Transcript Steps of Translation

The Central Theme of Molecular
Biology is Protein Synthesis
Step I: Going from DNA to RNA called Transcription
Step II: Going from RNA to Protein called Translation
Step I
Step II
The 3 types of RNA involved in
Protein Synthesis
• mRNA = Messenger RNA
– Carries information from nucleus to cytoplasm
• rRNA = Ribosomal RNA
– Make ribosomes which are where amino acids
are assembled into proteins
• tRNA = Transfer RNA
– Carries amino acids to the ribosome to be
assembled into proteins
Step 1 in Protein Synthesis is
Transcription
Transcription is the process of making mRNA from
DNA and then moving the mRNA from the nucleus
to the cytoplasm where protein synthesis takes
place.
First: Enzymes (RNA
polymerase) unzip the
molecule of DNA at the gene
being transcribed
• 2nd:
– A complementary mRNA
strand is assembled using
a template DNA strand
• Third:
– The new mRNA strand leaves the
nucleus and enters the cytoplasm
where it goes to the ribosome.
Summary of Transcription
1. It is the first stage of protein synthesis.
2. mRNA copy is made from a DNA template
3. mRNA copy travels from the nucleus to the
cytoplasm
Step 2 in Protein Synthesis
is Translation
•
•
Process of converting the mRNA strand
information into amino acids using codons.
Takes place at ribosomes located in the
cytoplasm
Amino Acids
Why is it called translation?
• RNA is written in the language of nucleotides
– AUG CUA
• Proteins are written in the language of amino
acids
– There are 20 amino acids that are the building blocks
of proteins
– Examples are arginine, histidine, glycine, etc……
• This means that the RNA message must be
translated into amino acids during translation and
we use CODONS to do this!
mRNA Codons
• A codon (triplet) is a group of three
nucleotides on mRNA that codes for a
specific amino acid
• Each amino acid has it’s own codon and
sometimes more than one codon!
Codon examples:
UCG = serine
CAU = histadine
UUU = phenylalanine
A CODON CHART
Codons continued
Codons are the code that
tells ribosomes
1.Which amino acid to
attach next
2. Where to start
translation
3. Where to stop
translation
Practice Time!
• Okay practice time is now over!
tRNAs: Transfer RNA
• Consists of 80 Anticodon
RNA nucleotides
• Has an Anticodon
which is made to
pairs up with an
mRNA codon
• tRNAs carry the
amino acids to
the ribosome
Steps of Translation
1. mRNA attaches to ribosome at the start
codon
2. A tRNA carrying an amino acid approaches
3. The Anticodon on the tRNA pairs with codon
4. The tRNA drops off it’s amino acid
5. An enzyme forms a peptide bond between
amino acids
6. This process continues to form a protein
until a STOP codon is reached and then the
new protein is released.