Unit 5 Cell Reproduction
Biology Lecture Notes
Cell Division: Mitosis
All cells arise from
pre-existing cells (except for the first cell(s) ever).
The genetic library
(genome) of a cell is passed onto divided (sister) cells.
Mitosis this is the process of how one
cell makes exact (almost) copies of itself.
Mitosis results in two
genetically identical (almost) daughter cell from one parent cell
which they are also identical with.
Prokaryotic Cell Division
DNA is circular.
DNA is not condensed
into chromosomes.
No nucleus
Simple
genome of ~ 3000 genes.
Prokaryotic Cell Division
Prior to division,
bacterium grows to twice its size
So does the PM and the
cell wall
During this time, the
circular DNA begins to replicate itself.
Circular DNA attached
to the cytoplasmic surface of the PM and replication
begins from this pt.
Eukaryotic Cell Division
DNA is not circular
DNA is linear and
organized into distinct structures called chromosomes.
Chromosome Numbers
Saccharomyces (yeast) 16
Mosquito 6
Garden pea 14
Frog 26
Mouse 40
Human 46 (~40,000
genes)
Chimpanzee 48
Chicken and dog 78
Horsetail fern 216
Eukaryotic Cell Division
In most eukaryotic
organisms, most cells are diploid (2n).
Diploid possess a
pair of every chromosome
Human = 46 chromosomes
They have a pair of
each of 23 chromosomes.
Gametes (eggs and
sperm) are haploid (1n).
Gametes possess one of
each chromosome
Human gametes possess
23 chromosomes.
Homologous chromosomes are a pair of the same number, i. e., pair #21
Sister chromatids are duplicates of the same
chromosome held together by a centromere.
The Mitotic Cell Cycle
Interphase
This is where the cell spends most of its life
..carrying
out its functions.
4 Stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase
A. Prophase
First stage of mitosis
Begins when
chromosomes actually begin to appear from the condensing DNA
Nuclear envelope
breaks down
Nucleolus disappears
Mitotic spindle begins
to form
B. Metaphase
Second stage of
mitosis
Mitotic spindle fully
formed
Chromosomes align in
single file on the metaphasic
plate.
Centromere splits and sister chromatids are no longer connected.
C. Anaphase
Third stage of mitosis
Sister chromatids are pulled in opposite directions toward the
opposite centrosomes.
D. Telophase
Fourth and last stage
of mitosis
Spindle apparatus is
disassembled.
Nuclear envelope is
reestablished.
DNA uncoils
Gene expression starts
up again.
Plant Cytokinesis
The parent cell is
surrounded with a rigid cell wall which cant be purse-stringed.
They assemble vesicles
between the 2 nuclei that contain membranes.
The vesicles fuse and
the membrane is assembled (cell plate) and fuses with parent
membrane.
After the new
membranes are assembled, the cell wall is then laid down externally.