cell cycle and cell division Flashcards
cell division in prokaryotes
cell division is less complex in prokaryotes such as bacteria mainly due to the smaller amount of DNA present
since all the DNA is in one circular chromosome and has few associated proteins , cell division can proceed after the DNA is replicated and the cell has doubled in size
bacterial chromosomes are often attached to the cell wall and the two daughter chromosomes get pulled apart when this elongates
there is no nucleus so this does not have to be broken down
the cell wall and cell membrane grows inward to split the cell
this type of cell division is called simple binary fission
normal cell division in eukaryotes : Mitosis
cell division is far more complex in eukaryotes mainly due to the larger amount of DNA present
there is so much DNA , that is has to be divided up into packages and wrapped up using special proteins such as histones: this forms the chromosomes in eukaryotes
the chromosomes are kept together in one area, the nucleus , which has a distinct membrane boundary the nuclear envelope
during cell division all of these components must be disassembled , replicated and two identical nuclei built up
in particular both daughter cells must get a copy of each chromosome, no matter how many there are
regulation of cell cycle
cyclins and cyclin dependent kinases determine a cell’s progress through the cell cycle
when activated by a bound cyclin , CDKs phosphorylate target proteins allowing coordinated entry into the next phase of the cell cycle
checkpoints prevent cell cycle progression at specific points , allowing verification of necessary phase processes and repair of DNA damage
three main checkpoints exist :
g1/ S
g2/ M
metaphase checkpoint
phase 1 : prophase
chromosome condensation
spindle assembly
kinetochore is a protein structure on chromatids where the spindle fibres attach during cell division to pull sister chromatids apart
centrosome regulated the cell cycle
stage 2 : pro metaphase
breakdown of nuclear envelope
chromosome attachment to spindle and movement
stage 3: metaphase
chromosomes are lined up at the equator
stage 4 : anaphase
chromatids separate
spindle poles move apart
5 : telophase
set of daughter chromosome at spindle pole
contractile ring starting to form
new nuclei form
cytokinesis begins
6: cytokinesis
completed nuclear envelope surrounds decondensing chromosomes
contractile ring creating cleavage furrow
contractile ring forms cleavage furrow
cytoplasmic division
importance of cytoskeleton in cell division
all three components of the cytoskeleton are involved in ensuring that the eukaryotic cell divides correctly.
the microtubules form the spindle ,which ensures that each daughter cell gets one copy , and one copy only of each chromosome
the actin filaments divide the cell in two by forming the contractile ring which squeezes together using myosin motor proteins
the nuclear lamina is a form of intermediate filament : its reversible breakdown reassembly cause the breakdown and reassembly of the nucleus
spindle formation
centrosome divides into two
rate of dynamic growth retraction increases due to phosphorylation
stabilisation of adjacent fibres by protein cross-links
three types of microtubule in a spindle
> unattached microtubules
kinetochore microtubules
polar microtubules
chromosomes are attached to kinetochore microtubules via a multi protein complex called the kinetochore. polar microtubules interdigitate at the spindle mid zone and push the spindle polars apart via motor proteins
nuclear lamina
the nuclear lamina is associated with the inner face of the double nuclear envelope
at the onset of mitosis the cellular machinery is engaged in the disassembled of various cellular components including structures such as nuclear envelope , the nuclear lamina and the nuclear pore complexes
this nuclear breakdown is necessary to allow the mitotic spindle to interact with the condensed chromosomes and to bind them at their kinetochores
after phosphorylation by cyclin B/ CDK1 ,the nuclear lamina depolymerises
