Nucleic acids: the code of life
•The next class of biological molecules, nucleic
acids, are the information-bearing “code of life”. Like
proteins, nucleic acid have specific linear sequence
of subunits. This linear structure is called a special
language of chemical letters. The letters spell out
instructions both for characteristics passed on to
offspring and for translating that hereditary message
into proteins, which will be built into new cell parts,
cells and organisms.
•Structure of the nucleic acids
•Nucleic acids are polymer chain made up of
building blocks called nucleotides. Each
nucleotide consists of a nitrogen –containing
base, a five –carbon sugar, and a phosphate
group. There are two types of nucleic acids:
deoxyribonucleic acid (DNA) and ribonucleic acid
(RNA). The main chemical difference is that the
DNA contains sugar molecules with a five carbon
monosaccharide called deoxyribose and the RNA
contain a similar sugar called ribose. These
sugars become bonded to the nitrogen containing
bases through a condensation reaction, creating
a nucleoside.
Nucleic Acid
Structure
Nitrogen-containing bases
These are five different nitrogencontaining bases in the nature –
adenine A, guanineG, cytosineC,
thymineT and uracil U. Each of
them has a slightly different chemical
composition. These are the “ letters”
that make up the nucleic acid alphabet,
and although they are fewer than the 20
amino acids in proteins, they are just as
capable of encoding diversity. The
addition of a phosphate group to the
sugar by another condensation reaction
yields a nucleotide.
Bio-molecule: Nucleic Acids.
There are two main types of nucleic acids
DNA(deoxyribonucleic acid) RNA (ribonucleic
Master copy of an
acid) Helps make
organism’s information
proteins.
code
•DNA monomers use all bases but uracil. The
DNA molecule itself consists of two polymer
chains twisted around each other in a double
helix. The outer spiral “rails” formed by
deoxyribose sugars are connected by phosphate
“bridges”, and the ladder rungs formed by pairs
of bases (adenine and thymine, or guanine and
cytosine) are attached by hydrogen bonds. The
precise order of the “rings” carries information
about the primary structure of enzymes and
other proteins. In turn, enzymes act on row
materials to build up all four types of biological
molecules – carbohydrates, lipids, proteins and
nucleic acids – as well as the cell part
constructed of them, DNA responsible for the
passing of hereditary information from one cell
generation to the next.
•DNA is the fundamental building block of
genetic material. DNA makes the genes. The
key how genes function lies in the unique
double helix structure of DNA. DNA stores
information in order of its bases. The order of
the bases specifies the order of amino acids in
polypeptides. The four bases can be in any
order, so that each gene has a different – but
specific – sequence. From this variability
comes DNA’s remarkable capacity to store
almost infinite amounts of information. Each of
the four bases tends to form weak hydrogen
bonds with only one of the other three bases.
•Adenine joint with thymine, and cytosine joints
with guanine. This phenomenon is called
complementary base pairing. Because of it, the
bases of the two – nucleotide chains bond to
each other, holding the two chains together, with
the bases facing inward. DNA in higher organisms
is extremely long and must be packaged neatly so
that it doesn’t tangle during cell division. It is
would around spools of proteins called histones
and coiled upon itself repeatedly. Because of
base pairing, each chain acts as a template for
the creation of a new copy of the other chain,
thus, two new strands are created one from each
half of the old chain in a process called semiconservative replication.
RNA
•RNA molecules are made up of single chains
that may fold into complex shapes or remain
stretched out as long threads. Because of their
structural and functional features RNA can be
divided into messenger RNA, transfer RNA,
and ribosomal RNA. The base uracil replaces
the base thymine. RNA molecules are also
much shorter than DNA molecules because
they tend to code only one or two genes. The
mRNA acids are about 5% of the cell’s RNA.
They translate the information from DNA and
take part in protein’s building processes.
•The tRNA translates the m RNA codons into
amino acid sequence. The t RNA acids are
about 15% from the cell’s RNA. They transport
amino acids to the ribosomes where the
proteins are built. There are 20 amino acids
and 20 types of tRNA . Every tRNA can be
paired with only one amino acid. Ribosomal
RNA is 80% of cell’s RNA. They take part in
building of cell’s organelle –ribosomes.
Proteins are built in ribosomes.
The genetic code
•Much of the genetic research in the midtwenty century went to reveal that a gene is
made of DNA and that it acts by specifying the
amino acid sequence in a polypeptide chain.
The next question arising from this work is :
exactly how does the information in DNA
become decoded and translated into protein
structure? The answer unfolded over decades
of research and can be summarized this way :
genetic information within each cell flows from
DNA to RNA to protein. Bulgarian /English
dictionary acts as a sort of code when you
translate a paragraph from Bulgarian into
English.
•
In a similar way cells need a code for
translating words from the language of
nucleic acids (bases) to the language of
proteins (amino acids). This code is called the
genetic code. During protein synthesis, the
translator is transfer RNA. The genetic code is
identical in nearly all organisms. A group of
three bases is a codon. Except for the start
codon and the three stop codons, each codon
specifies one amino acid. Several different
codons may specify the same amino acid but
no codon specifies more than one amino acid
RNA.
Protein Folding in Sickle Cell Anemia