Cell Division, cell diversity and cellular organisation Flashcards
How are all cell formed?
By division of existing cells
In which two processes do eukaryotic cells always divide in?
Mitosis
Meiosis
What is mitosis?
The division into two daughter cells that are genetically identical to each other and the parent cell
What is meiosis?
The division into four genetically unique daughter cells with half the chromosomes of the parent cell
What is the cell cycle?
The sequence of events between mitotic divisions which all cells follow
What is the G0 phase?
The name given to the phase when the cell leaves the cell cycle, either temporarily or permanently
What are the three reasons why a cell enters the G0 phase?
DNA may be damaged
Differentiation
Telomere erosion
What is differentiation?
When a cell becomes specialised to carry out a function, it can no longer divide
What does the G0 phase maintain?
It maintains a set number of cells in specific tissues
What is telomere erosion?
The most widely known cause of ceased cell division
Telomeres are sequences of DNA that are found at each end of the chromosomes. They consist of a DNA sequence of repeated nucleotides
How does telomere erosion cause a cell to enter the G0 phase?
In each replication, the telomeres lose a small part of DNA because the enzymes that are responsible for duplicating the DNA cannot reach the end of the chromosome.
The chromosomes are shortened after each replication until they reach a point at which, after having lost the telomere, they lose important genetic information
What is senescent?
When cells can no longer divide
What are the conditions for cell division?
Cells:
- are of appropriate size
- have error-free replicated DNA
- have correctly positioned chromosomes
What are the control mechanisms used by the cell to ensure the conditions for cell division?
Checkpoints
What happens if any of these checkpoints are ‘failed’?
The cell cycle stops
