Cell Cycle Control Flashcards
Why is cell division required?
For an organism to grow, mature and maintain tissues
What is mitosis?
Mitosis is the process of dividing the duplicated DNA of a cell into 2 new nuclei.
What are the stages of mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What happens after mitosis to form 2 new cells?
Cytokinesis
What happens during Prophase?
- The DNA condenses, organises and the classic chromosome structure appears
What happens during Prometaphase?
- Microtubules attach to the chromosomes
What happens during Metaphase?
- Where the chromosomes align
What happens during the Anaphase?
- Where the chromosomes separate
What happens during Telophase?
- Nuclear membranes reappear around the two sets of chromosomes
What happens during cytokinesis?
- Two new cells are formed
For many eukaryotic cells, a cell is duplicated every _____ hours.
24 hours
Where is most of the life of a cell spent?
In interphase
What are the stages in interphase?
- G1
- S phase
- G2
What happens during the G1 phase?
- G1 (Gap 1) is the first growth stage of interphase. Cell crowns and doubles the number of organelles
- The cell grows to nearly its full size and performs many of its specific biochemical functions that aid the organism
What happens during the S phase?
- DNA replication- During the S phase the DNA in the nucleus is replicated
What happens during the G2 phase?
- During G2 (Gap 2) is where the cell finishes growing
- Once the cell has duplicated DNA in the nucleus and 2 centrosomes have appeared in the cytoplasm, mitosis can begin.
How long does the mitotic phase last for a typical eukaryotic cell?
80 minutes
Outline the whole process of mitosis (long answer)
- The classical chromosome structure is seen, which occurs through a condensation process
- At the same time, protein strands called microtubules appear from the centrosomes in animals
- A structure found within the nucleus, the nucleolus, disappears
- Prometaphase begins when the nuclear membrane is broken down
- At the same time microtubule strands are growing from the centrosomes
- These strands attach to a protein structure called the kinetochore
- One kinetochore is attached to the centromere of each sister chromatid
- Then metaphase occurs where the sister chromatids align along the centre of the cell so that both chromatids face toward opposite poles of the cell
- Next Anaphase occurs where the sister chromatids are separated by a shortening of the microtubules attached to the kinetochores.
- The poles of the cell move farther apart and cause increased separation of sister chromatids.
- At the end of anaphase, the sister chromatids have moved to two ends of the cell
- During Telophase is where the components of the new cells begin to appear. At this point the spindle fibres are broken up.
- A new nuclear membrane surrounds the chromosomes at the end of each cell and the chromosomes uncoil and return to an uncondensed state.
Outline the process of cytokinesis (long answer)
- First the cell is compressed by a contractile ring that divides the cell in nearly equal halves
- Then the organelles in the cell have been replicated and are divided between the two halves of the cell - including mitochondria, Golgi bodies and rough ER - plant cells will also have chloroplasts
- Once split the cells are in G1 stage of interphase
How long is the cell cycle for embryonic cells?
2 hours
How long is the cell cycle for cells in adults
20-24 hours
What are the main points to remember about the G1 stage:
- Cells are metabolically active
- Cell increases in size
- Cell doubles its organelles such as ribosome and mitochondria
- Cells gather precursors/factors that will be used for DNA synthesis
- Chromosomes in nucleus are decondensed
What are the main points to remember about the S phase:
- DNA replicates -> Each chromosome is duplicated
- The sister chromatids will remain attached by the centromere until the end of mitosis
- Kinetochores develop on either side of the centromere during cell division
What is a chromatid
- Copy of a duplicated chromosome
- 2 copies are called sister chromatids
What are the main points to remember about the G2 stage:
- Cell increases in size further
- Cell synthesises proteins that will assist cell division such as tubulin (main component of microtubules)
- Centrosome is duplicated and both copies remain together on one side of the nucleus
What are microtubules and why are they important?
- The mitotic spindle is made of microtubules
- The mitotic spindle separates daughter chromosomes to opposite poles of the cell
- Mitosis required microtubules
What is the centrosome?
- The centrosome is the principle microtubule organising centre
- The centrosome must be duplicated before M phase begins (cell division)
What are the 3 classes of spindle microtubules (MT)?
- Astral
- Kinetochore
- Overlap microtubules (interpolar)
What are Astral microtubules?
They radiate from the centrosome and contribute to pole separation
What are Kinetochore microtubules?
They attach to the kinetochore on the duplicated chromosome
What are overlap microtubules (interpolar)?
They overlap at the equator and are responsible for bipolar shape of the spindle
What are the two microtubule motor proteins?
Kinesins and Dyneins
What do Kinesins do?
Kinesins are microtubule motor proteins that move towards the positive end of a microtubule (from centre towards periphery)
What do Dyneins do?
Dyneins are microtubule motor proteins that move towards the microtubules negative end
Why are Kinesins important?
- They are important for proper spindle length
- Involved in sliding microtubules apart within the spindle during prometaphase and metaphase
- Involved in depolymerising microtubules minus ends at centrosome during anaphase
Why are Dyneins important?
- Involved in the movement of chromosomes and positioning the mitotic spindles for cell division
When are microtubules in their dynamic state?
Before entering prophase
What is catastrophe in microtubules?
Period of growth to shrinkage
What is rescue in microtubules?
Period of shrinkage to growth
What does the phosphorylation of microtubule-associated protein (MAP) and catastrophins do?
Alters the stability of microtubules at the positive end and governs assembly of the mitotic spindle
What is the contractile ring?
It is the cytoskeletal structure responsible for cytokinesis
What is the contractile ring made of?
Mainly of actin and myosin filaments
How does the contractile ring work?
- It is arranged in a ring around the equator of the cell
- It starts to assemble beneath the plasma membrane at the end of mitosis
- As the ring contracts it pulls the membrane inward, dividing the cell in two
- It disassembles completely once the cell is divided in two
The progress of the cell cycle needs to carefully controlled by what 3 factors?
- In sequence
- In timing
- In response to external signals and internal
How do cells control their proliferation?
By controlling the activity of their proteins
How do cells control the activity of their proteins?
- Phosphorylation / Dephosphorylation
- Make more / Inhibit and degrade
