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Central Dogma:

Central Dogma:. Review of Transcription and Translation in bacteria. http://cats.med.uvm.edu/cats_teachingmod/microbiology/courses/gene_regulation/images/dij.tc.elong1.jpg. Sense, antisense. Compare the sense strand of the DNA to the mRNA.

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Central Dogma:

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  1. Central Dogma: Review of Transcription and Translation in bacteria

  2. http://cats.med.uvm.edu/cats_teachingmod/microbiology/courses/gene_regulation/images/dij.tc.elong1.jpghttp://cats.med.uvm.edu/cats_teachingmod/microbiology/courses/gene_regulation/images/dij.tc.elong1.jpg

  3. Sense, antisense Compare the sense strand of the DNA to the mRNA. Note that mRNA synthesis will be 5’ to 3’ and antiparallel. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/SenseStrand.gif

  4. The Process of Transcription-2 • RNA synthesis continues (Elongation), only one DNA strand (template) is transcribed. • RNA nucleotides, complementary to bases on DNA strand, are connected to make mRNA • Termination: must be a stop sign, right? • In bacteria, hairpin loop followed by run of U’s in the RNA. Of course, the DNA must code for complementary bases and a run of A’s. See next. Most common. OR • Termination factor “rho”. Enzyme.Forces RNA polymerase off the DNA.

  5. Termination of Transcription in Bacteria The hairpin loop destabilizes the interactions between the DNA, mRNA, and polymerase; U-A basepairs are very weak, and the complex falls apart. http://www.blc.arizona.edu/marty/411/Modules/Weaver/Chap6/Fig.0649ac.gif

  6. Transcription in prokaryotes • As mRNA is made, it is ready to use. • Info from more than one gene is typically found on one mRNA molecule. • Simpler process than in eukaryotes • no introns to remove • no cap or poly-A tail • no nuclear membrane to transport through • Transcription is expensive: each NTP leaves behind 2 Pi; like spending 2 ATP for every base used.

  7. The Genetic Code • Four bases taken how many at a time? Need to code for 20 different amino acids. • Each base = 1 amino acid: only 4 • Every 2 bases = 1 a.a.: 16 combinations, 4 short. • Every 3 bases: 64 combinations, enough. • Every 3 bases of RNA nucleotides: codon • Each codon is complementary to 3 bases in one strand of DNA

  8. Properties of the Genetic Code • Code is unambiguous: 1 codon always specifies only 1 amino acid. • Code is degenerate: although unambiguous, an amino acid can be coded for by more than one codon. • Punctuated: certain codons specify “start” and “stop”. • Universal: by viruses, both prokaryotic domains, and eukaryotes (except for some protozoa, mitochondria). • Ordered: similar codons specify the same amino acid; see especially the 1st two bases in the codon.

  9. The Genetic Code-2 http://www.biology.arizona.edu/molecular_bio/problem_sets/nucleic_acids/graphics/gencode.gif

  10. Bacterial ribosomes • Prokaryotic ribosomes are 70S; eukaryotic are 80S • S is Svedberg unit, how fast a particle travels during centrifugation. Affected by both mass and shape. • Large subunit: 50 S • 33 polypeptides, 5S RNA, 23 S RNA • Small subunit: 30 S • 21 polypeptides, 16S RNA • Note that 30 + 50 is not 70 • Ribosome structure and differences between prokaryotes and eukaryotes are important. • rRNAs important in taxonomy to be discussed later • Differences are the basis for success of many antibiotics

  11. Translation • Literally, information translated from language of nucleotides to that of amino acids • Ribosomes (large and small subunits), mRNA, tRNAs, amino acids, and source of energy. • And various protein factors • Ribosomes attach to mRNA, tRNAs read codons, match amino acid to codon and ribosome connects amino acids to make proteins. • mRNA has start codon AUG and stop codons. • Look for animations on line • http://www.ncc.gmu.edu/dna/ANIMPROT.htm; http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

  12. tRNA: the decoder a.a. attaches here anticodon http://www.designeduniverse.com/articles/Nobel_Prize/trna.jpg

  13. Simultaneous transcription and translation • No processing, no nucleus; mRNA already where the ribosomes are, so they get started quickly. http://opbs.okstate.edu/~petracek/Chapter%2027%20Figures/Fig%2027-30.GIF

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