STRUCTURE
OF DNA
TOPIC 1 - 2015
YEAR 10 BIOLOGY
Topics
Structure of DNA
 Chromosomes & Cell division
 Genetics & Inheritance
 Theory of Evolution
 Evidence for Evolution

YEAR 10 BIOLOGY
Assessment
Evolution poster
 Genetics prac report
 Unit test
 End of semester examination

and various worksheets
/ quizzes throughout the
course...
STRUCTURE OF DNA
Things to cover
History
 Location
 Components
 Base pairing
 Shape

HISTORY OF DNA
HISTORY OF DNA
1869
DNA was discovered by
Friedrich Miescher
 His team isolated it from pus
on bandages!
 He called their discovery
nuclein.

HISTORY OF DNA
1929
Phoebus Levene determined that
the compound had a repeating
structure.
 He called these repeated units
nucleotides.
 He also suggested that these units
link together to form chains.
 His theory was correct, but his
prediction about the way the
chains formed was not.

HISTORY OF DNA
1943-1953

Oswald Avery , and Alfred
Hershey and Martha Chase
made the suggestion that this
compound was capable of
transferring genetic
information between
generations
HISTORY OF DNA
1950
Erwin Chargaff
determined that there
were four types of
nucleotides that paired
up within the structure
of DNA
 This is known as
Chargaff’s rule or the
base pairing rule.

HISTORY OF DNA
1953
Rosalind Franklin
came very close to
solving the DNA
structure
 She made xray
crystallographic
portraits of DNA in
order to try to
determine its 3D
structure.

Source: www.makingthemodernworld.org.uk
HISTORY OF DNA
1953

Her work was given
without her consent
to a group of
scientists in another
laboratory by her
colleague, Maurice
Wilkins.
Source: www.makingthemodernworld.org.uk
HISTORY OF DNA
1953
James Watson and
Francis Crick made a
model of DNA that
incorporated the
findings of Chargaff,
Franklin and Wilkins.
 Their model fit the
experiential data so
perfectly that it was
almost immediately
accepted.

Source: tokresource.org
WATSON
CRICK
Watson, Crick,
and Wilkins won
the Nobel Prize
for physiology/
medicine.
 Rosalind Franklin
had died of cancer
in 1956.

WILKINS
1962
JOHN STEINBECK
HISTORY OF DNA
Source: achievement.org
HISTORY OF DNA
1962
The Nobel Prize only
goes to living
recipients, and can
only be shared among
three winners.
 Were she alive, do you
think she would have
been included in the
prize?

Source: omniscienceblog.com
LOCATION OF DNA
LOCATION OF DNA

DNA is a chemical located in the nucleus of
every living cell.
LOCATION OF DNA

It is a nucleic acid.

Its full name is deoxyribonucleic acid.

Its role is to store coded instructions about how
to make proteins.

In this way, it directs
cell division, growth
& function.
COMPONENTS
OF DNA
COMPONENTS OF DNA

DNA is a large molecule made up of smaller
sub-units called nucleotides

Each nucleotide consists of:
◦ a nitrogenous base
◦ a pentose sugar
◦ a phosphate group

There are four different DNA nucleotides
COMPONENTS OF DNA
Pentose sugars

There are two sugars that are used in
nucleotides:
◦deoxyribose sugar  used in DNA
◦ribose sugar  used in RNA
COMPONENTS OF DNA
Nitrogen bases

There are four nitrogen bases in DNA:
◦ A = Adenine
◦ T = Thymine
◦ G = Guanine
◦ C = Cytosine

There is a fifth nitrogen base found only in
RNA:
◦ U = Uracil
COMPONENTS OF DNA
Chemical bonds
The three components are held together by
covalent bonds.
 These bonds are strong so that the unit holds
together within the larger molecule.

CHARGAFF’S
BASE PAIRING
RULE
BASE PAIRING IN DNA
The nitrogen bases exhibit complementary
base pairing.
 This means that each base only join with one
other base:
◦ Adenine joins with Thymine (A=T)
◦ Guanine joins with Cytosine (C≡G)

A
T
C
G
BASE PAIRING IN DNA

Reasons behind the rule:
◦ Size of bases
◦ Number of hydrogen bonding sites
SHAPE OF DNA
SHAPE OF DNA

DNA is double stranded.

Each strand is made up of nucleotides,
connected through chemical bonds.

These two strands are twisted
around each other.

This is called a double helix.
SHAPE OF DNA

The structure is similar to a twisted ladder.

The “rungs” of the ladder are made from the
complementary nitrogen base pairs.

The “sides” of the ladder are made
from alternating sugar and
phosphate groups.

This is called the sugar-phosphate
backbone.
A
T
C
G
C
G
T
A
G
C
SUGAR-PHOSPHATE BACKBONE
SUGAR-PHOSPHATE BACKBONE
COMPLEMENTARY NITROGEN
BASE PAIRS
SHAPE OF DNA

The nucleotides are joined by covalent bonds
 these are very strong

The two strands are joined by hydrogen bonds
 these are very weak,

This allows the strands to be separated during
DNA replication and protein synthesis without
destroying the DNA completely
A
T
C
G
C
G
T
A
G
C