C8 - Mitosis Flashcards
What is mitosis?
Division of a cell into two daughter cells which are genetically identical to each other and the parent cell.
What are the 3 main stages of the cell cycle during mitosis?
Interphase (divided into 3 parts)
Mitosis (divided into 4 parts)
Cytokinesis
What are the 3 parts of interphase?
G1 (first growth)
S (synthesis phase)
G2 (second growth)
What occurs during the 3 stages of interphase?
G1 - The cell grows in size. Proteins are synthesised, enabling new organelles to be produced.
S - DNA is replicated
G2 - Cell growth and protein synthesis continue. Organelles grow and divide. The cell builds up its energy stores.
What are the four parts of mitosis/nuclear division?
Prophase
Metaphase
Anaphase
Telophase
What occurs during cell division / how does the cell divide in mitosis?
By cytokinesis at the end of the cell cycle
What are cyclins?
Proteins which regulate the cell cycle by activating enzymes known as cyclin-dependent kinases (CDKs) which control each step of the cycle.
This means the cell cycle can be stopped when errors are detected to enable the cell to repair the DNA. (If unsuccessful, it can cause cancer).
What proteins regulate the cell cycle?
Cyclins
They activate enzymes known as cyclin-dependent kinases (CDKs) which control each step of the cycle.
This means the cell cycle can be stopped when errors are detected to enable the cell to repair the DNA.
Why is mitosis / replication of genetically identical cells important?
For growth in multicellular organisms
Repair in tissues
Replacement
Asexual reproduction
What is DNA like during interphase?
It is uncoiled and not visible as chromosomes
What occurs during prophase?
DNA condenses (forming coils using proteins called histones) and chromosomes become visible.
Each chromosome consists of two chromatids which are identical due to DNA replication and are joined at their centromeres.
Centrioles move to opposite poles of the cell and begin to produce microtubules called spindle fibres.
The nucleolus and nuclear envelope break down so chromosomes are free to move
What occurs during metaphase?
The spindle fibres produced by the centrioles grow further and attach to the centromeres on each chromosome.
The chromosomes are then pulled in line to the equator of the cell.
What occurs during anaphase?
The microtubules that make up the spindle fibres are pulled back towards the centrioles causing the centromeres to divide and the two chromatids on each chromosome are pulled to opposite poles of the cell.
What occurs during telophase?
The spindle fibres break down and disappear.
Two new nuclear envelopes begin to form around the two identical sets of chromatids which can now be referred to as ‘daughter chromosomes’.
The DNA starts to uncoil again and the chromosomes disappear.
What occurs during mitosis?
Prophase - DNA condenses (forming coils using proteins called histones) and chromosomes become visible.
Each chromosome consists of two chromatids which are identical due to DNA replication and are joined at their centromeres.
Centrioles move to opposite poles of the cell and begin to produce microtubules called spindle fibres.
The nucleolus and nuclear envelope break down so chromosomes are free to move
Metaphase - The spindle fibres produced by the centrioles grow further and attach to the centromeres on each chromosome.
The chromosomes are then pulled in line to the equator of the cell.
Anaphase - The microtubules that make up the spindle fibres are pulled back towards the centrioles causing the centromeres to divide and the two chromatids on each chromosome are pulled to opposite poles of the cell.
Telophase - The spindle fibres break down and disappear.
Two new nuclear envelopes begin to form around the two identical sets of chromatids which can now be referred to as ‘daughter chromosomes’.
The DNA starts to uncoil again and the chromosomes disappear.
What takes place during cytokinesis?
(After telophase)
The cytoplasm is divided between the two daughter cells to finish the cycle.
What is mitotic index and how is it calculated?
How fast cells replicate
(Number of cells in mitosis / total # of cells) * 100
How does mitosis differ between animal and plant cells?
It occurs in all animal tissues (except sex cells) whereas it only occurs in meristematic tissues in plants
Cellulose cell wall of plant cells prevents shape change during division
Spindle fibres remain during cytokinesis for plant cells.
Microfilaments aren’t as significant in plants
What is apoptosis?
It is the ‘normal’, ‘programmed’ cell death during normal or biological processes.
It is the process where cells are removed (cell death)
What is necrosis?
‘Accidental’ or ordinary cell death due to a serious chemical or physical insult (infection or trauma)
Why is apoptosis necessary?
Cell death is required to prevent there from being too many cells.
This helps for digit formation during embryonic development.
It’s also necessary for nerve development and the destruction of potentially harmful immune cells
How does necrosis occur?
The volume of the cell increases and the cell is enlarged, causing the cytoplasm to swell.
This results in the release of hydrolytic enzymes
What are the stages of apoptosis?
1) The cell shrinks and the nucleus condenses (pyknosis)
2) Enzymes break down the cytoskeleton
3) The cell surface membrane alters and forms bulges known as blebs
4) The nucleus breaks down (karyorrhexis)
5) The cell is broken into fragments which are held in vesicles called apoptic bodies
6) Phosphatidylserine, a phospholipid normally found on the inside of cell membranes, is present on the outside of vesicles
7) Phosphatidylserine binds to receptors on immune cells called macrophages.
8) Macrophages engulf the fragments
What’s the purpose of phosphatidylserine during apoptosis?
Phosphatidylserine, a phospholipid present outside the vesicles, binds to receptors on immune cells called macrophages.
These macrophages engulf the fragments of the cell.
