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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.