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Lecture 5

BIOLOGY 1A03 Lecture Notes - Lecture 5: Sister Chromatids, Walther Flemming, G1 Phase

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Jurek Kolasa

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BIOLOGY 1A03 Theme 4 Module 1 and 2
November 1, 2015
Gabriel Kuper
Note: satellite stem cells are able to activate from G0 phase and differentiate into specialized
G0 phase – Pause in the cell cycle
G1 phase – Prepares the cell for DNA synthesis
S-Phase – DNA synthesis
G2 phase – Prepares the cell for mitosis
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Prior to Mitosis, DNA Replication
DNA sequences are replicated from end to end of the DNA molecule and the newly
synthesized molecule is associated with the histones and other chromosomal proteins that
allow for tight compaction
Centromere is fully replicated; it is highly compacted that the paired centromeres appear
fused together
Sister chromatids (chromosome that is duplicated into two identical copies)
23 distinct chromosome pairs (46 chromosomes)
Mitosis and cytokinesis occurs
Walther Flemming identified the stages by staining developing salamander embryos
Each chromosome will appear as identical sister chromatids that are
joined at their centromeres
Centrosomes (duplicated cellular microtubule organizing centers) begin
to radiate long microtubules, forming a mitotic spindle (crucial for
separating the chromosomes into the two daughter cells)
Centrosomes become positioned at opposite poles of the cell
Fragmentation of the nuclear envelope
Kinetochores are specialized protein structures that associate with each one
of the two sister chromatids on either side of the centromere
Kinetochore microtubules radiate from the centrosome attach directly to
the kinetochore regions (essential to help pull the chromosomes to the
poles of the cell during mitosis)
Polar microtubules radiate from the centrosome and interact with each
other and help push the poles of the cell away from each other during mitosis
Alignment of chromosomes at the center of the cell in a region identified as
the metaphase plate
Kinetochore microtubules begin to shorten
Sister chromatids separate into individual chromosomes that are pulled
towards the opposite spindle poles of the cell
Polar microtubules push against each other and help elongate the cell
Equal segregation of chromosomes at two ends of a dividing cell
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