Exam 4 (4)

Question 1

Connection between Temperature Sensitive Yeast and Cell Cycle

Answer 1

By increasing temperature, we stall colony growth; Injection of an intact plasmid allows us to figure out if this plays a role in cell division because we’d observe growth at the higher temperature

Question 2

What occurs with excess of the regulatory elements of the Cyclin-CDKs?

Answer 2

Wee1 Kinase Excess: Inhibited CDKs –> No cell cycle progression; all growth, no division –> elongated/big cells
Cdc25 Excess: Hyperactive CDKs –> Too much division with not enough time to grow –> many small cells

Question 3

Connection between Xenopus Oocytes and Cell Cycle

Answer 3

By injecting cytoplasmic of able to divide cells into oocytes –> induces mitosis; leads to discovery of some cytoplasmic “maturation promoting factor” (the Cyclin CDK pair)

Treated oocyte extracts with RNA-ases to discover progression of the cell cycle is dependent on [cyclin] increasing/decreasing

Question 4

Connection between Cyclin D and G1 –> S Transition

Answer 4

Required for G1 –> S Transition; exhibited using BrdU present experiment (replaces Thymine in newly synthesized DNA) –> when Cyclin D is not present, BrdU incorporation is slow, as opposed to instantaneous 100% incorporation with Cyclin D

Question 5

Definition of Meiosis

Answer 5

One cycle of chromosome replication with 2 rounds of division –> forms 4 haploid cells/cellular progeny

Question 6

What happens during Prophase I (a process unique to meiosis)?

Answer 6

Synapsis: the formation of a tetrad/bivalent of two homologous chromosomes; allows crossing over/chiasma to occur: exchange of DNA/info between maternal and paternal (relative to the “divider’s” parents) segments (meaning we have potentially new phenotypes than before)

Question 7

What happens during Anaphase I? What is the “Law” that is relevant here?

Answer 7

Each homologous pair (keep in mind, one is distinctly more maternal/paternal by nature) separates, gives the daughter cells a mostly paternal or maternal version of each allele; Independent Assortment claims the way these chromosomes align at the metaphase plate is stochastic; therefore, no allele influences the organization of the other, and it’s equally likely to get everything (no completely maternal or paternal daughter cell)

Question 8

What about Meiosis II?

Answer 8

Basically just like Mitosis without the DNA replication step –> centromeres divide and give 2 haploid cells each –> 4 total haploid cells from the process