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Chapter 9

BIOL 1000- CELL CYCLES (chap#9)

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York University
BIOL 1000
Julie Clark

Tanya Sivamanoharan Fri, Dec, 9/11 Biology- chap# 9 textbook notes CELL CYCLES 9.1- The Cycle of Cell Growth and Division -multicellular organisms require strictly controlled cell division by the process of mitosis -The newly cells are needed for growth (new leaves), asexual reproduction, and replacement of cells -before dividing, most cells enter a period of growth where they synthesize proteins, lipids, and carbohydrates, and they replicate their DNA -after growth period, the nuclei divide, and cytokinesis follows -cytokinesisdivision of cytoplasm -each daughter cell contains a copy of the original DNA -cell cycle sequence of events, including the period of growth, nuclear division, and cytokinesis 9.1a- The Products of Mitosis Are Genetic Duplicates of the Dividing Cell -mitosis divide and replicate DNA of parental cell equally and precisely -cables and motors of mitotic spindle separate DNA copies to 2 daughter cells with equal fidelity -certain stage of life cycle (sexual reproduction) requires daughter cells diff. from parent cell -meiosisproduces daughter nuclei, with only ½ the parental chromosomes -cells that are products of meiosis are gametes in animals and fuse with other gametes to make zygote -chromosomesnuclear units of genetic info., divided and distributed by mitotic cell division 9.1b- Chromosomes Are the Genetic Units Divided by Mitosis -DNAlinear molecules that carry heredity info. -each chromosome in a cell is composed of linear DNA molecules and their proteins -most eukaryotes have 2 copies of a chromosome in their nuclei (diploid/2n) ex: humans have 23 pairs of diff. chromosomes so they have 46 diploid chromosomes -some eukaryotes have 1 copy of their chromosome in nuclei so they are called haploid -ploidy # of chromosome sets -replication of DNA creates 2 identical molec. called sister chromatids -sister chromatids are held together until mitosis separates them, placing 1 in each daughter nuclei -since sister chromatids are split b/wdaughter cells, each daughter cell receives same # and type of chromosomes, with same genetic info. -chromosome segregation equal distributions of daughter chromsomes to each of the 2 cells hat results from cell division -except when mutation occur, mitotic cell cycle creates group of cells called a clone 9.2- The Mitotic Cell Cycle -cells show a repeating phase of growth and division known as the mitotic cell cycle -interphasethe first and longest phase, where cells grow and replicate its DNA to prepare for mitosis and cytokinesis -internal regulatory controls trigger each phase, controlling each phase happens timely and properly 9.2a- Interphase Extends from the End of One Mitosis to the Beginning of the Next Mitosis -interphase begins when daughter cell from previous cell division enter cytoplasmic growth -G1 phaseinitial growth stage of cell cycle, where cell makes various RNAs, proteins, and other types of cellular molecules BUT NOT DNA -if the cell is going to divide, DNA replication begins by initiating the S phase of cell cycle -S phase the cell duplicates the chromosomal proteins and DNA and continues synthesis of other cellular molecules -after S phase the cell enters G2 phase of cell cycle -G2 phase the cell continues to synthesize RNAs and proteins, including those required for mitosis, and cell continues to grow -end of G2 phase interphase is complete and mitosis begins -during interphase, chromosomes are loose but organized in nucleus -the G1 phase varies in time and determines speed of cell division of cell, the S phase takes about 10-12 hours, the G2 phase about 4-6 hours and mitosis takes about 1-4 hours 9.2b- After Interphase, Mitosis Proceeds in Five Stages -mitosis happens in 5 discrete phases: prophase, prometaphase, metaphase, anaphase, telophase -prophase extended chromosomes that were replicated during interphase, condense into compact, rodlike structures called chromatin -condensation in prophase packs long DNA molec. into smaller units to be divided during mitosis -while condensation take place, the nucleolus becomes smaller and disappears -the disappearing -in cytoplasm, mitotic spindle forms b/w 2 centrosomes that move opposite ends of cell to form spindle poles -the spindle develops as bundles of microtubules radiating from spindle poles -the nuclear envelope breaks down by the end of prophase -prometaphase spindle microtubules grow from the centrosomes at opposing spindle poles towards center of cell and some spindle microtubules attach to chromosomes -each chromosome is made up of 2 identical sister chromatids held together at their centromeres -complex of several proteins (kinetochore) is formed on each chromatid at centromere -metaphase the spindle reaches final form and spindle microtubules move chromosomes into alignment at spindle midpoint/metaphase plate -chromosome complete their condensation at this stage -when chromosomes are assemble at spindle midpoint, with 2 sister chromatids facing opposite poles, actual separation of chromatids occur -anaphasesister chromatids separate and move to opposite spindle poles -the sister chromatids move until they can be called daughter chromosomes -at this point, chromosome segregation is complete -telophasethe spindle disassembles and chromosomes at each spindle pole, decondense and return to extended state as they were before interphase -the nucleus reappears, RNA transcription resumes, and a new nuclear envelope forms around chromosomes at each pole making 2daughter cells -nuclear division is complete at this point, and cell has 2 nuclei 9.2c- Cytokinesis Completes Cell Division by Dividing the Cytoplasm between Daughter Cells -cytokinesisdivision of the cytoplasm, following nuclear division by mitosis, that produces 2 daughter cells -in most cells, cytokinesis occurs during late anaphase or telophase -when cytokinesis is complete, the cell enters the G1 phase of next cell cycle -in animals, protists, and fungi, a furrow is formed and deepens until it cuts the cytoplasm into 2 parts -in plants, a new cell wall called cell plate forms between daughter nuclei and divides the cytoplasm -furrowinglayer of microtubules that remain at former spindle midpoint at center of cell expand and stretch across entire dividing cell and cause a furrow -cell plate formationhappens at former spindle midpoint, where vesicles produced by ER and golgi apparatus collect together and fuse together to form new cell wall -the plasma membranes that line the 2 surfaces of the cell plate are derived from vesicle membranes 9.3- Formation and Action of the Mitotic Spindle -mitotic spindle is crucial to both mitosis and cytokinesis -spindle is made up of microtubules and their proteins, and its activity depends on their changing patterns of organization during cell cycle -during mitosis, microtubules disassemble from interphase arrangement and reorganize into spindle, which grows and fills entire cell -once organized, basic function of spindle is the same, regardless if centrosome is present 9.3a- Animals and Plants Form Sp
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