2.3 - Regulation of the Cell Cycle

What is the external cell cycle control (growth factor)?

A protein (growth factor) enters via a protein receptor and initiates a signal to the cell, suggesting that it has all the necessary requirements to be able to begin cell division

If DNA is unrepaired, what types of cell can it turn into?

Senescent cell: Will carry out its function if possible, but otherwise doesn't do anything (permanently stopped dividing) (can often come from the G0 stage)

Apoptotic cell: Cell will be destroyed

Cancer cell: The rapid uncontrolled multiplication of unnecessary cells

How can DNA be repaired (specific)?

The DNA strands will first unzip, then the DNA will be repaired:

• Direct renewal

• Base excision repair

• Nucleotide excision repair

• Mismatch repair

• Double strand break repair

• Homologous recombination

• Non-homologous end joining

How can DNA be repaired? (general)

• Cell cycle checkpoint activation

• Transcriptional program activation

• DNA repair

• Apoptosis

What are some causes to damage DNA?

• Cellular metabolism

• UV light exposure

• Ionizing radiation

• Chemical exposure

• Replication errors

What is Apoptosis? Provide an example of when it is necessary.

Apoptosis is a process which requires energy (active) that is the planned and controlled death of cells.

1. The cell begins to shrink (cell shrinkage) and blebs start to form

2. Chromosomes in the nucleus start to condense

3. Blebs break away from the body of the cell, still containing all of the information within the blebs (now apoptotic bodies)

4. Phagocytes then engulf the apoptotic bodies through endocytosis and uses the lysosomes (enzymes) to break down the apoptotic bodies

E.g. When human hands are being formed, they start out as being all connected, then they undergo planned cell death between each finger to form the hands.

What is necrosis? Provide an example of why this may occur.

A pathway for damaged cells to take, which requires no energy (passive), in which the cell ages over time or is damaged in another way, and loses all structural integrity and breaks apart.

Any cause of necrosis to take place could range from extreme increased temperatures (burn), decrease in oxygen levels, or being stabbed.

What is neoplasm?

Neoplasm is the abnormal growth of tissue. When a damaged cell is identified and then continues to replicate. This can be both benign and malignant.

What are some disruptions to the control of cell division?

Genetic factors: A mutation which can effect enzymes that aid in regulating cell division and mitosis.

Proto-oncogenes: A mutation in a gene that stimulates too much cell growth that could eventually turn into an oncogene (cancerous).

Tumour-supressor genes: Mutations in genes which code to slow down division, repair DNA or induce apoptosis.

Inherited genes: BRCA1 and BRCA2 (heavily increase the chances of breast cancer), which is passed down from parents, and includes mutations in proto-oncogenes and tumour-supressor genes.

How do cancer cells occur?

Tumours result from rapid, out of control cell division. This will occur, as while the cell is undergoing mitosis, it will bypass the G1 and G2 (checkpoint) stages. This will result in more mutations and disorganised/deformed cells.

What is the difference between benign and malignant?

Benign (not cancerous): These tumour cells grow only locally and cannot spread by invasion.

Malignant (cancerous): These cells invade neighbouring tissues, enter blood vessels, and spread to different sites around the body.