Nucleic acids like DNA and RNA are long biopolymers composed of nucleotides. DNA stores genetic information in cells and is made up of deoxyribonucleotides arranged in a double helix structure. RNA is involved in protein synthesis and comes in several types including mRNA, tRNA, and rRNA. Nucleic acids have a primary structure defined by their linear sequence of nucleotides joined by phosphodiester bonds, and a secondary structure involving base pairing of nucleotides that gives them their characteristic helical shape.

1. NUCLEIC ACIDS
HISTORY:
FriedrichMiescherin1869:
 isolatedwhathe called nucleinfromthe nuclei of puscells
RichardAltmannin 1889:
 Nucleinwasshowntohave acidicproperties,henceitbecame called nucleicacid
The Tetranucleotidehypothesis:
 Up to 1940 researcherswere convincedthathydrolysisof nucleicacidsyieldedthe fourbasesin
equal amounts.
 Nucleicacidwaspostulatedtocontainone of each of the four nucleotides,the tetranucleotide
hypothesis.
 Takahashi (1932) proposedastructure of nucleotidebasesconnectedbyphosphodiester
linkages.

2. NUCLEIC ACIDS:
• NucleicAcidsare verylong,thread-like polymers,made upof a lineararrayof monomerscalled
nucleotides.
• Nucleicacidsvaryin size innature
• tRNA moleculescontainasfewas80 nucleotides
• Eukaryoticchromosomescontainasmanyas
100,000,000 nucleotides.
Nucleicacids are moleculesthatstore informationforcellulargrowthandreproduction
DNA and RNA are nucleicacids, long,thread-likepolymers made upof a lineararrayof monomers
callednucleotides
Nucleic acids are biopolymers, or large biomolecules, essential for all known forms of life.
Nucleic acids, which include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are made
from monomers known as nucleotides. Each nucleotide has three components: a 5-carbon
sugar, a phosphate group, and a nitrogenous base. If the sugar is deoxyribose, the polymer is
DNA. If the sugar is ribose, the polymer is RNA.
Nucleic acid sequences:
One DNA or RNA molecule differs from another primarily in the sequence of nucleotides.
Nucleotide sequences are of great importance in biology since they carry the ultimate
instructions that encode all biological molecules, molecular assemblies, subcellular and cellular
structures, organs and organisms, and directly enable cognition, memory and behavior
Enormous efforts have gone into the development of experimental methods to determine the
nucleotide sequence of biological DNA and RNA molecules, and today hundreds of millions of
nucleotides are sequenced daily at genome centers and smaller laboratories worldwide. In
addition to maintaining the GenBank nucleic acid sequence database, the National Center for
Biotechnology Information (NCBI, provides analysis and retrieval resources for the data in
GenBank and other biological data made available through the NCBI Web site

3. TYPES OF NUCLEIC ACIDS
 There are twotypesof nucleicacids:
1. deoxyribonucleic acid (DNA) and
2. ribonucleic acid (RNA)
These are polymersconsistingof longchainsof monomerscalled nucleotides
A nucleotide consistsof anitrogenousbase,pentose sugaranda phosphate group.
All nucleotidescontainthree components:
 A nitrogenheterocyclicbase
 A pentose sugar
 A phosphate residue

4.  DNA:
deoxyribonucleicacid nucleicacidthatstores geneticinformation foundinthe nucleusof amammalian
cell.
DNA as geneticmaterial: The circumstantial evidence
1. Presentinall cellsandvirtuallyrestrictedtothe nucleus
2. The amount of DNA in somaticcells(bodycells)of anygivenspeciesis constant(like the number
of chromosomes)
3. The DNA contentof gametes(sex cells)ishalf thatof somaticcells.
In casesof polyploidy(multiplesetsof chromosomes) the DNA contentincreasesbya
proportional factor
4. The mutageniceffectof UV lightpeaks at 253.7nm. The peakfor the absorptionof UV lightby
DNA
Deoxyribonucleic acid (DNA) is a nucleic acid containing the genetic instructions used in the
development and functioning of all known living organisms . The DNA segments carrying this
genetic information are called genes. Likewise, other DNA sequences have structural purposes,
or are involved in regulating the use of this genetic information. Along with RNA and proteins,
DNA is one of the three major macromolecules that are essential for all known forms of life.
DNA consists of two long polymers of simple units called nucleotides, with backbones made of
sugars and phosphate groups joined by ester bonds. These two strands run in opposite
directions to each other and are, therefore, anti-parallel. Attached to each sugar is one of four
types of molecules called nucleobases (informally, bases). It is the sequence of these four
nucleobases along the backbone that encodes information. This information is read using the
genetic code, which specifies the sequence of the amino acids within proteins. The code is read
by copying stretches of DNA into the related nucleic acid RNA in a process called transcription.

