2. Nucleic acids are made up of
nucleotides.
Nucleic acids are RNA and DNA
–Ribonucleic Acid (RNA) and
–Deoxyribonucleic Acid (DNA)
3. Nucleotides are essential for all cells since
they make DNA and RNA
DNA and RNA are the genetic material for the
cells
Without DNA and RNA
Protein can not be synthesized
Cells can not proliferate
4. Nucleotides serve as carriers of activated
intermediates in the synthesis of some:
–Carbohydrate
–Lipids and
–Proteins
Nucleotides are structural components of
several essential co-enzymes:
–Coenzyme A
–NAD+
–NADP+
5.
6. Serve as the second messengers in signal
transduction pathways:
cyclic adenosine monophosphate (cAMP)
cyclic guanosine monophosphate (cGMP).
7. Nucleotide plays an important role as Energy
currency in the cell:
–ATP
–GTP
Nucleotides are important regulatory
compounds for many of the pathways of
intermediary metabolism, inhibiting or
activating key enzymes
8. Nitrogen Bases
There are two kinds of nitrogen-containing
bases Purines and Pyrimidines
Purines -2 rings (Six-membered and a Five-
membered nitrogen- containing rings fused
together.)
Pyridmidines –One ring (Six-membered
nitrogen-containing ring.)
9. There are 4 Purines and 4 Pyrimidines that
are important in Biochemistry
Purines
Adenine = 6-amino purine
Guanine = 2-amino-6-oxy purine
Hypoxanthine = 6-oxy purine
Xanthine = 2,6-dioxy purine
10.
11. Adenine and Guanine are found in
both DNA and RNA
Hypoxanthine and Xanthine are not
found in nucleic acids, but are
important intermediates in the
synthesis and degradation of purine
nucleotides
14. Cytosine is found in both DNA and RNA
Uracil is found only in RNA
Thymine is normally found in DNA and not in
RNA
Sometimes tRNA may contain some Thymine
as well as Uracil
15. Nucleosides
Results from addition of a sugar to the nitrogen
base, the sugar may be either ribose or 2-
deoxyribose
Carbon 1 of the sugar is attached to nitrogen 9
of a purine base, or to nitrogen 1 of a
pyrimidine base
16.
17. • Names of purine nucleosides end in osine
and examples are: Adenosine, Guanosine
and Inosine (from Hypoxanthine)
• The names of pyrimidine nucleosides end in
–idine eg: Uridine, Thymidine, Cytidine
The numbering of the ring atoms of the base is
written normally, while we use a number and a
prime sign eg. 1', 2', to distinguish the ring
atoms of the sugar.
18. Nucleotides
Results from addition of 1 or more phosphates
to the sugar portion of a nucleoside
Generally, the phosphate is in ester linkage to
carbon 5' of the sugar
19. E.g, 3'-5' cAMP indicates that a phosphate is in
ester linkage to both the 3' and 5' hydroxyl
groups of an adenosine molecule and forms a
cyclic structure.
Some representative names are:
- AMP = Adenosine Monophosphate
- CDP = Cytidine Diphosphate
- dGTP = deoxy Guanosine Triphosphate
- dTTP = deoxy Thymidine Triphosphate (TTP)
- cAMP = 3'-5' cyclic Adenosine Monophosphate
20.
21. Polynucleotides
Nucleotides are joined together by 3'-5'
phosphodiester bonds to form
polynucleotides.
Polymerization of ribonucleotides will
produce an RNA while polymerization of
deoxyribonucleotides leads to DNA.
22.
23. DNA, RNA, and the Flow of Genetic
Information
DNA and RNA are long linear polymers that
carry information in a form that can be passed
from one generation to the next
These macromolecules consist of a large
number of linked nucleotides
24. Sugars linked by phosphates form a common
backbone whereas the bases vary among four
kinds
Genetic information is stored in the sequence
of bases along a nucleic acid chain
25. The bases have an additional special property
of forming specific pairs with one another that
are stabilized by hydrogen bonds
The base pairing results in the formation of a
double helix structure consisting of 2 strands
These base pairs provide a mechanism for
copying the genetic information in an existing
nucleic acid chain to form a new chain
26. DNA is replicated by the action of DNA
polymerase enzymes.
DNA also is the template for synthesis of
RNAs
RNA, especially messenger RNA (mRNA)
forms the template for protein synthesis
Other RNA molecules, such as transfer RNA
(tRNA) and ribosomal RNA (rRNA), are part of
the protein-synthesizing machinery
27. Polymeric Structure of Nucleic Acids
A monomeric unit is a nucleotide consisting 3
components: a sugar, a phosphate, and a base
The phosphate and a sugar does not change from
one nucleotide to the other but the sequence of bases
changes.
The change in base sequences represents a form of
linear information.
28. RNA and DNA Differ in the Sugar Component
and One of the Bases
The sugar in deoxyribonucleic acid (DNA) is
deoxyribose while the sugar in RNA is ribose
30. The sugars in nucleic acids are linked to one
another by phosphodiester bridges
Specifically, the 3′-hydroxyl (3′-OH) group of
the sugar moiety of one nucleotide is esterified
to a phosphate group,
which is joined to the 5′-hydroxyl group of the
adjacent sugar.
