Cancer Hands

Compare and contrast the role of oncogenes, proto-oncogenes, and tumor suppressor genes in cancer.

Oncogenes are cancer causing genes, and proto-oncogenes are normal cellular genes that are responsible for normal cell growth and division. So proto is good, once the proto is gone, we’ve got cancer on our hands. Not actually, I mean you can get cancer nearly anywhere.. ANYWAYS,

tumor suppressor genes are responsible for repairing damaged DNA, controlling cell adhesion, and inhibiting the cell cycle when necessary. They also prevent uncontrolled cell growth/division.

DNA Methylation and Histone Acetylation

Describe the impact of DNA methylation and histone acetylation on gene expression.
DNA methylation adds methyl groups to specific bases in DNA, which leads to turning off the transcription of some genes. This typically causes long-term inactivation of a gene. For example, the gene for humans to grow tails has been methylated, we only have a tailbone and cannot grow tails. Histone acetylation adds acetyl groups to the lysines in histone tails that are positively charged. [See “Wiggly Purple Guys” under Ch 16 & 17] This functions to loosen up the chromatin structure, so that transcription can be initiated. Also, methylation in chromatin can cause it to condense more. Phosphate groups added to methylated amino acids also can loosen up wound up chromatin.

Why Repressing Stuff can be Good

Explain the role of repressor genes in operons and why they are important.

Repressors genes are important for these segments of DNA code for repressor proteins. Repressor proteins are necessary for the proper functioning of operons, repressors make sure operons are only active when they need to be, and not otherwise.

Inducible vs Repressible

Compare and contrast an inducible operon and a repressible operon. Include an example of each.

Inducible: The lac operon is an example of an inducible operon. It is usually off, but can be induced to turn on when needed. In these operons, there is an active operon always attached to the operator of the operon, until an inducer attaches to it and causes it to change shape and detach. This allows for RNA polymerase to go through reading the operon, to create the protein it codes for. The lac operon codes for enzymes that are used to hydrolyze and metabolize lactose. So, this operon will only be active when there is lactose present. When lactose is present, allolactose is the inducer which will inactivate the repressor attached to the operator.  

http://biology-forums.com/index.php?action=gallery;sa=view;id=11503

Repressible: The trp operon is an example of a repressible operon. It is usually turned off, but can be repressed when it is not needed. These operons are turned off by the binding of a repressor protein, that may need a corepressor in order to be activated, to the operator of the operon. In the trp operon, tryptophan is coded for. When there is tryptophan present in the cell and does not need to be synthesized, this acts as a corepressor and causes the operon to be blocked and turned off.

http://www.slideshare.net/kindarspirit/18-regulation-of-gene-expression

Oper-on or Oper-off?

Describe the structure of an operon. Include a model with your discussion.

An operon is a segment of DNA that includes an operator, a promoter, and a stretch of functionally related genes. Operons are regulatory switches for the production of specific proteins that are only needed during certain times.

https://diaryofanalevelstudent.wordpress.com/2013/02/23/the-lac-operon/