20.2 Stem Cells And Totipotency Flashcards
What is cell differentiation?
- Cell differentiation is the process by which cells become specialized in structure and function to perform specific roles in multicellular organisms.
- In early development, cells start off identical but gradually take on unique characteristics suited for specific tasks.
Why can’t single-celled organisms perform all life functions efficiently?
- Single-celled organisms perform all essential life functions within the boundaries of a single cell.
- However, no one cell can provide the optimal conditions for all functions because each function requires different types of cellular structures, enzymes, and proteins.
- For example, one activity might be best carried out by a long, thin cell, while another might need a spherically shaped cell.
- Thus, single-celled organisms cannot specialize in all functions simultaneously.
How do cells in multicellular organisms become specialized?
- In multicellular organisms, cells differentiate and specialize to perform specific functions.
- This process occurs as an organism develops from a fertilized egg (zygote) into a complex organism.
- Initially, all cells are identical but gradually take on different characteristics and structures suited for particular roles.
How are human cells derived and why do they all contain the same genes?
- All human cells are derived from the mitotic divisions of a fertilized egg (zygote), which means they all contain the same genes.
- Despite this, different cell types perform different functions because only certain genes are expressed in each cell.
How do cells produce different proteins despite having the same genes?
- Although all cells in an organism contain the same genes, they express different sets of genes at different times.
- Gene expression is regulated, so only specific genes are activated (switched on) in each cell, leading to the production of proteins that are specific to the cell’s function.
What is the difference between permanently expressed genes and conditionally expressed genes?
1) Permanently expressed genes:
- These are genes that are always “on” in all cells because they are essential for basic cellular functions, like those coding for enzymes involved in respiration or proteins for transcription and translation.
2) Conditionally expressed genes:
- These genes are switched on or off as needed by the cell for specific functions.
- For example, the gene for insulin is permanently off in cells of the small intestine but is expressed in pancreas B cells.
How do different cell types in the body produce different proteins if they all have the same genes?
- Different cell types produce different proteins because they express different sets of genes.
- For example, cells in the lining of the small intestine and pancreas B cells both contain the gene for insulin, but only B cells express this gene, while the cells of the small intestine do not.
- The proteins a cell produces are determined by which genes are activated (switched on) in that cell.
Explain why cells in the pancreas and the small intestine produce different proteins, even though they both contain the same genetic information.
- Both pancreas B cells and cells in the lining of the small intestine contain the same genetic information, as they are both derived from the same zygote.
- However, they produce different proteins because only certain genes are expressed in each cell type.
- In pancreas B cells, the gene for insulin is expressed, allowing the production of insulin, whereas in the cells of the small intestine, this gene is not expressed, so these cells produce different proteins suited to their role, such as maltase.
Why is the regulation of gene expression important for cellular function?
- The regulation of gene expression is crucial for cellular function because it ensures that the right proteins are produced in the right cells at the right time.
- This allows cells to specialize in different functions, such as those involved in metabolism, digestion, or defense, while maintaining the overall homeostasis of the organism.
What is meant by “totipotency” in biology?
- Totipotency refers to the ability of a cell, such as a fertilised egg, to give rise to all types of cells in an organism.
- A totipotent cell can differentiate into any body cell and has the potential to form a complete organism. This includes the ability to form both somatic cells and extra-embryonic tissues like the placenta.
Why is a fertilised egg considered totipotent?
- A fertilised egg is considered totipotent because it has the ability to develop into all types of cells in the organism, including all the somatic cells (e.g., skin, muscle, nerve) and the extra-embryonic tissues (e.g., placenta).
- The totipotency of the fertilised egg enables the formation of a complete organism from a single cell.
Are the early cells derived from the fertilised egg totipotent?
Yes, the early cells that are derived from the fertilised egg are also totipotent. These cells can still differentiate into any type of cell, contributing to the development of all tissues and organs of the organism.
What happens to totipotent cells as development progresses?
- As development progresses, totipotent cells differentiate into specialised cells.
- During differentiation, cells become adapted for specific functions.
- For example, mesophyll cells become specialised for photosynthesis, and muscle cells become specialised for contraction.
- The process of differentiation involves the selective expression of genes.
Why do cells only produce certain proteins during differentiation?
- During differentiation, only specific genes are expressed, meaning that only certain proteins are produced.
- This selective gene expression allows the cell to produce the proteins required for its specialised function.
- For instance, muscle cells produce proteins for contraction, and mesophyll cells produce proteins for photosynthesis.
Why is it important for a cell to avoid producing unnecessary proteins during differentiation?
- It is important to avoid producing unnecessary proteins to conserve energy and resources.
- Producing proteins that are not needed for the cell’s specialised function would be wasteful in terms of both energy and cellular resources, so only the proteins required for essential processes are synthesised.
