DNA Grade 12

LOCATION OF DNA IN
A CELL
: Position of gene on chromosomeLocus

LOCATION OF DNA IN
A CELL
•Chromatin is a complex of DNA and
protein, and is found in the nucleus
of eukaryotic cells.
•Histones are proteins that are
responsible for the first level of DNA
packing in chromatin
•The chromatin network in the
nucleus of a cell will coil up tightly
during cell division and form
individual chromosomes.

DNA : A LONG LINEAR POLYMER FOUND IN THE NUCLEUS OF A
CELL AND FORMED FROM NUCLEOTIDES AND SHAPED LIKE A DOUBLE
HELIX ASSOCIATED WITH THE TRANSMISSION OF GENETIC
INFORMATION .

THE STRUCTURE OF DNA
http://cronodon.com/BioTech/Cell_Nucleus.html

NUCLEIC ACID : (BIOCHEMISTRY) ANY OF VARIOUS
MACROMOLECULES COMPOSED OF NUCLEOTIDE CHAINS THAT ARE
VITAL CONSTITUENTS OF ALL LIVING CELLS.
TYPE OF NUCLEIC ACID :
DNA AND RNA

STRUCTURE OF A NUCLEOTIDE
A nucleotide is made of 3
components:
• A Pentose sugar
• This is a 5 carbon
sugar
• The sugar in RNA is
ribose.
• The sugar in DNA is
deoxyribose.

• A Phosphate group
• Phosphate groups are
important because they
link the sugar on one
nucleotide onto the
phosphate of the next
nucleotide to make a
polynucleotide.

• A Nitogenous base
• In DNA the four bases are:
• Thymine
• Adenine
• Cytosine
• Guanine
• In RNA the four bases are:
• Uracil
• Adenine
• Cytosine
• Guanine

WHAT IS DNA
• A nucleic acid that contains genetic information.
• Double helix shape
• Composed of nitrogenous bases (adenine,
cytosine, guanine and thymine), a five-carbon sugar
(deoxyribose), and a phosphate molecule.

SUGAR PHOSPHATE BONDS
(BACKBONE OF DNA)
• Nucleotides are connected
to each other via the
phosphate on one
nucleotide and the sugar on
the next nucleotide
• A Polynucleotide
Thursday, March 13, 2014

NITROGENOUS BASES – TWO
TYPES
Pyramidines
Thymine - T
Cytosine - C
Uracil - U
Purines
Adenine - A
Guanine - G

GUANINE

COMPLEMENTARY BASE PAIRING
Purines Pyramidines
Adenine Thymine
Adenine Uracil
Guanine Cytosine

BASE PAIRING
• The Nitrogenous Bases
pair up with other
bases. For example the
bases of one strand of
DNA base pair with the
bases on the opposite
strand of the DNA.

THE RULE:• Adenine always base pairs with Thymine (or Uracil if
RNA)
• Cytosine always base pairs with Guanine.
• This is beacuse there is exactly enough room for one
purine and one pyramide base between the two
polynucleotide strands of DNA.

.3DISCOVERY OF
THE DNA STRUCTURE
•Early in the 20th century, the identifi-cation
of the molecules of inheritance loomed as
a major challenge to biologists.

•Discovery of the genetic role of DNA began with research by
Frederick Griffith in 1928.
•pathogenic (S1,bacteriumof astrains2Griffith worked with
harmless (R cells)1&cells)
•ofliving cellsstrain were mixed withpathogenickilled-Heat
becameliving cellsstrain and the result = someharmless
pathogenic.
•now defined as a,transformationThis phenomenon was called
change in genotype & phenotype due to assimilation of foreign
DNA.

1952: A. Hershey & M. Chase
experiments showing that DNA is
the genetic material of T2 phage.
To determine the source of genetic
material in the phage, they
designed an experiment showing
that only 1 / 2 components of T2
(DNA or protein) enters an E. coli
cell during infection
They concluded that the injected
DNA of the phage provides the
genetic information

. THE ROLE OF DNA4
•DNA is vital for all living beings –
even plants.
•It is important for:
•inheritance,
•coding for proteins and
•the genetic instruction guide
for life and its processes.
DNA holds the instructions for an
organism's or each cell’s
development and reproduction and
ultimately death.
DNA can replicate itself.

CODING DNA-NON
Multicellular eukaryotes have many introns(non-coding
DNA) within genes and noncoding DNA between
genes.
The bulk of most eukaryotic genomes consists of
noncoding DNA sequences, often described in the past
as “junk DNA”
Much evidence indicates that noncoding DNA plays
important roles in the cell.
Sequencing of the human genome reveals that 98.5%
does not code for proteins, rRNAs, or tRNAs.

DNA REPLICATION
DNA replication is a biological process that occurs in
all living organisms and copies their exact DNA. It is
the basis for biological inheritance.

DNA: REPLICATION

The first major step for the DNA Replication to take
place is the breaking of hydrogen bonds between
bases of the two antiparallel strands.
The unwounding of the two strands is the starting
point. The splitting happens in places of the chains
which are rich in A-T. That is because there are only
two bonds between Adenine and Thymine (there are
three hydrogen bonds between Cytosine and
Guanine).
Helicase is the enzyme that splits the two strands.
The structure that is created is known as
"Replication Fork".

Origins initiate
replication at
different times.

REPLICATION FORK
The replication fork is a structure that forms within
the nucleus during DNA replication. It is created by
helicases, which break the hydrogen bonds holding
the two DNA strands together. The resulting
structure has two branching "prongs", each one
made up of a single strand of DNA.
These two strands serve as the template for the
leading and lagging strands, which will be created
as DNA polymerase matches complementary
nucleotides to the templates; The templates may be
properly referred to as the leading strand template
and the lagging strand template

DNA strands have a directionality, and the different
ends of a single strand are called the
"3' (three-prime) end" and the "5' (five-prime) end"
with the direction of the naming going 5 prime to the
3 prime region.
The strands of the helix are anti-parallel with one
being 5 prime to 3 then the opposite
strand 3 prime to 5.
These terms refer to the carbon atom in deoxyribose
to which the next phosphate in the chain attaches.
Directionality has consequences in DNA synthesis,
because DNA polymerase can synthesize DNA in
only one direction by adding nucleotides to the 3'
end of a DNA strand.

REFERENCES
• http://www.slideshare.net/guest93618/dna-
981508?qid=56427ae3-eee5-4740-a362-
2a25b50f7354&v=qf1&b=&from_search=35. Accessed on the 06
March 2014
• http://www.slideshare.net/lissyjyothish/dna-
9042838?qid=56427ae3-eee5-4740-a362-
2a25b50f7354&v=qf1&b=&from_search=25. accessed on the 06
March 2014
• http://www.slideshare.net/amalaielmorsy/dna-
30211742?qid=56427ae3-eee5-4740-a362-
2a25b50f7354&v=default&b=&from_search=48. Accessed on the
2014

• http://www.slideshare.net/aquanat/dna-
12598390?qid=56427ae3-eee5-4740-a362-
2a25b50f7354&v=qf1&b=&from_search=52from_search
=66.Accessed on the 06 March 2014
• http://www.slideshare.net/guestd6e7b3/dna-
presentation-910904?qid=56427ae3-eee5-4740-a362-
2a25b50f7354&v=default&b=&from_search=66.Accesse
d on the 06 March 2014

• LINK TO MY SLIDE SHARE
ACOOUNT
HTTP://WWW.SLIDESHARE.NET/201134827/D
NA-140120073506PHPAPP02-1-31984050

DNA Grade 12

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