Chapter 12 Mitosis Study Guide

1) Key roles of Cell Division: ➔ Reproduction- amoeba dividing into two cells, each constituting an individual organism ➔ Growth and Development- fertilized egg gives rise to two-celled sand dollar embryo ➔ Tissue renewal- dividing cells in bone marrow continuously make new blood cells 4) Humans have 46 chromosomes are in a human somatic cell 5) The two types of somatic cells are bone cells and liver cells 6) Gametes- are reproductive cells. 7) Two types of gametes: sperm in males and eggs in females. 8) 23 chromosomes are present in a human gamete. 9) Chromatin- is the entire complex of DNA and proteins that makes up chromosomes. When a cell is not dividing 10) 46 DNA molecules are in each of your somatic cells 11) A chromosomes is a packaged gene-carrying structure consisting of chromatin. A chromatid is one copy of a duplicated chromosome. A centromere is a region containing specific DNA sequences where the chromatid is attached more closely to its sister chromatid (represented by the narrow “waist”). 12) 1. One of the multiple chromosomes in a eukaryotic cell, a long, thin chromatin fiber containing one DNA molecule and associated protein, is duplicated, involving the replication of DNA, and condensed. 2. Once dublicatied, the chromosomes consists of two sister chromatids connected along their entire lengths by sister chromatid cohesion. Each chromatid contains a copy of the DNA molecule. 3. Molecular and mechanical processes separate the sister chromatids into two distinct chromosomes and distribute them to two daughter cells. 13) Mitosis, the division of the genetic material in the nucleus, is usually followed immediately by cytokinesis, the division of the cytoplasm. 17) Interphase includes G1, S, and G2. M phase includes prophase, metaphase, anaphase, and telophase Interphase: ★ G1 rapid growth and producing/copying organelles. ★ S DNA is replicated ★ G2 Growth and final preparation for division. M phase or Mitosis: ★ Prophase- The DNA condenses and organize and the classic chromosomes appears ★ Metaphase- where the chromosomes align along the center of the cells. ★ Anaphase- where the chromosomes separate, pulled apart by kinetochore microtubules. ★ Telophase- nuclear membrane reappear around the two sets of chromosomes. 18) In animal cells; the mitotic spindle, a structure consisting of fibers made of microtubules and associated proteins, emerges from the centrosomes, a subcellular region containing material that functions throughout the cell to organize the cell’s microtubules. 19) The microtubule-organizing center is another name for the centrosome. 22) During interphase in animal cells, the single centrosome duplicates, forming two centrosomes, which remain together near the nucleus. The two centrosomes move apart during prophase and prometaphase of mitosis as spindle microtubules grow out from them. By the end of prometaphase, the two centrosomes, one at each pole of the spindle, are at opposite ends of the cell. 23) Each of the two sister chromatids of a duplicated chromosome has a kinetochore, a structure of proteins associated with specific sections of chromosomal DNA at each centromere. 24) Explain the difference between kinetochore and nonkinetochore microtubules and the function of each. Unlike nonkinetochore microtubules, kinetochore microtubules attach to the kinetochores and jerk the chromosomes back and forth and pull the two sister chromatids apart, eventually aligning them along the metaphase plate. In a dividing animal cell, the nonkinetochore microtubules are responsible for elongating the whole cell during anaphase. 27. Describe cytokinesis in an animal cell. In animal cells, cytokinesis occurs by a process known as cleavage. The first sign of cleavage is the appearance of a cleavage furrow, a shallow groove in the cell surface near the old metaphase plate. On the cytoplasmic side of the furrow is a contractile ring of actin microfilaments associated with molecules of the protein myosin. The actin microfilaments interact with the myosin molecules, causing the ring to contract. The contraction of the dividing cell’s ring of microfilaments is like the pulling of a drawstring. The cleavage furrow deepens until the parent cell is pinched in two, producing two completely separated cells, each with its own nucleus and share of cytosol, organelles, and other subcellular structures. 28. Describe cytokinesis in a plant cell. Cytokinesis in plant cells, which have cell walls, does not involve a cleavage furrow. Instead, during telophase, vesicles derived from the Golgi apparatus move along microtubules to the middle of the cell, where they coalesce, producing a cell plate. Cell wall materials carried in the vesicles collect in the cell plate as it grows. The cell plate enlarges until its surrounding membrane fuses with the plasma membrane along the perimeter of the cell. Two daughter cells result, each with its own plasma membrane. Meanwhile, a new cell wall arising from the contents of the cell plate has formed between the daughter cells. 29. How is the cell plate formed? What is the source of the material for the cell plate? Vesicles from the Golgi apparatus containing cellulose move along microtubules to the center of the cell, where they coalesce, forming the cell plate, as new cell wall materials fuse with the plasma membrane and the old cell wall. 30. Prokaryote reproduction does not involve mitosis, but instead occurs by binary fission. Describe binary fission. In binary fission, a prokaryotic cell grows to roughly double its size, then divides to form two cells. 31. Besides the fact that prokaryotes lack a membrane-bounded nucleus, contrast prokaryotic and eukaryotic cells. Prokaryotes reproduce through binary fission, they produce asexual forming one identical daughter cell. 32. What controls the cell cycle? Molecules present in the cytoplasm. 34. Summarize what happens at each checkpoint. G1 “restriction point” in animal cells; continues on to G2 if go, will usually complete cycle; exits cell cycle and enters G0, a nondividing state, if no go; regulated by the activity of cyclin-Cdk protein complexes G2 MPF triggers cell’s passage past G2 checkpoint into M phase if all chromosomes have been replicated M irreversible anaphase stage entered only if all sister chromatids correctly attached to spindle microtubules 35. Describe the G0 phase. Most cells of the human body are in the G0 phase, a nondividing state. 36. What is a protein kinase? Protein kinases are enzymes that activate or inactivate other proteins by phosphorylating them. Particular protein kinases give the go-ahead signals at the G1 and G2 checkpoints. Cyclin+CDK produces MPF and then Mitosis occurs Cyclin- Varying concentration Increases During G2. CDK- Cyclin dependent kinases constant concentration. MPF when active, initiate mitosis. 39. What does MPF trigger? What are some specific activities that it triggers? MPF (maturation-promoting factor) triggers the cell’s passage past the G2 checkpoint into M phase. For example, MPF causes phosphorylation of various proteins of the nuclear lamina, which promotes fragmentation of the nuclear envelope during prometaphase of mitosis. 41. What are growth factors? How does PDGF stimulate fibroblast division? Growth factors are proteins released by certain cells that stimulate other cells to divide. Fibroblasts have PDGF (platelet-derived growth factor) receptors on their plasma membranes. The binding of PDGF molecules to these receptor tyrosine kinases triggers a signal transduction pathway that allows the cells to pass the G1 checkpoint and divide.