Eukaryotic Cell cycle and Division (brief) Flashcards
What are the three stages in cell division
- Interphase
-Mitosis - Cytokenesis
What does the cell cycle ultimately result in ?
The formation of two new identical daughter cells
What is interphase split into ?
G1, S , G2
Describe what happens in G1
- Cell absorbs material, grows and develops. Protein synthesis also happens in this phase
What happens in S?
-Protein synthesis occurs and chromosomes replicate via semi conservative replication
What happens in G2
Time where organelles and other materials needed for cell division are synthesised
What happens in mitosis ?>
- The stage where cells are actively dividing
Describe cytokenesis
Final stage of cell division where the cell membrane divides and the new cells seperate
What do the chromosomes appear as during interphase ?
- Chromatin, loose open structure so the DNA is available for DNA rep
What joins two sister chromatids ?
- Centromere
What happends during Prophase ?
- Chromosomes coil and condense and DNA becomes visible
- Nuclear membrane starts do break down
- Centrioles move to opposite poles of the cell and form proteins which attach to the centromere of each chromosome.
What happens during metaphase
- Chromosomes align along the equator of the cell.
- Spindle apparatus fully forms
What happens during anaphase ?
- Centromeres divide into two and spindle fibres start to shorten
- ## This pulls the sister chromatids to opposite poles of the cell
Describe what happens in telophase
- Spindle apparatus breaks down and nuclear membranes reform
- Chromosomes uncoil back to chromatin state
What happens during Cytokenesis
- Central cell membrane pulled inwards via the cytoskeleton, this this causes a groove.
- Eventually membranes fuse to form two independent cells
What are two roles of the cell cycle
- Growth and repair
- Asexual reproduction
Where does cell division by meiosis take place ?
- Sex organs of organisms
What does cell division by meiosis produce
- Gametes
Why is it important that meiosis produces haploid gametes ?
- Because during fertilisation, two haploid cells fuse to form a diploid zygote
What are two ways that genetic variation is introduced in meiosis ?
- Crossing over
- Independent assortment
Explain crossing over
- During prophase 1, the non sister chromatids of homologous chromosomes twist around each other causing tensions
- During the tensions the chromatids break off at the chiasma
- The broken parts of the non sister chromatids rejoin on the other chromosome of the homologous pair
- This arises genetic variation
Describe independent assortment
- Chromosomes which come from both parents are randomly distributed randomly in the parents
- Each gamete receives 23 chromosomes
- In each new gamete you could receive none to all 23 chromosomes from either maternal or paternal chromosomes
Explain the importance of meiosis in the production of gametes
- Halves the number of chromosomes to produce a haploid nucleus
- So then at fertilisation the full diploid number of chromosomes are restored
- It also allows genetic variation in organisms via independent assortment and crossing over
