1. Protein Synthesis The majority of genes are expressed as the proteins they encode. The process occurs in 2 steps: 1. Transcription (DNA---> RNA) 2. Translation (RNA ---> protein)

2. Overview of Protein Synthesis

3. Where does all this Happen?

4. Protein Synthesis Nucleic Acids (DNA & RNA) carry the hereditary information. Nucleic Acids (DNA & RNA) carry the hereditary information. This information is contained in codons. This information is contained in codons. What are Codons? What are Codons? A codon is a set of three base pairs (A, T, C, G) that directs or codes for amino acids. (ex. GCU – Alanine)

5. Transcription This process occurs in the nucleus. This process occurs in the nucleus. A section of DNA called a gene is unwound and unzipped. A section of DNA called a gene is unwound and unzipped.

6. How Does Transcription Start? An enzyme (RNA Polymerase) binds to a promoter sequence. RNA Polymerase proceeds down one strand moving in the 3’ to 5’ direction and assembles a complementary strand of RNA. A RNA copy of one of the DNA strands is made. This strand is made complimentary to the nucleotides on the the DNA Strand. DNA Bases: Adenine, Thymine, Cytosine, Guanine RNA Bases: Adenine, Uracil, Cytosine, Guanine

8. DNA Strand 1:AGCTATCGAGCAT DNA Strand 2:TCGATAGCTCGTA RNA copy:AGCUAUCGAGCAU Transcription stops when the termination sequence is reached. The completed RNA copy is now called messenger RNA or mRNA and carries the coded message to the ribosomes in the cytoplasm.

9. Translation There are 3 steps to translation: 1. Initiation 2. Elongation 3. Termination

10. Initiation 1. Ribosome attaches to mRNA and moves along until it reads the initiation codon AUG. 2. A transfer RNA molecule (tRNA for short) brings the correct amino acid to the ribosome & drops it off. ex: AUG (codes for methionine) tRNA brings methionine to ribosome.

11. T RNA

12. Elongation 3. The ribosome moves on to the next codon and another tRNA brings the next amino acid. 4. The amino acids in the growing chain are linked together by a peptide bond. The growing chain is called a polypeptide or protein molecule.

14. Termination End of the message is a STOP codon End of the message is a STOP codon STOP codons: UAA, UAG, UGA STOP codons: UAA, UAG, UGA Protein release factor sees these codons at the A site and tells the polypeptide chain to release from the ribosome site Protein release factor sees these codons at the A site and tells the polypeptide chain to release from the ribosome site Ribosome splits into its subunits until it is time to make more protein! Ribosome splits into its subunits until it is time to make more protein!

15. Transcription in Eukaryotes ie: Animal cells

16. Protein Synthesis in Prokaryotes ie: single celled Bacteria

17. Check out this link for an animation on Protein Synthesis http://www.lewport.wnyric.org/jwanamaker /animations/Protein%20Synthesis%20- %20long.html http://www.lewport.wnyric.org/jwanamaker /animations/Protein%20Synthesis%20- %20long.html