Mitosis 6.2 Flashcards
Mitosis
Mitosis is a division of the nucleus where the parent cell will divide in order to create two genetically identical daughter cells.
Why do you need mitosis?
For growth, replacement and repair of tissues as well as asexual reproduction for single-celled organisms like bacteria
Chromatid
DNA molecules that are unwinded from the histones to just look like straight lines. These are formed during the S phase of interphase.
Centromeres
The region that joins the two chromatids together. They must be kept together during mitosis so they can be precisely manoeuvred everywhere.
Chromosomes
Two identical sister chromatids joined together at the centromere
What are the stages of mitosis?
Prophase, Metaphase, Anaphase, Telophase
Prophase
Firstly, chromatin that is composed of DNA and RNA will condense into chromosomes and the nuclear envelope will disappear.
The microtubules will assemble spindle fibres that are needed to move the chromosomes.
The centrioles will line up at both poles of the cell
The spindle fibres will attach to the centromeres and the chromosomes will start moving towards the middle.
The nuclear envelope also disappears
What can you see in a microscope during prophase?
The chromosomes look like they are everywhere and disorganised.
Metaphase
The spindle fibres will move the chromosomes into the centre of the cell so they are called lined up at the cell equator called the metaphase plate and they are held there.
What do you see in a microscope during metaphase?
You will see the chromosomes clearly all lined up in the centre.
Anaphase
This is where the centromeres will divide, causing each chromatid to be dragged to opposite ends of the cell by shortening spindle fibres.
What do you see in a microscope during anaphase?
You’ll see a lot of the individual chromatids at either end of the cell, you might see some V shapes which is the chromatid being dragged through the cytosol.
Telophase
The chromatids have now reached the end of the cell to the poles where they are now called chromosomes and will be the genetic info in the nucleus. The nuclear envelope and nucleolus will reform, making its own nucleus
What do you see in a microscope during telophase?
It looks like two blobs or masses forming on both sides of the cell, which is actually both of the nuclei.
Cytokenesis
This is when the cell actually divides to form the two sister cells after telophase.
Cytokenesis in animal cells
A cleavage furrow forms in the middle of the cell caused by the cytoskeleton which will the pinch in both sides of the membrane until it is close enough to fuse and separate into separate cells.
Cytokenesis in plant cells
A cleavage furrow is not possible because of the cell wall, so instead, the Golgi body forms vesicles which assemble and combine on the metaphase plate until they combine with the cell membrane. The cell wall is then constructed on top to form two separate cells. The cell wall cannot be constructed first as the hydrostatic pressure would make it collapse.
Binary Fission
This is asexual reproduction for bacteria.
Firstly, their chromosome is uncoiled into a circuit shape and replicated. The cell will the grow and the chromosomes will move to either end of the cell. A septum will form in the middle and then the cell will form a cell wall and then split.
Budding
This is asexual reproduction that occurs in yeast cells for example. A protrusion will come out of the yeast cell called a bud. It will grow and remain attached until it is mature before it sections off making a genetically identical clone.
