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Cell Division: Limits and Reproduction

Explore the difficulties cells face as they grow in size, the process of cell division, and the comparison between asexual and sexual reproduction. Understand the phases and events of the cell cycle and mitosis.

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Cell Division: Limits and Reproduction

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  1. Chapter 10 - Cell Growth andDivision

  2. This liver cell has almost completed the process of cell division. During cell division, a cell splits into two roughly equal daughter cells (magnification: 11,500×).

  3. 10-1 Cell Growth, Division, and Reproduction Limits to Cell Size What are some of the difficulties a cell faces as it increases in size? The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane.

  4. Limits to Cell Size • DNA Overload • As a cell grows in size, its DNA does not • “information crisis” • Exchanging Materials • getting food into and wastes out of the cell • Ratio of Surface Area to Volume • volume increases more rapidly than surface area

  5. Division of the Cell • Before a cell becomes too large, it divides into two new “daughter cells” • This process is called “cell division” • Cell division solves all 3 problems

  6. Solutions: • DNA Overload • Before cell division occurs, the cell replicates (copies) all of its DNA so that each daughter cell will get a copy of genetic information • Exchanging Materials • Reduces cell volume • Ratio of Surface Area to Volume • Increases Surface Area to Volume Ratio

  7. Cell Division and Reproduction How do asexual and sexual reproduction compare? • Reproduction (the formation of new individuals) is one of the most important characteristics of living things.

  8. Asexual Reproduction • Offspring are produced from a single parent cell • Simple, efficient, effective • Enables populations to increase in number very quickly • The two daughter cells are genetically identical to the parent cell (in most cases) • Exs. – Bacteria – Single-celled organisms

  9. Sexual Reproduction • Offspring are produced by inheriting some of their genetic information from each parent cell • Involves the fusion of genetic information from two separate parent cells • Allows for genetic diversity in populations • The daughter cells are genetically different from the parent cell • Exs. – Most animals and plants

  10. Comparing Methods of Reproduction Asexual • Faster Reproduction • when conditions are right • Lack of Genetic Diversity

  11. Sexual • Slower Reproduction • More Genetic Diversity • Able to survive changes in environmental conditions

  12. Comparing Asexual & Sexual Reproduction Asexual Reproduction Sexual Reproduction Parent Cells Offspring

  13. 10-2 The Process of Cell Division Prokaryotic Chromosomes • Prokaryotes do not have a nucleus • Their DNA is found in the cytoplasm • Most Prokaryotes contain a single, circular DNA chromosome

  14. Eukaryotic Chromosomes • DNA is contained in the nucleus • Chromosomes are made up of DNA and proteins. • Chromosomes are not visible except during division. • Before division, each chromosome is replicated (copied).

  15. Chromosomes become visible at the beginning of cell division. • Each chromosome consists of two identical “sister” chromatids. • Each pair of chromatids is attached at an area called the centromere. Centromeres are usually located near the middle of the chromatids, some lie near the ends.

  16. A Human Chromosome • This is a human chromosome shown as it appears through an electron microscope. Each chromosome has two sister chromatids attached at the centromere.

  17. The Prokaryotic Cell Cycle • Takes place very rapidly under ideal conditions • DNA is replicated when bacteria reach a certain size • Cell Division begins when replication is complete

  18. The 2 DNA molecules attach to different regions of the cell membrane • The cell is pinched inward, dividing the cytoplasm and chromosomes between the two new cells • This results in a form of asexual reproduction called binary fission

  19. The Eukaryotic Cell Cycle • The cell cycle consists of 4 Phases: G1, S, G2, and M. • The length of the cell cycle and the length of each phase depends on the type of cell.

  20. Interphase – • a period of growth between cell divisions • Divided into 3 parts: • G1 - Cell Growth • Cells do most of their growing in this phase • S – DNA Replication (Synthesis) • DNA is replicated (copied) • The cell contains 2 copies of its DNA • G2 – Preparing for Cell Division • Usually the shortest phase • When completed, cell division begins

  21. M Phase – Cell Division • Produces 2 identical daughter cells • Two Stages: • Mitosis- Division of the Nucleus • Cytokinesis – Division of the Cytoplasm

  22. Events of the Cell Cycle • During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells.

  23. Mitosis • Mitosis – the part of cell division during which the nucleus divides. • Biologists divide the events of mitosis into four phases: • prophase • metaphase • anaphase • telophase • Mitosis may last anywhere from a few minutes to several days.

