Stem Cells and Totipotency - 20.2

Question 1

What is cell differentiation?

Answer 1

The process by which each cell develops into a specialised structure suited to the role it will carry out.

Question 2

How do single-celled organisms function?

Answer 2

Single-celled organisms perform all essential life functions inside the boundaries of a single cell.

Question 3

What is the problem with single-celled organisms?

Answer 3

While they can perform all functions adequately, they cannot be totally efficient at all of them. No one cell can provide theist condition for all functions.

Question 4

What happens to an organism’s cells as it matures?

Answer 4

In early development, an organism is made up of a tiny ball of identical cells. As it matures, each cell takes on its own individual characteristics that adapt it to the function that it will perform when it is mature.

Question 5

How are all the cells in a organism derived and what does it mean?

Answer 5

All the cells in an organism, such as a human, are derived by mitotic divisions of the fertilised egg (zygote). It follows that they all contain the exact same genes, therefore every cell is capable of making everything that the body can produce.

Question 6

If all cells are identical, how do they perform different functions?

Answer 6

Although all cells contain all genes, only certain genes are expressed (switched on) in any one cell at any one time.

Question 7

What are some examples of genes that are permanently expressed (switched on) in all cells?

Answer 7

• Genes that code for essential chemicals, e.g. enzymes involved in respiration.
• Genes coding for enzymes and other proteins involved in essential processes like transcription, translation, membrane synthesis, ribosomes and tRNA synthesis.

Question 8

What is an example of a gene that is permanently not expressed (switched off)?

Answer 8

The gene for insulin in cells lining the small intestine.

Question 9

How do differentiated cells differ from each other?

Answer 9

Differentiated cells differ from each other, often visibly so. This is mainly because they each produce different proteins.

Question 10

What determines the proteins that a cell produces?

Answer 10

The proteins that a cell produces are coded for by the genes that are expressed (switched on).

Question 11

What are totipotent cells?

Answer 11

Cells, such as fertilised eggs, that can mature into any body cell.

Question 12

What are some examples of specialisation?

Answer 12

• Mesophyll cells become specialised for photosynthesis.

- Muscle cells become specialised for contraction.

Question 13

What happens during the process of cell specialisation?

Answer 13

During the process of cell specialisation, only some of the genes are expressed, meaning only part of the DNA of a cell is translated into proteins. The cell therefore only makes those proteins that it requires to carry out its specialised functions.

Question 14

How do cells conserve energy and resources?

Answer 14

Although they are capable of making all proteins, these are not needed so it would be wasteful to produce them. In order to conserve energy and resources, a variety of stimuli (controlling factors) ensure the genes for these other proteins are not expressed.

Question 15

How are genes prevented form expressing themselves?

Answer 15

• Preventing transcription and so preventing the production of mRNA.
• Preventing translation.

Question 16

What is an example of specialisation being irreversible?

Answer 16

Xylem vessels, which transport water in plants, and red blood cells, which carry oxygen in animals, are so specialised that they lose their nuclei once they are mature. As the nucleus contains the genes, then clearly these cells cannot develop into other cells

Question 17

Is specialisation reversible or irreversible?

Answer 17

This is dependent on many things. Specialisation is irreversible in most animal cells. In mature mammals, only a few cells retain the ability to differentiate into other cells.

Question 18

What are stem cells?

Answer 18

Stem cells are undifferentiated dividing cells that occur in adult animal tissues and need to be constantly replaces. They therefore have the ability to divide to form an identical copy of themselves in a process called self-renewal.

Question 19

What are some examples of where stem cells originate in mammals?

Answer 19

• Embryonic stem cells
• Umbilical cord blood stem cells
• Placental stem cells
• Adult stem cells

Question 20

How are the types of stem cells classified?

Answer 20

They are classified according to their ability to differentiate.

Question 21

What are the four types of stem cells?

Answer 21

• Totipotent stem cells
• Pluripotent stem cells
• Multipotent stem cells
• Unipotent stem cells

Question 22

What are totipotent stem cells and give an example?

Answer 22

Totipotent stem cells are found in early embryo and can differentiate into any type of cell.
Since all body cells are formed from a zygote, it follows that the zygote is totipotent.

Question 23

What are pluripotent stem cells and give an example?

Answer 23

Pluripotent stem cells are found in embryos and can differentiate into almost any type of cell.
Examples of pluripotent stem cells are embryonic stem cells and fatal stem cells.

Question 24

What are multipotent stem cells and give an example?

Answer 24

Multipotent stem cells are found in adults and can differentiate into a limited number of specialised cells. They usually develop into cells of a particular type, for example, stem cells in the bone marrow can produce any type of blood cell.
Examples include adult stem cells and umbilical cord blood stem cells.

Question 25

What are unipotent stem cells?

Answer 25

Unipotent stem cells can only differentiate into a single type of cells. They are derived from multipotent stem cells and are made in adult tissue. They are basically any body cell.

Question 26

What are induced pluripotent stem cells (iPS cells)?

Answer 26

A type of pluripotent cell that is produced from unipotent stem cells. The unipotent cell may be almost any body cell. These body cells are them genetically altered in a lab to make them aware the characteristics of embryonic stem cells which are a type of pluripotent cell.

Question 27

How do unipotent cells acquire new characteristics?

Answer 27

To make the unipotent cell acquire the new characteristics involves inducing genes and transcriptional factors within the cell to express themselves.

Question 28

What does the fact that genes are able to be reactivated show?

Answer 28

Adult stem cells retain the same genetic information that was present in the embryo.

Question 29

What is one feature of iPS cells that is of particular interest and how could this help future scientific research?

Answer 29

They are capable of self-renewal. This means that they can potentially divide indefinitely to provide a limitless supply.
As such they could replace embryonic stem cells in medical research and treatment, overcoming many ethical issues surrounding the use of embryonic stem cells.

Question 30

What are some possible uses of pluripotent stem cells in treating human disorders?

Answer 30

• Skin grafts for serious burn damage

- Neuro-degenerative diseases, such as Parkinson’s disease

Question 31

What are some ethical issues with using embryonic stem cells?

Answer 31

• Using an embryo in this way undermines our respect for human life.
• Could progress to use of foetuses, and even newborn babies, for research or the treatment of diseases.
• Laws prohibiting cloning may not be sufficient evidence.
• It is wrong to use humans, including human embryos, as a means to an end.