Chapter 8 Cell Cycles.docx

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Biological Sciences
Effiette Sauer

Chapter 8 Cell Cycles 8.1 The Cell Cycle of Growth and Division  Cell cycles are strictly regulated o Cells divide too fast, daughter cell can end up with less cytoplasm and DNA o Cells divide too slow, daughter cell can end up with an extra chromosome, or be inefficiently large 8.2a Replication Occupies most of the Cell Cycle in Rapidly Dividing Prokaryotes  Binary Fission: the entire cell division mechanism in prokaryotes  Can be described in three periods o B) Growth that leads to initiating DNA synthesis o C) Chromosomes are replicated and moved to opposite ends of the cell o D) membrane pinches together between them and two daughter cells are formed  All genetic material in prokaryotes are packaged into one single circular chromosome, found in a compact area called a nucleoid  If nutrients in abundant than the cell cycle occurs rapidly along with growth 8.2b Replicated Chromosome are Distributed Actively to the Hales of the Prokaryotic Cell  Two replicated origins migrate to the poles of the cell while replication continues  Origin of replication: area in prokaryotes where replication enzymes are found and once the ori gets duplicated it move to opposite ends 8.3 Mitosis has evolved from Binary Fission  8.3a Chromosomes are the Genetic Units Divided by Mitosis  Hereditary information found in DNA  Chromosome: chromo means color, soma means body, composed of DNA and the associated proteins  Diploid 2n: two copies of each chromosome in their nuclei  Haploid n: once copy of each chromosome in their nucleus  Ploidy: more than 2 copies of the same chromosome  Sister Chromatids: replication of individual chromosomes creates two new identical molecules o Held together by centromere, until mitosis  Chromosome Segregation: the equal distribution of daughter chromosomes to each of the two cells that result from cell division  2 chromosomes, replicated creates 2 sister chromatids (4 chromosomes), after mitosis it becomes 2 cells each with two chromosomes 8.3b Interphase Extends from the End of One Mitosis to the Beginning of the Next Mitosis  Internal regulatory controls trigger each phase’s start  Interphase: during this phase the cell grows and replicated its DNA in preparation for Mitosis and Cytokinesis  G1 Phase: the cell makes various RNAs and proteins and other types of cellular molecules  S Phase: If a cell is going to divide DNA replication begins o In this phase the cell duplicates the chromosomal proteins and DNA o Synthesizes cellular molecules  As S phase ends G2 Phase Begins  G2 Phase: cells continues to synthesize RNAs and proteins required for mitosis  End of G2 marks end of interphase  G 0 stage where some cells stop division, i.e. nerve cells  During interphase cells are no disabled, they are undergoing gene expression, to support growth and metabolism 8.3c After Interphase, Mitosis Proceeds in 5 Steps  4 stages, prophase, metaphase, anaphase, and telophase  Prophase o Extended chromosomes are condensed into compact rods called chromatins o Packed into small enough units to be divided in mitosis o Nucleoid becomes smaller and disappears o Mitoic spindle being to form between the centrosomes and migrate to opposite ends  Prometaphase o Kinetochore is formed on each chromatid at the centromere  Metaphase o Spindle reaches the final form, and aligns sister chromatids at the spindle midpoint (metaphase plate) o Karyotype: complete collection of metaphase chromosomes arranged according to size and shape for a given species  Anaphase o Sister chromatids separate and move towards the opposite poles o Movement is seen at the centromeres are the kinetochores are the first section to move towards the opposite poles  Telophase o Spindles disassemble, chromosomes decondense, nucleolus reappears, RNA transcription resumes, and a new nuclear envelope forms 8.3d Cytokinesis Completes Cell Division  Cytokinesis: the division of the cytoplasm, usually follows the nuclear stage of mitosis produce two daughter cells containing a daughter nuclei  Begins earl anaphase, or during telophase  Two main pathways through furrow girddle or cell plate  Furrowing o The layer of microtubules that remains at the former spindle midpoint expands laterally until it divides it into two cells o Powered by motor proteins o The furrow deepens almost like a dr
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