  24. Prophase • Longest phase • Chromosomes become visible • Centrioles move to opposite sides of the nucleus • Spindles form • Nuclear membrane breaks down

  25. Metaphase • Lasts only a few minutes • Chromosomes line up in the center of the cell • Microtubules connect the centromere to the spindles

  26. Anaphase • Centromeres joining sister chromatids separate to become individual chromosomes • Chromosomes move apart • Ends when chromosomes are at the poles of the spindle.

  27. Telophase • Chromosomes begin to fadeinto a tangle of dense material • Nuclear envelope reforms • Spindle breaks apart • Nucleolus becomes visible • Last phase of mitosis

  28. Cytokinesis • Last phase of the M phase • Division of the cytoplasmoccurs • Cell plate is formed in plants

  29. 10-3 Regulating the Cell Cycle • Controls on Cell Division • Cells grown in the lab will continue to divideuntil they come into contact with other cells. Then they stop growing. • If you remove cells, the cells will divide again until they touch other cells. • This shows that controls on cell growth and division can be turned on and off.

  30. Cell Growth

  31. The Discovery of Cyclins • For many years, biologists searched for a signalthat would regulate the cell cycle – something that would tell cells when it was time to divide, replicate their chromosomes, or enter another phase of the cell cycle. • In the 1980’s, a protein was discovered that when injected, would cause a nondividing cell to form a mitotic spindle. • They named this protein Cyclin.

  32. Cyclins are proteins that regulate the timing of the cell cycle. • Scientists have discovered a family of cyclins that regulate the timing of the cell cycle in eukaryotic cells.

  33. Cell Cycle Regulation

  34. Regulatory Proteins • The cell cycle is controlled by regulatory proteins both inside and outside the cell. • Internal Regulators – proteins that monitor and respond to events inside the cell. • Examples: • Making sure the a cell does not enter mitosis until its chromosomes have replicated • Preventing a cell from entering anaphase until the spindle fibers have attached to the chromosomes

  35. External Regulators • proteins that respond to events outside the cell. • Can direct the cell to speed up or slow down their cell cycles. • Examples: • Growth Factors • Stimulate the growth and division of cells • Important during embryonic development and wound healing

  36. Cell Growth and Healing

  37. Apoptosis • A process of programmed cell death • Once triggered, a cell undergoes a series of controlled steps leading to its self-destruction: • The cell and its chromatin shrink • Then parts of the cell’s membranes break off • Neighboring cells then quickly clean up the cell’s remains

  38. Apoptosisplays a key role in development by shaping the structure of tissues and organs in plants and animals. • Example – the embryonic development of a mouse’s foot • The space between the toes is caused by cell death through Apoptosis • When Apoptosis does not occur as it should, a number of diseases can result • Examples: Cell loss in AIDS and Parkinson’s disease from too much Apoptosis

  39. Apoptosis

  40. Cancer: Uncontrolled Cell Growth • Cancer is a disorder in which body cells lose the ability to control cell growth and division • Cancer cells do not respond to the signals that regulate the growth of most cells. • As a result, most cancer cells divide uncontrollably.

  41. Cancer cells form a mass of cells called a tumor • Not all tumors are cancerous • Some tumors are benign, or noncancerous • A benign tumor does not spread to surrounding healthy tissue or to other parts of the body.

  42. Cancerous tumors are malignant • Malignant tumors invade and destroy surrounding healthy tissue • As cancer cells spread: • They absorb the nutrients needed by other cells • Block nerve connections • Prevent organs from functioning properly • This disrupts the delicate balances of the body, and life-threatening illness results

  43. Lung Cancer

  44. What Causes Cancer? • Cancer is caused by defects in the genes that regulate cell growth and division • Sourcesof defects: • Smoking or chewing tobacco • Radiation exposure • Defective genes • Viral Infection

  45. All cancers have one thing in common The control over the cell cycle has broken down. • Many cells have a defect in the gene p53. This gene normally stops the cellcycleuntil all of the chromosomes have properly replicated. • Cells lose the information they need to be able to respond to the signals that normally control cell growth.

  46. Treatments for Cancer • When a cancerous tumor is located, it can often be removed by surgery • Example – Melanomas (skin cancer) • Cancer cells grow rapidly so they must copy their DNA quickly. • This makes them vulnerable to damage from radiation

  47. Chemical compounds that would kill cancer cells (or at least slow their growth) are used in chemotherapy. • Great advances in chemotherapy has made it possible to cure some forms of cancer. • However, because chemotherapy compounds target rapidly dividing cells, they also interfere with cell division in normal, healthy cells.

  48. Chemotherapy produces some serious side effects in some patients • Researchers are searching to find highly specific ways in which cancer cells can be targeted for destruction while leaving healthy cells unaffected • Cancer is a serious disease. It is a disease of the cell cycle and conquering it will require a deeper understanding of the processes that control cell division

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