BIO SCI 99 Lecture Notes - Lecture 9: Sigma Factor, Repressor, Gel Electrophoresis
17 May 2018
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Bio 99 Part 2 – Lecture #3
chapter 20: pages 694-715 (regulation of gene expression in bacteria)
I. Specificity of transcription initiation
a. “iga fato
i. The first level of specificity
ii. Whole classes of genes are turned on or off depending on which sigma
factor is expressed at a given time
b. Regulators (DNA-binding proteins)
i. Regulatos id to speifi sites ea pootes ad affet the
ability/affinity of RNA polymerase to initiate
ii. Repessos: inhibit/block binding of polymerase
iii. atiatos: hae affiit fo polease
c. Transcription factors are regulated at a higher level by the sigma factors
d. Regulators are more like having the electricity flowing through the outlets but
in addition, we have individual switches that will allow for us to turn off some
of the lights even if we still have power flowing
II. Escherichia coli (E. coli)
a. Useful for scientists
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b. The fist phase is the lag phase, ad it ous eause the ateia still do’t
know if they want to replicate or not, and they are also still looking for
nutrients and such
c. Then we will see exponential growth once the bacteria begin to replicate
d. Then they will reach another phase in which they approach the limit of the
nutrients that will support the culture, this is the stationary phase, we do not
see more replication
e. Once the colony runs out of nutrients we they will start to die off and we see
a death phase
f.
III. Biphasic growth curve (glucose and lactose)
a. First the bacteria will grow on the use of glucose until they use all of it, this is
the first growth incline
b. Then there will be a lag phase due to the lack of glucose
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c. Then the second growth will be from the bacteria using lactose as their
nutrients
d. They begin to form enzymes that will degrade whatever they will be
consuming as a source of nutrients
e.
IV. Regulation of the Lac operon
a. Through genetic experiments, they were able to determine how expression
of these genes is coordinately regulated in response to the presence or
absence of lactose
b. Some genes encode proteins with the sole purpose of regulating the
expression of other genes
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