Mitosis Flashcards
What is mitosis?
Cell division where one (mother) cell divides to produce two new (daughter) cells that are genetically identical
What is purpose of mitosis?
Growth of organism
What is the cell in before mitosis?
Interphase
What occurs during interphase?
Cell has already copied its DNA so the chromosomes in the nucleus each consist of 2 connected copies - sister chromatids
What are the 5 phases of mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What can prophase be split into?
Early prophase and late prophase (pro metaphase)
What occurs during early prophase?
- Chromatin condenses into chromosomes
- Nucleolus disappears
- Mitotic spindle forms
Why do chromosomes start to condense during prophase?
Easier to pull apart
What is mitotic spindle?
Structure made of microtubules that grows between chromosomes as they move apart. Job is to organise and arrange chromosomes.
What is each chromosome made of during prophase?
Two genetically identical chromatids joined by centromere
Why does nucleolus disappear during prophase?
Sign that nucleus is ready to break down?
What occurs during prometaphase?
- Chromosomes finish condensing so are very compact
- Nuclear envelope breaks down, releasing chromosomes
- Mitotic spindle attaches to chromosomes
How does mitotic spindle attach to chromosomes?
Binds to chromosomes at kinetochore
What is the kinetochore?
Area at centre of centromere on each sister chromatid
What occurs during metaphase?
Chromosomes lined up at metaphase plate, with centrosomes at opposite ends of the cell
2 kinetochores of each chromosome should be attached to microtubules from opposite spindle poles
Checkpoint - checks correction of alignment
What occurs during anaphase?
Sister chromatids separate and pulled to opposite ends of cell
How are chromatids separated during anaphase?
Spindle fibres decrease in length, breaking chromatids at centromere
How is cell elongated during anaphase?
Spindle fibres not attached to chromosomes elongate the cell
What occurs during telophase?
Cell starts to re-establish normal structure:
- Mitotic spindle broken down
- 2 new nuclei form
- Nuclear membranes and nucleoli reappear
- Chromosomes decondense
What is cytokinesis?
Division of cell contents to form 2 new cells
Why do 2 new nuclei form?
1 for each set of chromosomes
When do errors in mitosis usually occur?
During metaphase
Usually due to misalignment along metaphase plate or failure of mitotic spindles to attach to one of the kinetochores
What can errors in mitosis result in?
Daughter cells having unequal distribution of chromosomes - cell with too many and cell with too few
Cell with too few usually dies, cell with too many can cause problems
What happens if cell with too many chromosomes carries gene that promotes cell growth?
Can lead to cancer
