DNA is made of three molecules: sugars, phosphates, and nitrogenous bases. These molecules bond together to form nucleotides, which link up in two chains that spiral into the iconic DNA double helix structure. DNA contains the genetic code and is found coiled tightly in chromosomes in the nucleus of cells. It can make copies of itself through a process called DNA replication that uses the base-pairing rules to produce two identical DNA molecules from one original.

1. DNA – The Molecule of LifeDNA – The Molecule of Life
Hidden in all life is aHidden in all life is a
unique codeunique code
This code is in the formThis code is in the form
of a chemical, calledof a chemical, called
DNADNA DDeoxyriboeoxyriboNNucleicucleic
AAcidcid
11

2. ChromosomeChromosome
uncoiled touncoiled to
show DNAshow DNA
Genes areGenes are
pieces of DNApieces of DNA
that code forthat code for
aa
characteristiccharacteristic
e.g. Eyee.g. Eye
colourcolour
ChromosomesChromosomes
in the cellin the cell
nucleusnucleus
OneOne
chromosomeschromosomes
enlargedenlarged
Where is DNA found in the cell?Where is DNA found in the cell?22

3. DNA – The Molecule of LifeDNA – The Molecule of Life
What does DNA look like?What does DNA look like?
A photo of DNA from an electronA photo of DNA from an electron
microscopemicroscope
33

4. DNA – The Molecule of LifeDNA – The Molecule of Life
We can’t see too much from this but if weWe can’t see too much from this but if we
look at the molecules that make up DNA welook at the molecules that make up DNA we
see a a truly amazing molecule – one thatsee a a truly amazing molecule – one that
contains the hidden code of all life on earthcontains the hidden code of all life on earth
44

5. DNA – The Molecule of LifeDNA – The Molecule of Life
What is DNA made up of ?What is DNA made up of ?
What results if a DNA molecule likeWhat results if a DNA molecule like
this is broken down?this is broken down?
55

6. DNA – The Molecule of LifeDNA – The Molecule of Life
DNA is found to be made of threeDNA is found to be made of three
types of molecules:types of molecules:
66

7. DNA – The Molecule of LifeDNA – The Molecule of Life
SugarSugar
This is a specialThis is a special
type of sugar calledtype of sugar called
deoxyribosedeoxyribose
77

8. DNA – The Molecule of LifeDNA – The Molecule of Life
PhosphatePhosphate
Similar to the chemicalsSimilar to the chemicals
used as fertilisersused as fertilisers to growto grow
plantsplants
88

9. DNA – The Molecule of LifeDNA – The Molecule of Life
BaseBase
D
O
O
M
Similar to the chemicalsSimilar to the chemicals
used in insecticides –used in insecticides –
NITROGENOUS BASENITROGENOUS BASE
99

10. DNA – The Molecule of LifeDNA – The Molecule of Life
SugarSugar
PhosphatePhosphate
Nitrogenous BaseNitrogenous Base
SUMMARY: DNA is made ofSUMMARY: DNA is made of
three types of moleculesthree types of molecules
1010

12. THE NUCLEUS
• Most plant and animal cells have a well-defined nucleus
surrounded by a double, permeable nuclear membrane made up
of proteins and phospholipids
• Ribosomes occur on the outer membrane and these are concerned
with protein synthesis.
• The nucleoplasm is the matrix, in which various substances are
suspended.
• There may be one or more nueleoli [singular = nueleolus] in the
nucleus. These contain proteins and nucleic acids found within the
nucleus and they manufacture RNA and are concerned with protein
synthesis.
• Chromosomes are long threads made of DNA and some protein.
They are the carriers of GENES which are responsible for our
hereditary traits. When a cell Is not dividing the chromosomes are
not visible but are in a very tangled mass, the chromatin network

13. FUNCTIONS OF THE NUCLEUS
• Controls metabolic activities of the cell by
dictating the type of proteins to be
manufactured.
• Carries hereditary traits and allows the
transmission of these from parent to
offspring.

14. During cell division, the chromatin is visible as
chromosomes. Chromosomes are the control
centres of the nucleus

15. • A DNA profile of a
person can be made
from these sources!
• Police and forensic
scientists use this
information in criminal
investigations!
• This is known as DNA
fingerprinting. No two
people except identical
twins have the same
DNA

16. DNA STRUCTURE
• DNA [deoxyribose nucleic acid] is known
as the key to life. It is the hereditary
material found in the chromosomes as
well as other parts of the cell e.g.
mitochondria.

17. • It is a very long
giant molecule
made up of
smaller units
called
NUCLEOTIDES.
Watson & Crick
were awarded the
Nobel Prize for
working out its
structure [although
a South African
woman was just
pipped at the post
(1953-1962)].

18. • Each side is made up of alternating
SUGARS [deoxyribose] and
PHOSPHATES.
• Forming the 'rungs' are PAIRED
NITROGENOUS BASES;

19. • ADENINE pairs with THYMINE A T
• GUANINE pairs with CTYOSINE G C
• These pairs are linked by weak hydrogen bonds.

20. • ONE sugar + ONE PHOSPHATE + ONE BASE
= A NUCLEOTIDE.
• Many nucleotides = one gene
• Thousands of genes may occur on one DNA
(chromosome) strand.

