Cell division Flashcards
Why do cells divide?
for growth and repair
What happens in interphase?
consists of G1, S, G2
DNA becomes dispersed through the nucleus
What happens in G1; Growth Stage 1?
growth and synthesis of proteins/enzymes and new organelles
synthesis of new centrosomes starts
cellular contents duplicated
What happens in the G1 Checkpoint?
check the cell to make sure there are no faults
- cell size
- nutrients
- DNA damage etc.
When are cyclins produced and what do they do?
at each checkpoint they are produced, which controls the cells passage into the next stage
What occurs at G0?
the cell won’t replicate
apoptosis occurs, kills the cell if it is faulty
What happens in the S phase; Synthesis?
DNA synthesis and repair, centrosomes finished, needs the following enzymes to occur:
- DNA polymerase + helicase and ligase
What happens in the G2: Growth Stage 2?
rapid growth of the cell, checking for DNA damage, and synthesis of molecules needed for cell division
What happens at the G2 Checkpoint?
… if there are any faults with the cell it moves into G0
- cell size4, DNA damage and cyclins produced to allow it to move into the next phase = mitosis
What are the next three stages after G2 Checkpoint, in the cell cycle?
- spindle assembly checkpoint
- mitosis
- cytokinesis
How is the cell cycle controlled?
regulated by your genes = in response to biochemical signals, stop dividing after a certain number of divisions
What are the two types of genes involved in the cell cycle?
- Proto - oncogenes
- Tumour
What do proto - oncogenes do?
start cell division
What do tumour genes do?
act as suppressor genes
How does cancer happen?
caused by loss of control of cell division, caused by mutation of the genes
What is the first stage of mitosis? What happens?
Interphase
every chromosome replicates to form a pair of identical sister chromatids, that are linked by a centromere
What is a centromere?
specialised DNA sequence to hold together sister chromatids
What is the second stage of mitosis? What happens?
Prophase
2 pairs of each chromosome within the cell
2n - 4n
DNA condensed so sister chromatids visible inside the nucleus
What is the third stage of mitosis and what happens?
Metaphase
- the nuclear envelope breaks down, no longer visible
- sister chromatids line up along the equator of the spindle
- centrioles move to the poles of the cell
What is the fourth stage of mitosis and what happens?
Anaphase
- each chromosome attached to a spindle fibre, which shorten and pull the chromatids apart by their centromere
- chromatids are now chromosomes
- each end of the cell has a full set of chromosomes
- cytoplasm begins to divide
What is the final stage of mitosis and what happens?
Telophase
- the nuclear envelope reforms around each set of chromosomes
- CLEAVAGE FURROW = pinching in of cytoplasm
- the chromosomes become less distinct, two new nuclei formed
What happens directly after telophase?
Cytokinesis = splitting of the cell, produces two genetically identical daughter cells
How to calculate the miotic index?
MI = number of cells within condensed chromosomes (divided by)
total no. of cells
x by 100
How does mitosis differ in plant cells?
- cell plate forms where the spindle equator was, cell wall material is laid down along the plate
- plants DON’T have centrioles
- meristem cells are capable of mitosis `
