3. OCCURRENCE
The term NUCLEIC ACID is the overall name for
DNA and RNA, members of a family of
biopolymers and is synonymous with
polynucleotide.
Nucleic acids were named for their initial
discovery within the nucleus, and for the
presence of phosphate groups (related to
phosphoric acid).
The first isolation of what we now refer to as
DNA was accomplished by JOHANN FRIEDRICH
MIESCHER circa 1870.
He reported finding a weakly acidic substance
of unknown function in the nuclei of human
white blood cells, and named this material
"nuclein".
4. A few years later, Miescher separated nuclein into
protein and nucleic acid components. In the
1920's nucleic acids were found to be major
components of chromosomes, small gene-
carrying bodies in the nuclei of complex cells.
Elemental analysis of nucleic acids showed the
presence of phosphorus, in addition to the usual
C, H, N & O. Unlike proteins, nucleic acids
contained no sulfur.
Although first discovered within the nucleus of
eukaryotic cells, nucleic acids are now known to
be found in all life forms as well as some
nonliving entities, including within bacteria,
archaea, mitochondria, chloroplasts, viruses and
viroids.
5. To reflect the unusual sugar component,
chromosomal nucleic acids are called
deoxyribonucleic acids, abbreviated DNA.
Analogous nucleic acids in which the sugar
component is ribose are termed ribonucleic
acids, abbreviated RNA. The acidic character of
the nucleic acids was attributed to the
phosphoric acid moiety.
All living cells contain both DNA and RNA
(except some cells such as mature red blood
cells), while viruses contain either DNA or RNA,
but usually not both. The basic component of
biological nucleic acids is the nucleotide, each
of which contains a pentose sugar (ribose or
deoxyribose), a phosphate group, and a
nucleobase.
6.
7. Complete hydrolysis of chromosomal nucleic
acids gave inorganic phosphate, 2-deoxyribose
(a previously unknown sugar) and four different
heterocyclic bases (shown in the following
diagram).
8. Nucleic acids are also generated within the
laboratory, through the use of enzymes (DNA
and RNA polymerases) and by solid-phase
chemical synthesis. The chemical methods also
enable the generation of altered nucleic acids
that are not found in nature, for example peptide
nucleic acids.
9. STRUCTURE
Nucleic acid structure refers to the structure of
nucleic acids such as DNA and RNA. Chemically
speaking, DNA and RNA are very similar. It is
often divided into four different levels primary,
secondary, tertiary and quaternary.
12. Primary structure consists of a linear sequence
of nucleotides that are linked together by
phosphodiester bonds. It is this linear sequence
of nucleotides that make up the primary
structure of DNA or RNA. Nucleotides consist of
3 things:
1.Nitrogenous base
1.Adenine
2.Guanine
3.Cytosine
4.Thymine(present in DNA only)
5.Uracil (present in RNA only)
2. 5-carbon sugar which is called deoxyribose
(found in DNA) and ribose (found in RNA).
3. One or more phosphate groups.
13. The nitrogen bases adenine and guanine are
purine in structure and form a glycosidic bond
between their 9' nitrogen and the 1' -OH group of
the deoxyribose. Cytosine, thymine and uracil
are pyrimidines, hence the glycosidic bonds
forms between their 1' nitrogen and the 1' -OH of
the deoxyribose.
For both the purine and pyrimidine bases, the
phosphate group forms a bond with the
deoxyribose sugar through an ester bond
between one of its negatively charged oxygen
groups and the 5' -OH of the sugar. The polarity
in DNA and RNA is derived from the oxygen and
nitrogen atoms in the backbone.
14. Nucleic acids are formed when nucleotides
come together through phosphodiester linkages
between the 5' and 3' carbon atoms.
A nucleic acid sequence is the order of
nucleotides within a DNA (GACT) or RNA
(GACU) molecule that is determined by a series
of letters. Sequences are presented from the 5'
to 3' end and determine the covalent structure of
the entire molecule.
Sequences can be complementary to another
sequence in that the base on each position is
complementary as well as in the reverse order.
An example of a complementary sequence to
AGCT is TCGA.
15. DNA is double-stranded containing both a sense
strand and an antisense strand. Therefore, the
complementary sequence will be to the sense
strand.
16. Nucleic acid design can be used to create
nucleic acid complexes with complicated
secondary structures such as this four-arm
junction. These four strands associate into this
structure because it maximizes the number of
correct base pairs, with A's matched to T's and
C's matched to G's.
Secondary Structure
Secondary structure is the set of interactions
between bases, i.e., parts of which is strands are
bound to each other. In DNA double helix, the
two strands of DNA are held together by
hydrogen bonds. The nucleotides on one strand
base pairs with the nucleotide on the other
strand.
