Chapter 3 Mitosis (3.7-3.8) Flashcards
How do eukaryotic divide
Meiosis or mitosis
How do prokaryotic cells divide
Binary fission
Why can’t viruses undergo cell division
As they are non living
How do viruses replicate
By injecting their nucleic acid into a the host cell they invade to replicate virus particles
Stages of cell division
1) interphase (G1,S,G2)
2) mitosis (M phase)
3) cytokinesis (M phase)
What happens in interphase
- G1 phase= size of cell increases, transcription and translation occurs and organelles replicate
- S phase = DNA synthesis occurs so that chromosomes replicate to form sister chromatids joined together by a centromere
- G2 = repairs damaged chromosomes, energy stores are replicated , transcription and translation occurs, size of cell increases
Stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
What happens in Prophase
1) chromosomes condenses and become visible when in the nucleus
2) nuclear envelope breaks down
3) a pair of centrioles move to opposite poles of the cell
4) centrioles form spindle fibres
What happens in metaphase
1) spindle apparatus is completely formed and attaches to the centromeres of the chromosomes and the chromosomes line up at the equator of the cell
What happens in anaphase
1) the centromeres divide into two and the spindle fibres start to retract, pulling the sister chromatids towards the opposite poles with the help of motor proteins
2) this results in each pole getting a full set of chromosomes which are identical to each other
What happens in telophase
1) The chromatids uncoil and become long and thin again so become invisible under a microscope (and are now reffered to as chromosomes)
2) the spindle apparatus breaks down
3) the nuclear envolope reforms around each chrmosomes
What happens in cytokinesis
The cytoplasm splits in two
The central cell membrane is pulled inwards by the cytoskeleton creating a groove which deepens and the membranes fuse to form two daughter cells that are genetically identical
How to calculate the mitotic index
Number of cells in mitosis/ total number of cells x 100
What does the mitotic index tell us
A percentage of cells that are undergoing mitosis
How many pairs of chromosomes do humans have
23 pairs
What do we use mitosis for
- growth - all cells grow from other cells and therefore are genetically identical and mitosis ensures that this happens
- repairs - if a cell is damaged or dies it is important that new cells are produced and have an identical structure and function to the one that is lost
- asexual reproduction
How is the cell cycle different in plant cells
- They don’t have centrioles but do have a spindle apparatus that forms straight from the cytoplasm
- when a plant cell undergoes cytokinesis the cell membrane cannot form a groove so instead vesicles from the Golgi apparatus form membrane structures down the centre of the cell, which the fuse together to form a new cellulose cell wall and dividing the cytoplasm into two
What happens if there is a mutation to the gene that controls the rate of mitosis
Leads to uncontrolled cell division formimg tumours
How do drugs that treat cancer (chemotherapy) disrupt the cell cycle
- prevent DNA from replicating
- inhibit the metaphase stage of mitosis by interfering with spindle formation
Problems with chemotherapy (drugs that treat cancer)
Can disrupt the cell cycle of normal cells
They damage rapidly dividing cells to a great degree such as hair producing cells (and cancer cells)
Why can’t prokaryotic cells undergo mitosis
As mitosis is a nuclear division and prokaryotic cells do not have a nucleus
Why does size of the cell need to increase in interphase
To ensure when the cell divides the daughter cells are the correct size
Why would cells exit the cell cycle and enter the G0 phase
- if the cell is a fully differentiated cells so stays in G0permanently
- if the DNA in cells is damaged, so can no longer divide ( called senescent cell) and stay in G0 permanently
- some cells are temporarily stored in the G0 phase to be let out if there is any infection or disease in the cell cycle
Why does the chromosomes in chromatin have a loose open structure in interphase
So that the DNA is accessible for transcription and replication
