1. Protein Synthesis Introduction Chapter 17

2. What you need to know! Key terms: gene expressions, transcription, and translation How eukaryotic cells modify RNA after transcription (splicing)

3. Gene Expression The process by which DNA directs the synthesis of proteins (sometimes RNAs) One gene-one polypeptide hypothesis

4. Genes A sequence of nucleotides on DNA –Specific in number and order At the front of each gene is a promoter region –Made of a TATA Box and a RNA polymerase binding region Promoters determine how often a gene is transcribed –Strong/weak Each gene codes for 1 polypeptide (usually)

5. RNA A major role in all stages of protein synthesis Oldest nucleotide (been around the longest) –Hereditary code –Catalytic properties (regulates chemical reactions during protein synthesis)

6. Protein Synthesis in 2 to 3 steps 1.Transcription 2.RNA processing (Eukaryotes only) 3.Translation (step 2 in prokaryotes)

7. Prokaryotes 1212 DNA  mRNA  Protein

8. Eukaryotes 1 (nucleus) 2 (nucleus) 3 (cytoplasm) DNA  pre-mRNA  mRNA  Protein

9. Transcription Similar to replication DNA unwinds Free RNA nucleotides (ATP, UTP, GTP, CTP) compliment template DNA strand mRNA separates from DNA Example: DNA:A T C C G A T A G mRNA:________________ Non- Template:________________ DNA

10. RNA processing 5’ cap and poly-A tail attached for protection and to facilitate ribosome attachment Introns are removed by a spliceosome leaving only exons Spliceosomes consist of protein and small nuclear RNA (snRNA) snRNA is a ribozyme (a catalytic RNA molecule)

11. RNA Processing

12. Translation mRNA leaves the nucleus and enters the cytoplasm Ribosomes attach to mRNA mRNA is complemented by tRNA tRNA are three dimensional molecules with a triplet anti-codon sticking out and an amino acid attached Amino acids bond together to form a growing polypeptide

13. Codons 4 different nitrogenous bases (A, U, C, G) must code for 20 Amino Acids (AA) 1 letter codon codes for 4 1 different AA –4 1 = 4 (20 AA – 4 = 16 missing AA) 2 letter codon codes for 4 2 different AA –4 2 = 16 (20 AA – 16 = 4 missing AA) 3 letter codon codes for 4 3 different AA –4 3 = 64 (plenty)

14. Codons 64 possible combinations and only 20 AA allows for multiple codons to code for the same amino acid (Wobble) Charts can be used to decode the codons in mRNA into their respective AA