Interphase and Microtubules

How long is the cell cycle in embryonic cells?

2 hours

How long is the cell cycle in adult cells?

20-24 hours

Describe interphase.

- Around 20-22 hours.

- Contain 3 stages within it:

G1, S, G2

Describe G1 of interphase.

- Cells are metabolically active and increases in size.

- Cell doubles its organelles such as ribosome and mitochondria.

- Cells accumulate precursors that will be used for DNA synthesis.

- Chromosomes in nucleus are decondensed.

What type of cancer drugs work on the G1 stage of interphase?

- Alkylating agents e.g., Temozolomide.

- Platinum based e.g., cisplatin.

- Hormonal e.g., Tamoxifen.

- Enzymes e.g., asparginase

- Miscellaneous e.g., levamisole

Describe the S stage of interphase.

- DNA replicates where each chromosome is duplicated to form sister chromatids which are attached at the centromere.

- Protein complexes called kinetochores develop on either side of the centromere.

What type of cancer drug work on the S phase?

Antimetabolites e.g., Gemcitabine.

Describe Interphase G2.

- Cell increases in size again and synthesises proteins that assist cell division e.g., tubulin.

- Centrosome is duplicated and both copies remain together on one side of the nucleus.

What cancer drugs work on the G2 stage of interphase?

- Topoisomerase e.g., topotecan.

- Podophyllostoxins e.g., Etopside.

- Antitumor antibiotics e.g., Bleomycin.

Describe the M (mitotic) phase of the cell cycle.

- Mitosis and cytokinesis takes place.

What are microtubules?

Hollow structures made up of the protein tubulin, they maintain a cells shape.

What is the mitotic spindle?

- A structure made of microtubules that segregates daughter chromosomes to opposite poles of the cell.

- Contains a centrosome that organises the microtubule.

What must happen to the centrosome before the M phase begins?

Must be duplicated

What are the three classes spindle microtubules (MT)?

- Astral

- Kinetochore

- Interpolar

Describe how Astral spindle microtubules work.

They radiate from the centrosome and influence the positioning of spindle fibres. This ensures poles of the cell stay separated and not come together so cell division can occur successfully.

Describe how Kinetochore spindle microtubules work.

They attach to the kinetochore of the sister chromatids which allow chromosomes to split apart during anaphase.

Describe interpolar microtubules.

They overlap at the equator of the cell and elongate spindle fibres which allows chromosomes to move to opposite poles of the cell during anaphase

Describe kinesins.

- They carry molecules from the centre of a cell towards the outside.

- Involved in sliding microtubules apart within the spindle during prometaphase and metaphase.

- Also involved with depolymerising microtubule minus ends at the centrosomes during anaphase.

Describe dyneins.

- Carry molecules toward the centre of the cell.

- Involved in the movement of chromosomes and correctly positioning the mitotic spindle for cell division.

Describe how microtubules perform their function.

- Microtubules remain in a dynamic state.

- This is when they switch between periods of catastrophe and rescue.

- Phosphorylation of MAP and catastrophins alter the stability of molecules and govern assembly of the mitotic spindle.

What is catastrophe and rescue of microtubules?

- Catastrophe is the period of growth to shrinkage of microtubules.

- Rescue is period of shrinkage to growth of microtubules.