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Transcript Molecular Biology - hrsbstaff.ednet.ns.ca
Molecular
Biology
2.7 DNA Replication,
transcription and translation
DNA to Protein Synthesis
The
function of most genes is to specify
the sequence of amino acids in a
particular polypeptide.
Two processes are needed to produce a
polypeptide using the base sequence of
a gene.
Transcription
Translation
Transcription
Transcription is the synthesis
of mRNA copied from the
DNA base sequences by RNA
polymerase.
The enzyme RNA polymerase
binds to a site on the DNA at
the start of a gene
The RNA polymerase
separates the double strand
of DNA and pairs up RNA
nucleotides with
complementary bases.
Transcription
The
RNA polymerase forms
covalent bonds between
the nucleotides
Transcription stops at the
end of the gene. The
completed mRNA is
released.
Transcription
The
completed mRNA has
a base sequence that is
complementary to the
template DNA strand.
Note: Uracil replaces
Thymine
Complete the transcription portion of
the practice sheet
Translation
Translation
is synthesis of
polypeptides on
ribosomes
Ribosomes
are complex
structures that consist of
a small and large subunit with binding sites for
each of the molecules
used in translation.
Translation
The
amino acid
sequence of
polypeptides is
determined by mRNA
according to the
genetic code
Translation
Codons
of three bases
on mRNA correspond to
one amino acid in a
polypeptide
“Genetic
Code” = The
translation “dictionary”
that enables the cellular
machinery to convert
the base sequence on
mRNA into the amino
acid sequence
Translation
There
are 20 amino
acids and only 4
nucleotide bases.
Living organisms use a
triplet code with 3 bases
coding for an animo
acid.
The sequence of 3
bases on the mRNA =
CODON
Examine the list of codons
Translation
There
are 3 “stop”
codons that code for
the end of translation.
Different codons can
code for the same
amino acid.
The code is
“degenerate”
Translation
Translation
depends on
complementary base
pairing between codons
on mRNA and
anticodons on tRNA
The
amino acids are
carried on tRNA
The tRNA has a 3 base
ANTICODON
complementary to the
mRNA codon
Complete the
translation portion of
the worksheet