Genes and Gene Expression
Ribonucleic acid RNA
RNA unlike
DNA forms a single strand in which nucleotides make up.
Each
nucleotide is made of:
·
The
pentose sugar ribose
·
An
organic base Adenine (A) , Guanine (G) Cytosine (C) and Uracil (U)
·
A
phosphate group
·
There
are two types of organic bases; purines and pyrimidines.
·
Purines
are made up of Hexagonal and Pentagonal rings, Adenine and Guanine are purines.
·
Pyrimidines
are made up of a single Hexagonal ring and consist of Thymine, Cytosine and
Uracil.
·
Remember
form AS - Guanine with Cytosine and Adenine with Uracil (RNA) or Thymine (DNA)
Transcription= DNA à RNA
Translation = RNA à Protein
Therefore
DNAà RNA àProtein
There are
two types of RNA that are important in protein synthesis, they are
·
Messenger
RNA (mRNA)
·
Transfer
RNA
Important
Note!
·
When
we talk about a triplet code or a codon we are talking about messenger RNA
·
In
RNA there is no Thymine but rather it is replaced by Uracil
Messenger
RNA (mRNA)
·
mRNA
is a long strand that is arranged in a single helix
·
mRNA
leaves the nucleus via pores in the nuclear envelope and enters the cytoplasm
where it comes into contact with the genetic code.
Transfer
RNA (tRNA)
·
tRNA
is a smaller molecule but is still made up of a single strand.
·
The
single strand is folded into a clover-leaf shape where one end of the strand
extends beyond the other.
This extended section is that which an amino acid can be attached to.
·
At
the opposite end of the tRNA there is an anticodon. The anticodon is made up of
three other bases.
·
For
each amino acid there is a different sequence of organic bases on the
anticodon.
During
protein synthesis the anticodon pairs with the three complementary bases that
make up the triplet bases (codon) on mRNA. The structure of tRNA means that is
structurally suited to its role in lining up amino acids on the mRNA template
during the protein synthesis.
·
The
end chain is for attaching amino acids
·
The
anticodon is for pairing with the codons of mRNA
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