus, yet
proteins are synthesized outside the nucleus in the cytoplasm. This means there
has to be an intermediary molecule which carries the message of the DNA (the
code) to the cytoplasm where the enzymes, ribosomes, and amino acids are found.
This intermediary molecule is called messenger RNA or mRNA.
The nucleoplasm (fluid in the nucleus) contains free nucleotides as discussed
earlier. In addition to the free nucleotides used for DNA replication, the
nucleoplasm also contains free RNA nucleotides. Each of these is different from its
DNA counterpart as RNA nucleotides contain the sugar ribose (not deoxyribose).
236
TOK links provide an ethical and moral
dimension to the student’s study experience.
Discussion-points are suggested, and
questions posed for wider consideration.
A TOK chapter at the end of the book draws
many of these strands together.
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A G
RNA
synt
T T
C G
hesis
A G
G A
G A
A T
contains a 5-carbon sugar
C C
C C
T A
T G
P is ribose
C C
5-carbon sugar
G A
C
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G
each nucleotide also has one of four
DNA polymerase
nitrogenous bases
the nitrogenous bases are cytosine, guanine,
adenine, and uracil
single-stranded molecule
Another major difference is that no RNA nucleotides exist that contain thymine,
instead there is a nitrogenous base unique to RNA, called uracil.
The process of transcription begins when an area of DNA of one gene becomes
unzipped (see Figure 3.15). This is very similar to the unzipping process involved
in DNA replication, but in this case only the area of the DNA where the particular
gene is found is unzipped. The two complementary strands of DNA are now
single-stranded in the area of the gene. Recall that RNA (including mRNA) is a
single-stranded molecule. This means that only one of the two strands of DNA
will be used as a template to create the mRNA molecule. An enzyme called RNA
polymerase is used as the catalyst for this process.
As RNA polymerase moves along the strand of DNA acting as the template, RNA
nucleotides float into place by complementary base pairing. The complementary
base pairs are the same as in double-stranded DNA, with the exception that
adenine on the DNA is now paired with uracil on the newly forming mRNA
molecule. Consider the following facts concerning transcription:
only one of the two strands of DNA is ‘copied’, the other strand is not used;
mRNA is always single-stranded and shorter than the DNA that it is copied
from as it is a complementary copy of only one gene;
look for the presence of thymine in a molecule to identify it as DNA (the
presence of deoxyribose is another clue);
look for the presence of uracil in a molecule to identify it as RNA (the presence
of ribose is another clue).
Global perspective
The human genome project was
truly an international initiative, as
China, France, Germany, Japan,
the United Kingdom and United
States all provided major funding
and lab work towards the goal of
sequencing all of the genes of a
human. Today over 18 countries
have laboratories involved in the
continuation of this project.
RNA polymerase
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the gene
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Figure 3.15 Transcription (synthesis of
an RNA molecule).
Students are
encouraged to
consider the
global impact and
international reach
of the subject being
studied, through
indicators of global
perspectives. This can
lead to further enquiry,
class discussion, or
simply a broader
awareness of the
real-life context of
the material being
studied, following the
intentions of Aim 8.
Full-colour diagrams
complement the text
in illustrating key
concepts.
A
G
RNA-free nucleotides
The genetic code is written in triplets
The mRNA molecule produced by transcription represents a complementary
copy of one gene of DNA. The sequence of mRNA nucleotides is the transcribed
version of the original DNA sequence. This sequence of nucleotides making up
the length of the mRNA is typically enough information to make one polypeptide.
As you will recall, polypeptides are composed of amino acids covalently bonded
together in a specific sequence. The message written into the mRNA molecule
is the message that determines the order of the amino acids. Researchers found
experimentally that the genetic code is written in a language of three bases. In
other words, every three bases is enough information to code for 1 of the 20
amino acids. Any set of three bases that determines the identity of one amino acid
is called a triplet. When a triplet is found in a mRNA molecule, it is called a codon
or codon triplet.
237
RESOURCES FOR THE IB DIPLOMA
HEINEMANN
BACCALAUREATE
Titles in the series
Title
Authors
ISBN
Price
Publication date
Biology Higher Level
Alan Damon
Randy McGonegal
Patricia Tosto
William Ward
978-0-435994-24-2
£29.50
December 2007
Biology Standard Level
Alan Damon
Randy McGonegal
Patricia Tosto
William Ward
978-0-435994-27-3
£22.50
December 2007
Physics Standard Level
Chris Hamper
Keith Ord
978-0-435994-26-6
£22.50
December 2007
History: The Cold War
Keely Rogers
Jo Thomas
978-0-435994-28-0
£18.50*
December 2007
Chemistry Standard
Level
Catrin Brown
Mike Ford
978-0-435994-25-9
£22.50
June 2008
Mathematics Standard
Level
Tim Garry
Ibrahim Wazir
978-0-435994-23-5
£22.50
September 2008
Mathematical Studies
Ron Carrell
David Wees
978-0-435994-31-0
£27.50*
September 2008
Theory of Knowledge
Sue Bastian
978-0-435994-32-7
£22.50*
September 2008
*These prices to be confirmed
What next?
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