BOT 200 Chapter 4
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This 4 page Class Notes was uploaded by Keely Egelhoff on Friday September 9, 2016. The Class Notes belongs to 200 at Western Illinois University taught by Dr. Meiers in Fall 2016. Since its upload, it has received 13 views. For similar materials see Introduction to Botany in Botany at Western Illinois University.
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Date Created: 09/09/16
Chapter 4 Cell Cycle the cycle of individual organisms includes stages or initiation, growth, and dead usually creates two daughter cells Cell cycle arrest is when cell division stops in a plant Leaves cannot be elongated or repaired if they are damaged Root and stems will resume cell division until the damaged portion has been fixed Growth Phase of the Cell Cycle Resting phases/interphase- Scientists first believed that the time between cell divisions were a resting period G1 Phase/ Gap 1- first stage after division and the cell is recovering and running through most of the normal metabolism Cell cycles will vary depending on the type of the cell G1 is the longest part of the cell cycle even though the time spent in it can vary greatly S Phase- the genes in the nucleus are replicated Genome- is the entire complex of genes for an organism to survive All genes are connected to each other by short pieces of DNA Chromosome- thousands of genes attached together in a linear sequence Usually plants about 5-30 chromosomes Histones- in Eukaryotes carry this protein that gives DNA protection and structure Centromere- located near the center of the chromosome is capped by a telomere During S Phase linking pieces of DNA as well as genes are replicated and new histone molecules complex with the new DNA Chromatid- half of the doubled chromosome Endoreduplication- When entering the S phase, the replicate their DNA before the differentiate this can be just a single cycle or can be more resulting in large nucleus. Happens in many extremely rapid and intense metabolisms Gene amplification- similar to endoreduplication but only some genes are repeatedly replicated G2 Phase- cells prepare for division Only lasts about 3-5 hours A- and b- tubulins necessary for spindle microtubuoles are synthesized and the cell produces proteins necessary for processing chromosomes and breaking down the nuclear envelope After G2 division can occur Division Phase of the Cell Cycle Karyokinesis- division of the nucleus- Mitosis and Meiosis Cytokinesis- division of the cytoplasm Mitosis- duplication division more common type of karyokinesis Is used by multicellular organism as the body grows and the number of its cells increases The nuclear genes are first copied and then one set of genes are separated from the other and packed into its own nucleus Prophase- chromosomes condense, chromosomes begin to coil repeatedly becoming shorter and thicker Chromosome condensation continues until chromosomes are only 2-5 um long then they can be moved more easily Nucleolus becomes less distinct and completely disappears by the end of prophase The duplicated daughter sets move to the opposite poles Spindle is the middle set of long microtubules Kinetochore is the point of microtubule attachment Two layers of proteins one layer bound tightly to centromere DNA other attached to spindle microtubules Metaphase Metaphase plate is when they push and pull on the chromosomes and gradually move to the cell center No boundary between meta and prophase, chromosomes gradually become visible and gradually move to metaphase plate End of metaphase a protein degrading enzyme called separase is activated and digests cohesion the number of chromosomes is doubled buy sized is halved Anaphase Begins just after cohesion releases the centromeres freeing the two kinetochore faces from each other Spindle microtubules that run to the kinetochores shorten depolymerizing at the end near the spindle pole pulling each daughter away from its twin Only 20 ATP are needed to move a chromosome from the metaphase plate to the end of the spindle Telophase As chromosomes approach the ends of the spindle fragments of nuclear envelope appear near them, connect with each other and from complete nuclear envelopes at each end of the cell Gradually new nucleoli are formed Most events in telophase are reversals of those in prophase Cytokinesis Genes cannot replicate anything that is missing but it can if it is just a member to the cell Preprophase band identifies the plane of division and it marks the region where the new cell wall will attach to the existing wall. If the preprophase band forms around the middle of a long cell the cell will divide into two equal-sized cells but if it forms at one end then division will produce a large and small cell If nuclear division occurs without cell division a preprophase band is not formed Phragmoplast- is a set of short microtubules aligned parallel to the spindle microtubules Forms in the cell center where the metaphase plate had been Microtubules trap dictyosome vesicles that then fuse into a large flat plate like vesicle in which two new primary walls and a middle lamella begin to form Cell plate- are phramoplast vesicle and wall Phragmosome help divide a vacuole with microtubules actin filaments and cytoplasm Microtubules pull the nucleus to the site where it will divide then enlarges as a thin plate like sheet of cytoplasm and cytoskeleton pushing into the vacuole dividing it in two Just after the phragmosome reaches the far side of the vacuole the phragmoplast and cell plate pass through and join with the plasma membrane and cell wall Meiosis Daughter nuclei are replicates of the original mother nucleus Two sex cells (gametes) fuse together forming a zygote Haploid is one set of chromosomes in each nucleus A zygote has two complete sets which makes it diploid If the adult were to produce gametes by mitosis the gametes would be diploid as well and the next zygote would be tetraploid Meiosis involves two rounds of division without allowing the S phase to occur after the first division Divisions are called Meiosis I and Meiosis II Meiosis I/ Prophase I Nucleolus and nuclear membrane break down, centrioles separate, a spindle forms, microtubules attach to centromeres an chromosomes condense and become visible Leptontene chromosomes begin to condense and become distinguishable although they appear indistinct Zygotene each chromosome of one set finds and pairs with the equivalent chromosome its homolog of the other set the pairing in synapsis Synaptonemal complex is present between the paired homologous chromosomes composed of linear central protein elements A synapsed pair of homologous chromosomes is called a bivalent Pachytene is a condensed and shorter/thicker chromosome Several places in each chromosome breaks If paternal and maternal parings are detected it means that the synapsis and crossing over are finished Diplotene is the homologous chromosomes of each bivalent begin to move away from each other buy do not separate completely because they are held together at their paired centromeres and chiasmata When all four chromatids are paired it is called tetrads Diakinese homologs continue to separate and chiasmata are pushed to the ends of the chromosome Metaphase I Spindle microtubules move the tetrads to the center of the cell forming a metaphase plate Anaphase I Homologous chromosomes separate completely from each other Cohesion is not digested thus centromeres do not divide and each chromosome continues to consist of two chromatids Chromosomes are pulled away from the other set and two new nuclei are formed Nuclei are now haploid Telophase I Chromosomes start to uncoil and the nucleolus and nuclear envelope start to reappear Interkinesis is when the cells progress fully into interphase and no replication of the DNA occurs