1. Protein Synthesis
Chapter 12 Section 3 Pg

2. Proteins Review Elements: C, H, O, N Monomer = Amino Acids (20 kinds)
Foods- Fish, poultry, soy, beans

3. Proteins Review
Amino acids are connected by peptide bonds during dehydration synthesis reactions.
The sequence of amino acids determines the folding and shape of proteins.
The shape of the proteins determines the function.
Protein function is also affected by temperature and pH fluctuations.

4. Amino Acid Structure Review
A central carbon with four things attached:
A single hydrogen atom
A carboxyl group
(–COOH)
An amino group
(–NH2)
An R group - functional group which is different for each amino acid
Amino acids are connected during dehydration synthesis reactions

5. Going from DNA to Proteins
What have we done so far?
The DNA message is converted into RNA in a process called transcription. We get:
mRNA with the DNA code
tRNA waiting with the amino acid
rRNA making ribosomes for translation
This happens in the nucleus.
Our proteins are made from Amino Acids so we need a bridge to go from the RNA we just made to amino acids…

6. The Genetic Code
The language of mRNA is called the Genetic Code (A, G, U, C) and contains only 4 letters.
It is based on codons, which are 3 bases together on an mRNA chain (like 3 letter words).
Each codon codes for a specific amino acid.
There are 64 codons and 20 amino acids so several codons will code for the same amino acid.
NOTE: The Genetic Code is Universal: Most organisms follow the same code to produce proteins, demonstrating that we are all evolutionarily related.

7. Special Codons: Start/Stop Condons
Start Codon: AUG
Signals the beginning of protein synthesis/translation
Protein synthesis can only begin at this codon.
Also codes for the Amino Acid: Methionine
Stop Codons: UAA, UAG, UGA
Signals protein synthesis to stop.
Similar to the period at the end of a sentence.

8. Genetic Code Square

9. Genetic Code Circle

10. How do we get from RNA to Proteins?
Translation!!
Changing the DNA code into actual proteins the cell can use.
It happens in the ribosome.

11. tRNA and Anticodons
Amino acids are free floating in the cytosol and are carried to the ribosome by tRNA molecules
Top part of loop allows for 1 AA to bind
Bottom part of loop is the anticodon (sequence of 3 nucleotides) that pairs with its complementary mRNA
Ex: mRNA codon: GCC
tRNA anticodon: CGG
Note: the pairing of a anticodon with a codon ensures that the Amino Acids are joined in the correct order

12. Setting the Stage for Translation…
mRNA has been made and is moving to the ribosome
tRNA’s are transporting the amino acids to the ribosome.
Translation is ready to begin.

13. Steps of Translation
Step 1: Ribosomes attach to the start codon (AUG) of the mRNA.
Step 2: A tRNA with the anticodon of UAC and a methionine binds to the mRNA inside the ribosome.
Step 3: In the 2nd binding site, the next codon is read and a tRNA is attached. A peptide bond forms between the two amino acids.

14. Steps of Translation (continued)
Step 4:The 1st tRNA is released and the ribosome moves to the next codon.
Step 5: The process continues until a stop codon is reached. Translation stops and the ribosome releases the mRNA and the created protein.

15. Protein Synthesis Analogy

16. Animations http://biology.kenyon.edu/slonc/bio3/ribo/ribo3.html