Cell cycle and cell division Flashcards
How does cell division take place 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 membranes grow inward to split the cell
▪ This type of cell division is called “simple binary fission”
Where does meiosis take place?
In the reproductive cells
Where does mitosis take place?
In the somatic cells
What is interphase?
This is when the cell is growing and preparing for mitosis.
What is the M phase?
nuclear division takes place and cytokinesis. under a microscope this can be seen
How is the cell cycle regulated?
*Cyclins and cyclin-dependent kinases (CDKs), 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
▪ Two main checkpoints exist
✓G1/S checkpoint
✓G2/M checkpoint
What happens during prophase?
The chromosomes condense and become visible.
spindle fibers emerge from the centrosomes
the nuclear envelop breaks down
and finally the nucleolus disappears
What happens during prometaphase?
Chromosomes continue to condense
kinetochores appear at the centromeres
mitotic spindle microtubules attach to kinetochores
chromosomes move towards the poles
What happens during metaphase?
Mitotic spindle is developed, centrosomes are at opposite poles of the cell.
Chromosomes are lined up at the metaphase plate
Each sister chromatid is attached to a spindle fiber originating from opposite poles
What happens during anaphase?
cohesion proteins binding the sister chromatids together break down
sister chromatids are pulled toward opposite poles
non-kinetochore spindle fibers lengthen, elongating the cell
What happens during telophase?
Chromosomes arrive at opposite poles and begin to decondense.
nuclear envelope material surrounds each set of chromosomes.
the mitotic spindle breaks down.
Outline the differences in cytokinesis in an animal cell and a plant cell.
In animal cells, a cleavage furrow separates the daughter cells.
In plant cells a cell plate separates the daughter cells
What is the importance of the cytoskeleton in cell division?
*All three components of the cytoskeleton are involved in ensuring that
the eukaryotic cell divides correctly:
* The microtubules form the mitotic 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: it’s reversible
breakdown and reassembly cause the breakdown and reassembly of
the nucleus
Outline the process of spindle formation
Centrosome divides into two
▪ Rate of dynamic growth and retraction increases due to
phosphorylation
▪ Stabilization of adjacent fibers by protein cross-links
What is the 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 disassembly of various cellular components including structures such as
the nuclear envelope, the nuclear lamina and the nuclear pore complexes.
▪ After phosphorylation by cyclin B/Cdk1, the nuclear lamina
depolymerises.
▪ This nuclear breakdown is necessary to allow the mitotic spindle to interact with the condensed chromosomes and to bind them at their kinetochores.
