Download the nucleic acids - Y11-Biology-SG

THE NUCLEIC ACIDS
Introduction
Nucleotides
The DNA
Differences between DNA and RNA
What is a nucleic acid?
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Nucleic acids were molecules first discovered in
the nucleus of cells.
These molecules are essential to life, are
composed of 4 repeating units which, unlike
proteins, are always the same: the nucleotides.
There are 2 types of nucleic acids: the DNA and
the RNA.
The nucleotides
The nucleotides are the units that are covalently
linked forming a long chain. They comprise a
nitrogenous base, a pentose (a 5 C sugar) and
a phosphate group.
Two types of bases
Purines
Pyrimidines
Big bases
Small bases
(2 rings)
(1 ring)
What’s so special about DNA?
DNA is one of the most chemically boring
macromolecules imaginable - its made of
only four building blocks and has a
perfectly monotonous structure.
DNA just sits there - it doesn’t catalyze
reactions or build the cell or organism.
So, what’s so good about DNA?
The answer lies in DNA’s ability to store
and copy information.
A race to fame and glory
THE PLAYERS
IN THE UK
IN THE USA
CAMBRIDGE Watson & Crick (models)
CALIFORNIA (Caltech)
LONDON Franklin & Wilkins – (X-ray diffraction)
Linus Pauling (protein expert)
Rosalind
Franklin’s
famous DNA
image
“Chargaff’s rule”
A = T
&
C = G
And the winners are…
The DNA structure was finally
deduced by James Watson
and Francis Crick in 1953,
based on studies carried out
by Dr. Rosalind Franklin
and Dr. Pauling.
This discovery was a revolution
in biology.
Knowledge has grown
exponentially ever since,
from merely knowing the
DNA to its replication and
link to protein synthesis; to
cloning organisms and the
deciphering of the human
genome, among other
current achievements, in
less than 60 years.
So what is the DNA?
The deoxyribonucleic acid is a huge
molecule composed of 2 long
strands of thousands of repeating
monomers called NUCLEOTIDES.
What is the DNA for?
The DNA stores and passes on
the genetic information; it has
the instructions to make all the
proteins
a cell needs and at the same time
it is what gives the
characteristics to an organism.
DNA STRUCTURE
It is like a spiral staircase, with the sides
made by sugars linked to phospahte
groups and the rungs made by the bases
paired up in a specific way. What holds
the two strands together are the H bonds
that form between complementary bases.
Complementary bases
Bases on opposite strands pair up according to a rule:
A pairs up with T
C pairs up with G
This simple rule always applies in nucleic acids and it is key
for replication and transmission of genetic information to the
next generation.
3 weak H–bonds
2 weak H–bonds
G and C are complementary
as are A and T
The other nucleic acid: RNA
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The ribonucleic acid plays a crucial role in
protein synthesis. It is also made by
nucleotides as the DNA but with some
differences and it is found both in the nucleus
and in the cytoplasm of a cell.
Unlike the DNA, there are three types of
RNA in a cell:
mRNA, tRNA and rRNA
Main differences
between RNA and DNA
Characteristics
DNA
RNA
Nº of strands
2
1
Name of sugar
deoxyribose
ribose
Bases
A, T, C, G
A, U, C, G
Shape
Double helix
Linear or folded
Types
1
3
nucleus
Nucleus and
cytoplasm
Location in
eukaryotes