5. Within cells DNA is organized into long structures called chromosomes. During cell division
these chromosomes are duplicated in the process of DNA replication, providing each cell its
own complete set of chromosomes. Eukaryotic organisms (animals, plants, fungi, and protists)
store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as
mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA
only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact
and organize DNA. These compact structures guide the interactions between DNA and other
proteins, helping control which parts of the DNA are transcribed.
TYPES OF DNA:
Have three Types
A-DNA B-DNA Z-DNA
1) A- DNA:
 Right-handedhelix
 Widest
 planesof the base pairs inclinedtothe helix axis
 6A hole alonghelix axis
 narrow + deepmajorgroove
 Wide + shallowminorgroove
2) B-DNA:
i. Right-handedhelix
ii. intermediate
iii. planesof the base pairsnearlyperpendiculartothe helix axis

6. iv. tinycentral axis
v. wide + deepmajorgroove
vi. narrow + deepminorgroove
3) Z-DNA:
i. Left-handedhelix
ii. Narrowest
iii. planesof the base pairsnearlyperpendiculartothe helix axis
iv. no internal spaces
v. no majorgroove
vi. narrow + deepminorgroove
 RNA
ribonucleic acid
Ribonucleic acid (RNA) functions in converting genetic information from genes into the amino
acid sequences of proteins. The three universal types of RNA include transfer RNA (tRNA),
messenger RNA (mRNA), and ribosomal RNA (rRNA). Messenger RNA acts to carry genetic
sequence information between DNA and ribosomes, directing protein synthesis. Ribosomal
RNA is a major component of the ribosome, and catalyzes peptide bond formation. Transfer
RNA serves as the carrier molecule for amino acids to be used in protein synthesis, and is
responsible for decoding the mRNA. In addition, many other classes of RNA are now known.
3 typesof RNA in a cell
I. Ribosomal RNAs(rRNA) are componentsof ribosomes
II. MessengerRNAs(mRNA) carrygeneticinformation
III. TransferRNAs(tRNA) are adaptermoleculesintranslation
1: Ribosomal RNA:
 Ribosomesare the sitesof proteinsynthesis

7. - theyconsistof ribosomal DNA (65%) and proteins(35%)
- theyhave twosubunits,alarge one and a small one
2: Messenger RNA:
 MessengerRNAcarriesthe geneticcode tothe ribosomes
- theyare strands of RNA thatare complementarytothe DNA of the gene forthe proteintobe
synthesized
3: Transfer RNA:
 Transfer RNA translatesthe geneticcode fromthe messengerRNA andbrings specificamino
acidsto the ribosome forproteinsynthesis
 Each aminoacid isrecognizedbyone or more specifictRNA
 tRNA has a tertiarystructure that isL-shaped
- one endattachesto the aminoacid and the otherbindstothe mRNA bya 3-base
complimentarysequence

8. RNA and Transcription:
DNA is inthe nucleus
Proteinsare synthesizedonribosomesinthe cytoplasm
RNA carriesthe geneticinformationfromthe nucleustothe cytoplasm
ThisRNA iscalledmessengerRNA (mRNA)
RNA Structure
Transcriptionof a DNA molecule resultsinamRNA
molecule thatis single-stranded.
RNA moleculesdonothave a regularstructure like DNA.
The structuresof RNA moleculesare complexandunique.
RNA moleculescanbase pairwithcomplementary DNA
or RNA sequences.
G pairswithC,A pairs withU, andG pairswithU.

9.  STRUCTURE OF NUCLEIC ACID
Nucleic acid structure refers to the structure of nucleic acids such as DNA and RNA. Chemically
speaking, DNA and RNA are very similar. Nucleic acid structure is often divided into four
different levels: primary, secondary, tertiary and quaternary
1: Primary structure:
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 components:
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
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. 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. DNA is double-stranded containing
both a sense strand and an antisense strand. Therefore, the complementary sequence will be to
the sense strand.

10. 2: Secondary structure
Secondary structure is the set of interactions between bases, i.e., which parts of 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. 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)). 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.
3: Tertiary structure:
Tertiary structure refers to the locations of the atoms in three-dimensional space, taking into
consideration geometrical andsteric constraints. It is 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.
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