Biology Homework Chapter 8: Cell division - Mitosis
Textbook assignment: Chapter 8:The Cellular Basis of Reproduction and Inheritance, sections 1-10.
We start a new unit with chapter 8. If you have questions or confusion about the material in chapters 1-7, now is the time to review and identify where those problems exist, study the material, and ask questions.
Meiosis and mitosis are sometimes confusing, because the names and the processes are similar. The only cells produced by meiosis are gametes, "half-cells" that have to eventually join together to form not merely a new cell, but a new organism.
All other eukaryotic cells are produced by mitosis. This process is similar to the binary fission used by single celled prokaryotes, but includes the extra steps necessary to reproduce the organelles and nucleic DNA structures found only in eukaryotes.
- 8.1 Asexual reproduction produces clones (genetic replicas of the single parent cell) that are duplicates of the single parent cell. Sexual reproduction produces cells that fuse together some characteristics (but not all) of each parent cell.
- 8.2 Prokaryotic cells reproduce by binary fission, so the offspring cells are clones of the parent cell. Prokaryotes duplicate their single DNA strand and increase in size before splitting in two; each daughter cell inherits its own copy of the circular DNA strand.
NOTE: There can be genetic variation in bacteria species, but it is introduced a different way than through reproduction.
- 8.3 When eukaryotic cells replicate through mitosis, the result is the same as binary fission in prokaryotes: duplicate daughter cells. However, because of the complex organization of eukaryotes, simple binary fission isn't possible. Instead, the process of mitosis guarantees that each daughter cell inherits a complete set of the multiple DNA strands in the nucleus, as well as enough organelles to continue to function.
- 8.4 Each eukaryotic cell goes through specific stages.
- Interphase -- the time between cell replication events
- G1: the cell grows and manufactures more organelles as it needs them.
- S: the cell synthesizes a copy of its own DNA
- G2: the cell grows some more
- Mitosis -- the actual cell replication event
- M: the cell undergoes mitosis to separate complete sets of its DNA
- C: the cell splits through cytokinesis; the precise details depend on whether the cell is animal or plant
- 8.5 The phases of mitosis have been identified in different ways at different times. Other, older textbooks and websites may show only four phases, or may use different names for the phases below. The current most widely accepted description identifies five phases:
- Prophase: chromatids form
- Prometaphase: chromatids attache to spindles
- Metaphase: chromatids line up
- Anaphase: chromatids separate
- Telophase and cytokinesis: cell components condense and separate into two new cells
- 8.6 Plant cells undergo cytokinesis by growing a plate within the cell that eventually extends to split the cell in two. Animal cell membranes "pinch in" to split the cell in two after all inheritable material has been replicated and organized.
- 8.7 Cells will undergo mitosis when they receive certain triggers and under certain conditions.
- Anchorage Dependence: Cells must be attached to another surface to reproduce.
- Density-dependent inhibition: Cells in contact with other cells on all sides will stop reproducing; on the other hand, if space opens up (through growth or injury), cells will begin reproducing.
- Growth factors: Cells receive hormons that singly or in combination trigger reproduction or inhibit it.
- Cancer cells: These cells ignore anchorage dependence, density-dependent inhibitions, and growth factor inhibitors and simply continue to reproduce.
- 8.8 Growth factors are hormones that trigger a cell to move to a new phase of the cell cycle. Checkpoints such as the G2 checkpoint verify that the cell is ready to enter the next state. If there are errors in DNA replication, for example, these must be fixed in the G2 stage before the cell can proceed to undergo mitosis. If it does not, or cannot, receive these hormone signals, the cell may enter a permanent "no growth" phase (G0). Nerve cells switch to G0 state, which helps preserve memory.
- 8.9 Cells can mutate such that they no longer respond to growth control factors, and can reproduce without waiting for hormone triggers. Such cells are malign cancer cells. When out of control, these cells produce tumors that use up body resources and push healthy tissues out of the way.
- 8.10 Breast cancer treatment should be individualized, based on age, ethnicity, and other health factors.
Read the following weblecture before chat: Cell Reproduction
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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