Exam 1 grade distribution

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0-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-100

grade category

# in category

Exam II grade distribution

0

1

2

3

4

5

6

7

8

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10

0-59 60-64 65-69 70-74 75-79 80-84 85-89 90-94 95-100

grade category

# in category

Average = 79

Average = 85

Kavanagh et al discussion moved up to next Tuesday

- Allows for last class to be a review session

Goals

-Lac operon

-Eukaryotic enhancers

-Transcription factors

-Signal integration

The lac operon promoter

LacZ - BetaGalactosidase - cleaves lactose into usable subunits

LacY - Lactose permease - transports lactose across the cell membrane

LacA - Eliminates toxic molecules that are co-transported

Operator - Binds repressors

CAP site - binds cap proteins (activator)

The activator and repressor are both inhibited by sugars

Physical interactions regulate lac operon transcription

Cap recruits Polymerase via interaction with the CTD of the alpha subunit

The cap activator is a helix-turn-helix motif

-Bind DNA as a dimer

-Requires two similar sequences of DNA in reverse order

Lac repressor forms a tetramer between two operator sites (primary and secondary)

Discovery of the cis-trans model of gene regulation

Repressor acting in trans

Operator (repressor binding site) operates in cis

Regulation in eukaryotes follows the same principles as prokaryotes, but involves more regulatory sequences

- *Can regulate access to DNA via nucleosomes

Transcriptional regulators (tx factors) are modular

- Experimental loss of n-terminal end of activator

- Experimental fusion of n-terminal domian of an activator to c terminal of a repressor

Homeodomain DNA recognition

Zinc finger domain

Helix turn helix domain

Common DNA binding motifs

Eukaryotic activators don’t often interact directly with RNA polymerase

Interaction with the mediator complex

Interaction with histones

Regulatory elements can be kilobases away, or on different chromosomes

Signal integration

Theoretical mechanisms of repression

Example of signal transduction

- Extracellular signaling molecule (ie SHH) initiates a cascade that alters transcription

Lac operon integrates signals from outside the cell

Kavanagh et al discussion moved up to next Tuesday

- Allows for last class to be a review session