17. The secondary structure is responsible for the
shape that the nucleic acid assumes. The bases
in the DNA are classified as Purines and
Pyrimidines.
The purines are Adenine and Guanine. Purines
consist of a double ring structure, a six
membered and a five -membered ring containing
nitrogen. The pyrimidines are Cytosine and
Thymine. It has a single ringed structure, a six -
membered ring containing nitrogen. A purine
base always pairs with a pyrimidine base
(Guanosine (G) pairs with Cytosine(C) and
Adenine (A) pairs with Thymine (T) or Uracil (U).
18. DNA's secondary structure is predominantly
determined by base-pairing of the two
polynucleotide strands wrapped around each
other to form a double helix. There is also a
major groove and a minor groove on the double
helix.
The secondary structure of RNA consists of a
single polynucleotide. Base pairing in RNA
occurs when RNA folds between
complementarity regions. Both single- and
double-stranded regions are often found in RNA
molecules. The antiparallel strands form a helical
shape.
21. Z-DNA is a relatively rare left-handed double-
helix. Given the proper sequence and
superhelical tension, it can be formed in vivo but
its function is unclear. It has a narrower, more
elongated helix than A or B.
22. Tertiary structure is the locations of the atoms in
three-dimensional space, taking into
consideration geometrical and steric
constraints. A higher order than the secondary
structure in which large-scale folding in a linear
polymer occurs and the entire chain is folded
into a specific 3-dimensional shape. There are 4
areas in which the structural forms of DNA can
differ.
1.Handedness - right or left
2.Length of the helix turn
3.Number of base pairs per turn
4.Difference in size between the major and
minor grooves
23. The tertiary arrangement of DNA's double helix in
space includes B-DNA, A-DNA and Z-DNA.
B-DNA is the most commons form of DNA in
vivo and is narrower, elongated helix than A-
DNA. Its wide major groove makes it more
accessible to proteins.
A-DNA is shorter and wider than helix B. Most
RNA and RNA-DNA duplex in this form. A-DNA
has a deep, narrow major groove which does not
make it easily accessible to proteins. On the
other hand, its wide, shallow minor groove
makes it accessible to proteins but with lower
information content than the major groove.
25. Encoding Information
Perhaps the most familiar function of a nucleic
acid in the body is that of DNA, or
deoxyribonucleic acid. DNA contains the genetic
code, which consists of the sum of all
information a cell or organism requires
performing its functions.
Your cells, for instance, have a central nucleus
that contains your DNA. Based upon the
information contained in the DNA, the cell can
produce structural and functional proteins that
allow it to function, explain Drs. Reginald Garrett
and Charles Grisham in their book
"Biochemistry."
26. The quaternary structure of nucleic acids is
similar to that of protein quaternary structure.
Although some of the concepts are not exactly
the same, the quaternary structure refers to a
higher-level of organization of nucleic acids.
Moreover, it refers to interactions of the nucleic
acids with other molecules. The most commonly
seen form of higher-level organization of nucleic
acids is seen in the form of chromatin which
leads to its interactions with the small proteins
histones.
Also, the quaternary structure refers to the
interactions between separate RNA units in the
ribosome or spliceosome.
27. There are many different roles that nucleic acids,
which include DNA and RNA, play in the human
body and in other living organisms. Scientists
continue to identify new and different functions of
nucleic acids on a regular basis. The most common
functions, however, relate to the encoding of
genetic information and production of proteins.
FUNCTIONS
28. Transferring Information
To make a structural or functional protein, a cell
needs to get genetic information from DNA out
of the nucleus and into the rest of the cell,
where the protein-producing machinery is
located. Nucleic acids called mRNA, for
messenger ribonucleic acid, form in the
nucleus.
They copy information from the DNA, and then
leave the nucleus. Out in the cytoplasm, or
liquid medium of the cell, the mRNA serves as a
working template of genetic information for the
protein-producing machinery.
29.
30. References
Biochemistry
By H. Stephen Stoker
Chemistry for Changing Times
By John W. Hill, et. al.
www.olemiss.edu/depts/chemistry/courses/chem471
/ch08_10.ppt
www.saburchill.com/IBbiology/.../02_THE_NUCLEIC_
ACIDS.ppt
www.biologyjunction.com/Nucleic%20Acids.ppt
www.biology-
resources.com/powerpoints/Genetics/01-
DNA/DNA.ppt
www.karentimberlake.com/Nucleic%20Acids.ppt
31. The Swiss scientist Johann Friedrich Miescher
discovered nucleic acids (DNA) in 1869. Later,
he raises the idea that they could be involved in
heredity.
