Monday, March 9, 2009

Notes for Chapters 19 and 21


Here are the notes I promised you in class. Sorry about the formatting but Blogger's text editing is a bit clunky. It may be best to copy and paste the text into a word document so you can edit the formatting. Have your book in hand as you read through the notes. I want your TQT for this week to come from this material. I will write a post for your TQT on Wednesday and please write your TQT as a comment to that post.

Mr. Baker

Chapter 19 – Cancer

1. Proto-oncogene – normally codes for a cell growth or division regulating protein. If it mutates, it may result in a change in the control of cell growth an division and cause the cell to rapidly divide and become a tumor.
2. The mutated proto-oncogene is now an oncogene.
3. There are three means to cause a proto-oncogene to become an oncogene.
a. Translocation to a new chromosomal region and promoter
b. Gene duplication
c. Point mutation of the DNA code
4. Another family of genes that are implicated in cancer is the tumor-suppressor genes. These genes have many functions such as DNA repair, cause cell death, and contact inhibition.
5. See your text for the function of the ras and p53 genes.
6. See your text (pp 359-361) for an explanation of how multiple mutations are implicated in tumor development and specific examples.

Chapter 21 – The Genetic Basis of Development

1. Embryonic development involves
a. Cell division
b. Differentiation
c. Morphogenesis
2. Model organisms
3. Differential Gene Expression
a. All cells have the same genes. The cells of a zygote are totipotent. They have not differentiated and can become any part of an organism.
i. Carrot cloning
ii. Frog embryo – from early cells, normal tadpole. From intestinal cells, only 2%. Conclusion, nuclei change as cells differentiate.
iii. Sheep clone accomplished with transplantation of the nucleus of an udder cell into a de-nucleated egg cell.
1. cultured udder cell in nutrient poor medium
2. cell went into G0 phase
3. then inserted into egg cell
4. one of several hundred survived and became Dolly
b. As a cell differentiates it expresses specific proteins.
i. These proteins regulate development and function
ii. In muscle cells it is due to a regulatory protein myoD that is is a transcription factor.
c. How does it start?
i. Maternal signals from the egg such as mRNA. These are called cytoplasmic determinants.
ii. Induced by signals from other cells
4. There is a pattern to Development
a. The pattern formation is the result of positional information given through molecular signals that tell a cell where it is relative to the body axes.
b. As your book states on page 397. “In Drosophila, cytoplasmic determinants that are present in the unfertilized egg provide positional information for the placement of the two axes even before fertilization. After fertilization, positional information operating on a finer and finer scale establishes a specific number of correctly oriented segments and finally triggers the formation of each segment’s characteristic structures.” These “cytoplasmic determinants” are mRNA that were produced by the egg during its development.
c. Read the section – “Gradients of maternal molecules in the early embryo control axis formation” on page 399 to understand how the concentration of the bicoid gene mRNA at the end of an egg determines where the body segments go.
d. Homeotic genes direct the identity of body parts.
i. The development and placement of body parts requires the identification of body regions. The genes that regulate this are the homeotic genes.
ii. For example, in Drosophila homeotic genes of the thorax direct the production of proteins that cause leg development.
e. The Hox (homeobox) genes.
i. All homeotic genes have an identical sequence 180 nucleotides long called the homeobox. Genes with this region are therefore called Hox genes.
ii. Most homeobox genes are associated with development and Hox genes are found in other animals.

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