1.6

Microtubule spindle fibres

Microtubule spindle fibres

pulls the sister chromatids to the poles of the cell

Prophase

-chromosomes become shorter and fatter→ supercoiling

-nucleus breaks down

Metaphase

-microtubule depolymerisation causes spindle fibres to shorten in length and contract

-chromosomes move to the centre with the help of fibres

Anaphase

-sister chromatids separate and move to the poles, they are carried by spindles

Telophase

-Spindle fibres dissolve

-Chromosomes decondense

-Nuclear membranes form

Cytokinesis

-Part of M stage, but not part of mitosis

Cytokinesis in animals

-a cleavage forms and it deepens towards the centre

-it is described as centripetal since it moves from the outside and moves towards the centre

Cytokinesis in plants

-Vesicles form a row at the centre of the cell

-They fuse together and for an early cell plate

-Fuses with the cell wall to form two daughter cells

-it is described as centrifugal as it moves laterally

Mitotic Index

Cells in mitosis/ total number of cells

Cell cycle order

G1 → S → G2 → Mitosis → Cytokinesis

What happens in interphase

-DNA Replication (S phase)

-Organelle Duplication

-Cell Growth

-Transcription/ Translation

-Obtain Nutrients

-Respiration (cellular)

Chromotin vs chromosome

Chromotin→

-loosely packed DNA

-accessible to transcription

-interphase

Chromosome→

-supercoiled

-inaccessible to transcription

-mitosis

Cyclins

-They activate cyclin-dependent kinases (CDKs)

-cyclins and CDK form a complex that binds to a target protein and modifies it via phosphorylation

-target protein triggers specific events which regulate the cell cycle

Phosphorylation

the addition of a phosphoryl (PO3) group to a molecule

CDK’s and cyclins patterns

Cyclin levels will peak before CDKs

Mutagen

an agent that changes the genetic material of an organism

physical: UV, X-ray

chemical: metals

biological: viruses

Carcinogens

Mutagens that lead to the formation of cancer

Onconogene

a gene that has the potential to cause cancer

Proto-oncongens

code for proteins that stimulate the cell cycle and promoto cell growth

Tumour suppressor genes

-code for proteins that repress cell cycle progression

-aka anti-onconogenes

Metastasis

-the spread of cancer from one location to another

-secondary tumours are made up of the same type of cell as the primary tumour

2 types of tumour

Benign→ remain in one location

Malignant→ spread and invade neighbouring tissue

Cigarette link to cancer

-Cigarette smoke contains over 60 carcinogenic substances