1. Lecture 19 Homework Review Today: Apoptosis and Cancer Monday April 23rd- Cell-Cell Interactions/Tissues Thursday April 26 th -Early Development and Stem Cells Monday April 30 th - Review Final Exam May 9 th 12-1:30pm in this classroom For Exam III- You are not responsible for any material in assigned chapters relating to Plants!

2. Homework Lecture 15 and 16 1)In cells, the concentration of actin monomer is higher than required for purified actin monomers to polymerize in vitro. Thymosin is a protein that can bind actin monomers and sequesters them. If you add a drug that inhibits the ability of thymosin to bind actin monomers, what would be the effect on actin polymerization? INCREASE POLYMERIZATION Actin Filament Assembly

3. 2. Which of the following changes occurs when a skeletal muscle fiber contracts? A) The A bands Shorten B) The I Bands Shrink C) The Z lines slide farther apart D) The Thin Filaments Contract E) The Thick Filaments Contract Dark Band- A band Light Band- I band

4. 3.Consider an Individual Microtubule: What must happen at the end of the microtubule in order for it to stop shrinking and start growing? -Binding of GTP Tubulin Heterodimers to form a GTP Cap How would a change in the tubulin concentration affect this switch? Increase in Tubulin Heterodimers- Promote Rescue Decrease in Tubulin Heterodimers- Continue Shrinking What would happen if only GDP, but no GTP, were present in the solution? MT Depolymerization would occur What would happen if the solution contained a nonhydrolyzable form of GTP? MT Continued Polymerization until no available Heterodimers left

6. MAPs to Influence MT Filament Stability

7. 4. Nucleation of Actin Monomers or Microtubule Heterodimers is the Slow Step in the formation of Actin and Microtubule Filaments in vitro. How do cells bypass the slow step in vivo in the formation of A) MT filaments – MTOCs and B) Actin Filaments? ARP COMPLEX

8. 5) What is the role of Nexin in the Axoneme of Cilia and Flagella. What would happen if it wasn’t present? Couldn’t bend-filaments would slide With NEXIN

9. 6)The Hydrolysis of GTP to GDP carried out by Tubulin Molecules: A) Provides Energy Needed for Tubulin to Polymerize B) Occurs Because the Pool of Free GDP Has Run Out C) Tips the Balance in Favor of Assembly D) Allows the Behavior of Microtubules called Dynamic Instability D

10. Homework 17 and 18. Due Monday- we will go over these answers. True or False and Why? 1)Cells do not pass from G1 to M phase of the cell cycle unless there are sufficient nutrients to complete the whole cell cycle. No cell goes from G1 directly to M

11. Homework 17 and 18. Due Monday- we will go over these answers. True or False and Why? 2) Rb is a transcription factor that must be phosphorylated in order for expression of G1/S and S phase Cyclins.FALSE- not functioning as a transcription factor in this case- but as inhibitor of transcription factor

12. True or False and Why? 3) Once a Cyclin binds to a CDK, the kinase is active and can immediately begin phosphorylating targets. FALSE

13. 4) Separation of sister chromatids requires kinetochore MT assembly and cytoplasmic dynein activity. FALSE Anaphase A Movement Plus End of Kinetochore Microtubules Dissassembles Minus End Directed Motor (Dynein) Proteins Pull Toward Spindle Pole (-) Pac Man Mechanism MT Depolymerize Dynein Walks Toward Minus End

14. 5) When a cell that is in the process of replicating DNA is fused with a cell in G1: A)The replication of DNA occurring in the original S nucleus is terminated B) DNA synthesis begins immediately in the original G1 nucleus C) The two Nuclei Fuse and Further Division is Arrested D) The Chromosomes of the Original G1 Nucleus condense in preparation for mitosis E) The original G1 cell will divide immediately B

15. 6.) Sister chromatids: A) Are created when DNA is replicated B) Are attached at the centromere prior to Division C) Are separated during anaphase D) Have matching copies of the chromosome’s DNA E) all of the above 7.) In some cases, Mitosis occurs without cytokinesis occurring. This will result in: A) Cells with more than one nucleus B) Cells that are unusually small C) Cells lacking nuclei D) Destruction of chromosomes E) Cell cycles lacking an S phase E A