FACULTY OF MEDICINE AND HEALTH SCIENCES
NUCLEIC ACIDS
NUCLEIC ACIDS
• Nucleic acids are the information molecules of cells;
• Nucleic acids are the molecules which carry genetic
information that determines the morphological and
physiological processes in the nature of organisms.
• Nucleic acids, which contain the elements carbon,
hydrogen, oxygen, nitrogen and phosphorus, are
made up of monomer units or building blocks known
as the nucleotides
Historical background on Nucleic acids.
• Nucleic acids were discovered by Friedrich Miescher in 1869.
• The nucleic acids were named as such because they were
initially discovered within the nucleus of eukaryotic cells, and
because of the inherent presence of phosphate groups that
are related to phosphoric acid.
Nucleic acids
• Nucleic acids are now known to be found in all kinds
of life forms, including the prokaryotic organisms
such as the bacteria and the non-cellular living
particles called the viruses
• Outside the nucleus, nucleic acids are also found in
such organelles as the chloroplasts and mitochondria.
Structure of a nucleotide
There are three
components that
make up a
nucleotide;
• Phosphate group
• Pentose sugar
• Nitrogenous-base
Formation of the nucleotide
• When a pentose sugar is linked to a nitrogenous base, this
leads to the formation of a molecule known as the
nucleoside.
• When the phosphate group is attached to the nucleoside,
this leads to the formation of the nucleotide.
• A chain (polymer) of nucleotides eventually leads to the
formation of the nucleic acid molecule.
• The nucleic acid has a skeleton (backbone) of sugarphosphate with a nitrogenous bases projecting outwardly.
Classification of nitrogenous bases
TYPES OF NUCLEIC ACIDS
• The two types of nucleic acids are: DNA (Deoxyribonucleic
acid) and RNA (Ribonucleic acid).
• All living cells and organelles contain both DNA and RNA.
• However, viruses contain either DNA or RNA, but usually not
both.
• Nucleic acids are generally very large molecules which
consist of long chains of nucleotides.
• Nucleotides are, therefore, the basic building blocks that
constitute DNA and RNA molecules.
Furanose form of DNA and RNA
Structure of DNA
• Crick and Watson discovered in 1953
that DNA is a double helix consisting
of:
• two polynucleotide strands with
nitrogenous bases found on the
inside of the helix
• strands held together by hydrogen
bonds between the paired bases.
• Ten per turn of the helix
• two antiparallel strands of a double
helix.
Structure of DNA
• The pairing of bases is between adenine and thymine (A and
T) and between cytosine and guanine (C and G).
• These are the only combinations that fit together along the
helix.(complementary base pairing)
• Pairing of bases is by the formation of hydrogen bonds: two
are formed between adenine and thymine and three are
formed between cytosine and guanine.
Structure of DNA
Structure of DNA
• DNA is a double-stranded molecule.
• DNA molecules exist as two chains wrapped about each other in long
linear molecules in eukaryotic cells, but occur as circular molecules in
most prokaryotic organisms
• DNA contains the genetic instructions that are used in the
development and functions of all forms of living organisms.
• The main function of DNA molecules is the long-term storage of
genetic information.
• DNA contains the instructions needed to construct other components
of the cells.
• The DNA portions that carry this genetic information are called the
genes.
Structure of RNA
• The RNA is a single stranded molecule,
produced by transcription (copying)
from DNA.
Three functional types of RNA.
1.messager RNA (mRNA) whose role is
to carry genetic information from the
nucleus to the cytoplasm.
2. transfer RNA (tRNA) brings the
rightful amino acid on the ribosome.
• Ribosomal RNA(rRNA)combines with
ribosomes in the synthesis of proteins.
Replication of DNA
• Strands of the DNA double helix are built up from free nucleotides.
• Before nucleotides can be replicated, the DNA double helix has to
unwind and the hydrogen bond, holding these strands together must
be broken.
• enzyme helicase brings about the unwinding process and hold, the
strands apart for replication to occur. Each point along the DNA
molecule where this occurs is called a replication fork.
• At a replication fork, both strands act as templates.
• the enzyme DNA polymerase binds to each of the DNA strands and
begins to move along them.
Replication of DNA
• New nucleotides could then line up along each strand and
join up to form complementary strands along each half of
the original molecule.
• The new DNA molecules would be just like the old ones,
because each base would only pair with its complementary
one.
• Each pair of strands could again form into a double helix,
exactly like the original one.
• semi-conservative replication, because half of the original
molecule is kept (conserved) in each of the new molecules.
Replication of DNA
ATP - a nucleotide with unusual features
• It is a relatively small, soluble
organic molecule - a nucleotide
which carries three phosphate
groups linked together in a linear
sequence
• ATP is formed from adenosine
diphosphate (ADP) and a
phosphate ion (Pi) by transfer of
energy from other reactions.
SUMMARY
• Nucleic acids are polymers. They are polynucleotides composed of long
chains of nucleotide monomers (a pentose, phosphate molecule and a
nitrogenous base)combined together.
• There are two forms of nucleic acid, DNA and RNA These forms differ in the
sugar and in the bases they contain and in their function in the cell.
• DNA is found in the chromosome and RNA in both the nucleus and the
cytoplasm.
• DNA also in found mitochondria and chloroplasts
• ATP is the universal energy currency molecule by which energy is
transferred to do useful work.
• ATP is a soluble molecule, formed in the mitochondria but able to move
into the cytosol by facilitated diffusion. It diffuses freely within cell.
• DNA molecule is the genetic code. The sequence of bases in the DNA
molecule may be transcribed to a complementary sequence in
messenger RNA (mRNA).
• Once formed, messenger RNA passes out of the nucleus into the
cytoplasm and to a ribosome where polypeptide synthesis occurs.