1. F. PROTEIN SYNTHESIS [or translating the message]
1. The code mRNA
a. the message on mRNA is written in 3-letter triplets called codons
there are 20 different amino acids, so how many codons do we need?
given the words are 3 letters long and we have a choice of 4 letters,
how many words do we make?
b. there are 43 or 64 possible codons
c. pg 248 shows the codons – you will have to learn the patterns but NOT memorize this with the exception of the START and the STOP codons

2. 2nd BASE
3rd BASE
1st BASE U C A G
UUU Phe
UUC Phe
UUA Leu
UUG Leu
UCU Ser
UCC Ser
UCA Ser
UCG Ser
UAU Tyr
UAC Tyr
UAA stop
UAG stop
UGU Cys
UGC Cys
UGA stop
UGG Trp
CUU Leu
CUC Leu
CUA Leu
CUG Leu
CCU Pro
CCC Pro
CCA Pro
CCG Pro
CAU His
CAC His
CAA Gln
CAG Gln
CGU Arg
CGC Arg
CGA Arg
CGG Arg
AUU Ile
AUC Ile
AUA Ile
AUG Met
ACU Thr
ACC Thr
ACA Thr
ACG Thr
AAU Asn
AAC Asn
AAA Lys
AAG Lys
AGU Ser
AGC Ser
AGA Arg
AGG Arg
GUU Val
GUC Val
GUA Val
GUG Val
GCU Ala
GCC Ala
GCA Ala
GCG Ala
GAU Asp
GAC Asp
GAA Glu
GAG Glu
GGU Gly
GGC Gly
GGA Gly
GGG Gly

3. d. notice that UUU & UUC both code for phe and CUU,
d. notice that UUU & UUC both code for phe and CUU, CUC, CUA & CUG all code for leu this indicates that the 3rd letter is the least important in the code
e. only two amino acids have a unique code UGG  trp and AUG  met
f. all proteins must start with met as AUG is the start code; this may be removed later
g. there is no amino acid that is coded by UAA, UAG or UGA and so the protein breaks here and these are called STOP codes

4. 2. The ribosomes [rRNA]
a. the rRNA holds together the large subunit [60s] and the small subunit [40s] to form the active ribosome [80s]
b. the 5’ [CAP region] adheres to the active ribosome
c. the ribosome will move the mRNA through it starting at the 5’ end and going toward the 3’ end

5. 3. The tRNA
a. each tRNA has a cross-like structure [pg 251]
at the base there is an anticodon which is the complement of the codon on themRNA
eg the mRNA has the codon AUG for met  the tRNA—met has the anticodon UAC
c. at the 3’ end of the tRNA is the acceptor site that holds the amino acid
d. it requires 1 ATP to attach each amino acid to the correct tRNA to make an amino-acyl tRNA
e. there are 61 possible tRNA for the 20 amino acids, therefore a cell needs 61 enzymes for this

6. show animation,
then complete notes

7. STEPS IN PROTEIN SYNTHESIS
1. The mRNA, rRNA and tRNA are transcribed from DNA in the nucleus.
They randomly drift around in the cytoplasm where the large and small subunits of the ribosome are also drifting.
UAC
tRNA
rRNA
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC
mRNA
large subunit of ribosome
small subunit of ribosome

8. 2. The mRNA leaves the nucleus and encounters the small
2. The mRNA leaves the nucleus and encounters the small subunit of the ribosome.
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC

9. The rRNA attaches the large ribosome subunit to the small
The rRNA attaches the large ribosome subunit to the small subunit that is attached to the mRNA.
The tRNA’s are activated by the attachment of an amino acid, by the use of an ATP.
GGU
Pro
UAC
Met
UAG
Ile
CCG
Gly
GUC
Gln
CAU
Val
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC
P-site A-site

10. 4. The tRNA with Met attached, randomly enters the
P-site on the ribosome.
Because its anti-codon matches the codon in the P-site, this tRNA is held in place by hydrogen bonds.
CCG
Gly
UAC
Met
GUC
Gln
Ile
UAG
GGU
Pro
CAU
Val
UAC
Met
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC
P-site A-site

11. 5. The tRNA for the next amino acid randomly moves into the A-site.
GGU
Pro
CCG
Gly
GUC
Gln
Ile
UAG
CAU
Val
UAC
Met
GGU
Pro
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC
P-site A-site

12. The tRNA for the next code now fits into the A-site
6. The tRNA that brought Met now is released after Met is bonded to the Pro.
The mRNA is now moved through the ribosome until the tRNA with Met-Pro is in the P-site.
The tRNA for the next code now fits into the A-site
CCG
Gly
UAG
Ile
GUC
Gln
UAC
CAU
Val
Met-
GGU
Pro
UAG
Ile
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC
P-site A-site

13. 7. The processes of step 5 & step 6 are repeated until one of the
7. The processes of step 5 & step 6 are repeated until one of the STOP codes is in the A-site.
At this point all of the amino acids have been bonded into a polypeptide chain connected to the last tRNA in the P-site.
UAG
UAC
GGU
CCG
Met-Pro-Ile-Gly-Gln-Val
CAU
GUC
P-site A-site
CC GAG CUC AUG CCA AUC GGC CAG GUA UAG GGG ACC

14. and the ribosome falls apart.
Because there was no tRNA to match UAG, the polypeptide chain is released.
and the ribosome falls apart.
The mRNA will be broken down.
C AUG CCA AUC GGC C
CC GAG CU
AG GUA UAG GGG ACC
mRNA
Met-Pro-Ile-Gly-Gln-Val
polypeptide chain
large subunit of ribosome
small subunit of ribosome

16. Now attempt the assignment at the bottom of the page

17. From the piece of DNA below, make the complimentary strand of DNA, transcribe the appropriate strand, package it for the cytoplasm and then translate it as described in the steps below.
In row A; make the complimentary DNA strand;
In row C, transcribe the DNA into RNA;
In column 1 and 28, place the appropriate 3’ or 5’;
In column 2 & 27, ‘package’ the RNA in row C;
In row D, underline the ‘words’ in the RNA;
In row E, translate the RNA into amino acids using the 3-letter codes for them 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 28 A G B T C D E 5 3 3 5 C A T G 5 C A U G
CAP
polyA
met
arg
trp
ser