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Nucleic acids and
nucleoproteins
The variety and complexity of
functions that are carried out by
proteins, in a number of cases
demands, besides the amino
acids residues presence, and
other components.
Depending on a chemical nature of non-protein component the
conjugated proteins are subdivided on:
chromoproteins (contains coloured component), glycoproteins (contains
carbohydrates and their derivates), lipoproteins (contains lipids),
phosphoproteins (contains a phosphoric acid), metalloproteins (contain
various atoms of metals),
and nucleoproteins (complexes of proteins and
nucleic acids).
Nucleic acid in nucleoprotein structure provides
storage, realization and transfer of the hereditary
information
In 1868 the Swiss chemist F. Mischer for
the first time extracted from human
leucocite nuclei a new type of compound
unknown before and named them nucleins
(from lat. nucleus). Then nucleins were
obtained from a nuclear material of various
organisms. Later Mischer determined, that
nuclein is a complex compound consisting
of an acid component, phosphoruscontaining about 10 %, which was named
nucleic acid, and protein component. So
were discovered the nucleic acids and a
new group of conjugated proteins nucleoproteins.
In the middle 80es of ct. XIX
nucleins were found in
chromosome structure , in this
connection the first
representation about their
important role in transfer of
hereditary properties was
generated. However these
representations have not
received further development, as
transfer of genetic properties is
connected with proteins. And
only in the 50es of ct. XX. the
convincing experimental proofs
of a major role of the nucleic
acids (DNA, RNA) in storage and
transfer of a heredity were
received. So it was proved, that
nucleic acids are present in all
cells of organisms, and are
material carriers of the genetic
information.
Nucleic acids are linear directed
heterobiopolymers, monomer parts
of which are nucleotides .
• Nucleotide - a compound
that consists of nitrogencontaining base,
carbohydrate component
and a phosphoric acid
residue.
Nucleotides composition:
1. NITROGENOUS BASES
Five bases are found in nucleic acids. Two purine bases (adenine
and guanine) and three pyrimidine bases (cytosine, uracil and
thymine). Adenine and guanine are present in both DNA and
RNA. Cytosine and thymine are the pair of pyrimidines in DNA,
and cytosine and uracil is the pair in RNA.
1
2
6
3
5
7
4
9
8
Purine
3
2
4
5
1 6
Pyrimidine
Cytosine
Uracil (in
RNA)
Thymine ( in DNA)
2. Carbohydrates (function - giving of
hydrophylity): one of two pentoses - ribose
(in RNA) or deoxyribose (in DNA).
In nucleotides, both types of pentoses are in their
β-furanose (closed five-member ring) form.
3. The residue of a phosphoric acid Н3РО4 (function the hinge connecting cyclic structures;
Giving steady negative charge)
Nucleoside=nitrogenous base+carbohydrate
Purine bases between 9th nitrogen atom, and pyrimidine is linked through 1st –
formed N-glycosidic bond with ribose or 2'-deoxyribose. Glycosidic bonds in
nucleosides and nucleotides are always of the -configuration.
Depend on pentose nature nucleosides are divided on ribonucleosides and
deoxyribonucleosides. The names of nucleosides build of the trivial names
according to nitrogenous base by addition suffix -idine at pyrimidinic, -osine
- at purinic nucleosides:
Name of nucleotide =
name of base +
-osine (purins)
-idine (pirimidines)
Glycosidic
bond
Cytidine
Glycosidic
bond
Adenosine
Nucleotides - phosphoric ethers of nucleosides.
Usually in nucleosides esterified hydoxyle group at С-5 ' or at С-3 ' of
pentose residue. Depending on a pentose structure are distinguished
ribonucleotides and deoxyribonucleotides.
Nucleotides is possible to consider, on the one hand, as ethers of nucleosides
(their phosphates), and on the other hand - as acids, in connection with
presence in their structure of the residue of a phosphoric acid.
Name of nucleotide = name of nucleoside + number of phosphates
Adenosine 5' monophosphate (АМP),
adenylic acid
Deoxythymidyine 5' monophosphate
(ТМP), thymidylic acid
Nucleoside 5'-Triphosphates
are carriers of chemical energy
Nucleoside 5'-triphosphates are indispensable agents
in metabolism because the phosphoric anhydride bonds they
possess are a prime source of chemical energy to do
biological work. Adenosine 5'-triphosphate (ATP) has been
termed the energy currency of the cell. Guanosine 5'triphosphate GTP is the major energy source for protein
synthesis.
