MITOSIS
Tresha Edwards tae2101
Nadia Goodwin ng2021
Texts: See Ross’s Histology, 4 ed. (pp. 60-62; 68-69) for additional reference.
Part 1: Cell Cycle
The cell cycle has two principal phases, each of which is comprised of a number of subdivisions:
a) Interphase
-G1 = gap 1 phase, a period of cell growth; no DNA synthesis. (2n)
-S = synthesis phase; DNA and centrosomes double. (2n-4n)
-G2 = gap 2 phase preceding mitosis; no DNA synthesis; DNA is checked to ensure
replication is complete. (4n)
*Note: G0, a phase of “terminal” differentiation, is considered to be outside the cell cycle.
b) Mitosis (M phase)
Mitosis is divided into 5 stages:
1) Prophase- mitotic spindle begins to form, and chromosomes condense so that sister
chromatids are attached at the centromere.
2) Prometaphase- the nuclear envelope disassembles, and chromosomes attach to spindle
apparatus via kinetochores.
3) Metaphase- chromosomes migrate to align centrally on the metaphase plate.
4) Anaphasea) A- sister chromatids separate and move towards the pole.
b) B- two spindle poles move apart. Cytokinesis begins.
(see diagram on next page)
5) Telophase- nuclear envelope reforms, chromosomes decondense, and cytokinesis is
completed.
Interphase
Nuclear
Envelope
Yes
Prophase
Yes
Prometaphase
Disassembles
Metaphase
No
Anaphase
No
Telophase
Reassembles
Stage
Mitosis Summary Table
Chromosome
Spindle
Degradation
Apparatus
Decondensed
Not formed
Centrosomes
Condensed
separate
Chromosomes
Condensed
attach
Condensed
Fully formed
K-MTs shorten;
Condensed
Polar MTs
elongate
Decondensing
*MTs=microtubules (K-MTs= kinetochore microtubules)
Disassembling
Chromosome
Location
Nucleus
Nucleus
Nucleus/Cytoplasm
Metaphase plate
Spindle poles
Within reforming
nuclear envelope
Part 2: Karyotype Analysis
Enables visualization of large chromosome abnormalities:
 Nondisjunction: defect in chromosome number due to failure in homologous
chromosome separation in Meiosis I or in chromatid separation during Meiosis II. (eg.
Trisomy 21, Turner Syndrome).
 Translocation: defect in chromosome structure resulting from transfer of one piece of a
chromosome to a non-homologous chromosome.
 Deletion, Insertion, or Duplication
Karyotyping Procedure: Stimulate cells to divide (so chromosomes condense) and then arrest
them in metaphase using colchicine which blocks spindle formation. Stain chromosomes with
Geimsa, or do a trypsin digest followed by Giemsa to get a G-banding pattern.
There are 3 classes of chromosomes as defined by centromere position:
Metacentric
Submetacentric
Acrocentric
Part 3: Fluorescence Microscopy
 Epi-illumination- only detect light from fluorescent label (blue, green, red).
o Background – black
IMMUNOFLUORESCENCE – visualizing a specific protein
 Get primary antibody for protein you want to mark.
 Get a secondary antibody to bind your 1 antibody and mark it with a fluorescent tag.
 Apply the 1 antibody, then the 2, excite under fluorescent microscope and view – the
protein of interest will glow.
FISH (Fluorescence In Situ Hybridization) – visualizing a specific DNA sequence
 Get a DNA probe that matches your desired sequence and make it fluorescent.
 Allow the probe to hybridize with the cell and see which areas light up.
MITOSIS PRACTICE QUESTIONS
1) Put the numbered cells in sequential order.
a) 1, 3, 4, 2, 5
b) 2, 4, 5, 1, 3
c) 4, 5, 3, 2, 1
d) 4, 3, 5, 2, 1
2) This structure is part of the
a) Kinetochore
b) Centromere
c) Microtubule Organizing Center (MTOC)
d) Cleavage furrow
e) Chromatid
3) What characteristics would you expect to find in the cell at the pointer:
i) Spindle apparatus
ii) Nuclear envelope
iii) Contractile ring
iv) Equatorial plate
a) I and II only
b) I, II, and IV
c) I and IV
d) All
4) All of the following pertain to the cell labeled 1, EXCEPT:
a) Nuclear envelope has disbursed
b) Mitotic spindle has begun formation
c) Centrosomes have separated
d) DNA has been duplicated
ANSWERS
1)
2)
3)
4)
C
C, EM (slide 13)
C, #112 (slide 2)
A, #112 (slide 3) Cell labeled 1 is in prophase. Nuclear envelope will disburse during prometaphase.