Download Bio101 Topic 5 - Nucleic Acids

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Biomolecules
Nucleic Acids.
There are two nucleic acids
„ RNA: Ribonucleic Acid
„ DNA: Deoxyribonucleic Acid
The composition and Structure of
DNA and RNA
„
„
DNA and RNA are polymers of monomers called
nucleotides.
A nucleotide consists of three distinct parts:
¾A 5 carbon (pentose)
sugar
¾A phosphate group PO4-3
¾A nitrogen base
The pentose sugar
ƒ Pentose = C5
ƒ Each carbon is numbered clockwise beginning at 12:00.
ƒ Only four carbons are used in the cycle which is
enclosed with an
-O-.
ƒ The fifth carbon is part of the cycle.
The Phosphate Group
„ The phosphate forms a bond with the
pentose’s carbon # 3. It has negative
charge, thus all the nucleic acid molecule
will be negatively charged.
The nitrogen bases
„
„
The are four nitrogen
bases
Adenine or A, Guanine
or G. These are call
purines and they have a
double cycle. Cytosine
C, Thymine, T and
Uracil are called
pyrimidines and they
have a single cycle.
RNA Ribonucleic Acid
„
The 5 C sugar is =
RIBOSE
„
The nitrogen bases are:
A, C, G and U, never T
„
RNA is a single strand
There are 3 types of RNA.
„ mRNA: messenger RNA
„ tRNA : transfer RNA
„ rRNA: ribosomal RNA
Function of RNA:
All RNA is involved in protein
synthesis (manufacturing)
DNA Deoxyribonucleic Acid
„
The 5 C sugar is = DEOXYRIBOSE
„
The nitrogen bases are: A, C, G and T,
never U
„
DNA is a double strand
„
„
The addition of multiple
nucleotides using
deshydration synthesis
lead to the formation of
a large chain.
Notice that the last
nucleotide (C3) does not
have a phosphate group,
thus this strand of DNA
“runs” from a 5’
3’
and it is known as the
“sense” strand.
The Chargaff Rule
„
„
1948 Edwin Chargaff hydrolized DNA from
different organisms and demonstrated that the
composition of double stranded DNA was 50%
purine and 50% pyrimidine.
A+G ==1
1
C+T
Furthermore, he demonstrated that the amount of
Adenine was very similar to the amount of Thymine
and the amount of Guanine was similar to the
amount of Cytosine. These equivalencies are known
as Chargaff rules.
Watson and Crick discovered the double
helix by building models to conform to Xray data
„
By the beginnings of the 1950’s, the race was on to
move from the structure of a single DNA strand to
the three-dimensional structure of DNA.
„
Among the scientists working on the problem were
Linus Pauling, in California, and Maurice Wilkins
and Rosalind Franklin, in London.
„
Maurice Wilkins and Rosalind Franklin used X-ray
crystallography to study the structure of DNA.
The Watson and Crick Model
Watson and Crick
used the data
produced by
Wilkins and
Franklin to
produce a three
dimensional model
of the structure of
DNA.
The second strand
„
„
„
The second strand of DNA follows the same principles
that we have studied so far. It is positioned “upside
down” and it is a mirror image of the first strand (a 180
degree vertical rotation).
However, if this was a “true” mirror image, the
nitrogen bases should be the same and that is not the
case: The nitrogen bases are complementary.
Complementary bases mean, that if in the first strand
we find a purine base, in the second strand we will find
a pyrimidine and viceversa.
Complementary bases
First strand (sense)
Second strand (antisense)
ƒThe two strands are
linked together by
hydrogen bonds.
Once the two strands are bond together, the entire
structure twists to the right (right handed or clock
wise) to form a helical structure known as a “double
helix”.
And the rest is History!
Some DNA information
„
Cellular DNA is organized into chromosomes.
„
The genome is all the genetic information (all
the genes) of one organism.
„
A gene is a fragment of DNA that has the
information for one specific trait. Examples:
color of the eyes.
„
All the variations of one gene are called alleles:
for example, blue, green, almond, brown, red,
etc.
„
„
What is the name of the movie?
What did the teacher tell his students?