21. • The DNA is twisted
into a double helix

22. These threeThese three
molecules aremolecules are
bonded in abonded in a
special way tospecial way to
form the units ofform the units of
the DNA moleculethe DNA molecule
calledcalled
NUCLEOTIDESNUCLEOTIDES
A SINGLEA SINGLE
NUCLEOTIDENUCLEOTIDE
Consists of aConsists of a
SugarSugar
and a base joinedand a base joined
to the sideto the side
a Phosphatea Phosphatejoined tojoined to
11

23. In the DNAIn the DNA
molecule,molecule,
nucleotides linknucleotides link
together to formtogether to form
long chains calledlong chains called
polynucleotidepolynucleotide
chains.chains.
(poly=many)(poly=many)
22

24. The sugar andThe sugar and
phosphates are thephosphates are the
same throughout thesame throughout the
DNA molecule but …DNA molecule but …
There are fourThere are four
different bases.different bases.
33

25. The four bases are eitherThe four bases are either
single or doubled ringedsingle or doubled ringed
AA singlesingle ringedringed
basebase
AA doubledouble ringedringed
basebase
44

26. There are two types ofThere are two types of singlesingle ringedringed
basesbases
ThymineThymine
CytosineCytosine
TT
CC
55

27. AA
GuanineGuanine
AdenineAdenine
GG
There are two types ofThere are two types of doubledouble ringedringed
basesbases
66

28. Four different nucleotides thereforeFour different nucleotides therefore
occur in the DNA moleculeoccur in the DNA molecule
A
GC
T
77

29. TheThe
polynucleotidepolynucleotide
chain now withchain now with
the fourthe four
different basesdifferent bases
A
G
C
T
88

30. The DNAThe DNA
moleculemolecule
consists ofconsists of
TWO chainsTWO chains
The sugarThe sugar
andand
phosphatesphosphates
form theform the
backbonebackbone
99

31. It is arrangedIt is arranged
in thein the
oppositeopposite
direction todirection to
the firstthe first
chainchain
What do youWhat do you
notice aboutnotice about
the secondthe second
chain?chain?
1010

32. ?
But how areBut how are
the basesthe bases
arranged toarranged to
link the twolink the two
chains?chains?
?
?
?
1111

33. When bases combine ..When bases combine ..
always links toalways links to
a one ringeda one ringed
basebase
A two ringedA two ringed
basebase
1212

34. AA
GG
TT
CC
AdenineAdenine ThymineThymine
GuanineGuanine CytosineCytosine
Adenine
always joins
to Thymine
Guanine
always joins
to Cytosine
1313

35. A
G
C
T
C
A
T
G
Now look at
how the
bases link
with each
other to join
the two
chains of the
DNA
molecule
1414

36. DNADNA
UNIT 3UNIT 3
DNA ReplicationDNA Replication

37. • The DNA molecule has many
nucleotides
•To see this clearly we need to
simplify a nucleotide
A
SugaSuga
rr
PhosphatePhosphate
BaseBase
11

38. C
C
G
T
A
A
A
A
T
T
T
G
G
G
C
A
T
T
T
T
A
A
A
C
Try to
determine
which
nucleotide will
link to the form
the second
DNA chain
WhichWhich
nucleotide willnucleotide will
link to A ?link to A ?
Remember
A joins to T and
G to C
22

39. As the bases
link to each
other, the DNA
molecule is
twisted into a
double helix
Two Sugar-Two Sugar-
PhosphatePhosphate
backbonesbackbones
Inter-Inter-
linkinglinking
basesbases
33

40. DNADNA
replicationreplication
How DNA is copiedHow DNA is copied
44

41. When a cell
divides, the DNA
needs to be
copied so that
each new cell
has the same
DNA as the
parent cell
DNA replicationDNA replication
55

42. An enzymeAn enzyme
breaks thebreaks the
hydrogenhydrogen
bondsbonds
linking thelinking the
two chainstwo chains
The two chainsThe two chains
separateseparate
New strandsNew strands
formform
complimentarycomplimentary
to parent strandsto parent strands
DNA replicationDNA replication66

43. C
C
G
T
A
A
A
A
T
T
T
G
G
G
C
A
T
T
T
T
A
A
A
C
A closer view ofA closer view of
DNA replicationDNA replication
looking at partlooking at part
of a strandof a strand
An enzyme unzipsAn enzyme unzips
the DNA moleculethe DNA molecule
77

44. C
C
G
T
A
A
A
A
T
T
T
G
G
G
C
A
T
T
T
T
A
A
A
C
DNADNA
StrandsStrands
separateseparate
88

45. C
C
G
T
A
A
A
A
T
T
T
G
G
G
C
A
T
T
T
T
A
A
A
C
C
C
G
T
A
A
A
A
T
T
T
G
G
G
C
A
T
T
T
T
A
A
A
C
FreeFree
NucleotidesNucleotides
link tolink to
formform newnew
chainschains andand
twotwo
identicalidentical
DNADNA
moleculesmolecules
99

46. DNA REPLICATION
• The weak hydrogen bonds holding the
complementary base pairs together break
as a result of enzyme action.
• Two single strands now result.
• Each single strand picks up free nucleotides
from the nucleotide pool in the nucleoplasm
and becomes double again.
• Since Thymine can only combine with
Adenine, and Guanine with Cytosine, the
two new double strands are identical to
each other as well as to the original strand.

48. The drawing below summarises the functions of the nucleotides:
D.N.A R.N.A
D.N.A.
mR.N.A.
tR.N.A.
Proteins

51. Transcription

52. Translation