1. Modern Genetics: Protein Synthesis

2. Protein Synthesis Gene: Sequence of DNA on a chromosome which codes for a protein. How do genes code for traits? A gene determines the amino acid sequence for a protein. The amino acid sequence determines the protein’s shape and therefore its function. The interaction of various proteins result in traits. Gene → mRNA → Amino acid sequence → Trait

3. The central dogma Protein synthesis is often referred to as the “Central Dogma”. This is due to the discovery that information, as encoded in DNA underlies all of biology.

4. Protein Synthesis Protein synthesis is made up of two distinct processes. 1.Transcription: A gene is copied from DNA to mRNA. 2.Translation: Genetic instructions copied onto mRNA are used to direct a ribosome to assemble a protein from a chain of amino acids.

5. Protein Synthesis Overview

6. Transcription Transcription: The process of copying a gene from DNA to mRNA. Occurs in the nucleus Why must genes be transcribed into mRNA? Because DNA cannot leave the nucleus of the cell to contact a ribosome (chromosomes are too big). mRNA is much smaller and can leave the nucleus. Transcription is like copying notes from the board into your notebooks. It’s a portable way to record information

7. Transcription Transcription is very similar to DNA replication except that mRNA uses Uracil and not Thymine. In transcription, only one gene is copied into mRNA. In DNA replication all of the chromosomes get duplicated.

8. Translation Translation: The process by which mRNA, containing information copied from a gene on DNA, is used to direct the synthesis of a polypeptide chain of amino acids. Occurs on the ribosomes. tRNA (transfer RNA)is used to deliver each amino acid to the ribosome to be added on to the growing polypeptide chain.

9. The big picture

10. Codons, Anticodons, and Amino Acids Codon: Three letter sequence of mRNA bases that code for an amino acid. Start Codon: codon that initiates synthesis of a protein. Stop Codon: codon that terminates synthesis of a protein. Anticodon: Three letter sequence of tRNA that matches up to the corresponding mRNA sequence of a codon.

12. Codon Key

13. Why three letters for codons? There are 4 nitrogenous bases (A,C,U,G). With two letters there would be 4 2 possibilities (4X4=16 possibilities – Need at least 20 for all amino acids– too few) 4 letters gives you 4 4 possibilities (4X4X4X4=256 possibilities –far too many.) With 3 letters there will be 4 3 possible combinations of codons. (4X4X4 = 64 possibilites) Three letters is the most economical way to be sure that all 20 amino acids are represented by at least 1 codon.

14. But there are 64 codons for 20 amino acids! This is true. That is why the genetic code is referred to as a degenerate code. Degenerate code: A particular amino acid may be represented by more than one codon. There are also codons which code to start and end a protein. This has huge implications on the process of evolution.

15. How do tRNA molecules “know” where to add each amino acid? A tRNA molecule has two important parts: 1.Amino acid binding site: where the amino acid is attached to the tRNA. 2.An anticodon which corresponds to a codon on mRNA *This tRNA molecule will deliver its amino acid to which mRNA codon? GCC

16. tRNA in Translation

17. Transcription Animation

18. Ribosome, tRNA, and mRNA molecules during translation

19. Protein synthesis animations/tutorials http://www.lewport.wnyric.org/JWANAMAKER/animations/Protein%20Synth esis%20-%20long.htmlhttp://www.lewport.wnyric.org/JWANAMAKER/animations/Protein%20Synth esis%20-%20long.html http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter15/animations.html#http://highered.mcgraw- hill.com/sites/0072437316/student_view0/chapter15/animations.html# http://207.207.4.198/pub/flash/26/transmenu_s.swf