The Genetic Code

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The Genetic Code
The main features of the genetic code are as follows:
Each amino acid in a protein is coded for by a sequence of three nucleotide bases
The code is a degenerative code in that most amino acids have more than one codon
The code is non-overlapping as each base code is only read once
The code is universal as it is the same in all organisms
Ribonucleic Acid (RNA)
There are three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA
(rRNA ­ although this isn't required by the specification.) RNA is a nucleic acid and consists of a single
polynucleotide chain. Its subunits (monomers) rare nucleotides, each nucleotide contains three
components; a pentose sugar molecule, a phosphate molecule, and a nitrogenous base. The pentose
sugar (5 carbon) is ribose and there are four possible nitrogenous bases; adenine, cytosine, guanine,
and uracil (A, C, G, U.)
Pentose Sugar Yes Yes
Phosphate Group Yes Yes
Nitrogenous Base Yes Yes
Which sugar? Deoxyribose Ribose
Which bases? A,C,G,T A,C,G,U
Strand/s? Double Single
Hydrogen Bonds? Yes Sometimes (see later notes)
Polynucleotide? Yes Yes
Messenger RNA (mRNA)
mRNA is manufactured when DNA
forms a mirror copy of one part of one
of its two strands (mRNA is about a
gene length long) and so it has great
variety. Once formed it leaves the
nucleus via nuclear pores and enters
the cytoplasm, where it associates
with ribosomes. It's suited to such a
function as it has sequences of many
triplets of organic bases that code for
specific polypeptides. It can also be
easily broken down so that it only
exists whiles needed to produce a

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Transfer RNA (tRNA)
tRNA is a small, single stranded molecules of
about 80 nucleotides. It is folded into a clover
leaf shape with one end of the chain beyond the
other, allowing amino acids to attach easily to it
here. Each tRNA can only carry a single amino acid.
Three organic bases, known as the anticodon, are
at the other side of the molecule. For each amino
acid there is a different organic base on the
anticodon.…read more

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