DNA DOUBLE HELIX
COMPLEMENTARY
BASE PAIRING AND
HYDROGEN BONDS
THE MODEL OF WATSON AND CRICK

NUCLEIC ACIDS (DNA AND RNA)
Organic molecule
Made of nucleotides (monomers)
Millions of nucleotides bond to make
nucleic acids (polymers, polynucleotides)

RNA
Cyclic
nitrogen
containing
molecule with
properties of
a base.
Organic
compounds.

NUCLEOTIDE

DNA
Nucleic acid (polimer, polinucleotide)

DNA
DNA is organized into chromosomes; when the cell is not dividing,
the chromosomes appear as stringy chromatin, which is DNA
wrapped around proteins (histone)
A human has 46 chromosomes; around 6 feet of DNA is inside
each cell nucleus (1.8 m) but is constrained in no more than 0.09
mm.

1950’s Rosalind Franklin &
Maurice Wilkins
X-ray crystallography
• Watson & Crick (1953 described their model)
Saw the photos of R.Franklin and created a 3d model.
MODEL:
Sugar-phosphate backbone on the outside and bases inside
of the double helix. Nitrogen bases aligned formed
hydrogen bonds.
Complementary base pairs, due to size of bases and ability to
form hydrogen bonds with each other.
They won the Nobel Prize in Physiology or Medicine 1962 "for
their discoveries concerning the molecular structure of
nucleic acids and its significance for information transfer in
living material".
DNA DOUBLE HELIX THE MODEL OF WATSON AND CRICK

COMPLEMENTARY BASE PAIRING AND HYDROGEN
BONDS (DNA DOUBLE HELIX )
Base pairing: each type of nucleobase on one strand bonds
with just one type of nucleobase on the other strand
Hyrogen Bonds: purines form hydrogen bonds to
pyrimidines.
Adenine bonding only to Thymine in two hydrogen bonds
Cytosine bonding only to Guanine in three hydrogen bonds
Two nucleotides binding together across the double helix is called
a base pair.

BASE PAIRING

DNA DOUBLE HELIX

DNA DNA is organized into chromosomes; when the cell is not dividing,
the chromosomes appear as stringy chromatin, which is DNA
wrapped around proteins (histone)
A human has 46 chromosomes; around 6 feet of DNA is inside
each cell nucleus (1.8 m).

VIDEOS
What is dna
http://youtu.be/1YDTOcAVJrE
Dna double helix structure
http://www.youtube.com/watch?v=VegLVn_1oCE

 Even though it codes for all the information that
makes up an organism, DNA is built using only
four building blocks, the nucleotides adenine,
guanine, thymine, and cytosine.
 Every human being shares 99% of their DNA
with every other human.
 If you put all the DNA molecules in your body
end to end, the DNA would reach from the
Earth to the Sun and back over 600 times (100
trillion times six feet divided by 92 million miles).
 A parent and child share 99.5% of the same
DNA.
 You have 98% of your DNA in common with a
chimpanzee.
AMAZING FACTS ABOUT YOUR DNA

If you could type 60 words per minute, eight hours a
day, it would take approximately 50 years to type the
human genome.
Scientists at cambridge university believe humans
have DNA in common with the mud worm and that it
is the closest invertebrate genetic relative to us. In
other words, you have more in common, genetically
speaking, with a mud worm than you do with a
spider or octopus or cockroach.
Humans and cabbage share about 40-50% common
DNA
Friedrich miescher discovered DNA in 1869,
although scientists did not understand DNA was the
AMAZING FACTS ABOUT YOUR DNA