Cell Division Study Guide U3.2.3: Eukaryotic chromosomes are linear DNA molecules associated with histone proteins. (Oxford Biology Course Companion page 151). 1. Describe the structure of eukaryotic DNA and associated histone proteins during interphase (chromatin). -Eukaryotic DNA is linear -Associated with histone proteins in a structure called the nucleosome -During interphase the DNA is NOT supercoiled into chromosomes, it is in a loose form called chromatin 2. Explain why chromatin DNA in interphase is said to look like beads on a string. -The basic unit of chromatin is the nucleosome connected by sections of linker DNA -Structure gives the appearance of "beads on a string" U1.6.2: Chromosomes condense by supercoiling during mitosis (Oxford Biology Course Companion page 52). 3. Describe the structure of a replicated chromosome, include the centromere and sister chromatids. -Centromere: location where the two identical DNA strands (sister chromatids) are attached -Replicated chromosome: identical copies attached to each other 4. Explain why chromosomes must condense during mitosis. -DNA condenses during mitosis so that it can more easily be moved to the poles of the cell U7.1.2: Nucleosomes help to supercoil the DNA. (Oxford Biology Course Companion page 347). 5. Draw and label the structure of a nucleosome, including the H1 protein, the octamer core proteins, linker DNA and two wraps of DNA. -DNA wraps twice around -Linker DNA connects to the next nucleosome -8 histone proteins form an octomer core
6. Explain the levels of supercoiling (DNA nucleosome beads on a string 30nm fiber unreplicated interphase chromosome replicated metaphase chromosome). 1. DNA double helix 2. Nucleosome 3. Multiple nucleosomes "beads on a string" 4. Compacted/coiled nucleosomes (30 nm fiber) 5. Unreplicated chromosome 6. Replicated chromosome S7.1.2: Utilization of molecular visualization software to analyze the association between protein and DNA within a nucleosome (Oxford Biology Course Companion page 348). 7. Identify nucleosome structures using molecular visualization software. Nucleosomes can be identified because of the octomer core of histones and two wraps of DNA around the core 8. Outline the mechanism of histone-dna association. Histones are proteins that have many positively charged amino acids (lysine and argenine). The positive charge allows them to associate with the negatively charged DNA. Once the charge is neutralized, the nucleosomes can tightly pack together. U1.6.4: Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm (Oxford Biology Course Companion page 52). 9. List example metabolic reactions occurring during cell interphase. -During G1, the cell is performing its specialized function, which requires extensive protein synthesis (in nucleus and cytoplasm). -During S, the DNA replication occurs in the nucleus 10. Outline events of G1, S, G2 and G0 phases of interphase.
U1.6.1: Mitosis is division of the nucleus into two genetically identical daughter nuclei (Oxford Biology Course Companion page 51). 11. State the function of mitosis. To create two daughter cells with genetically identical nuclei. 12. List four processes which involve mitosis. -Tissue repair (after injury or burn) -Growth of the organism -During embryonic development (from zygote on...) -Replace cells that die naturally -Asexual reproduction (creating organisms that are genetic clones) 13. State the names of the four phases of mitosis. PMAT -Prophase -Metaphase -Anaphase -Telophase 14. Draw typical eukaryotic cells as they would appear during the interphase and the four phases of mitosis.
15. Outline four events that occur during prophase. -Nuclear membrane begins to break apart -Nucleolus "disappears" -DNA supercoils into replicated chromosomes -Spindle fibers form and centrioles move towards the cell poles 16. Outline the process of metaphase, inclusive of the role of microtubules and the kinetochore. -Replicated chromosomes align at the cell equator -A protein complex called the kinetochore, located at the centromere, is connected to microtubules (a type of spindle fiber) 17. Outline the process of anaphase. -The identical chromatids (now unreplicated chromosomes) are pulled towards the poles of the cell by motor proteins moving along the kinetochore microtubules -non-kinetochore microtubules elongate cell 18. Outline four events that occur during telophase. -Nuclear membrane reforms -Nucleolus reappears -Chromosomes decondense into chromatin -Spindle fibers break apart S1.6.1: Identification of phases of mitosis in cells viewed with a microscope or in a micrograph (Oxford Biology Course Companion page 52).
19. Determine the phase of mitosis of a cell viewed in a micrograph or with a microscope. S1.6.2: Determination of a mitotic index from a micrograph (Oxford Biology Course Companion page 55). 20. State the formula for calculation of a mitotic index. - M.I = # of cells in mitosis/total # of cells AKA: M.I = P+M+A+T/I+P+M+A+T 21. Calculate the mitotic index of a tissue as seen in a micrograph. - M.I = 8 cells in mitosis/26 total cells = 0.32 - Will ALWAYS fall between 0 and 1. - 1: all cells in sample in mitosis - 0: no cells in sample in mitosis 22. Outline the use of mitotic index calculations in diagnosis and treatment of cancer. DIAGNOSIS: the higher the M.I. relative to a tissue-specific standard M.I., the more likely a tissue is cancerous TREATMENT: cancer treatments work by stopping cell division, so if a cancer treatment is working fewer cells will be in mitosis. As a result, the M.I. will decrease if a treatment is working.
U1.6.3: Cytokinesis occurs after mitosis and is different in plants and animal cells (Oxford Biology Course Companion page 55). 23. Define cytokinesis. Division of the cytoplasm of a parent cell into two daughter cells. 24. State the difference between mitosis and cytokinesis.. -Mitosis refers to the division of the nucleus (and DNA in it) -Cytokinesis is splitting of the cytoplasm (and organelles) 25. Contrast cytokinesis in plant and animal cells. -Plant cells create new cell wall between the daughter cell cytoplasm -Animal cells do not have to form cell wall, they form a cleavage furrow 26. Describe the formation of the cleavage furrow in animal cell cytokinesis. -Ring of contractile proteins at the cell equate constrict, pulling in the cell membrane and creating a cleavage furrow. -Cleavage furrow continues to pinch in until the two sides are touching creating two cells 27. Describe the formation of the middle lamella and cell wall in plant cell cytokinesis. -Middle lamella cements the cell walls of two adjoining plant cells together -Golgi buds vesicles containing pectin -Vesicles move and align at the cell equator
-Vesicles fuse, forming a continuous phospholipid membrane with pectin sandwiched in between ("Cell plate") -Additional vesicles bring and secrete cellulose to the cell plate, forming the cell wall between the two daughter cells