A.  Chapter Summary 

The main focus of this chapter was gene regulation, and the prominent differences and similarities of the process in eukaryotes and prokaryotes. Organisms regulate genes so genes are made only when required. Multicellular eukaryotes can regulate their genes to harbor various different cell types. 

Gene regulation is bacteria is controlled by repressors and activators. Genes in bacteria are organized by function. Each 'functional unit' is called an operon, and contains a operator site and a promoter site. The operator site is like the control panel to initiate transcription, and the promoter site is where transcription actually begins by RNA polymerase. An example the book uses is of the Lactose (lac) Operon, a catabolic pathway. For the lac operon to be "on", glucose must be in low levels, and lactose must be in high levels. Lack of glucose, builds up cAMP around the DNA. cAMP then binds to CAP, a activator, which form a complex and binds to the CAP site on the operator of the operon. This part is now switched "on". High levels of lactose causes the production of allolactose. Allolactose binds to the lac repressor and prevents it from inhibiting the lacO site, thus allowing transcription. Another operon we looked at was the trp operon, which follows a anabolic pathway. When there is abundant tryptophan in the cell, tryptophan binds to the its repressor, turning it "on", and inhibits transcription, whereas in the the catabolic pathway, an abundant amount of lactose allowed transcription and inhibited the repressor, turning it "off".

In Eukaryotes, genes are organized individually, and each has its own promoter. The main units of the promotor are transcriptional sites, TATA box (upstream, determines transcription start point), and regulatory elements (upstream: enhancers and silencers). Inhancers increase the rate of transcription, and silencers reduce the rate when gene expression is not needed. Transcription begins with three different protein complexes. The first two, RNA polymerase and general transcriptor factors (5 of them) assemble at the TATA box forming a preinitiation complex. Mediators than wrap themselves around the complex to control rate of transcriptions. Transcription rates can also be controlled by repressors, activators, recruiting enhancers and silencers, or by changing gene accessibility.  

B.  Useful Materials

1. Androgen Receptor Signalling in Prostate Cancer - This pubmed journal talks about androgens and Prostate Cancer. Tumor growth and expression of androgens, by androgen receptors (AR). AR recruits many acetylation cofactors (from my knowledge, acetylation of DNA, loosens chromatin-histone complexes to allow easier transcription) to fine tune androgen gene expression, resulting is a speedy progression of prostate cancer. 

2. Transcription Eukaryotes

This video talk about the construction of the initiation complex of eukaryotic transcription. Its an easy visual to understand what kinds of proteins are involved to start transcription. 

3. 

This picture clearly shows what i talked about before, about the lac operon being tuned on or off. the lac repressor is active when not bound to lactose, and inactive when it is bound to lactose.