CELL DIVISION
Jan 05, 2016
CELL DIVISION
Chromatin
� Cell’s collection of DNA and associated proteins (histones)
� Appearance changes as cell divides
2
DNA and proteins arranged as cylindrical fiber
DNA
histone one nucleosome
Chromosome
- supercoil or highly folded chromatin
chromatin
duplicated chromosome
Sex chromosomes - function in sex determination XY, XX, ZZ, ZW Autosome - chromosome that is not a sex chromosome and that
appears as a homologous pair in a somatic cell. - 22 pairs of autosomes (transmit all genetic traits
and conditions other than those that are sex-linked) - Euchromosome - chromosomes that are alike - not involved in determining sex
Ploidy - term referring to the number or sets of chromosomes a. Diploid - 2 sets of chromosomes - 2N b. Haploid - one set of chromosomes - N
Polyploidy
- condition when animals have more than two sets of chromosomes
- abnormal cell division
Cellular Reproduction:
- growth in multicellular organisms is chiefly by multiplication of cells
- Cell division
a. Embryonic development
b. Growth
c. repair of tissue
Figure 12.2 The functions of cell division
20 µm 100 µm 200 µm
(a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).
(b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).
(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).
Mitosisfunctionssister chromatidscell cycleStagescytokinesis
Cell division
an orderly sequence of events that extends from the time a cell divides to form two daughter cells to the time those daughter cells divide again
Cell division
Mitosis Meiosis somatic cells gametes 1 cell cycle 2 cell cycles
2 daughter cells 4 daughter cell Diploid haploid
Cell cycle
- period from the cell is produced until it completes
a. mitosis (body cells)
b. meiosis (egg and sperm)
- consists of 2 major phases:
1. Interphase/Growth Phase “resting phase”
3 subphases:
a. G1
b. S
c. G2
2. M phase
The Cell Cycle � Growth Phase/Interphase (Resting
Phase) - longest - 90% of cell cycle � M Phase - 2 processes 1. division of nucleus 2. division of cytoplasm
INTERPHASE
G1 S
(DNA synthesis)
G2
G1
- cells grow in size
S phase
- Growth continues
- DNA synthesis
chromatids
- copy of the chromosome produced by
replication
G2
- Cells continue to grow
- Protein synthesis
- assemble structures organelles, microtubules
-
Figure 12.4 Chromosome duplication and distribution during cell division
0.5 µm
Chromosomeduplication(including DNA synthesis)
Centromere
Separation of sister
chromatids
Sisterchromatids
Centrometers Sister chromatids
A eukaryotic cell has multiplechromosomes, one of which is
represented here. Before duplication, each chromosome
has a single DNA molecule.
Once duplicated, a chromosomeconsists of two sister chromatids
connected at the centromere. Eachchromatid contains a copy of the
DNA molecule.
Mechanical processes separate the sister chromatids into twochromosomes and distribute
them to two daughter cells.
Mitosisfunctionssister chromatidscell cycleStagescytokinesis
Chromatid
- copy of the chromosome produced by replication
Parts of a chromatid:
Centromere
- point of attachment between (2) sister chromatids
Kinetochore
- plate-like trilaminar structure or disc-like protein complex that develops on each side of the centromere
The duration of the cell cycle phases varies considerably in different kinds of cells. For a typical rapidly proliferating human cell with a total cycle time of 24 hours, the G1 phase might last about 11 hours, S phase about 8 hours, G2 about 4 hours, and M about 1 hour.
2. M- Phase (Mitosis) - process by which a eukaryotic cell divides into two cells
2 steps: 1. karyokinesis “nuclear division” 2. cytokinesis “cytoplasmic division”
Phases: a. Prophase - period of preparation b. Metaphase – period of separation c. Anaphase – period of migration d. Telophase – period of reconstruction
Interphase
Animal Cell Plant Cell
Photographs from: h4p://www.bioweb.uncc.edu/biol1110/Stages.htm
Early Prophase
� chromosomes become visible
� duplicated chromosomes begin to condense
� centrioles radiate an array of microtubules called aster
Late Prophase
� New microtubules are assembled
� One centriole pair is moved toward opposite pole of spindle
� Nuclear envelope breaks up
� Spindle microtubules become attached to the two sister chromatids of each chromosome
Metaphase
� Sister chromatids are lined up at the spindle equator
� Chromosomes are maximally condensed
� During Late metaphase sister chromatids begin to separate (period of separation)
Anaphase � microtubules in the
mitotic spindle shorten
� Sister chromatids of each chromosome are pulled apart
� Once separated, each chromatid is a full pledged chromosome (daughter chromosome)
� each pole has an identical complete set of chromosomes
Early Telophase
� begins once the daughter chromosomes arrive at the opposite poles
� mitotic spindle disassembles
� nuclear envelope forms around each set of chromosomes
Late Telophase
� cell begins to pinch at the middle
Cytoplasmic Division
� usually occurs late telophase
� Cytoplasmic division occurs after nuclear division
� Two mechanisms
� Cleavage furrow (animals)
� Cell plate formation (plants)
Results of Mitosis
� Two daughter nuclei
� Each with same chromosome number as parent cell
Figure 12.9 Cytokinesis in animal and plant cells
Daughter cells
Cleavage furrow
Contractile ring of microfilaments
Daughter cells
100 µm1 µmVesicles
forming cell plate
Wall of patent cell Cell plate
New cell wall
(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (SEM)
Mitosisfunctionssister chromatidscell cyclestagescytokinesis
Vesicle = small membrane-lined —bag“
Animal Cell Division
Cell Plate Formation
REMEMBER! Interphase Prophase Metaphase Anaphase Telophase Cytokinesis
IPMATC
I Pray More At The Church
Animal Mitosis -‐-‐ Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase