Control of cell division Flashcards
(28 cards)
What are stem cells?
The undifferentiated cells in the body that divide rapidly.
What are features of stem cells?
- One daughter cell remains a stem cell, and the other differentiates or at least greatly reduces its rate of division.
- Differentiated cells tend not to be able to revert back to their undifferentiated state
- The division of cells is thus carefully coordinated
Define the cell cycle.
The alternating process of enlargement and cell division, and it is comprised of three main processes: interphase, mitosis and cytokinesis.
After a cell is formed as a result of cell division…
…a new cell enlarges by taking in water and by synthesising new cell components
What are the different phases and checkpoints of the cell cycle?
G1, S, G2 and three checkpoints.
Explain G1 and checkpoint 1.
- Gap 1 or growth phase involves the accumulation of energy (ATP/glucose/oil)
- Checkpoint 1 (restriction point) is the decision to divide (size of cell is appropriate and the cell has received an external signal to divide - growth factor)
Explain S phase.
DNA is synthesised (replicated)
Explain G2 and checkpoint 2.
- Gap 2 or growth phase 2 continues to grow.
- Checkpoint 2 ensures that DNA replication has occurred properly
How does mitosis begin?
The presence of mitosis promoting factor (MPF). MPF rises when an enzyme (Cdk) and a protein cyclin combine.
How is MPF formed?
Cdk (enzyme) + cyclin (substrate) —> MPF.
Explain checkpoint 3.
Checks sister chromatids are attached correctly to spindle. Anaphase begins when there is a drop in MPF.
What phase is cytokinesis?
A cell that differentiates is said to be at G0; its division apparatus is dismantled and if it is ever stimulated to divide again, it does so very slowly.
What are key triggers for the cell to divide?
- Its size and the signals it receives from the environment. If both are favourable, it commits itself to DNA replication and the completion of the cell cycle. The decision point of whether to divide or not occurs in late G1, at the restriction point (R). During G1, the cell has accumulated energy (ATP/glucose/oil droplets)
- External signals called growth factors (hormones) send messages to divide. These are received by receptor molecules in the plasma membrane, passing on the message to relay proteins which move through the cytoplasm to the nucleus.
The basis of the regulation at checkpoint 2 rests with two types of protein. One is the enzyme cyclin-dependent kinase (Cdk) and the other is a regulatory protein called cyclin which activates the enzyme. They combine to create MPF. An increase of cyclin stimulates the start of mitosis, as the concentration of MPF will increase.
What are external factors?
The external signals that stimulate cells to divide are called growth factors (hormones). These are proteins secreted by other cells and they bind to receptor cells in the plasma membrane. Once this has occurred, the receptor molecules induce changes in proteins in the cytoplasm. These are called relay proteins, as they relay the signal from the growth factors to the cell cycle control mechanism which causes it to proceed past the restriction checkpoint.
What are internal factors?
- Cyclin is a regulatory protein (levels rise and fall) which attaches to the enzyme Cdk (levels remain consistent throughout the cycle) to produce MPF (checkpoint 2).
- A rise in MPF (due to a rise in cyclin) initiates mitosis, and a drop in MPF initiates anaphase (checkpoint 3).
What stimulates growth in plants?
Hormones like cytokinins (roots), auxins and gibberellins )stem tips/ripening seeds) work together for coordinated growth.
Define contact inhibition.
Cells stop dividing and moving when they come into physical contact with other cells. This mechanism helps regulate cell growth and prevents overcrowding in tissues. When this process is disrupted, it can lead to uncontrolled cell growth, which is a characteristic of cancer.
Define cancer.
The uncontrolled division of cells. Cancer cells produce daughter cells which both stay as stem cells and continue division, or if one of the cells enter G0, its division continues, but at a slower rate. Cancer cells have faulty checkpoints, and no growth factors are needed for it to continue the cycle.
What has cancer been linked to?
- Chemical carcinogens: causing changes in nucleotide sequence of the DNA (e.g., tobacco smoke)
- Radiation: causes chromosome breaks (e.g., x-rays and UV light)
- Viruses: cause an addition of foreign DNA sequences into the host DNA
What is cell culturing, and what are its primary uses?
Involves the ability to grow very small organisms in the laboratory. This allows for millions of cells to be grown in a small area, with hundreds of generations able to be studied over a short time period. This also allows mutations to be detected, isolated and studied.
What do animal cell cultures require?
- An appropriate medium to grow them on (agar or in a broth)
- The optimum temperature
- Correct osmotic balance
- Suitable pH
- Oxygen (if aerobic)
- Aseptic (free from any bacteria
What is a major difference between culturing plant cells and animal cells?
Plant cells are more readily able to divide than animals cells after they have differentiated; that is, when they are at stage G0 in the cell cycle.
List some contemporary uses of cell culturing.
- Cosmetic and drug testing
- Production of human tissues
- Production of insulin
- The Ames test (test to check if a substance contains a carcinogen - makeup/food etc)
- The production of organs (potential future)
