NUCLEIC ACIDS
 Nucleic acids are macromolecules, found in all cells, precipitate in the storage, transmission and
translation of genetic information
‒
are the largest and the most complex organic molecules
‒
Friedrich Miescher who discovered nucleic acids in 1871
TYPES OF NUCLEIC ACIDS
 Deoxyribonucleic acid (DNA)
‒
present in the chromosomes of the nucleus
‒
contains the organism’s genetic information, including instructions for how to make
proteins
 Ribonucleic acid (RNA)
‒
present both inside and outside the nucleus
‒
directs the building of protein
NUCLEOTIDES
‒
the building blocks (monomers) of nucleic acid
o N – base (Nitrogenous base)
o Sugar – ribose or deoxyribose
o Phosphate (Phosphoric acid)
COMPONENTS OF NUCLEOTIDES
 Bases
‒ Purine
‒
o
adenine (A)
o
guanine (G)
Pyrimidines
o
o
o
cytosine (C
thymine (T)
uracil (U)
DNA - adenine (A), guanine (G), cytosine (C), thymine (T)
RNA - - adenine (A), guanine (G), cytosine (C), uracil (U)
 Sugars
‒
The sugar component of RNA is D-ribose
‒
In DNA, it is 2-deoxy-D-ribose
‒
the combination of sugar and base is known a nucleoside
‒
all the bases are attached to the corresponding pentose sugar by a β-N-glycosidic bond
between the first carbon of the pentose sugar and Nꝰ' of a purine or N¹' of a pyrimidine
 Phosphate
‒
Nucleotides may have a single phosphate group, or a chain of up to three phosphate
groups, attached to the 5’ carbon of the sugar
‒
when this group forms a phosphate ester bond with the CH, OH group of a nucleoside,
the result is a compound known as nucleotide
‒
the sugar-phosphate backbone
‒
when a polynucleotide is formed, the 5′ phosphate of the incoming nucleotide attaches
to the 3′ hydroxyl group at the end of the growing chain
‒
these nucleoside linkages are called phosphodiester bonds and are the same in RNA
and DNA
STRUCTURE OF NUCLEIC ACIDS
‒
NA structure is often divided into three different levels:
‒
Primary Structure
‒
Secondary Structure
‒
Tertiary Structure
 PRIMARY STRUCTURE
‒
Linear sequence of nucleotides
‒
the backbone of the molecule
‒
the bases that are the side-chain groups
 SECONDARY STRUCTURE
‒
is the three-dimensional shape of a nucleic acid polymer
‒
In 1953, James Watson and Francis Crick established the three dimensional structure of
DNA.
‒
DNA is composed of two strands entwined around each other in a double helix
‒
the set of interactions between bases
‒
The nucleotides on one strand base pairs with the nucleotide on the other strand
‒
Erwin Chargaff (1905)
adenine (A) = thymine (T)
guanine (G) = cytosine (C)
 TERTIARY STRUCTURE
‒
packaging of DNA in the nucleus
‒
supercoiling
‒
DNA molecules in the nuclei coiled around basic protein molecules called histones
‒
The acidic DNA and the basic histones attract each other by electrostatic forces,
combining to form units called nucleosomes
PLASTICITY AND STABILITY
 HYDROGEN BONDING
‒
hydrogen bonds formed between the bases
 BASE STACKING
‒
the bases are hydrophobic, so they try to avoid contact with water
‒
through their hydrophobic interactions, they stabilize the double helix.
‒
stacking eliminates any gapes between the bases and excludes the maximum amount
of water from the interior of the double helix
‒
The backbone provides structural stability for the DNA and RNA molecules