Chapter 6 Mitosis Flashcards
Why do we need mitosis?
For growth, development and repair.
In mitosis, what occurs in prophase?
Chromatin fibres coils and condenses to form chromosomes.
Nuclear membrane breaks down.
Protein microtubules form spindle fibres connected to the poles of the cells.
The spindle fibres attach to the centromere on the chromosomes, to start moving the chromosomes to the centre of the cell.
In mitosis, what occurs in the metaphase stage?
Chromosomes are moved by spindle fibres to the centre of the cell, called the metaphase plate.
In mitosis, what occurs in the anaphase stage?
The shortening of spindle fibres causes chromatids in each chromosome to be separated and reach opposite ends of the cell.
In mitosis, what occurs in the telophase stage?
The chromatids at either ends of the cell uncoils and a nuclear membrane forms around each set of DNA.
In mitosis, what occurs in the cytokinesis stage?
The cell separates into two cells. These cells are referred to as ‘daughter cells’ and are genetically identical to the parent cell. In animal cells, cytokinesis occurs when a cleavage furrow forms around the middle of the cell (when the cell surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle).
Relative to all the other stages in mitosis, how much of mitosis is taken up by the interphase stage?
Interphase takes up most of mitosis- it takes up around 95% of the cell cycle.
State the stages chronologically that occur in interphase (and checkpoints).
G1
G1 checkpoint
S phase
G2
G2 checkpoint
What occurs in the G1 phase?
In the G1 phase:
Organelles replicate.
Increase in cell size.
Protein synthesis.
Respiration occurs.
What does the G1 checkpoint check for?
G1 checks if:
Enough replication of organelles has occurred.
Checks cell size.
Checks for DNA damage before any DNA replication occurs- it could lead to a faulty cell.
What occurs in S (synthesis) stage?
DNA replication occurs.
What is G0?
G0 is also referred to as cell arrest, and a cell may enter G0 after entering the G1 checkpoint. A cell may enter G0 temporarily or permanently because:
The cell is already differentiated.
There is DNA damage.
The cell has already reached the maximum number of divisions.
What occurs in G2 phase?
Organelles replicate.
Increase in cell size.
Protein synthesis.
Respiration.
What is checked in the G2 checkpoint?
The G2 checkpoint occurs after S phase, so it checks if there were any errors in the DNA replication- as this may lead to mutations.
After interphase, mitosis and cytokinesis occurs. Within the mitosis stage, there is a spindle fibre checkpoint. What does this check for?
This checkpoint makes sure the spindle fibres are correctly attached to the centromeres of the chromosomes. If not, this can lead to uneven splitting of chromosomes, and hence the daughter cells would not be genetically identical.
A cancer cell is a cell that initially has DNA damage. Theoretically, where in the cell cycle should it stop?
As a cancer cell is a cell with DNA damage, it should theoretically stop at the G1 checkpoint and enter G0 (cell arrest). However, cancer is known as the ‘uncontrolled division of cells’. This means the cancer cell has somehow surpassed the G1 checkpoint and gone through the whole cell cycle.
In meiosis, what occurs in prophase 1?
Chromosomes coils and condenses.
Nuclear membrane breaks down.
Protein microtubules start to form spindle fibres.
The maternal and paternal chromosomes undergo crossing over. The crossing over means that alleles from the mum may be swapped with the dad and vice versa. This leads to genetic variation. (The point at which the alleles cross over is called the chiasmata).
Alleles are genes coding for the same general characteristic; a gene coding for a blue eye colour, and a gene coding for a green eye colour are alleles of each other.
