IB Bio Cell Division D.2.1.15 - 17

control of cell cycle using cyclins, consequences of mutations in genes that control the cell cycle, and differences between tumours

What do ‘checkpoints’ in the cell cycle allow?

• hold cells until progressing in the next stage of cell cycle is appropriate

• ensures cells stop dividing when there has been enough cell proliferation in a tissue

Cyclins

Group of proteins that coordinate the sequence of changes during the cell cycle

Cyclin-dependent kinases

• enzymes that are activated by cyclin proteins to regulate cell cycle

• bind phosphates to other proteins (activation) that perform actions during a specific phase of the cell cycle

The cell cycle does not progress until a threshold ________ of _______ is reached.

concentration, cyclins

How do tumours form, in relation to gene mutations

• when gene mutations occur, cells lose control of the cell cycle and divide uncontrollably

• number of cells increases exponentially (no control) forming a mass of cells (tumour)

What are the two classes of mutagens that increase the chance of tumour formation?

1. Mutagenic chemicals

2. High-energy radiation (X-rays, gamma rays, alpha particles, UV)

What roles do proto-oncogenes play in a cell?

• regulating cell proliferation

• control cell cycle

• regulate growth factors and receptors

Oncogenes

• formed by mutations in proto-oncogenes (usually missense)

• promote uncontrollable cell division

• genetically dominant

Roles of tumor-suppressor genes

• prevent cell proliferation (‘brakes’ on cell cycle)

• correct DNA replication errors

• apoptosis (programmed cell death) if there is irreparable DNA damage

Mutations of tumor-suppressor genes

• increase risk of tumour formation

• base substitutions (mostly nonsense) cause loss of function

• Recessive if one pair of genes in unmutated (still some functioning polypeptides)

_____ type(s) of cells can become tumour cells

Any

Is one gene mutation enough to cause tumour formation?

No, as many as 10 mutations are needed to cause some tumors to form

How can chance of tumour formation be increased between generations?

• mutated genes are passed to daughter cells

• larger pool of cells in which further mutations can occur

What is the structure of cells in a primary tumour?

• all adhere to each other as a single mass

• often benign (unlikely to cause much harm)

How might tumor cells move to different parts of the body?

• invade neighboring tissues

• travel through transport routes (ex. blood, lymph)

Metastasis

• spread of tumor cells from one part of the body to another, forming secondary tumors

• often malignant (likely to cause harm) 

Which tissues are more likely to produce malignant tumours and why?

• breasts, ovaries, testes, and thyroid gland

• these tissues have hormonal stimulation of cell division

What factors can effect outcomes of tumor formation?

• tumor type

• promptness of detection

• effectiveness of medical treatment