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STRUCTURE OF DNA
TOPIC 1 - 2015
YEAR 10 BIOLOGYTopics
Structure of DNAChromosomes & Cell divisionGenetics & InheritanceTheory of EvolutionEvidence for Evolution
YEAR 10 BIOLOGYAssessment
Evolution posterGenetics prac reportUnit testEnd of semester examination
and various worksheets / quizzes throughout the course...
STRUCTURE OF DNAThings to cover
HistoryLocation ComponentsBase pairingShape
HISTORY OF DNA
HISTORY OF DNA1869
DNA was discovered by Friedrich Miescher
His team isolated it from pus on bandages!
He called their discovery nuclein.
HISTORY OF DNA1929
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 DNA1943-1953
Oswald Avery , and Alfred Hershey and Martha Chase made the suggestion that this compound was capable of transferring genetic information between generations
HISTORY OF DNA1950
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 DNA1953
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 DNA1953
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 DNA1953
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
HISTORY OF DNA1962
Watson, Crick, and Wilkins won the Nobel Prize for physiology/ medicine.
Rosalind Franklin had died of cancer in 1956.
Source: achievement.org
WIL
KIN
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ICK
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HISTORY OF DNA1962
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.
NUCLEUS
DNA
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 DNAPentose sugars
There are two sugars that are used in nucleotides:
◦deoxyribose sugar used in DNA
◦ribose sugar used in RNA
COMPONENTS OF DNANitrogen 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 DNAChemical bonds
The three components are held together by covalent bonds.
These bonds are strong so that the unit holds together within the larger molecule.
COVALE
NT BOND
COVALE
NT BOND
CHARGAFF’SBASE 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)
C G
A T
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.
C G
A T
C G
G C
T A
SU
GA
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SP
HATE B
AC
KB
ON
E
SU
GA
R-P
HO
SP
HATE B
AC
KB
ON
ECOMPLEMENTARY 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
C G
A T
C G
G C
T A
COVA
LENT
BONDS
HYD
ROGE
N B
ONDS
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