Download 1.6 Cell Division

Topic 1: Cells
Cell Division
Why divide?
Chromosomes
 Growth
 Each DNA strand is condensed into a chromosome
 Replacement of infectious cells
structure
 Cell differentiation
 All sexually reproducing animals have pairs of
 Replacement of dead cells
chromosomes. One set of each pair comes from each
parent
The Cell Cycle - ordered set of events that cumulates in cell growth and division into two
daughter cells
Interphase
Standard condition of cell, spends most of its time here
o
Growth 1
 Active stage
 Growing
 DNA transcribed
 Proteins Synthesized
 Organelles Replicates
o
Synthesis
 DNA Replicated
 2 sister chromatids form from each chromosome
o
Growth 2
 Growth till mitosis
 Mitochondria divide
 Chloroplasts divide in plants
Mitosis
Division of the nucleus into two genetically identical daughter nuclei
Division of diploid eukaryotic nucleus
o
Prophase
 DNA supercoils
 Chromosomes become visible
 Nuclear membrane breaks down
 Centrosomes migrate to poles
o
Metaphase
 Chromosomes line up centromeres on equator cell
 Centrosomes form spindles
o
Anaphase
 Spindles grip centromeres and chromosomes
migrate to poles
o
Telophase
 Nuclear membranes reform
 Chromosomes disperse
 Cytokinesis begins
Cytokinesis
o
Division of the cytoplasm to form two daughter cells
 Occur during or after Telophase
 Cell splits to form two new cells each containing a full set of chromosomes
identical to parent
 Capable of doing all parent cell can
Animal:
Plant
 Plasma membrane is pulled
 Vesicles move to equator and form a tubular
inwards around equator of cell
structure
 Creates a furrow accomplished
 Two layers of membrane are formed which
by using a contractile ring of
develop into membrane
 Vesicles bring pectin and other materials that are
actin and myosin
deposited by exocytosis, forming lamella and cell
wall.
Topic 1: Cells
Cell Division
Cell Cycle Checkpoints
 G1-S, G2-M, Exit M
 Cell asses conditions (favourable for division)
 If not favourable (eg. DNA damaged) p53 protein stops cycle and cell dies)
 Absent checkpoint protein can lead to mutant or absent cells which can divide
uncontrollably, causing cancer.
Cyclins
 Proteins that bind to enzymes called cyclin dependent kinases.
 Become active and attach to phosphate groups on other proteins to become active in
different stages of the cell cycle.
 Cyclins have to reach threshold concentration to progress to the next stage.
Cancer:
 Mutagens
o Physical or chemical agent that changes genetic material
o Causes replication error
o Ionizing radiation, UV radiation, deaminating agents, viruses, bacteria
 Oncogenes
o Potential to cause cancer
o Prevent apoptosis (programmed cell death) and lead to proliferation
o Promote cell cycle in various ways
o Tumour suppressor genes inhibit cell cycle in various ways
o Normally regulated in coordination with organisms growth plan
o Either mutates, can loose control and become oncogene
 Metastasis
o Movement of cells
o Primary tumour to set us secondary tumours in other parts of the body