1. MACROMOLECULES
EVOLUTION

2. History of life on Earth
Billions of years ago before life on Earth began
the Earth’s atmosphere was very different from
what it is like today.
Experiments have shown that organic molecules
could have formed under those different
conditions.

3. Miller-Urey experiments
Stanley Miller and Harold Urey
conducted experiments trying
to recreate the conditions of
pre-biotic Earth.
They succeeded in creating
organic molecules.
Miller and Urey concluded
that organic compounds could
have formed on pre-biotic
Earth.

4. Nucleic acids
For life to exist organic molecules are not
enough.
A method of storing and transmitting
information to enable the living structures to
function is needed. Nucleic acids can perform
this role.
There are two types of nuclei acid:
• DNA – Deoxyribose Nucleic Acid
• RNA – Ribose Nucleic Acid

5. DNA and Evolution
All living things use DNA to store and transmit
genetic information.
Some viruses use RNA as their genetic material (but
viruses are not considered living)
DNA is the fundamental chemical of living things.
The structure of DNA determines the characteristics
of the organism made possible by the different
arrangements of its building blocks – nucleotides.
DNA is universal to all living things.

6. Two main roles of DNA
The fact that all living things share this common
genetic code is strong evidence that all life evolved
from a common ancestor.
1. To pass on the hereditary characteristics from
one generation to another
2. To act as a code for the production of other vital
molecules in living things, particularly proteins.

7. If life had many separate beginnings, we would
expect different mechanisms for storing and
transmitting genetic information.
However, all living organisms use the same
genetic code, the same 20 amino acids in their
proteins and the same cellular processes.
But not all organisms have the same DNA, so
changes to genetic information must have
occurred over the billions of years since life first
evolved.
These changes to DNA are called Mutations.

8. DNA has diversified over billions of years leading
to the wide range of different organisms on the
Earth.

9. DNA has diversified
Mutations have led to a diversity of DNA which has
produced diversity of life.
The first organisms (prokaryotes) had circular
chromosomes.
Eukaryote DNA has since broken up into linear sequences.
Now there is more DNA in cells due to increased number
of genes and non-coding (junk) DNA.
Eukaryote genes contain introns and exons.
Exons are translated into proteins
Introns are transcribed but removed from mRNA before
translation
Prokaryotes don’t have introns.

10. eg
Mouse gene for dihydrofolate reductase has
31000 base pairs of which 558 base pairs code
for the amino acids required.

12. Evolution
Using information from studies of:
• comparative anatomy
• comparative embryology
• fossil studies
Scientists have been able to piece together
possible evolutionary pathways.
This has provided strong evidence that
organisms evolved from a common ancestor.

13. Comparative anatomy
DNA is the genetic code responsible for the features
and inheritable characteristics of all living things.
Charles Darwin first proposed the theory of
evolution claiming that all living things have evolved
from common ancestors.
He established evolutionary relationships on the
basis of structural similarities. Such structures are
termed homologous
E.g. limbs of different vertebrates
We call this comparative anatomy

14. Modifications to the forelimb of
related animals
A well documented example of comparative anatomy is
the pentadactyl limb of many vertebrates.
Similar bone structure has evolved for different functions.

15. Comparative embryology
Another method of
making evolutionary
links is through
Comparative
Embryology.
Comparing the early
embryonic
development of
different species.

16. DNA evidence
It is now possible with modern technology to
analyse and compare the DNA and protein
molecules from different organisms.
If different species produce proteins what are
very similar in their amino acid sequences, it is
logical to infer that their DNA is very similar,
inherited from a common ancestor.

17. Phylogenetic trees
Scientists have been able to construct evolutionary
trees based on DNA analysis of different organisms.
Phylogenetic trees show the evolutionary
relationships in a variety of organisms based on
studying the amino acid sequence of a particular
protein.
Two proteins studied extensively are:
• Cytochrome C
• Haemoglobin

19. If 2 species have evolved from a common
ancestor and their separation was recent, it is
likely that there will not have been enough time
for many new mutations to have taken place.
Their DNA sequences should therefore be very
similar.
They occur close together on a phylogenetic
tree.

