1. Protein Synthesis (Transcription and Translation)

2. RNA vs DNA structure RNA sugar: ribose Single stranded
DNA is not the only nucleic acid. It has a helper called RNA.
RNA
sugar: ribose
Single stranded
A, C, G, and Uracil (U)
DNA
Sugar: deoxyribose
Double stranded
A, C, G, and Thymine (T)

3. 3 Types of RNA
DNA cannot leave the nucleus, so RNA actually does the work to build the proteins (protein synthesis)
messenger RNA (mRNA): carries the DNA instructions from the nucleus to the ribosome
ribosomal RNA (rRNA): creates the ribosome
transfer RNA (tRNA): transfers amino acids to the ribosome to build the protein

4. Protein Synthesis Steps
Transcription – copy the needed gene onto an mRNA
RNA Editing – check the mRNA for mistakes and remove introns (junk DNA)
Translation – use the final mRNA to build a protein at the ribosome; each mRNA codon represents an amino acid; amino acid chains make a protein; mRNA is the instructions, tRNA brings in the correct amino acid based on the instructions Overview

5. Transcription
The enzyme RNA polymerase builds the mRNA strand by unzipping the DNA with helicase and base pairing at the correct gene (similar to replication except using RNA nucleotides)

6. Transcription Each chromosome contains thousands of genes!
How does RNA polymerase “know” where to start and stop making the RNA copy of DNA?
Each gene begins with a promoter region that signals the start of the gene
The middle is the coding region and this is the instructions for the protein
At the end of the gene there is a termination sequence that signals the RNA polymerase to stop copying

7. RNA Editing DNA contains unnecessary information
Introns: Junk DNA, must be removed from the pre mRNA
Exons: expressed DNA, this is the DNA used to make the protein
RNA editing after transcription removes the introns, splices back together the exons, and adds a protective cap and tail to the mRNA so that it can leave the nucleus

8. Translation
The final mRNA can then leave the nucleus and go out to a ribosome where it is “translated” into a chain of amino acids (which form proteins!)

9. How does the ribosome “read” the mRNA?
The mRNA is read 3 base pairs (A, U, C, or G) at a time in groups called codons
The 64 possible codons each represent one of the 20 different amino acids
Sometimes different codons will give the same amino acid
example:
RNA sequence UCGCACGGU
would be read UCG CAC GGU
which would give Serine – Histidine – Glycine
“AUG” (methionine) is always the start
Three stop codons

10. The Codon Wheel

11. The Codon Box

12. Translation
Remember: the mRNA was made and edited in the nucleus before translation begins

13. Translation
To begin translation, the mRNA molecule attaches to a RIBOSOME in the cytoplasm (or on the rough ER)
The ribosome attaches at the first AUG (methionine)
tRNAs with the complementary codon (called an anti-codon) are in the cytoplasm carrying the amino acids. They enter the ribosome and base pair to the mRNA to ensure the amino acids are placed in the correct order. The tRNAs will leave their amino acid behind, but they can be reused later after picking up a new amino acid

14. Translation
This continues like a polypeptide/protein “assembly line” until the first stop codon is reached. Then the ribosome releases both the mRNA and the new protein.

15. Protein Synthesis