Class Notes (838,402)
Canada (510,881)
Biology (2,229)
BIO230H1 (243)
Lecture 3

BIO230 LECTURE 3.docx

9 Pages
Unlock Document

Darrel Desveaux

BIO230 LECTURE 3 Sept 17, 2013 The notes only make sense when read alongside the slides. If something's on the slides, it probably isn't in my notes. Prokaryotic Gene Regulation: DNA cis elements: regulatory elements (2 kinds) one type of gene regulatory protein turns repressors on the other type turns repressors off The only time you turn the lactose on is if you are all out of glucose because glucose is the preferred energy source for bacteria Negative regulation: competition between RNA polymerase and repressor protein for promoter binder Positive regulation: activator protein recruits RNA polymerase to the promoter to activate transcription Regulatory elements can also be found: -far upstream of gene -downstream of gene (eukaryotes) -within gene (introns, eukaryotes) DNA looping Lac repressor is a tetramer (four identical subunits) and can bind two operators simultaneously Bacteriophage Lambda Gene regulatory switch that controls lifestyle of BL (molecule that infects bacteria) lands on a bacterial cell and injects its DNA into bacterial cell Two proteins repress each others synthesis (a simple transitional circuit) one protein affects expression of other protein Bacteriophage Lambda Lifestyle: Prophage pathway: minimal amount of BL expression But if cell is compromised, BL chooses lifestyle of Lytic Pathway. Results in a lot of BL expression. Original cell undergoes lysis and then tonnes of BL bacteria released into environment 2 regulatory proteins involved from switching between Prophage pathway and Lytic Pathway. they are: 1. lambda repressor (cI) 2. cro protein two proteins repress each other's synthesis In prophage stage, lambda repressor protein active. inhibiting expression of cro. positive regulator of self. negative regulator of cro. repressor protein one of the only proteins being expressed. in lytic stage, cro protein takes over. cro expressed. cro turns off lambda repressor protein. cro is positive regulator of self. cro negative regulator of lambda repressor. State 1 of Prophage lambda repressor blocks synthesis of cro activates its own synthesis most bacteriophage DNA is not transcribed State 2 of Lytic Cro occupies operator. blocks synthesis of repressor protein allows its own synthesis most bacteriophage DNA is extensively transcribed What triggers the switch? To go from Prophage to Lytic. under favourable environments, will have Prophage. Under harsh environments, bacteria will undergo lytic. often under harsh environments DNA of bacteria damaged. Dna repair proteins deployed in bacteria to repair DNA. DNA repair proteins actually inactivate lamdba repressor causing lytic state. when lambda repressor inactivated, lambda repressor no longer supressing cro. cro will then express causing lytic stage. host response to DNA damage inactivates repressor -switch to lytic state under good growth conditions, repressor protein turns off cro and activates itself. positive feedback loop. -maintains prophage state example of a transcriptional circuit Transcriptional circuits Cro-repressor switch is a flip-flop device inhibit each other. when one is active, it inhibits the other. either one or the other being expressed feed forward loop: both A and B required for the expression of Z Positive feedback loop of A A sends transient signal which expresses protein A created protein A then comes back and turns on another transient signal will end up with a lot of
More Less

Related notes for BIO230H1

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.