Nucleic Acids: DNA, RNA, and Nucleotides
General
biochemistry
Nucleic acids
(DNA and
RNA)
are
essential materials found
in
all
living organisms.
Their main
function
is
to maintain and
transmit the genetic
code. This
information
is
stored in
the
form
of
long
polymer
chains.
Nucleic acids
are
the
polymers
of
nucleotides
(polynucleotides)
held
by
3’
and
5’
phosphate
bridges.
In
other
words,
nucleic acids
are
built
up
by
the monomeric units
of nucleotides
(It
may
be
recalled
that
protein
is
a
polymer
of
amino
acids).
What
are
nucleosides and
nucleotides?
Nucleosides
consist
of
the nitrogenous
base and
the
sugar without
the
phosphate.
According
to
the
pentose type
involved, two
different species
of
nucleosides are
distinguished: deoxyribonucleosides containing
2’-deoxyribose,
and
ribonucleosides containing
ribose.
thymidine
uridine
Chemical
structure
of
nucleosides
Nucleotides
are composed
of
a
nitrogenous
base
, a
pentose
sugar
and a
phosphate
. Nucleotides perform a
wide
variety
of
functions
in
the
living cells, besides being
the
building blocks or monomeric
units
in
the
nucleic
acid
structure.
The
term
nucleoside
refers to base +
sugar. Thus, nucleotide
is
nucleoside +
phosphate.
S
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a
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p
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f
i
g
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r
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.
p
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r
i
n
e
s
adenine
guanine
t
h
y
m
i
n
e
u
r
a
c
i
l
cytosine
.
Structures
of
nitrogenous
bases.
Major
bases in
nucleic
acids:
The
structures
of
major
purines
and
pyrimidines
found
in
nucleic
acids
are
shown in above
figure.
DNA
contains:
Purine
bases
namely:
adenine
(A)
and
guanine
(G).
Pyrimidine
bases namely: cytosine
(C)
and
thymine
(T)
RNA
contains:
Purine
bases
namely:
adenine
(A)
and
guanine
(G).
Pyrimidine
bases namely: cytosine
(C)
and uracil
(U).
Sugars
of
nucleic
acids:
pyrimidines
The
five
carbon
monosaccharides
(pentoses)
are
found
in
the
nucleic
acid
structure.
RNA
contains
D-ribose
while
DNA
contains
D-deoxyribose
.
Ribose
and
deoxyribose differ in
structure
at
C
2
.
Deoxyribose
has
one
oxygen
less
at
C
2
compared
to
ribose
as
ehown
in
below
figure.
Phosphate:
The
inorganic
acid
H
3
PO
4
(phosphoric acid) gives
the
nucleic acids
an overall
net
negative
charge.
Most of the
interactions
between
the
DNA
and
proteins are with the
phosphate
groups.
Nomenclature
of
nucleotides:
The
addition
of
a pentose sugar to base
produces
a
nucleoside.
If
the
sugar
is
ribose,
ribonucleosides
are formed.
Adenosine, guanosine, cytidine
and
uridine are the
ribonucleosides
of
A,
G,
C
and
U
respectively.
If
the
sugar
is
a deoxyribose, deoxyribonucleosides
are
produced.
Adenosine,
guanosine,
cytidine
and
Thymine are the
ribonucleosides
of
A,
G,
C
and
T
respectively.
Note:
Add
to purine bases
end
(in
NSs)…..sine:
adeno
s
ine and
guano
s
ine.
Add
to pyrimidine bases
end
( in NSs)…..dine:
cytidine,
uri
d
ine,
deoxythymi
di
ne.
Use
the same names
in NTs
with
momo,
di
and
tri
phosphate.
For
examples:
adenosine monophosphate, guanosine
triphosphate,
deoxythymidine
monophosphate
.
The
term
mononucleotide
is
used
when a single phosphate
moiety
is
added
to a
nucleoside. Thus
adenosine
monophosphate
(AMP) contains adenine + ribose +
phosphate. While dAMP
contains
adenine
+
deoxyribose + phosphate.
The
principal bases,
their respective
nucleosides
and
nucleotides
found
in
the
structure
of
nucleic
acids
are
given in below
figure.
What
is
DNA?
DNA
is
a
polymer
of
deoxyribonucleotides
(or
simply deoxynucleotides).
It
is
composed
of
monomeric units
namely deoxyadenylate (dAMP), deoxyguanylate (dGMP),
deoxycytidylate
(dCMP)
and
deoxythymidylate
(dTMP).
Propritie
of
DNA:
1.
The structure
of
DNA
is
double
helical strands
(helix)
2.
