biophysics 101 biology section #2 sept. 30 2003 today’s topics: dogmas operons cis and trans...
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BioPhysics 101 Biology section #2 Sept. 30 2003
Today’s topics:
•Dogmas
•Operons
•Cis and Trans
•Haplotypes
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 anti-sense 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: 5' T G A C C T T C G A A C G G G A T G G A A A G G 3'
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: 5' U G A C C U U C G A A C G G G A U G G A A A G G 3'
Plus strand, Minus strand, Sense Strand, Anti-sense strand.
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 hydrocarbonssome 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 absentpresent in some
genespresent
antibiotic sensitivitygrowth inhibited by streptomycin
and chloramphenicolnot inhibited by these antibiotics
not inhibited by these antibiotics
A comparison of the three domains of life.
Cis/Trans effect testing for markers in the E. coli lac operon using a plasmid.
Cis/Trans testing in haploid organisms
Genotypes vs. HaplotypesConsider 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
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.
Cis vs. Trans
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.
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.