Module 2 Section 6 - Cell Division Flashcards
Smithson & Pyper
What happens in interphase?
- Replication of DNA
- Production of organelles
- Cell elongation
Third stage of the cell cycle
cytokinesis
purpose of mitosis
growth, repair and replacement of cells
G1 (+ what happens in it?)
gap/growth phase 1
cell growth and synthesis of new organelles & proteins
S phase (+ what happens in it?)
synthesis
DNA replication
G2 (+ what happens in it?)
gap/growth phase 2
further cell growth and synthesis of proteins (spindle fibres) needed for cell division
ATP level increases
How is G2 different to G1?
The proteins are more specific in G2 than in G1
ATP level increases in G2 because the proteins (spindle fibres) will need to contract lots during mitosis
M phase
mitosis and cytokinesis
G0 (+ three reasons why cells are in this stage)
Nothing much occurs - it’s the resting phase
- Cells may have already differentiated
- Cells may have become senescent so has damaged DNA
- Cells may have been programmed to die (if they were only needed temporarily)
senescent cell (+ why has it become senescent?)
An old cell - one that has done the max number of divisions e.g. because it has lost lots of bases off the end of the DNA sequence
What cells aren’t in G0? Give at least two examples.
The majority of cells are in G0
Cells that aren’t in G0:
* Stem cells
* Cells that experience lots of wear & tear so need renewing frequently such as skin cells, intestine and stomach lining cells
* Nail cells
Name the phase where DNA replication occurs.
Interphase - more specifically, S phase
What four things are checked for in the G1 checkpoint?
- That enough organelles have been produced that the cell can continue in its cycle
- That there’s enough nutrients (e.g. fats & proteins) to sustain the cell
- That the DNA is undamaged before entering the S phase
- That the cell has grown to a sufficient size
What three things are checked for in the G2 checkpoint?
- That the DNA has replicated without many errors (most important)
- That there are enough protein reserves
- That the cell has grown to a sufficient size
If a cell has DNA with lots of errors, what will it do?
1) Try and repair the DNA damage
2) If there are too many problems, it will perform apoptosis - although this is a last resort
What two things are checked for in the M checkpoint?
- That the chromosomes have lined up at the equator of the cell (so that the sister chromatids will separate half and half)
- That the spindle fibres have attached to all the chromosomes’ centromeres
stages of mitosis in order
PMAT
Prophase
Metaphase
Anaphase
Telophase
Why can it be problematic to describe mitosis in stages?
It’s one continuous process i.e. cells within an organ are all in different stages at one point in time
Describe what happens in prophase in mitosis.
- Chromosomes condense (become visible, shorter & fatter) as the DNA wraps around proteins
- Nuclear envelope breaks down
- Nucleolus breaks up and disappears
- Centrioles move to opposite poles of the cell
- Spindles form - these are networks of protein fibres across the centrioles
Describe what happens in metaphase in mitosis.
- Chromosomes line up in a plane across the equator (middle) of the cell
- Spindle fibres attach to the chromosomes via their centromeres
Describe what happens in anaphase in mitosis.
- The centromere divides - the spindle fibres contract to pull the sister chromatids to opposite poles of the cell, centromeres first
- Cell elongates
Describe what happens in telophase in mitosis.
- Chromatids reach the opposite poles on the spindle
- Chromatids uncoil, becoming long & thin again
- Centrioles disappear
- Nuclear envelopes reform, forming two nuclei
- Nucleolus reforms
- Spindle fibres disintegrate
Where are the chromosomes found after prophase occurs?
Free in the cytoplasm because the nuclear envelope disappears
difference between a chromatid and a chromosome
Chromatid - one strand of a chromosome
Chromosome - the whole structure; it can be made of a single chromatid like in normal cells not undergoing mitosis, or two sister chromatids like before mitosis occurs