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Chapter 8

Biology 1201A Chapter Notes - Chapter 8: Kinetochore, Microfilament, Telomerase

Course Code
BIOL 1201A
Jennifer Waugh

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Bio Chapter 8
Diploid: Two copies of each chromosome
Haploid: One copy of each chromosome
-Humans have 23 pairs of chromosomes
Ploidy: the number of chromosome sets of a species
Sister Chromatids: Identical copies of each chromosome before division in mitosis
Sister chromatids are glued together along their length by protein complex “cohesion”
One chromatid is one DNA strand
-Each daughter nucleus is identical to the parent
We only refer to chromatids when there is a replicated chromosome formed.
Chromatin: During interphase
Chromosome segregation: the equal distribution of daughter chromosomes into each of the two
daughter cells.
-Before replication one chromosome is composed of one DNA molecule and after replication
composed of two DNA molecules.
G1- period of growth before the DNA replicates
S- The cell duplicates each chromosome
G2- No synthesis, cell continues to grow
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Mitosis- Prophase, Metaphase, Anaphase, Telophase
Experiments done by Robert Johnson and Potu Rao – fused human HeLa cells in diff stages
of cell cycle (tried to find if one nucleus could influence others)
Results: suggested that specific molecules in the cytoplasm cause the progression of
cells from G1 to S and from G2 to M
Leland Hartwell – investigated yeast mutants that become stuck at some point in cell cycle
only when cultured at high temp
Growing mutant cells initially at standard temp and shifting them to higher temp found
if/when growth and division were affected using time lapse photo microscopy
Isolated many cell division mutants allowed him to identify stage in cell cycle where each
mutant type was blocked by noting whether nuclei has divided, chromosomes condensed and
mitotic spindle has formed, cytokinesis had occurred, etc
Identified genes that code for proteins involved in yeasts cell cycle
Hypothesized where in cell these proteins operate
Some were in DNA replication some in cell cycle regulation
Paul Nurse – identified gene ‘cdc2’ in yeast that encodes protein needed for the cell to progress
from G2 to M
Discovered that all eukaryotic cells have this gene
Cdc2 is a protein kinase enzyme that catalyzes the
phosphorylation of a target protein
-In cytokinesis for animals furrowing occurs at the former spindle point, the cell is slowly
girdled and deepens until it cuts the cytoplasm in two.
-In plants, a new cell wall called the cell plate forms between the daughter nuclei at the former
spindle point and grows laterally until it divides the cytoplasm.
-The mitotic spindle is central to both mitosis and cytokinesis, it is made up of microtubules and
their proteins.
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