The
deoxyribose
sugar
consist
his
backbone
3.
It
is
a
right handed
double
helix.
4.
It consists
of
two
polydeoxyribonucleotide
chains
(strands)
5.
The
strands
are twisted
around each other on a common
axis.
6.
.
The
two strands
are
antiparallel
, one
strand
runs
in
the
3’ to 5’
direction
while the other
in
3’
to
5’
direction.
7.
The
two strands
are
held
together
by
hydrogen
bonds
formed
by
complementary
base
pairs.
8.
Complementary base pairing in
DNA
is
Thymine
pairs
with
adenine
by
2 hydrogen bonds
and
Cytosine
pairs
with
guanine
by
3 hydrogen
bonds.
9.
The A
= T and
G
=
C.
What
is
RNA?
RNA
is
a
polymer
of
ribonucleotides
held
together
by
3’,
5’
-phosphodiester
bridges.
Although
RNA
has
certain
similarities
with
DNA
structure and
they
have
specific differences
in:
1.
Pentose sugar
:
The
sugar in
RNA
is
ribose in contrast to deoxyribose in
DNA.
2.
Pyrimidine
bases :
RNA contains
the
pyrimidine uracil in
place
of
thymine
(in
DNA).
3.
Single strand
:
RNA
is
usually a single stranded
polynucleotide.
4.
Due
to
the
single-stranded
nature,
there
is
no
specific
relation between purine
and
pyrimidine contents.
Thus
the guanine
content
is
not
equal
to cytosine
(as
is
the
case in
DNA).
Types
of
RNA:
The three major
types of RNAs with
their
respective cellular composition
are
given
below:
1.
Messenger RNA
(mRNA) :
The mRNA
is
synthesized in
the nucleus
(in
eukaryotes) and
It
participates in
the
information
transfer from
DNA
(replication) to
the
site
of
protein synthesis (on
ribosome).
2.
Transfer RNA
(tRNA)
:
It
participates in
the
activation
of
amino acids,
their
transport
to ribosome,
and
collecting
the
polypeptides
from amino acids
on
ribosome.
3.
Ribosomal
RNA
(rRNA) : Form
of
RNA in
the
cytoplasm
(or
mitochondria),
It participates
to
link
amino acids
with
others
to form
protein.
Structure and
levels
of
organization
of
nucleic
acids:
Nucleic
acids possess
primary,
secondary, tertiary and quarternary
levels
of
organization.
Physico-chemical properties
of
nucleic
acids:
Physico-chemical properties
of
nucleic acids
are
primarily determined
by
their
high
molecular
mass
and
by
the
level
of
structural organization. Specific
features
of
nucleic
acids
show up in
their:
colloidal and
osmotic
properties,
high viscosity and density
of
solutions,
optical
properties,
aptitude
to
denaturation.
In
solution,
the molecules
of
nucleic
acids exist
as polyanions with distinctly pronounced
acidic
properties.
Nucleic acids, essential for all organisms, store genetic information as long polymer chains of nucleotides. Nucleosides contain bases and sugars, while nucleotides include a phosphate. Purines and pyrimidines are the aromatic bases in nucleotides, with DNA having A, G, C, T and RNA having A, G, C, U bases. The sugars in nucleic acids differ between RNA (D-ribose) and DNA (D-deoxyribose). Learn about the structural elements, nomenclature, and functions of nucleotides in living cells.
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Presentation Transcript
General biochemistry Nucleic acids (DNA and RNA) are essential materials found in all living organisms. Their main function is to maintain and transmit the genetic code. This information is stored in the form of long polymer chains. Nucleic acids are the polymers of nucleotides (polynucleotides) held by 3 and 5 phosphate bridges. In other words, nucleic acids are built up by the monomeric units of nucleotides (It may be recalled that protein is a polymer of amino acids). What are nucleosides and nucleotides? Nucleosides consist of the nitrogenous base and the sugar without the phosphate. According to the pentose type involved, two different species of nucleosides are distinguished: deoxyribonucleosides containing 2 -deoxyribose, and ribonucleosides containing ribose. thymidine uridine Chemical structure of nucleosides Nucleotides are composed of a nitrogenous base, a pentose sugar and a phosphate. Nucleotides perform a wide variety of functions in the living cells, besides being the building blocks or monomeric units in the nucleic acid structure. The term nucleoside refers to base + sugar. Thus, nucleotide is nucleoside + phosphate.
