Mitosis + Meiosis + Apoptosis Flashcards
How many cells are in the human body
3.7 x 10^13
What does quiescence mean
Cells can no longer divide anymore
What are the 3 phases in interphase
- G1 phase
- S phase - DNA synthesis
- G2 phase
What are the the 6 phases in mitosis
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis (not part of mitosis)
What happens in interphase
- The cell grows – doubling proteins
- The organelles double in size or number
- During S-phase DNA is synthesised
- The centrosome (microtubule organising centre) replicates
- G1 and G2 phase - cell checks that everything is ready for mitosis
What happens in prophase
- Chromosomes condense
- Mitosis spindle (micro tubules) forms in the 2 poles
- Centrosomes move apart
- Protein complex (kinetochore) forms at the centromere of the chromosome (attaches chromosomes to microtubules)
What happens during prometaphase
- Nuclear envelope breaks down (not degraded, separated because it has to be put back together)
- Which allows microtubules access to the chromosomes
- Chromosomes attach to the microtubules via kinetochore complex
What happens in the metaphase
- Chromosomes align at the equator
- Sister chromatids attach to opposite poles by kinetochore microtubules
What happens in anaphase
- Cohesive link between sister chromatids is released
- Kinetochore microtubules shorten
- Centrosomes move apart
- Sister chromatids pulled to opposite poles
What happens in telophase
- Daughter chromosome reach the poles
- New nuclear envelope forms from fragments attached to individual chromosomes creating 2 nuclei
- Contractile ring begins to form around the equator
What happens in cytokinesis
- The ring contracts partitioning cytoplasm into two daughter cells
- DNA decondenses and the cells return to resting interphase (G1)
What is a cancer treatment that involves microtubules
Poisoning microtubules can stop the cell dividing
For the cell cycle to be successfully completed it is crucial that each step
- Occurs at the right time
- Occurs only once per cycle
- Goes to completion
What are the 3 checkpoints in the cell cycle
- Restriction point (end of G1)
- G2 - M transition (beginning of mitosis)
- Meta-Anaphase transition (end of mitosis)
How is the cell cycle controlled
- Using cyclins
- Cyclins turn on cyclin dependent kinases (Cdks)
- They regulate transition through different stages of cell cycle
- They phosphorylate target proteins
What type of cells are made from meiosis
- Haploid
- Gametes (egg and sperm)
What does haploid mean
One copy of each chromosome
What does diploid mean
Two copies of each chromosome
What does homologous chromosomes mean
A set of one maternal and one paternal chromosome
How do cells end with half the number of chromosomes in meiosis
Cell divides twice
4 cells with half the number of chromosomes
What happens during prophase I in meiosis I
- DNA condenses
- Chromosomes arranged in homologous pairs
- Crossing over of non-sister chromatids at chiasmata
- Spindle fibers formed
- Nuclear envelope breaks down
What happens during metaphase I in meiosis I
- Homologous pairs line up along equator (one pair from mom one from dad)
- Spindle fibers joined
- Independent assortment
What happens during anaphase I in meiosis I
- Microtubules pull whole chromosomes to opposite ends of spindle
(Pairs of parental chromosomes separated)
What happens during telophase I during meiosis I
- Spindle fibers break down
- Nuclear envelope form around the two groups of chromosomes
