Biology 151 1st Edition Lecture 11 Outline of Last Lecture 1."Central Dogma" - from DNA to RNA to protein2. Processes shared by all 3 "domains" of cellular life3. Messelson and Stahl (1954)4. Proteins in DNA replication5. DNA replication: The big picture6. Problem 1 - Unwinding a helix creates supercoiling7. Problem 2 - DNA polymerase can only add bases to extant DNA or RNA strand8. Problem 3 - Polymerase only works in one direction (adds bases to free 3' end)9. Problem 4 - Cells with linear chromosomes: how do you replicate the ends?10. TelomeraseOutline of Current Lecture 1. What is a gene?2. What do genes on DNA do?3. Beadle and Tatum (1941)4. How does DNA make a protein?5. Ribosomes and Ribosomal RNA (rRNA)6. Structure of RNA7. Ribosomes are the sites of protein synthesis8. RNA9. Transcription of RNA from DNA template10. RNA polymerase11. Messenger RNA (mRNA) carries info. from DNA to ribosomeCurrent Lecture - 2/13/15What is a gene?:- originally defined by inheritable mutation- change from normal ("wild type") version to one that causes a heritable change in a trait- error in nucleotides in DNA - wrong, deletion, insertion of extra, etc.What do genes on DNA do?: - What gets changed in a mutant?- "one gene-one enzyme" hypothesis (later, "one gene-one protein" hypothesis)- DNA contains instructions for making proteins- proving that genes direct protein synthesis during the Neurospora fungus- "red bread mold" = orange spores- "slants" of Neurospora spores- normal "wild type" Neurospora can grow on minimal medium (MM) that lacks amino acidsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- wild type Neurospora can synthesize all 20 amino acids (unlike the "essential" amino acids humans cannot make)Beadle and Tatum (1941): - DNA damage via X-rays make Neurospora mutants that require arginine to grow (defect in arginine synthesis) - several steps in the synthesis of the amino acid Arginine, each requiring a different enzyme- each mutation blocks only one of these steps- conclusion: "one gene - one enzyme" hypothesis-later: "one gene - one protein" hypothesis-mostly true...How does DNA make a protein?:- 1st: transcription of mRNA from DNA- 2nd: translation of mRNA into protein at ribosome- RNA - U not T-single stranded-ribosomal RNA - rRNA-messenger RNA - mRNA-transfer RNA - tRNA- RNA - containing ribosomes isolated from cells by density, identified in cells by election microscopy- ribosomes in cell cytoplasm- density gradient centrifugationRibosomes and Ribosomal RNA (rRNA):- large, stable rRNAs assemble with proteins into dense particles = ribosomes- large and small subunits, slightly different in eukaryotes and prokaryotesStructure of RNA:- single stranded and floppy (one 5' end and one 3' end)- but bases can bind complementary bases in the same strand (red regions)- wraps itself into different shapes because of this - can have enzymatic activity (ribozymes)Ribosomes are the sites of protein synthesis:- 1st evidence: size of radioactivity - labeled proteins at ribosomes increases over time- eukaryotic cells - DNA membrane, wrapped nucleus, ribosomes outside nucleus in cytoplasm- how do you get information from DNA in nucleus to ribosome in cytoplasm?-found a 2nd population of RNA = mRNA (messenger RNA) -mRNA carries sequence of information from DNA to the ribosomeRNA:1) ribosomal RNA - fixed sizes2) mRNA - variable sizes, large to small- evidence that mRNA carries information from DNA:-mRNA nucleotide content similar to cell's DNA-if cell was infected with virus, mRNA became similar to DNA of virusTranscription of RNA from DNA template:- requires RNA polymerase- only single strand of RNA made from single DNA template strand- only parts of the DNA are used as templates - RNA - DNA attachment is temporary- RNA uses U (uracil) instead of TRNA polymerase:- made of 12 different proteins- builds single-stranded complementary RNA from DNA template- temporarily separates DNA strands- does not require primer - easier to start from nothing - own helicase and primase- new strand built 5' to 3' in RNA- template strand 3' to 5'Messenger RNA (mRNA) carries info. from DNA to ribosome:- eukaryotes: mRNA exported from nucleus to reach ribosomes in cytoplasm- prokaryotes: no nucleus, ribosomes attach to mRNA as it is being transcribed- both: can have polyribosomes - many ribosomes attached to the same mRNA- no way of telling % of U with RNA because it's single stranded, unlike DNA which is double
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