BIOL 2112 Chapter Notes - Chapter 12: Spindle Apparatus, Sister Chromatids, Cell Cycle
3 May 2018
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Lecture 22 – The Cell Cycle and mitosis
1) List three important roles for cell division. Asexual reproduction, Growth and
development, Tissue renewal 2) A. What is a genome? A ell’s DNA, it’s geeti
information; in prokaryotes – single DNA molecule; in eukaryotes – multiple DNA
molecules; during cell division can occur to produce identical daughter cells, the genome
must be replicated and then separated so each daughter cell ends up with complete
genome B. What is chromatin? The entire complex of DNA and proteins that is the
building material of chromosomes (varies in degree of condensation during process of cell
division) C. How do somatic cells and gametes differ with respect to their genomes?
Gametes consist of half as many chromosomes as somatic cells do. 3) A. How many
strands of DNA are in a chromosome during G1? Two Strands (one DNA molecule not yet
duplicated) B. How many strands of DNA are in a pair of sister chromatids? Four
strands (two chromatids – each containing a parent template and a replicated copy) 4)
List and describe the phases of the cell cycle. What are the relative lengths of each
phase? A human cell might undergo one division in 24 hours. The mitotic phase would
occupy less than 1 hour, while the S phase might occupy 10-12 hours, or about half the
cycle. The rest of the time would be apportioned between the G1 and G2 phases. The G2
phase usually takes 4-6 hours, G1 (in this example) would occupy about 5-6 hours. G1 is
the most variable in length in different types of cells. Cells spend time in G1 performing
their job in the organism. 5) List the stages of mitosis (M phase) in the order in which
they happen. For each stage note the state of both the nuclear envelope and the
mitotic spindle. Mitosis is broken down into five stages: Prophase, Metaphase, Anaphase,
and Telophase. Cytokinesis overlaps with the latter stages of mitosis and completes the
mitotic phase. G2 of interphase: nuclear envelope encloses nucleus, nucleus contains one
or more nucleoli, two centrosomes formed by duplication of single centrosome,
chromosomes not yet condensed. Prophase: chromatin condensed into chromosomes,
nucleoli disappear, duplicated chromosomes associate as sister chromatids joined at
centrosomes and cohesins, mitotic spindle begins formation, centrosomes move apart.
Prometaphase: nuclear envelope fragments, microtubules from centrosomes invade
nuclear area, chromosomes even more condensed, kinetochore (protein) forms at
centromere of each chromatid, microtubules begin to attach to kinetochores (kinetochore
microtubules). Metaphase: centrosomes at opposite poles, chromosomes aligned at
metaphase plate attached to kinetochore microtubules from each pole. Anaphase:
cohesin proteins cleave, sister chromatids part becoming separate chromosomes, cell
elongates as new daughter chromosomes move toward opposite ends of cell, two ends of
cell have equivalent and complete collections of chromosomes. Telophase: two daughter
nuclei form in cell, nuclear envelopes arise, nucleoli form, chromosomes become less
condensed, spindle microtubules depolymerized, mitosis complete. Cytokinesis: daughter
cells appear after division of cytoplasm, cleavage furrow in animal cells. 6) A. From what
is the mitotic spindle composed? Begins to form in cytoplasm during prophase and
consists of fibers made of microtubules and associated proteins. While mitotic spindle
assembles, other microtubules of cytoskeleton partially disassemble providing material
used to construct spindle. Spindle microtubules elongate (polymerize) by incorporating
more subunits of the protein tubulin and shorten (depolymerize) by losing subunits. B.
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Document Summary
Lecture 22 the cell cycle and mitosis: list three important roles for cell division. Asexual reproduction, growth and development, tissue renewal 2) a. Gametes consist of half as many chromosomes as somatic cells do. Two strands (one dna molecule not yet duplicated) b. Four strands (two chromatids each containing a parent template and a replicated copy) 4) List and describe the phases of the cell cycle. A human cell might undergo one division in 24 hours. The mitotic phase would occupy less than 1 hour, while the s phase might occupy 10-12 hours, or about half the cycle. The rest of the time would be apportioned between the g1 and g2 phases. The g2 phase usually takes 4-6 hours, g1 (in this example) would occupy about 5-6 hours. G1 is the most variable in length in different types of cells. Cells spend time in g1 performing their job in the organism.
