3.7 Mitosis Flashcards
Summarise the stages of the cell cycle in eukaryotic cells
Stage 1:Interphase
● DNA replicates semi-conservatively (S phase)
○ Leading to 2 chromatids (identical copies) joined at a centromere
● Number of organelles & volume of cytoplasm increases, protein synthesis (G1 / G2)
Stage 2:Mitosis
● Nucleus divides
● To produce 2 nuclei with identical copies of DNA produced by parent cell
Stage 3:Cytokinesis
● Cytoplasm and cell membrane (normally) divide
● To form 2 new genetically identical daughter cells
What happens in stage 1 of mitosis (3)
Prophase
● Chromosomes condense, becoming shorter / thicker so visible
○ Appear as 2 sister chromatids joined by a centromere
● Nuclear envelope breaks down
● Centrioles move to opposite poles forming spindle network
● Spindle fibres start to attach to chromosomes by their centromeres
What happens in stage 2
Metaphase
● Spindle fibres attach to chromosomes by their centromeres
● Chromosomes align along equator
What happens in stage 3 of mitosis
Anaphase
● Spindle fibres shorten / contract
● Centromere divides
● Pulling chromatids (from each pair) to opposite poles of cell
Requires ATP
What happens in stage 4 of mitosis
Telophase
● Chromosomes uncoil, becoming longer / thinner
● Nuclear envelopes reform = 2 nuclei
● Spindle fibres / centrioles break down
Describe how prok cells replicate (3)
Through binary fission:
*Replication of circular DNA
* Replication of plasmids
* Divison of cyroplasms to produce two daughter cells
-Single copy of circular DNA
-Variable number of copies of plasmids
Why do some Euk cells not undergo the cell cycle
WIthin multicelluar organisms, not all cells retain the ability to divde_e.g. neurons)
Only cells that do retain this ability go through a cell cycle
Nuerons do not have centrioles
What is the importance of Mitosis in the life of an organism
Parent cell dvides to produce 2 genetically identical daughter cells for:
* Growth of multicellular organisms by increasing cell number
Replacing Cells to repair damaged tissues
Asexual reproduction
Describe how viruses replicate (4)
Being non living, viruses do not undergo cell division:
* Attatchment proteins attatch to complimentary receptors on host cell
* They inject viral nucleic acid (DNA/RNA) into host cell
* Infected host cell replicates virus particles such as nucelic acid viral proteins/ enzymes
* virus is then assmebled and then released
Explain how Prophase can be identified
Chromosomes are visible bevcause they are condensing
They are randomly arrnaged due to no spindle activity
Explain how metaphase canb be identifed
Chromosomes are lined up on the equator of the cell as they are attching to a spondle fibre
Explain how anaphase can be identified
Chromatids are at poles of spindle
Chromatids are a vshape because they are being pulled apart at their centromeres by spindle fibres
Explain how telophase can be identified
Chromosomes are in two sets one at each pole
What are the rules of scinefic drawing
Has to look similar to the spcimen/ image
No skteching/shading only clear anmd continuous lines
Include a magnifcation scale
Label with staright uuncrossed lines
WHat is a mitotic index
Proportion of cells undergoing mitosis( with visible chromosomes
mitotic index=Number of cells undergoing mitosis
Suggest how to calculate the time cells are in a certain phase in mitosis
Number of cells in that phase/ total number of cells observed
Multiply by length of cell cycle
Explain how to determin a reliable Mitotic Index from observed squashes
- Count cells in mitosis in FOV
- Count only whole cells
- Divide this by the total number of cells in FOV
- Repeat with at least 5 FOVs selected at random
- Calculate a mean
Three stages of interphase in detail
G1 and G2- Number of organelles and volume of cytoplasm increases, protein synthesis
S phase-DNA replicates semi conservatively
Features of mitosis
one round of divison
Genetically identical cells
Dipoloidcells
Growth and repair-e.g. clonal expansion of B cells
Cytokinesis
Cytoplasm splits ending up with two genetically identical cells
