Transcript Protein Synthesis - East Aurora Schools

Protein Synthesis
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Background Information
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All information is stored in DNA
RNA “reads” the DNA code
DNA is found in base triplets (sets of
three letters)
Complimentary sequence of RNA
(after reading DNA) will be called a
codon
Done in the cell Nucleus
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Transcription
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In this phase the genetic information represented
by the sequence of each DNA base triplet serves
as a template for copying the information into a
complimentary sequence of RNA
Three kinds of RNA will be made from the DNA
template
1. Messenger RNA (mRNA) directs protein
synthesis
2. Ribosomal RNA (rRNA) joins with ribosomal
proteins to make ribosomes
3. Transfer RNA (tRNA) binds to an amino
acid and holds it in place on a ribosome until it is
incorporated into a protein during translation
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Transcription Cont.
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The process is catalyzed by the enzyme
RNA polymerase
This enzyme needs to be told where to
begin and where to end
The PROMOTER is the nucleotide sequence
of DNA that instructs RNA polymerase
where to begin.
During the transcription process the bases
are paired up in a complimentary manner
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Cont.
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The bases C, G, and T from DNA pair up
with G, C, and A in the RNA.
However, adenine in the DNA template
pairs up with U (uracil) and not thymine in
the RNA sequence
So, DNA (CGA) reads (GCU) in RNA.
Transcription continues until the
terminator sequence is read
Once this happens RNA Polymerase
detaches and the process ends.
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Translation
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Process where the nucleotide
sequence in an mRNA molecule
specifies the amino acid sequence of
a protein
Occurs on a ribosome in the cytosol
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Stages of Translation
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mRNA binds to the small part of a
ribosome at the mRNA binding site
Initiator tRNA binds to the start codon
(AUG) on mRNA.
The tRNA anticodon (UAG) attaches to the
mRNA codon (AUG) by pairing between
the complementary bases
AUG is the start codon, and it is the codon
for methionine, which means that
methionine is always the first amino acid
in the protein building process
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Stages Cont.
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From this point, the ribosome will continue
to add amino acids in the sequence that is
given to it by the mRNA strand.
The ribosome reads the remainder of the
strand one codon at a time, and from here
the protein lengthens
The process moves in what we call a 3’ to
5’ direction
The process ends when a stop codon is
read, which leads to the detachment of
the protein from the final tRNA.
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Final Translation Facts
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Occurs at about a 15 peptide bond
per second rate
As one ribosome finishes with a
strand of mRNA, another one usually
picks it up and translates it, so that
more than one copy of protein can
be made
Process constantly occurs.
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