1. Unit 5: Molecular Genetics

3. DNA Transcription Translation TraitRNA Protein The “Central Dogma” of Molecular Genetics

4. When does it begin? When mRNA leaves the nucleus Where does translation take place? In the cytoplasm, on a ribosome

5. The information on The mRNA is translated from language of RNA (nucleotides) to the language of proteins ( amino acids)

6. Each ‘word’ is called A codon. Codon - A sequence of three nucleotides on mRNA that code for one amino acid

7. There are 20 different types of amino acids.

8.  There are 4 bases ( A, U, G, C ). This means that there are 64 groups of three that are possible  Scientists have discovered which triplet of three bases codes for each amino acid. Ex: AUG codes for Methionine

11.  Most of the 64 possible triplets code for an amino acid.  Some amino acids may be specified by two, four, or even six different codons. Example: UCA and AGU both code for the amino acid serine.  Others require a single codon before they are added to an amino acid chain Example: AUG is the only codon that codes for methionine.

12.  They act like punctuation marks in a sentence.  They provide the start signal for protein production, as well as the stop signal, when the protein is complete

13. Take 2 minutes to summarize what you have learned regarding the information that a mRNA molecule actually contains.

14. What Translation Accomplishes In translation, information present in the mRNA is read by the ribosome to synthesize a protein (polypeptide). The sequence of amino acids determines the structure, and therefore the function, of a protein.

15. Translation Is Complicated Translation requires : ribosomes mRNA tRNA amino acids

16. Each tRNA is folded into a compact shape; has a specific amino acid on one end, and an ANTICODON on the other end. Anticodon - a 3 nucleotide sequence on tRNA that is complementary to an mRNA codon.

17. Ribosomes are made of rRNA and protein. Each ribosome temporarily holds  1 mRNA molecule  2 tRNA molecules * There are 3 binding sites that can be occupied at any given time **

18.  mRNA “start” codon AUG signals the beginning of assembly of the protein chain.  tRNA carries methionine to the start codon, where it binds. This spot on the ribosome is called the P site.

19.  Codon in the region of the ribosome called the A site is ready for the next tRNA.  tRNA with the complementary anticodon binds to the codon. It has the specific amino acid on the other end.

20. A peptide bond forms between the amino acids that are next to each other when both the P site and A site are occupied

21.  tRNA molecule at P site moves to the E site, while the one at the A site slides over to the P site. (everyone shifts to the left)  The tRNA at the E site then detaches and leaves the new polypeptide chain (protein) attached to the tRNA at the P site.

22.  The tRNA molecule then moves away from the molecule  A new codon is present at the A site ready to receive the next tRNA and its amino acid  A amino acid is carried to the A site by the tRNA and is bonded to the growing peptide chain

23. Steps 3-4 are repeated until a stop codon is reached. (UAG,UAA,UGA)

24.  Since the A site remains unoccupied, no more amino acids are added and protein synthesis stops  The newly made protein is released into the cell.

25. Translation Is a Cyclic, Multistep Process Translation Animation

26. Take 2 minutes to summarize how proteins are assembled during translation.

27. Basic Genetic Mechanisms are Universal The storage of genetic information in DNA, the use of an RNA intermediate that is read in three letter words, and the mechanism of protein synthesis are essentially the same in all organisms. It appears that all life forms have a common evolutionary ancestor with a single genetic code.

28. Among other things, this means cancer can be studied productively in flies or yeast. A universal code also means that human genes can be expressed in a plant or mouse genes in a yeast. A tobacco plant expressing the firefly luciferase gene.

29. Take 2 minutes to summarize what you have learned by answering the following questions: What does it mean when we say the genetic code is ‘universal’? How does this help humankind make advancements in science?