1. Translation: From Messenger RNA to Protein
The information encoded in DNA is transferred to
messenger RNA and then decoded by the ribosome to
produce proteins.
The major molecules involved in translation are:
-Messenger RNA (mRNA)
-Transfer RNA (tRNA)
-Ribosomes
-Enzymes, other factors, energy sources

2. 5’-ATGCCTAGGTACCTATGA-3’ 3’-TACGGATCCATGGATACT-5’
DNA
Transcription
5’-AUGCCUAGGUACCUAUGA-3’
mRNA
decoded as
5’-AUG CCU AGG UAC CUA UGA-3’
Translation
N-MET-PRO-ARG-TYR-LEU-C
Protein

3. Messenger RNA
Carries information copied from DNA in nucleus to ribosomes in cytoplasm
Will become associated with ribosomes
Will direct protein synthesis, putting amino acids in the proper order on the growing chain

4. Transfer RNA
Carrier molecule which transfers amino acids to the protein chain
tRNA is made in the nucleus from a DNA template
Each tRNA is specific to carry one of the 20 amino acids used to make proteins
tRNA’s sit attached to their specific amino acids in a pool in the cytoplasm
tRNA are about 80 nucleotides long, are folded uniquely, due to hydrogen bonding
Are recyclable, can be used again and again

5. Generalized tRNA

7. Ribosomes
Very small particles (25nm) that are key components in protein synthesis
Made up of 2 subunits, a large and a small.
Are found as subunits in the cytoplasm and attached to ER. They assemble on the mRNA when translation begins

8. What Ribosomes Look Like

9. What Ribosomes Look Like

10. Getting Started: The Genetic Code
The bases of DNA code for the placement of amino acids on a growing chain
20 different amino acids must be coded for:
How long is the code?
a.) If code is 1 base long – only code for 4 amino acids
b.) If code is 2 bases long – only 16 amino acids can be coded for
c.) *If code is 3 bases long – 64 amino acids can be coded for*
This means the code is a triplet. The 3 mRNA bases are known as the codon, the 3 tRNA bases that match up are the anti-codon

11. Getting Started: The Genetic Code
Facts about the code:
It is continuous (no comma’s)
It is non-overlapping
It is almost universal
It shows degeneracy – with 2 exceptions, most amino acids have more than one codon
this degeneracy is a built in guard against point mutations
The code has start and stop signals

12. The Genetic Code
Note: AUG is the start codon

13. How Translation Works
tRNA becomes “charged” by picking up an amino acid.
This is done by the enzyme “amino-acyl tRNA synthetase”
-One synthetase for each amino acid
-A single synthetase may recognize multiple tRNAs
for the same amino acid
5’ end of mRNA comes together with 2 ribosome subunits:

15. Steps in Translation Once the tRNA is charged, translation can begin
It will occur in 3 steps:
1.) initiation
2.) elongation
3.) termination

16. Three tRNA binding sites: A site = amino-acyl tRNA binding site
1.) Initation
needs energy (GTP) + proteins called initiation factors
“AUG” is always first codon added. tRNA binds to “p-site” (has anticodon “UAC”)
Three tRNA binding
sites:
A site = amino-acyl
tRNA binding site
P site = peptidyl-tRNA
binding site
E site = exit site

17. In addition to the APE sites there is an mRNA binding groove
that holds onto the message being translated

18. Next step in translation is elongation
Amino acid binds to A-site
2 amino acids undergo peptide-bond synthesis; catalyzed by the enzyme peptidyl transferase
Dipeptide is attached to A-site, empty t-RNA shifts to e-site, called translocation; requires the enzyme translocase.

20. Termination of translation is triggered by stop codons
When a stop codon is reached, the following happens:
1.) protein chain is released
2.) mRNA + ribosomes separate (ribosome splits into subunits)
requires “release factors” + GTP

21. Release of the protein causes
the disassociation of the
ribosome into its constituent
subunits.