DNA contains the genetic instructions for making proteins and is found in all living organisms. It exists as a double helix structure with two strands bonded together via hydrogen bonds between complementary nucleotide bases. DNA stores and transmits genetic information from one generation of cells to the next through replication and protein production. It is studied for its central role in heredity and importance to life, as well as potential medical benefits like disease cures.

1. 1

2. 2
DNA
• DNA is often
called the
blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.

3. 3
Why do we study DNA?
We study DNA for
many reasons,
e.g.,
• its central
importance to all
life on Earth,
• medical benefits
such as cures for
diseases,
• better food crops.

4. 4
Chromosomes and DNA
• Our genes are on
our chromosomes.
• Chromosomes are
made up of a
chemical called
DNA.

5. Genetic material of cells…
• GENES – units of genetic material
that CODES FOR A SPECIFIC
TRAIT
• Called NUCLEIC ACIDS
• DNA is made up of repeating
molecules called NUCLEOTIDES

6. The Shape of the Molecule
6
• DNA is a very long
polymer.
• The basic shape is
like a twisted ladder
or zipper.
• This is called a
double helix.

7. 7
The Double Helix Molecule
• The DNA
double helix
has two
strands
twisted
together.

8. 8
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphates and
deoxyribose
sugar
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases

9. 9
Nucleotides
C C
C
O
O
O -P O
O
Phosphate
O
O -P O
O
O -P O
O
O
O One deoxyribose together
with its phosphate and base
make a nucleotide.
Nitrogenous
base
Deoxyribose

10. 10
One Strand of DNA
• One strand of
DNA is a polymer
of nucleotides.
• One strand of
DNA has many
millions of
nucleotides.
nucleotide

11. 11
Four nitrogenous bases
DNA has four different bases:
• Cytosine C
• Thymine T
• Adenine A
• Guanine G

12. Two Kinds of Bases in DNA
12
• Pyrimidines are
single ring bases.
• Purines are
double ring
bases.
C
C
C
N
C
N
O
N
C
C
C
C
N
N
N
N
N
C

13. 13
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
C
C
C
C
N
N
O
N
cytosine
C
C
C
C
N
N
O
O
C
thymine

14. 14
Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
C
C
C
C
N
N
N
Adenine N
N
C
C
C
C
C
N
N
O
N
Guanine N
N
C

15. 15
Two Stranded DNA
• Remember, DNA
has two strands
that fit
together
something like a
zipper.
• The teeth are
the nitrogenous
bases but why
do they stick
together?

16. 16
C
C
C
C
N
N
O
N
N
C
N
C
C
C
N
O
N
N
C
Hydrogen Bonds
• The bases attract each
other because of
hydrogen bonds.
• Hydrogen bonds are weak
but there are millions
and millions of them in a
single molecule of DNA.
• The bonds between
cytosine and guanine are
shown here with dotted
lines

17. 17
Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine
• Adenine always
pairs up with
thymine
• Adenine is bonded
to thymine here
C
C
C
C
N
N
O
O
C

18. 18
Chargraff’s Rule:
• Adenine and Thymine
always join together
A T
• Cytosine and Guanine
always join together
C G

19. 19
DNA by the Numbers
• Each cell has about 2
m of DNA.
• The average human has
75 trillion cells.
• The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
• DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.

20. Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.

21. The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…

22. DNA is wrapped tightly around
histones and coiled tightly to
form chromosomes

23. DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of
base pairing:
A-T, G-C
•Each strand of the
original DNA serves
as a template for the
new strand

24. DNA Replication
• Semiconservative
Model:
1. Watson and Crick
showed: the two
strands of the parental
molecule separate, and
each functions as a
template for synthesis
of a new
complementary Parental DNA
strand.
.
DNA Template
New DNA

25. (1961) Watson & Crick proposed…
• …DNA controlled cell function by
serving as a template for PROTEIN
structure.
• 3 Nucleotides = a triplet or CODON
(which code for a specific AMINO
ACID)
• AMINO ACIDS are the building
blocks of proteins.

26. DNA Transcription
• DNA can “unzip”
itself and RNA
nucleotides match
up to the DNA
strand.
See p.301
• Both DNA & RNA
are formed from
NUCLEOTIDES and
are called
NUCLEIC acids.

27. DNA Translation
• The cell uses
information from
“messenger” RNA to
produce proteins

28. For more detail let see the movie….