The Central Dogma of Molecular Biology

1. The Central Dogma of Molecular Biology Transcription of the DNA code into mRNA

2. http://www.ncbi.nlm.nih.gov/Class/MLACourse/Modules/MolBioReview/central_dogma.htmlhttp://www.ncbi.nlm.nih.gov/Class/MLACourse/Modules/MolBioReview/central_dogma.html

3. The Central Dogma • The classic view of the central dogma of biology states that "the coded genetic information hard-wired into DNA is transcribed into individual transportable cassettes, composed of messenger RNA (mRNA); each mRNA cassette contains the program for synthesis of a particular protein (or small number of proteins)." • Lodish, et al (2000) Molecular Cell Biology, 4th edition

4. One gene/one polypeptide hypothesis • http://www.learnerstv.com/animation/animation.php?ani=16&cat=biology • http://wps.prenhall.com/wps/media/objects/1552/1589869/web_tut/21_04/21_04_01a.swf • The role of a particular gene is to produce one enzyme that has a role in a metabolic pathway • One gene/one enzyme theory was proven by Beadle and Tatum in the 1930’s • Has since been altered since proteins may be made of more than one polypeptide

5. The Central Dogma • 1. The DNA replicates information in a process that involves many enzymes: replication • 2. the DNA codes for the production of messenger RNA (mRNA) during transcription • 3. In eucaryotic cells, the mRNA is processed and migrates from the nucleus to the cytoplasm • 4. Messenger RNA carries coded information to the ribosomes. The ribosomes “read” this information and use it for protein synthesis. This process is called transcription

6. RNA • Is a carrier of genetic information • Contains a ribose sugar rather than a deoxyribose • Ribose sugar has a hydroxyl group on its 2´ sugar

7. RNA • Instead of thymine, RNA contains uracil • RNA is single stranded

8. RNA • There are three major classes of RNA: • Messenger RNA (mRNA) • Transfer RNA (tRNA) • Ribosomal RNA(rRNA)

10. Transcription • Not all genes are transcribed all the time. • Genes are controlled so that transcription occurs only when the product of the gene is required • There are three phases to transcription: • Initiation • Elongation • Termination http://schoolworkhelper.net/2010/07/protein-synthesis-transcription/

11. Transcription movie • http://vcell.ndsu.edu/animations/transcription/movie-flash.htm

12. Initiation • RNA polymerase binds to the DNA molecule upstream of the gene at the gene’s promoter region • A promoter region has a high number of A and T bases • DNA strand is unwound exposing the template strand • The RNA that is polymerized will be complementary to the template strand

13. Elongation • RNA builds the single stranded RNA in the 5´ to 3´ direction • DNA already transcribed rewinds into the double helix http://www.mun.ca/biology/scarr/2250_DNA_replication_&_transcription.html

14. Termination • RNA polymerase reaches the terminator sequence • The newly formed RNA disassociates from the DNA template strand • RNA polymerase leaves and is free to bind to another promoter region

15. mRNA processing • Before mRNA can be used by ribosomes as a template for building proteins, it must first be processed. • Soon after RNA polymerase begins transcription, a methylated cap is added to the 5' end.

16. mRNA processing • Poly A polymerase synthesizes the polyadenylated tail by adding adenine residues to the 3´ end. • The poly-A tail makes the RNA molecule more stable and prevents its degradation. • The processed mRNA is now ready to undergo splicing in preparation for translation.

17. mRNA processing • http://vcell.ndsu.edu/animations/mrnaprocessing/movie-flash.htm • http://vcell.ndsu.edu/animations/mrnasplicing/movie-flash.htm

18. mRNA splicing • Introns are non-coding RNA sequences that must be removed before translation. • The process of removing the intron is called splicing • The intron is looped out and cut away from the exons by snRNPs (small nuclear ribonucleoprotein) (snurps) • The exons are spliced together to produce the translatable mRNA • The mRNA is now ready to leave the nucleus and be translated into protein

19. http://www.phschool.com/science/biology_place/biocoach/transcription/premrna.htmlhttp://www.phschool.com/science/biology_place/biocoach/transcription/premrna.html

20. Alternative splicing http://www.ncbi.nlm.nih.gov/Class/MLACourse/Modules/MolBioReview/alternative_splicing.html

21. The Genetic Code • There are only 4 nucleotide bases in RNA but 20 amino acids • The minimum combination of bases to code for 20 amino acids was a triplet code called a codon

22. http://scienceblogs.com/oscillator/2010/02/expanding_the_genetic_code.phphttp://scienceblogs.com/oscillator/2010/02/expanding_the_genetic_code.php

23. ://www.sparknotes.com/biology/molecular/geneticcode/section1.rhtml://www.sparknotes.com/biology/molecular/geneticcode/section1.rhtml

24. Genetic Code • The genetic code is nearly universal. • Almost all organisms build proteins with the same genetic code • Fruit fly codon will code for the same amino acid as in a human • This is important in cloning

25. Genetic Code • The genetic code is redundant • More than one codon can code for the same amino acid • Three codons do not code for an amino acid – these are “stop” codons to end protein synthesis • Stop codons are: UGA, UAA, UAG

26. Genetic Code • The genetic code is continuous • It reads as a series of 3-letter codons without spaces, punctuation or overlap