1. Protein Synthesis Unit 5

2. Protein Synthesis DNA  RNA  Proteins 4 Steps: 1)Transcription  information is DNA is copied to RNA (nucleic acid  nucleic acid) 2)Pre-mRNA modification  removing of non-coding regions (introns) 3)Translation  information in RNA used to build proteins (nucleic acid  proteins) 4)Post-Translation Modification  folding of protein and transporting to location inside the cell

3. Transcription DNA template is read (3’  5’) by RNA Polymerase which builds mRNA (5’  3’) from A, C, G, and U Base pairing rules regulated the formation of mRNA No primers are needed; however RNA Poly needs a promoter (DNA sequence that promotes transcription) Promoter is followed by coding region (transcription unit)

4. What is the mRNA sequence? DNA is always read from 3’  5’

5. Pre-mRNA modification Only in eukaryotic cell mRNA must be edited before use Introns- sections that are removed “Introns are in the way” Exons- expressed mRNA

6. Translation Translation- changing mRNA into an amino acids chain (protein) called a polypeptide mRNA moves to the cytoplasm; read 5’  3’ by ribosomes, which bind amino acids together brought by tRNA A group of three nitrogenous bases in mRNA code for one amino acid. Each group is known as a codon There are 20 Amino Acids How do we know a codon is 3 bases long?

7. Codons How many different DNA bases are there? -4 (A, T, C, G) How many mRNA bases are there? -4 (A, U, C, G) If a codon was only 1 base long how many amino acids could you have? -Only 4 (A= AA #1, U= AA #2, C= AA #3, G = AA #4) If a codon was 2 bases long how many amino acids could you have? -4 2 = 16 (AA, AU, AC, AG, UU, UA, UC, UG, CC,CA, CU, CG, GG, GA, GU, GC) Since there are 20 Amino Acids, a codon must be 3 bases 4 3 =64 Multiple codons code for the same Amino acid

8. The “Wobble Effect” Most of the time only first 2 bases are needed to get the correct animo acid

9. Translation: The Parts tRNAs  – RNA folded to make clover shape; tail has exposed complimentary bases to codons in mRNA (anticodons) – Brings amino acid to ribosome and only if the tRNA anticodon matches the mRNA codon does the ribosome use the amino acid

10. Translation: The Parts Ribosomes  – complex made of 2 subunits (small and large) – 3 Active sites (A, P, and E) – A-site  amino; where tRNA load next amino acid – P-site  peptide; where peptide bond forms between Amino Acids – E-site  exit; tRNA (now free of Amino acid) is released

11. Translation Changing mRNA into an AA sequence One mRNA can make many proteins, so multiple Ribosomes can translate different parts at the same time (polyribosomes) 3 Steps: 1)Initiation: – Methionine-tRNA (UAC), GTP, and the small Ribosome subunit form a complex – Complex scans mRNA till AUG is found – GTP is used to complete ribosome when by attaching large subunit

12. Translation 2) Elongation – tRNA enter A-site – AA in P-site binds to AA in A-site; What type of bond is this? Peptide Bond – Ribosomes moves down one codon – tRNA in E-site is released – Process restarts 3) Termination – Stop codon (empty space) causes ribosomes to release protein and mRNA strand

13. Post-Translation Modification and Sorting Proteins to fold into the right 3D shape Sorting: Cytosol  – made by free ribosomes ER/Golgi  – made by free and ER ribosomes; Signal sequence says where to send it (zip code) Other Organelles  – moves protein to other part of the cell; guided by transit sequence Nucleus  – nuclear localization signal

14. What is the AA sequence? Codons to remember: Start codon- AUG All proteins start with Methoinine Stop Codons- UAA, UAG, UGA

15. Codons and Mutations Codons are degenerate  multiple codons for the same AA Reading frame  read in three base sections, so the frame of those three letters must be right – THECATCUTTHEDOG – HECATCUTTHEDOGS Frame shift  mutation where deletion or addition of a base pair change all AA after mutation point

16. Types of Mutations Frame Shift is a very dangerous mutation Nonsense mutation  early stop codon appears in mRNA; protein is too short Missense mutation  mRNA codes for a different amino acid than should be present; effects depend on differences between AA switched – Polar vs Non-polar – Acid vs Base Silent mutation  mRNA code sequence is changed but codes for the same AA; no effect on protein

17. Most Mutations Are Silent Single base pair changes might not create a missense mutation if they are in the right spot Wobble Effect  The 1 st and 2 nd base in a codon are important; however most combinations for the 3 rd base code for the same AA – Decreases the effects of mutations