Answer Key: Segregating Chromosomes

BIOL230W Week 8 – Segregating Chromosomes We have spent the first half of the semester focused on the flow of information from DNA à RNAà protein using cystic fibrosis as a model. Now we will spend a few weeks looking at the roles different proteins play in the cell including signaling, cell division and cell cycle regulation. These processes are important to cell function and when they fail can result in the development of cancer. Day 1 Learning Objectives 1. Compare and contrast centromere, chromosome, chromatid, and kinetochore with respect to structure, function, location, stage, and phase. 2. Compare and contrast the amount and location of DNA at each stage of the cell cycle. 3. Describe the main processes occurring in each of the four stages of the cell cycle. 4. Outline the structures and result of each phase of mitosis. Mini-Lecture: Intro to Cell Cycle and Cancer Small Group Activity: Previous Knowledge Activate! Form a scaffold to which new knowledge can be attached. 1. What are the 4 stages of the cell cycle? G1, S, G2, M 2. Which stages are included in interphase? G1, S, G2 3. What happens in S-phase? Growth and ONE round of replication of genetic material 4. In which stages would you find sister chromatids? S, G2, M 5. What macromolecule makes up the centromere? DNA Mini-Lecture: DNA in Interphase 6. Is G0 a part of interphase? No 7. Compared to G1, how much DNA is in the nucleus of a cell in G2? Twice as much 8. What is the function of cohesin? Attaches sister chromatids Small group activity: DNA in Interphase 9. Using the images below highlight the interphase stages and the mitotic stages. 1 BIOL230W Week 8 – Segregating Chromosomes 10. Given the provided cellular membranes below, draw two individual chromosomes in G1, S and G2 ONLY. Indicate the presence of euchromatin vs heterochromatin, sister chromatids, cohesion, the centromere and the nuclear membrane. Mini Lecture: DNA In Mitosis 11. What is the purpose or result of mitosis? Splitting of replicated DNA into 2 separate daughter cells 12. Compared to G2 how is the structure of chromosomes different in M-Phase (i.e., mitosis)? Cohesin is removed between metaphase and anaphase and so sister chromatids separate 13. Compared to interphase, how would you expect the level of gene expression to differ in mitosis? Interphase shows higher expression– less tightly packed 14. Compared to G2, how much DNA is in the cell in prophase? The same 15. Compared to metaphase, how much DNA is in the cell in anaphase? The same 2 BIOL230W Week 8 – Segregating Chromosomes Small Group Activity: DNA in Mitosis Go back to the cell drawing for DNA structure in interphase. Use what you have learned in class today and previous knowledge to now draw your interpretation of the structure of DNAphases in the of mitosis. Be sure to include the two chromosomes, sister chromatids, cohesin, the nuclear membrane and the centromere. Make sure your drawing reflects the heterochromatic nature of the chromosomes. Day 2 Learning Objectives 1. Compare and contrast the polymerization of microtubules with the polymerization of DNA/RNA and proteins. 2. Describe how the structure of microtubules contributes to its function in interphase and in mitosis. 3. Apply the concept of “dynamic instability” to the structure and function of microtubules in mitosis. 4. Compare and contrast the 3 different types of microtubules that create the mitotic spindle with respect to attachment and function. 5. Draw and label the different stages of mitosis (with respect to the DNA structure, microtubule structure, kinetochore, nuclear membrane, and centrosome and cohesin). Mini-Lecture: How does the DNA Move? Microtubules and Kinetochores 16. Tubulin monomers polymerize when they are bound to GTP and depolymerize when they are bound to GDP. 17. How might a GEF effect the stability of a microtubule? It will increase stability by increasing amount of GTP that can activate and therefore rapid polymerization. 18. Given your answer to Q16, in what category of protein might you place the tubulin monomer? G-protein 19. Take a few minutes to compare and contrast the microtubule polymer with two other polymers (DNA/RNA and proteins) we have studied. Use Q. 20 and 21 to record your answers. Monomers Polarity Connecting bond Polymerizing Agent DNA/RNA Nucleotides Yes (3’/5’) Phosphodiester DNA/RNA polymerase Protein Amino Acids Yes (N/C) Peptide Bond Ribosome Microtubules Tubulin Dimers Yes (+/-) Hydrogen Bonds Nothing 20. How is the polymerization of microtubules similar to the polymerization of nucleic acids and proteins? It is dependent on the presence of a certain molecule (GTP in this case) 21. How is the polymerization of microtubules different from the polymerization of nucleic acids and proteins? There is no agent required as it will self-polymerize. 3 BIOL230W Week 8 – Segregating Chromosomes 22. What unique characteristic of the microtubule polymer (not found in the protein nor the DNA/RNA polymers) allows forrapid depolymerization(hint – microtubules are not permanent structures)? Hydrogen bonds 23. What organelle nucleates (i.e., initiates polymerization of) microtubules? Centrosome Small Group Activity: Microtubules During Interphase Go back to the cell drawing for DNA structure in interphase. Use what you have learned in class today to draw your interpretation of the location of microtubules in interphase. Be sure to include the microtubules, the centrosome(s) and nuclear membrane. Mini-Lecture: Spindle formation and chromosome attachment 24. What cellular event allows microtubules to invade the nuclear space during prometaphase? The nuclear membrane disintegrates. 25. What type of macromolecule is a kinetochore? Protein 26. How is the kinetochore different from a centromere? It is not part of the DNA. 27. What does the + end of each of the three types of mitotic microtubules attach to? One type extends toward membrane (stabilize spindle), another attaches to a microtubule coming from another pole, and another connects to the centrosome on the kinetochore. 28. How does the dynamic instability of the microtubule relate to the attachment of microtubules to chromosomes? 29. What provides the force to position the chromosomes at the center of the cell at metaphase? Kinesin walking along the microtubule and pulls it to pole. Small Group Activity: Microtubules During Mitosis 4 BIOL230W Week 8 – Segregating Chromosomes Go back to the cell cycle drawing. Use what you have learned in class today to draw your interpretation of the location of microtubules in mitosis. Be sure to include the microtubules (Polar, kinetochore and Astral), the centrosome(s), kinetochore, and nuclear membrane. At Home Practice: We posted some extra cell outlines in our Canvas. Please use those (or create your own) and see if you can remember all the structures and locations in the different stages of the cell cycle without looking! Try using different colors to highlight the various structures. 5