20. However, if 2 species have evolved from a
common ancestor and they have been
separated for a much longer time, it is likely
many more mutations have occurred in each
species. Their DNA sequences should therefore
be very different.
They occur further apart on a phylogenetic tree.

21. Phylogenetic Tree - primates

22. Cytochrome c
A phylogenetic tree indicates the evolutionary
relationship of organisms based on studying the
amino acid sequence on a particular protein
called cytochrome c.
Cytochrome c is a protein that is necessary for
respiration in all living organisms. It can vary
from one species to another. The more similar,
the closer the evolutionary relationship.

23. Cytochrome c
The sequences for humans and chimpanzees
match all of the 104 amino acid positions.
Haemoglobin is another protein molecule used
for amino- acid sequencing.

24. DNA analysis
To compare 2 species the same segment of DNA
from each species must be analysed.
Two techniques are:
• DNA Sequencing
• DNA Hybridisation

25. DNA Sequencing
• Involves determining the base sequence of a
segment of DNA.
• Very precise method.
• Costly and time consuming.
• Only used for small segments.
Comparative DNA

26. Comparative DNA
DNA Hybridization
• Involves heating DNA from 2 species to get
complementary strands.
• Upon cooling DNA strands recombine.
• The degree of bonding between 1 species
DNA and another gives a measure of how
closely related the 2 species are.

27. DNA
Hybridization

28. Comparison of Primate DNA

29. Mutations
A permanent change in the DNA sequence is called a
Mutation. (http://www.hhmi.org/biointeractive/damage-
dna-leads-mutation)
Mutation rates can be increased by certain environmental
conditions
• Radiation
• Heat
• Mutagenic chemicals
Factors that cause increased mutation rates are called
Mutagens.

30. Mutagens
While natural mutations do occur spontaneously at
a low rate others occur by physical or chemical
factors or agents called mutagens. These mutations
are often passed from one generation to another
They occur during DNA replication or
recombination and are called spontaneous
mutations.
(http://www.hhmi.org/biointeractive/mismatch-
repair)
All alter genes in control of cell division leading to
the development of cancerous cells

32. Cancer
Many forms of cancer are the direct result of
mutation.
Chemical agents that cause or increase the
incidence of cancer are called carcinogens.

33. In nature, mutations are random events that can be
caused by mutagens.
The vast majority of mutations are harmful but in
some circumstances they can provide a source of
variation which nature can select from.
This process is called Natural Selection.
Natural Selection works on the changes within
individuals of a species brought about by
mutations.

34. Base substitutions
One nucleotide is
substituted for another i.e.
wrong base is placed into
position on the DNA,
leading to a different amino
acid placed in the protein
Eg sickle cell anemia

35. Base insertions or deletions
Adding or deleting nucleotides on the mRNA will
alter the reading of the nucleotide during
translation – “frameshift” mutations
Bigger mutations involve changes to
chromosomes
http://www.hhmi.org/biointeractive/evolution-
y-chromosome
Eg down syndrome

36. Mutations in DNA

37. Translocations
Part of one chromosome is moved to another
Inversions
Segment of one chromosome may be flipped
upside down from its normal position
Duplication
Parts of chromosomes appear twice

38. Inheritable Human Diseases
Sickle cell anaemia
A fatal blood condition located on chromosome
11, coding for the haemoglobin protein which
has an altered base leading to single amino acid
alteration.
The haemoglobin formed is abnormal gives rise
to red blood cells that do not carry oxygen
efficiently

39. Sickled Blood Cells
Distorted red blood cells often block blood
vessels.
Amino acid glutamic acid is replaced by valine

40. Mutations in Human Chromosomes

41. Haemophilia
Genetic disorder where those afflicted bleed
excessively because of an abnormal gene which
prevents blood clotting
A carrier for the disease may not actually suffer
from the disease but can pass on the mutant
gene to their offspring.

42. Inheritance of Haemophilia