MBI- Translation Flashcards
describe the basic structure of t-rna
tRNA has an
anticodon loop
that has bases
complementary to
the code, and it also
has an amino acid
acceptor end to
which it binds to
amino acids.
tRNAs are specific
for each amino acid
(Figure 5.12). For
initiation, there is
another specific tRNA that is referred to as initiator tRNA. There are no
tRNAs for stop codons. In figure 5.12, the secondary structure of tRNA
has been depicted that looks like a clover-leaf. In actual structure, the
tRNA is a compact molecule which looks like inverted L.
why are trna called adapter molecules
Francis Crick postulated the presence of an adapter molecule
that would on one hand read the code and on other hand would bind
to specific amino acids. The tRNA, then called sRNA (soluble RNA),
was known before the genetic code was postulated.
define translation
Translation refers to the process of polymerisation of amino acids to
form a polypeptide (Figure 5.13). The order and sequence of amino acids
are defined by the sequence of bases in the mRNA.
what is charging or aminoacylation of trna
The amino acids are
joined by a bond which is known as a peptide bond. Formation of a
peptide bond requires energy. Therefore, in the first phase itself amino
acids are activated in the presence of ATP and linked to their cognate
tRNA – a process commonly called as charging of tRNA or
aminoacylation of tRNA to be more specific. If two such charged tRNAs
are brought close enough, the formation of peptide bond between them would be favoured energetically. The
presence of a catalyst would enhance
the rate of peptide bond formation.
what is the protein synthesizing machine?
The cellular factory responsible for
synthesising proteins is the ribosome.
The ribosome consists of structural
RNAs and about 80 different proteins.
In its inactive state, it exists as two
subunits; a large subunit and a small
subunit. When the small subunit
encounters an mRNA, the process of
translation of the mRNA to protein
begins. There are two sites in the large
subunit, for subsequent amino acids
to bind to and thus, be close enough
to each other for the formation of a
peptide bond. The ribosome also acts as a catalyst (23S rRNA in bacteria
is the enzyme- ribozyme) for the formation of peptide bond.
describe a translational unit in mrna
A translational unit in mRNA is the sequence of RNA that is flanked
by the start codon (AUG/ at 5’ end) and the stop codon(UAG/UGA/UAA/ at 3’end) and codes for a polypeptide.
An mRNA also has some additional sequences that are not translated
and are referred as untranslated regions (UTR). The UTRs are present
at both 5’ -end (before start codon) and at 3’ -end (after stop codon). They
are required for efficient translation process.
explain intiation
For initiation, the ribosome binds to the mRNA at the start codon (AUG)
that is recognised only by the initiator tRNA.
explain elongation
The ribosome proceeds to the
elongation phase of protein synthesis. During this stage, complexes
composed of an amino acid linked to tRNA, sequentially bind to the
appropriate codon in mRNA by forming complementary base pairs with
the tRNA anticodon.
explain translocation
The ribosome moves from codon to codon along the
mRNA. Amino acids are added one by one, translated into Polypeptide
sequences dictated by DNA and represented by mRNA. At the end, a release
factor binds to the stop codon, terminating translation and releasing the
complete polypeptide from the ribosome.
