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Lecture 10

BIOL107 Lecture Notes - Lecture 10: Sister Chromatids, Characteristic Class, Cell Division


Department
Biology (Biological Sciences)
Course Code
BIOL107
Professor
Carla Salvado
Lecture
10

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Sunday, October 27, 2019
Biology 107 - Topic 10
Eukaryotic Cell Division: Mechanisms & Regulation
Cell Division
-Ability of organisms to reproduce best distinguishes living things from non-living matter.
-Continuity of life is based on the reproduction of cells or cell division.
Functions of Cell Division
-Organisms depend on cell division for:
-Reproduction, growth and development, repair.
Eukaryotic Cell Division
-Eukaryotes are (usually) multicellular.
-One cell division does not equal reproduction of the organism.
-Eukaryotes must control which cells divide at which times, tightly regulate cell division through specialized
cell cycles.
Cell Cycle
-Cell division is integral part of cell cycle.
-Cell cycle:
-The life of a cell from formation to its own division.
-“Every cell from a cell”
-Most cell division results in daughter cells with identical DNA.
-Exception is meiosis:
-A special type of division that produces sperm and egg cells.
Cellular Organization of the Genetic Material
-All DNA in cell constitutes cell’s genome:
-Genome can consist of single DNA molecule (common in prokaryotic cells)
-Or a number of DNA molecules (common in eukaryotic cells)
Eukaryotic Chromosomes
-DNA is packaged into chromosomes.
-Consists of chromatin:
-Complex of DNA and protein that condenses during cell division.
-Every eukaryotic species has a characteristic number of chromosomes.
-Somatic cells (non-reproductive cells) have two sets of chromosomes.
-In humans: (2 × 23 = 46 total)
-Gametes (reproductive cells: sperm and eggs) have half as many
chromosomes as somatic cells.
-In preparation for cell division:
-DNA is replicated.
-Chromosomes condense.
-Each duplicated chromosome consists of two sister chromatids
-Held together by cohesion proteins.
-The centromere is the constriction that can be seen in the duplicated
chromosome, where sister chromatids are most closely attached.
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Sunday, October 27, 2019
Phases of the Cell Cycle
-Cell cycle consists of:
-Interphase:
-Cell growth.
-Copying of chromosomes in preparation for cell division.
-Mitotic (M) phase (cell division):
-Mitosis (the division of the genetic material in the nucleus)
-Cytokinesis (the division of the cytoplasm)
Cell Cycle
-Time spent in each phase varies by tissue, and by organism.
-Most mammalian cells = 24-hour cell cycle.
-Interphase = 22 hours
-Mitosis (M-phase) = 1 to 2 hours
Interphase
-Interphase can be divided into sub-phases:
-G1 phase (“first gap”)
-S phase (“synthesis”)
-G2 phase (“second gap”)
-Cell grows during all three sub-phases of interphase, but chromosomes are duplicated
only during S phase.
-Interphase » 90% of typical animal cell's life
-Characteristics of interphase:
-DNA is diffuse, transcriptionally active (Euchromatin).
-Proteins synthesized, cell can increase in size.
-Contains pairs of chromosomes.
Euchromatin vs. Heterochromatin
-Major difference between heterochromatin & euchromatin:
-Heterochromatin is the part of the chromosomes that is firmly packed and genetically inactive.
-Euchromatin is uncoiled (loosely) packed chromatin and is genetically active.
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Sunday, October 27, 2019
Mitotic Phase
Mitosis
-Mitosis: a series of phases in cell division during which the nucleus of a cell divides into two nuclei with
identical genetic material.
-Mitosis only occurs in Eukaryotes.
-Mitosis is conventionally divided into five phases:
1. Prophase
2. Pro-metaphase
3. Metaphase
4. Anaphase
5. Telophase
Mitotic Spindle
-The mitotic spindle is made of microtubules that control chromosome movement during mitosis
-In animal cells, assembly of spindle microtubules begins in the centrosome, the microtubule organizing centre:
-The centrosome replicates during interphase.
-The two resulting centrosomes migrate to opposite ends of the cell during prophase and pro-metaphase.
-Asters (radial array of short microtubules) extends from each centrosome.
-The spindle includes:
-Centrosomes
-Spindle microtubules
-Asters
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