Nucleic acids are linear
polymers of nucleotides
linked 3' to 5' by
phosphodiester bridges.
They are formed as 5'nucleoside
monophosphates are
successively added to
the 3'-OH group of the
preceding nucleotide
DNA chain fragment
Types of nucleic acids
Deoxyribonucleic acid (DNA) - function is storage
and transfer of the hereditary information
Ribonucleic acid (RNA) - function is realization of
the hereditary information
Differences between DNA and RNA
1. In
composition:
1.1. In nitrogenous
bases:
in RNA – uracile,
in DNA – thymine.
Cytosine
Uracile
Thymine
1.2. In carbohydrate
component:
in RNA – ribose,
in DNA – deoxyribose.
2. In structure: most of RNA molecules – singlestrained, DNA- always double-stranded
Two-chained DNA increases reliability of information
storage , but results in necessity of RNA existence for
its realization.
3. In cellular localization:
The majority of
DNA is concentrated in a nucleus, majority of RNA - in
cytoplasm
Deoxyribonucleic acid (DNA)
Chargaff rules (1949 г.):
[A] = [T]; [C] = [G];
[A] + [G]=[T]+[C] ([purines] =
[pyrimidines]).
[A] + [G]=[T]+[C] [aminogroups] =
[oxogroups].
James Watson and Francis Crick, working in the Cavendish
Laboratory at Cambridge Universityin 1953, took advantage of
Chargaff’s results and the data obtained by Rosalind Franklin
and Maurice Wilkins in X-ray diffraction studies on the
structure of DNA to conclude that DNA was a complementary
double helix.
The specific pairing of the nitrogenous bases causes
complementarity,
I.e. supplementarity and interdependence of DNA strands each other.
The nucleotids sequence in one polynucleotidic chain automatically
determines a sequence of nucleotids in another, complementary
strand.
The two DNA
strands are
antiparallel :
in one chain
direction
51→ 31,
in other – 31→ 51.
Between planes
of these pairs
bases located
the one above
the other hydrophobic
stacking interaction
(from stacking laying in piles).
DNA helix is usually rightinvolute
The total
material of
chromosomes chromatine contains DNA,
hystonic and
non-hystonic
proteins, small
amount of RNA
and ions of
metals.
Protein component of nucleoproteins
1. Structural proteins – positive charged, reached
by diaminoacids
1.1. Histones: large (mass 15-20 thousands)
Classes :
Н1- reached by lysine,
Н2А - reached by arginine and
lysine,
Н2В – modestly reached by
arginine and lysine,
Н3 – reached by arginine
Н4 – reached by arginine and
glycine.
Functions: histones Н2А-Н4 form
hystonic octamere, on which
Is wound DNA, forming
nucleosome;
Histone Н1 connects separate
nucleosomes together
Protein components of nucleoproteins
1.2 Protamines – small (М 4-12
thousands) proteins, in which about
80% of amino acids is represented by
arginine.
Function - enter into nucleosome
structure, filling space between
histones
2. Regulatory proteins – negatively
charged, reached by dicarboxylic
amino acids – acid non-histonic
proteins –
protein factors of transcription and
translation
DNA occurs in various
forms in different cells. The
single
chromosome
of
prokaryotic cells is typically a
circular
DNA
molecule.
Relatively little protein is
associated with prokaryotic
chromosomes. In contrast,
the
DNA
molecules
of
eukaryotic cells, each of
which defines a chromosome,
are linear and richly adorned
with proteins.
Ribonucleic aсid (RNA)
RIBOSOMAL RNA
- the largest - structural and functional component of ribosomes
Ribosomal RNAs characteristically contain a number of specially modified
nucleotides, including pseudouridine residues, ribothymidylic acid, and
methylated bases.
Ribonucleic aсid (RNA)
TRANSFER RNA
Transfer RNA (tRNA) serves as a carrier of amino acid residues
for protein synthesis. The tRNAs are the smallest RNAs (size range—23 to
30 kD) and contain 73 to 94 residues, a substantial number of which are
methylated or otherwise unusually modified.
.
Unusual (minor) bases in tRNAs
Ribonucleic aсid (RNA)
.
MESSENGER RNA
Messenger RNA (mRNA) serves to carry the information that is
encoded in genes to the sites of protein synthesis in the cell, where this
information is translated into a polypeptide sequence.
RNA copy is made of the sequence of bases along one strand of
DNA. This mRNA then directs the synthesis of a polypeptide chain as the
information that is contained within its nucleotide sequence is translated into
an amino acid sequence by the protein-synthesizing machinery of the
ribosomes.