Lecture 9 : Mitosis Flashcards
Definition : Cell cycle
Life of a cell, from when it is first formed until it’s own division.
True or false? There is no genetic variation in mitosis.
True
What is the duration of each phase in mitosis?
G1 : 5-6 hours
S : 10-12 hours ( almost half the cycle, longest phase )
G2 : 4-6 hours
M : less than 1 hour
When are the 3 checkpoints during the cell cycle, and what does the checking? If a fault is found, what occurs?
Cyclins ( internal proteins ) check at 3 key points for ;
- G1: damaged DNA
- G2: poor replication
- M: misalignment of spindles
Apoptosis occurs if fault is found during each checkpoint.
Definition: Genome, Mitosis, Cytokinesis
Genome : Collection of DNA a cell contains.
Mitosis: Cell division
Cytokinesis: cytoplasm division
What are chromosomes made of? How many chromosomes are found in somatic cells and gametes?
Chromatin; a complex of DNA & proteins.
Somatic cells: 46
Gametes: 23
What are the stages of the interphase? What occurs during each stage?
G1 :
- cell growth occurs + cytokinesis can continue from previous cell division
S :
- Chromosome composed of a double helix (chromatin)
- DNA synthesis/replication occurs
- Chromosome now composed of 2 identical double DNA helix molecules
G2 (early prophase) :
- centrosome duplication
- each centrosome composed of 2 centrioles
What are the stages of Mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Describe the prophase stage:
- chromatin condenses into X shaped discrete chromosomes. ( now light microscope visible)
- nucleoli disappears
- each duplicated chromosome appears as two identical sister chromatids joined
- mitotic spindle is formed
- centrosomes move away from each other to opposite sides of cell, pushed away by lengthening microtubules between them.
What is the mitotic spindle composed of? What are asters?
Mitotic spindle: centrosomes and microtubules extending from them.
Asters (stars): radial arrays of shorter microtubules that extend from the centrosomes.
Describe the Prometaphase stage:
- nuclear envelope fragments
- chromosomes condense further
- microtubles extend from each centrosomes and invade nuclear area ( middle area of the cell )
- each of the 2 chromatids of a chromosome has a kinetochore
- some microtubules attach to the kinetochore, jerking them back and forth
- non-kinetochore microtubules interact with microtubles from the opposite pole spindle
What is a kinetochore?
Specialized protein structure located at the centromere of a chromatid, used to attach the chromatid to the spindle apparatus.
Describe the metaphase stage :
- Longest stage of mitosis (20 minutes)
- centrosomes are at opposite ends of cell
- chromosomes located at metaphase plate, middle of the cell.
- each kinetochore is attached to microtubule from the opposite pole
Describe the anaphase stage:
- shortest stage in mitosis ( few minutes )
- Sister chromatids begin to part, becoming fully fledged chromosomes
- each chromosome moves towards opposite ends of the cell due to their kinetochore microtubules shortening. They move centromere- first at 1 um per minute.
- Towards the end, cleavage furrow starts to form.
- cell begins to elongate as non-kinetechore microtubles lengthen
- By the end, two ends of the cell have equal and complete sets of chromosomes
Describe the Telophase Stage :
- Two daughter nuclei begin to form in the cell
- nuclear envelope forms from parental fragments
- chromosomes decondense
- mitosis is complete