In addition to the standard 3′→5′ linkage, a
2′→5′ linkage is possible for RNA, which is
important for the formation of mature RNA
31. Backbones of DNA and RNA.
The backbones of these nucleic acids are formed by 3′-to-5′ phosphodiester
linkages. A sugar unit is highlighted in red and a phosphate group in blue.
32. Backbones of DNA
and RNA.
The backbones of
these nucleic acids
are formed by 3′-to-5′
phosphodiester
linkages. A sugar
unit is highlighted in
red and a phosphate
group in blue.
33. Whereas the backbone is constant in DNA and
RNA, the bases vary from one monomer to the
next
Two of the bases are derivatives of purine
— Adenine (A) and Guanine (G)
and two of pyrimidine
— Cytosine (C) and Thymine (T, DNA only) or
Uracil (U, RNA only),
34. Note that each phosphodiester bridge has a
negative charge.
This negative charge repels nucleophilic
species such as hydroxide ion;
As a result, phosphodiester linkages are much
less susceptible to hydrolytic attack than are
other esters such as carboxylic acid esters.
35. This resistance is crucial for maintaining the
integrity of information stored in nucleic acids.
The absence of the 2′-hydroxyl group in DNA
further increases its resistance to hydrolysis
The greater stability of DNA accounts for its
use rather than RNA as the hereditary material
in all modern cells and in many viruses
36. DIRECTIONALITY OF NUCLEOTIDE CHAINS
Note that, a DNA chain has polarity
One end of the chain has a free 5′-OH group
(or a 5′-OH group attached to a phosphate),
whereas the other end has a 3′-OH group,
neither of which is linked to another nucleotide
37.
38. By convention, the base sequence is written in
the 5′-to-3′ direction.
Thus, the symbol ACG indicates that the
unlinked 5′-OH group is on deoxyadenylate,
whereas the unlinked 3′-OH group is on
deoxyguanylate.
Because of this polarity, ACG and GCA
correspond to different compounds.
A striking characteristic of naturally occurring
DNA molecules is their length.
39. A DNA molecule must comprise many
nucleotides to carry the genetic information
necessary for even the simplest organisms
E.g, the RNA of a virus such as HIV, which
causes AIDS, is 9719 nucleotides in length
The E. coli genome is a single DNA molecule
consisting of 4.6 million nucleotides( 4.6 x 106
base pairs =4.6 x 103 kilo base pairs) kbp
40. DNA molecules from higher organisms can be
much larger
The human genome comprises of 3 billion
nucleotides [3 x 109], divided among 23
distinct DNA molecules (chromosomes) of
different sizes.
One of the largest known DNA molecules is
found in the Indian muntjak, an Asiatic deer; its
genome is nearly as large as the human
genome but is distributed on only 3
chromosomes
41. The Indian Muntjak
and Its
Chromosomes.
Cells from a female
Indian muntjak
contain three pairs
of very large
chromosomes
(stained orange).
The cell shown is a
hybrid containing a
pair of human
chromosomes
(stained green) for
comparison.
42. The largest of these chromosomes has chains
of more than 1 billion nucleotides
If such a DNA molecule could be fully
extended, it would stretch more than 1 foot in
length
43. The Double Helix is Stabilized by Hydrogen
Bonds and Hydrophobic Interactions
In Nucleic acids, there is specific base-pairing
interactions
This was discovered in the studies directed at
determining the three-dimensional structure of
DNA
It was shown that DNA was formed of two
chains that wound in a regular helical structure
45. The features of the Watson-Crick model of DNA
deduced from the diffraction patterns are:
1. Two helical polynucleotide chains are coiled
around a common axis. The chains run in
opposite directions.
2. The sugar-phosphate backbones are on the
outside and, therefore, the purine and
pyrimidine bases lie on the inside of the helix.
46. 3. The bases are nearly perpendicular to the helix
axis, and adjacent bases are separated by
3.4 Å.
– The helical structure repeats every 34 Å, so there
are 10 bases (= 34 Å per repeat or 3.4 Å per base)
per turn of helix.
– There is a rotation of 36 degrees per base (360
degrees per full turn or 10 bases per turn).
4. The diameter of the helix is 20 Å.
47. How is such a regular structure able to
accommodate the sequence of bases, given
the different sizes and shapes of the purines
and pyrimidines?
Watson and Crick discovered that:
–Guanine can be paired with Cytosine and
–Adenine with Thymine to form base pairs that
have essentially the same shape
A=T and G=C
49. The bases are held together by hydrogen
bonds.
Erwin Chargaff reported, The ratios of Adenine
to Thymine and of Guanine to Cytosine were
nearly the same in all species studied.
All the Adenine:Thymine and
Guanine:Cytosine ratios are close to 1,
whereas the adenine-to-guanine ratio varies.
50. Base compositions experimentally determined
for a variety of organisms
Species A:T G:C A:G
Human being 1.00 1.00 1.56
Salmon 1.02 1.02 1.43
Wheat 1.00 0.97 1.22
Yeast 1.03 1.02 1.67
Escherichia coli 1.09 0.99 1.05
Serratia
marcescens
0.95 0.86 0.70