Structural elements of the most common nucleotides Purines and pyrimidines bases: The nitrogenous bases found in nucleotides (and, therefore, nucleic acids) are aromatic compounds. The bases are two types: purines and pyrimidines as shown their structure in below figure. purines
adenine guanine pyrimidines thymine uracil cytosine . Structures of nitrogenous bases. Major bases in nucleic acids: The structures of major purines and pyrimidines found in nucleic acids are shown in above figure. DNA contains: Purine bases namely: adenine (A) and guanine (G). Pyrimidine bases namely: cytosine (C) and thymine (T) RNA contains: Purine bases namely: adenine (A) and guanine (G). Pyrimidine bases namely: cytosine (C) and uracil (U). Sugars of nucleic acids:
The five carbon monosaccharides (pentoses) are found in the nucleic acid structure. RNA contains D-ribose while DNA contains D-deoxyribose. Ribose and deoxyribose differ in structure at C2. Deoxyribose has one oxygen less at C2 compared to ribose as ehown in below figure. Phosphate: The inorganic acid H3PO4 (phosphoric acid) gives the nucleic acids an overall net negative charge. Most of the interactions between the DNA and proteins are with the phosphate groups.
Nomenclature of nucleotides: The addition of a pentose sugar to base produces a nucleoside. If the sugar is ribose, ribonucleosides are formed. Adenosine, guanosine, cytidine and uridine are the ribonucleosides of A, G, C and U respectively. If the sugar is a deoxyribose, deoxyribonucleosides are produced. Adenosine, guanosine, cytidine and Thymine are the ribonucleosides of A, G, C and T respectively. Note: Add to purine bases end (in NSs) ..sine: adenosine and guanosine. Add to pyrimidine bases end ( in NSs) ..dine: cytidine, uridine, deoxythymidine. Use the same names in NTs with momo, di and tri phosphate. For examples: adenosine monophosphate, guanosine triphosphate, deoxythymidine monophosphate.
The term mononucleotide is used when a single phosphate moiety is added to a nucleoside. Thus adenosine monophosphate (AMP) contains adenine + ribose + phosphate. While dAMP contains adenine + deoxyribose + phosphate. The principal bases, their respective nucleosides and nucleotides found in the structure of nucleic acids are given in below figure.
What is DNA? DNA is a polymer of deoxyribonucleotides (or simply deoxynucleotides). It is composed of monomeric units namely deoxyadenylate (dAMP), deoxyguanylate (dGMP), deoxycytidylate (dCMP) and deoxythymidylate (dTMP). Propritie of DNA: 1. The structure of DNA is double helical strands (helix) 2. The deoxyribose sugar consist his backbone
3. It is a right handed double helix. 4. It consists of two polydeoxyribonucleotide chains (strands) 5. The strands are twisted around each other on a common axis. 6. . The two strands are antiparallel, one strand runs in the 3 to 5 direction while the other in 3 to 5 direction. The two strands are held together by hydrogen bonds formed by complementary base pairs. 7. 8. Complementary base pairing in DNA is Thymine pairs with adenine by 2 hydrogen bonds and Cytosine pairs with guanine by 3 hydrogen bonds. 9. The A = T and G = C.
What is RNA? RNA is a polymer of ribonucleotides held together by 3 , 5 -phosphodiester bridges. Although RNA has certain similarities with DNA structure and they have specific differences in: 1. Pentose sugar : The sugar in RNA is ribose in contrast to deoxyribose in DNA. 2. Pyrimidine bases : RNA contains the pyrimidine uracil in place of thymine (in DNA). 3. Single strand : RNA is usually a single stranded polynucleotide. 4.Due to the single-stranded nature, there is no specific relation between purine and pyrimidine contents. Thus the guanine content is not equal to cytosine (as is the case in DNA). Types of RNA: The three major types of RNAs with their respective cellular composition are given below: 1.Messenger RNA (mRNA) : The mRNA is synthesized in the nucleus (in eukaryotes) and It participates in the information transfer from DNA (replication) to the site of protein synthesis (on ribosome). 2.Transfer RNA (tRNA) : It participates in the activation of amino acids, their transport to ribosome, and collecting the polypeptides from amino acids on ribosome. 3.Ribosomal RNA (rRNA) : Form of RNA in the cytoplasm (or mitochondria), It participates to link amino acids with others to form protein.
Structure and levels of organization of nucleic acids: Nucleic acids possess primary, secondary, tertiary and quarternary levels of organization. Physico-chemical properties of nucleic acids: Physico-chemical properties of nucleic acids are primarily determined by their high molecular mass and by the level of structural organization. Specific features of nucleic acids show up in their: colloidal and osmotic properties, high viscosity and density of solutions, optical properties, aptitude to denaturation. In solution, the molecules of nucleic acids exist as polyanions with distinctly pronounced acidic properties.
