Class Notes (1,000,000)
CA (620,000)
McMaster (50,000)
BIOLOGY (2,000)
Lecture 4

BIOLOGY 1A03 Lecture Notes - Lecture 4: G1 Phase, Cell Plate, Metaphase


Department
Biology
Course Code
BIOLOGY 1A03
Professor
Rosa Da Silva
Lecture
4

This preview shows pages 1-2. to view the full 8 pages of the document.
Theme 4 – DNA Replication and Mitosis – Module 1 – The Cell Cycle
Unit 1: Cell Proliferation in Prokaryotes
Bacterial Cell Division
-Process of cell division means dierent things to
dierent organisms, prokaryotic cells is also
reproduction since the division of one prokaryotic
cell gives rise to a new organism
-Cells are capable of making exact copies of their
genomes and segregating one copy of each genome
to each of two daughter cells
Process of Binary Fission
-Cell division in prokaryotes is a form of asexual
reproduction often referred to as binary &ssion
-Initiated when DNA is attached by proteins to the
inside of the plasma membrane
-DNA replication begins along an origin of replication
region
-Chromosome continues to replicate, cell beings to
elongate and newly synthesized DNA is also
anchored to the plasma membrane
-Continues to elongate until two DNA attachment
sites are at opposite ends of the cell
-Bacterium approximately double its original size,
starts to constrict along midpoint of the cell
oAccompanied by synthesis of a new cell
membrane and cell wall
Unit 2: The Eukaryotic Cell Cycle
Dividing and Non-Dividing Eukaryotic Cells
-Cell division allows for an unicellular fertilized egg to develop into a
multicellular organism
-Early embryos contain stem cells: unspecialized cells that reproduce
inde%nitely and under appropriate conditions, can dierentiate into
specialized cells of one or more types
-After an organism is fully grown, cell division leads to continual renewal and
repair of cells
-Adult stem cells cannot give rise to all cell types, but replace non-reproducing
specialized cells
oEx. Mammalian skeletal muscle is a stable tissue with little cell
turnover or division
oIf it gets injured, quiescent (non-dividing) satellite stem cells
present in the basement membrane can be activated and being
dividing to enable muscle regeneration

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

oLeads to proliferation, dierentiation, and fusion of muscle precursor
cells; myoblasts that
commit to forming the
mature muscle cells that
make up muscle %bers
(myo%bers)
oAfter myo%bers formed, they
can no longer divide
-Why can some cells be dormant and then divide once again while others are
terminally dierentiated and are no longer able to divide?
Eukaryotic Cells Reproduce by Mitosis
-Main distinctions between prokaryotic and
eukaryotic cell division – eukaryotic DNA
is larger, and organized into linear
chromosomes that are highly condensed
in the nucleus
-Cell division therefore requires more
regulated control
-Consists of two distinct stage
oInterphase – S phase (where DNA
synthesis occurs) 2 gap growth
phases G1 and G2
oM phase (mitosis and cytokinesis)
-During interphase, cells make
preparations for cell division
oReplication of DNA in the nucleus
and an overall increase in cell size
oReplication of DNA occurs in the S phase
oG1 and G2 prepare for DNA synthesis and mitosis respectively
-Time taken for cells to pass through the cell cycle depends on the type of cell
-Many cells can pause in the cell cycle in the G0 phase somewhere between M
and S
oPause ranges from many days to more than a year
-Some cells enter G0 permanently and are non-dividing (lenses of eyes, nerve,
mature muscle)
Stem Cells Di.erentiate into Specialized Cells
-Reproduce inde%nitely but also have periods of quiescence and undergo no
cell division
-Fully dierentiated skeletal muscle – little to no cell division
oInjury – quiescent satellite stem cells activated from dormant G0 phase
and renter cell cycle
oEnables proliferation, dierentiation and maturation of new muscle
precursors that fuse and repair muscle tissue with new muscle %bers
oAfter new myo%bers are formed, they exit the cell cycle and enter the
G0 phase again
You're Reading a Preview

Unlock to view full version

Only pages 1-2 are available for preview. Some parts have been intentionally blurred.

Phases of Mitosis
-5 distinct stages that can be morphometrically characterized based on
distinctive changes that occur to chromosomes
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
-
Walther Flemming
(1882) analyzed
developing salamander embryos he stained to visualize the chromosomes of
the dividing cells
oDiscovered that stages of mitosis could be staged based on
chromosomal positions
Prior to Mitosis, DNA Replication
-Before mitosis, chromosomes must be duplicated and condensed, so
daughter cells can acquire the same amount of genetic information in a short
period of time
-Most of interphase, chromosomes are in the form of a long, thin %ber
-Dna replicated from end to end and the centromere is fully replicated just
so compacted that the paired
centromeres appear fused together
-22 chromosome pairs are homologous
(one maternal and one paternal in
origin), 1 pair sex chromosome
-Not until M-phase that chromosomes
compact into structure shown
oTwo sister chromatids of each
duplicated chromosome separate
and move into two new cells
Unit 3: Chromosome Dynamics
Prophase
-During interphase, speci%c
chromosomes cannot be identi%ed as
they are organized into long
chromatin %bers
-As cells transitions from G2 to M-
phase, duplicated chromosomes
begin condensing and individual
chromosomes become visible even
with a light microscope
-Each chromosome appears as
identical sister chromatids, joined at their centromeres
-Duplicated cellular microtubule organizing centres – centrosomes begin to
radiate long microtubules, forming a mitotic spindle
You're Reading a Preview

Unlock to view full version