BIO 202 Lecture 8: Week 8 - Chapter 16
7 Aug 2018
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• A chromosome is made up of two sister chromatids, attached at the centromere.
o There is a kinetochore outside the centromere that attaches to mitotic spindles.
o Cohesin holds the replicated chromosomes together at the centromere.
• Chromosome- A single cellular structure with one DNA molecule and associated
proteins.
o A eukaryotic cell typically has multiple, linear chromosomes, which are located in
the nucleus.
• Chromatid- Each copy of a chromosome when duplicated.
• G1- Cell grows and synthesizes mRNA and proteins.
o DNA is invisible in nucleus in its uncondensed form.
• S- DNA is unwound and duplicated.
• G2- The nucleus is filled with thin fibers of uncondensed chromatin, which were
duplicated during the S phase.
• Prophase- Chromatin condenses into chromosomes in the nucleus.
o In regular diploid cells, there are two copies of each chromosome.
• Prometaphase- Chromosomes, which are now even more dense, attach to spindle via
kinetochores and are actively moved.
• Metaphase- Chromosomes are lined up at the equator, between the spindle poles. The
kinetochores attach sister chromatids to opposite poles of the spindle.
• Anaphase- The sister chromatids separate to form two daughter chromosomes, each
pulled towards a pole.
• Telophase- The new daughter chromosomes arrive at the poles and de-condense, while a
nuclear envelope begins to surround the DNA.
• Prophase- Chromatin fibers condense.
o Nucleoli disappear.
o Duplicated chromosomes appear as two identical sister chromatids.
o Mitotic spindle begins to form.
o Centrosomes move away from each other, holding the mitotic spindle in between.
• Prometaphase- Nuclear envelope fragments.
o Microtubules invade nuclear area.
o Chromosomes condense even more.
o Microtubules attach to chromosome kinetochores.
o Non-kinetochore microtubules attach to other non-kinetochore microtubules from
the other pole outside the nuclear area.
• Metaphase- Centrosomes are on opposite poles.
o Chromosomes are lined up on equator (metaphase plate).
• Anaphase- Shortest stage, only few minutes long.
o Cohesin proteins cleave and two sister chromatids separate.
o The daughter chromosomes move toward opposite ends of the cell as
microtubules shorten, moving centromere first.
o Cell elongates as non-kinetochore microtubules lengthen.
• Telophase- Two daughter nuclei form in the cell, with new nuclear envelopes forming
from old fragments.
o Nucleoli reappear.
o Chromosomes de-condense.
o Remaining microtubules are depolymerized.
