2. Mitosis Flashcards
What happens after spontaneous muatation?
population no longer clonal
organism is a genetic mosaic
What is a genetic mosaic?
Mixture of genetic types
Describe the process of binary fission in bacteria? (5)
1) DNA duplicates, Cell gets bigger
2) Replicated chromosomes move apart
3) Protein called FtsZ marks the middle
4) New cell wall
5) Two daughter cells
Describe the eukaryotic cell cycle? (5)
S- phase - where replication occurs
Two Gap phases (G phases) on either side
Where cell grows and synthesizes various proteins for both growth and synthesis
G1,S,G2 is known as Interphase
Time in between M phase (mitosis) – where there is a nuclear division
G0 phase, inactive cells (“quiescent”) are removed from cycle
How do chromosomes change in the eukaryotic cell cycle? (2)
s-phase - chromosomes replicate
mitosis - chromosomes segregate
Describe interphase?
G1,2,G2
DNA amount doubles
Describe prophase?(2)
- Chromosomes condense so they are now visible as thread-like structures. Each chromosome comprises 2 chromatids and a single centromere
- Later in prophase, the nuclear membrane breaks down (some give this period its own name = prometaphase)
What are sister chromatids held together by?
protein called cohesin
What is the cytoskeletal structure, largely made of?
microtubules = polymers of small tubulin protein subunits
What does the mitotic spindle do?
The spindle’s job is to separate sister chromatids to different daughter cells
This happens because microtubules get shorter – pulling chromosomes towards the poles
What is a centromere?
specialised chromosome regions that direct the equal segregation of chromosomes during mitosis (and meiosis)
Centromeres are connected to the microtubules via a large protein complex called the ……………….
kinetochore
Describe metaphase?
Centromeres align at spindle equator – midway between the two poles
Microtubules attaching to each pole – tension between these keeps chromosomes in the centre
Describe anaphase?
- Chromatids become separate chromosomes
- Centromeres start moving to opposite poles
- Depending on position of the centromere - each chromosome can form a V shape as it’s dragged behind the centromere
Describe telophase?
- Chromosomes arrive at the cell poles
- Chromosomes decondense – no longer recognisable thread structures
- Daughter nuclei reform
Describe cytokinesis?
- Division of the rest of the cell
- “Cleavage furrow” forms in-between the two poles
- Constriction to give two daughter cells
- Can be symmetrical or give two unevenly shaped daughter cells (eg in budding yeast)
Describe ploidity in eukaryotic cell cycle? (4)
G1/G0 -Haploid
S phase -Diploid
G2 - Diploid
M Phase - Becomes Haploid
