Protein Synthesis
Step 2: Translation
Review
Protein Synthesis: The process by which
the message of DNA is used to make
proteins
 Step 1: Transcription

◦ Takes place in the nucleus
◦ Changes DNA to mRNA
◦ Base Pairs: A-U and C-G
Step Two: Translation “to decode or
decipher the meaning of”
 Now that our mRNA molecule has
been made, it’s time for its message
to be made into a protein
sequence.
 How does the mRNA sequence
translate into an amino acid
sequence?
Step Two: Translation
 Problem:
◦ There are 20 different amino acids.
◦ There are 4 RNA bases.
A
T
phe
C
G
ile
leu
val
met
pro
ser
ala
thr
his
tyr
asn
gln
asp
lys
cys
glu
arg
trp
gly
Step 2: Translation

Translation in 3 steps:
1. mRNA leaves the nucleus and finds a
ribosome in the cytoplasm
2. tRNA brings amino acids to the ribosome
3. rRNA joins the amino acids together by
matching the codes between mRNA and
tRNA
tRNA
Ribosome
(rRNA)
Step Two: Translation
Watch this simplified animation:
http://www.stolaf.edu/people/giannini/flasha
nimat/molgenetics/translation.swf

Watch the more complex animation!
 http://wwwclass.unl.edu/biochem/gp2/m_biology/ani
mation/gene/gene_a3.html

Step Two: Translation
So how do you exactly go about
determining what protein your cells are
going to make?
FIRST, divide the mRNA sequence into
codons.
1.
2.
◦
Codons are three-base sections of mRNA:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
Step Two: Translation
Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
2.
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
?
Use a Codon Chart!
Step Two: Translation
2.
Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
?
Step Two: Translation
2.
Since each 3-letter combination “codes”
for an amino acid, you need to figure out
what amino acid matches up with each
codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
Important Codons/Amino Acids!
Codon
Amino
Acid
Signal
AUG
Methionine
START
UAA
None
STOP
UAG
None
STOP
UGA
None
STOP
tRNA
Ribosome
(rRNA)
How does tRNA know where to go?
tRNA has an anticodon that coordinates with
the codon on mRNA
Anti-codon
Anti-codon
and codon
pair up!
RECAP:
1.
2.
3.
DNA is transcribed
into mRNA in the
nucleus.
The mRNA leaves the
nucleus and enters the
cytoplasm.
The protein is
translated from the
mRNA sequence using
tRNA and amino acids.