1. Chapter 17 Central Dogma of Molecular Biology From Genes to Protein One gene – one polypeptide hypothesis One gene dictates the production of a single polypeptide

2. transcription Transcription: synthesis of mRNA under the direction of DNA - one step in prokaryotic cells - Two steps in eukaryotic cells 1. creating a 1 o transcript 2. RNA processing (editing) to create 2 o transcript Translation: synthesis of a polypeptide under the direction of mRNA translation RNA Processing Central Dogma of Molecular Biology Prokaryotic Cell Eukaryotic Cell mRNA 1 o transcript mRNA polypeptide ribosome mRNA 2 o transcript

3. Directional Triplet-code Instructions for a polypeptide Transcription 3’ to 5’ direction on DNA Translation 5’ to 3’ direction on RNA A C C A A A C C G A G T U G G U U U G G C U C A trppheglyser 3’ 5’ DNA mRNA polypeptide

4. 3 RNA Players Involved mRNA = DNA transcript tRNA = type of RNA that carries the amino acids to the ribosome rRNA = RNA that, combined with protein, makes up the structural component of a ribosome Central Dogma

5. Transcription 3 steps 1)Initiation 2)Elongation 3)Termination Initiation Transcription begins at a “Promotor” region of DNA, recognized by a TATA box sequence A transcription factor binds to help RNA polymerase (RNA pol.) to bind to the DNA RNA pol. binds and begins to unwind DNA

6. Elongation RNA pol unzips 10-20 DNA bases at a time in a 3’  5’ direction and base pairs with the DNA using RNA nucleotides Base-pair occurs at a rate of 60 nucleotides/second A-U; G-C base-pair rules New 1 o transcript (initial copy) of mRNA peels away from DNA template

7. Termination 1) RNA sequence, not DNA sequence, is used to end transcription. Once RNA pol. creates the AAUAAA termination sequence, the primary mRNA transcript peels away from the DNA template. mRNA 2) RNA processing occurs: (creating of 2 o transcript) - 5’ cap of guanine nucleotides are added to protect mRNA from hydrolytic enzymes and to provide a starting site for ribosomes in translation - 3’ poly A tail is added to protect mRNA from hydrolytic enzymes and to help with mRNA export from the nucleus Transcription video

8. Termination RNA Processing Continues Primary transcript of mRNA is long and includes introns (non-coding regions) and exons (coding regions) Evolutionary Significance? Non-coding RNA regions were the result of non-coding DNA regions. Longer DNA increased chances of X- over during meiosis. During RNA processing, introns must be cut out (spliced) before a functional polypeptide can be made mRNA

9. Termination RNA Processing Continues 3) RNA splicing A “spliceosome” complex recognizes intron sequences and deletes them Spliceosomes are made up of special RNA called snRNA + various proteins 2 o mRNA transcript is now ready

10. t-RNA Activation for Translation tRNA = brings in the corresponding AA coded by the mRNA to the ribosome for polypeptide (protein) synthesis Aminoacyl-tRNA synthase (enzyme) catalyzes the binding of a specific amino acid to a free tRNA. Activated t-RNA is now ready for translation.

11. Structure of a Ribosome Large subunit Small subunit Ribosome= rRNA + protein E P A A = Aminoacyl- tRNA binding site P = Peptidyl-tRNA binding site E = Exit Site tRNA Anticodon mRNA codon A = tRNA brings in new AA P= Creates peptide bonds between AA and holds the growing polypeptide chain E= Free t-RNA detaches from ribosome

12. Translation 1)Initiation 2)Elongation 3)Termination Initiation - Small ribosomal subunit attaches near the 5” end of mRNA at AUG start codon - tRNA carrying AA Methionine attaches to AUG start codon - Large ribosomal subunit attaches to mRNA w/ tRNA occupying the “P” site.

13. Elongation New tRNA brings in another amino acid, based on the codon on the mRNA. Base- pairing occurs. A peptide bond forms between the two adjacent AA Ribosome slides down the 3’ end of the mRNA Free tRNA exits and can return to bind with other AA for repeat deliveries

14. Termination Ribosome encounters a “stop” codon: UAA, UAG, or UGA Release factor facilitates the release of both ribosomal subunits Translation Video

15. http://www.dnai.org/a/in dex.html Watch these real- time videos on DNA transcription and translation…Totally Cool Dude!

16. Redundancy in AA -Notice…several codons code for the same AA  Evolutionary advantage? Redundancy helps to minimize errors in protein synthesis due to mutations Although A pairs with U and G pairs with C, U can sometimes pair with G  wobble effect Other ways of increasing redundancy:

17. Endo-membrane System Recall that glyco-proteins (made by attached ribosomes) are processed by the ER and golgi before being incorporated within vesicles (ie. lysosomes), exported from the cell, or incorportated into the plasma membrane.