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BioPhysics 101 Biology section #2 Today’s topics: •Dogmas •Operons •Cis and Trans •Haplotypes Sept. 30 2003 Plus strand, Minus strand, Sense Strand, Anti-sense strand. Transcription For a given gene, only one strand of the DNA serves as the template for transcription. An example is shown below. The bottom (blue) strand in this example is the template strand, which is also called the minus (-) strand,or the sense strand. It is this strand that serves as a template for the mRNA synthesis. The enzyme RNA polymerase synthesizes an mRNA in the 5' to 3' direction complementary to this template strand. The opposite DNA strand (red) is called the coding strand, the non-template strand, the plus (+) strand, or the antisense strand. The easiest way to find the corresponding mRNA sequence (shown in green below) is to read the coding, non-template, plus (+), or anti-sense strand directly in the 5' to 3' direction substituting U for T. PLUS (anti-sense) STRAND: G A A A G G 3' 5' T G A C C T T C G A A C G G G A T G MINUS (sense) STRAND: 3' A C T G G A A G C T T G C C C T A C C T T T C C 5‘ mRNA STRAND: A G G 3' 5' U G A C C U U C G A A C G G G A U G G A A Prokaryotic cell Eukaryotic cell Tree of life A comparison of the three domains of life. Characteristic Euacteria Archaea Eukarya nuclear envelope absent absent present membrane-enclosed organelles absent absent present peptidoglycan in cell wall present absent absent membrane lipids unbranched hydrocarbons some branched hydrocarbons unbranched hydrocarbons RNA polymerase one kind several kinds several kinds initiator amino acid for start of protein synthesis formyl-methionine methionine methionine introns absent present in some genes present antibiotic sensitivity growth inhibited by streptomycin and chloramphenicol not inhibited by these antibiotics not inhibited by these antibiotics The central dogma At what stage do prokaryotes and eukaryotes differ? Eukaryote central dogma Operons: DNA segment = protein sequence + control circuitry RNA polymerase transcription Prokaryotic vs Eukaryotic RNA PolII Transcription initiation: get bent Prokaryotic Transcription initiation Eukaryotic transcription initiation Eukaryotic pre-initiation Eukaryotic mRNA packaging. What is this? mRNA nuclear export Nuclear pore The E. coli Lactose operon lacZ: Betagalactosidase Lactose transporter: lacY V-class proton pumps P-class pumps F-class proton pumps Cell membrane receptors for hormones, neurotransmitters, odors, and light. The potassium channel Cis/Trans testing in haploid organisms Cis/Trans effect testing for markers in the E. coli lac operon using a plasmid. Genotypes vs. Haplotypes Consider a diploid organism, such as a mouse (two copies of each gene per cell). Consider two mouse markers MA, and MB, that are biallelic (two known alleles for each). Represent the alleles as A, a, B, and b. For a mouse cell with the genotype AaBb, there are two possible haplotypes: Haplotype (AB, ab) Haplotype (Ab, aB) *Haplotypes ignore the (maternal, paternal) chromosome labels Cis vs. Trans Cis and Trans are terms that express a relationship between two linked markers that influence a given phenot The genotypes AAbb, aaBB and aabb would all result in the phenotype l. ype. Using our mouse example, suppose the linked markers MA, and MB , both influence a phenotype controlling hair length. Furthermore, assume that the wild type alleles A and B are dominant: •The genotypes AAbb, aaBB and aabb would all result in the phenotype l. •The genotype AABB would result in the phenotype L. •The genotype AaBb would result in the phenotype L if both markers were dominant and trans acting. If one or more of the markers was cis acting: The haplotype (AB, ab) would result in the phenotype L. The haplotype (Ab, aB) would result in the phenotype l.