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tutorial 2 mitosis notes.docx

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Western University
Biology 1201A
Jennifer Waugh

Jessica Hogle Chapter 8: Cell Cycles 8.2 The cell cycle in prokaryotic organisms - entire mechanism of prokaryotic cell division is binary fission - binary fission: splitting and dividing into two parts - cells may grow for some time before initiating DNA synthesis - once chromosomes are replicated and separated to opposite end of cell, membrane pinches together between them and two daughter cells formed 8,2a Replication Occupies most of the cell cycle in rapidly dividing prokaryotic cells - All bacteria and archae use DNA as their hereditary info. And the vast majority of species package it all in a single circular chromosome of double stranded DNA - Chromosomes compacted in a central region called the nucleoid throughout the cell cycle 8.2b Replicated chromosomes are distributed actively to the halves of the prokaryotic cell - Origin of replication (ori) :located in the middle of the cell were the enzymes for DNA replication are located - Once ori duplicated, two new origins migrate towards the two opposite ends (poles) of the cell as replication continues for the rest of the chromosome - Cytoplasmic division associated with an inward constriction of a cytokinetic ring of cytoskeletal proteins - New plasma membrane and cell wall material assembled to divide the cell into two equal parts 8.3 Mitosis and the eukaryotic cell cycle - it is the result for three elegantly interrelated systems o First: elaborate master program of molecular checks and balances that ensures an orderly and timely progression through the cell cycle o Second: DNA synthesis replicates each DNA chromosome into two copies with almost perfect fidelity o Last: structural and mechanical web of interwoven “cables” and “motors” of the cytoskeleton that separates the DNA copies precisely into the daughter cells - process of DNA synthesis replicates each DNA chromosome into two copies with almost perfect fidelity 8.3a Chromosomes are the genetic units divided by mitosis - each chromosome in a cell is composed of one of these DNA molecules, along with its associated proteins - most eukaryote have two copies of each type of chromosome in their nuclei, and their chromosome complement is said to be diploid (organism or cell with two copies of each type of chromosome in its nucleus) or 2n - Haploid: an organism or cell with only one copy of each type of chromosome in its nuclei - Ploidy: the number of chromosome sets in a cell or species - Replication of DNA of each individual chromosome creates two new identical molecules called sister chromatids - Sister chromatids held together by centromere until mitosis separates them - Chromosome segregation: equal distribution of daughter chromosomes to each of the two daughter cells that result from cell division - before replication, one chromosome is composed of one DNA molecule; after replication, one chromosome is composed of two DNA molecules 8.3b Interphase extends from the end of one mitosis to the beginning of the next mitosis - first phase is interphase - cell
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