The cell cycle
Ciliated epithelial cells:
- The airways, specifically the trachea, bronchus, and bronchioles, contain it, along with the oviduct.
- It collects dust and mucus and directs them toward the throat.
Sperm cell:
Egg cell:
Muscle cell:
- Stripe/Quite long
- Only one type of cell has the ability to contract and relax.
Neurone (nerve cell):
- Extremely long with branched endings.
- Only cells are capable of sending electrical impulses to the brain.
Root Hair Cell:
- Long extension—larger SA—can absorb more water and nutrients.
Red blood cells:
Another example—the palisade cell
Differentiation
- Differentiation is the term used to describe cells becoming specialised.
- For instance, changes in the shape of the cell, the quantity of a specific organelle, or its contents could occur.
- Cells need to be specialised to do their job.
- All cells start out regularly and become specialised over time.
- Tissue: A group of cells working together to do one job, e.g., muscle tissue.
- Organ: A system of tissues working together to do one job, e.g., lungs.
- Organ system: A group of organs working together to perform a life function, e.g., digestive system.
Cell Cycle and Division
- The SA:V ratio limits cell size, explaining why we cannot form a single large cell.
- One cell becoming two is mitosis (a type of cell division).
- Mitosis is important for:
→ Growth (in humans)
→ Replacement of cells (in humans)
→ Repair cells (in humans)
→ Asexual reproduction (not in humans)
- Human cells have 46 chromosomes (23 pairs) in the nucleus.
- When a cell has pairs of chromosomes, they're diploid cells.
- Mitosis creates new diploid cells; the two new daughter cells are genetically identical (Women = XX, Men = XY).
DNA replication: The cell must copy its DNA before dividing to ensure that each new cell has all 46 chromosomes.
Cell Cycle:
1) The cell grows, and numbers of organelles, e.g., mitochondria, increase.
2) DNA replication
3) Further growth and DNA are checked for errors; repairs are made.
4) Mitosis
5) Cell differentiation
- Cells occasionally exit the cell cycle, such as when they become specialised.
DNA Replication
- DNA replication happens before mitosis.
- In a double helix.
- Original DNA strand/original chromosome.
- After DNA replication is complete, chromosomes split into two sections, known as double chromosomes.
Mitosis
1. Parent, diploid cell
- The cell has grown, and organelles have been replicated.
2. Chromosomes supercoil (shorten and thicken)
3. A nuclear membrane has disintegrated.
- Chromosomes attach to spindle fibres and line up along the equator of the cell.
4. Spindle fibres pull chromatids apart and move them to the opposite poles of the cell.
5. One chromatid reaches the poles of the cell, cytoplasm splits, and nuclei reform.
6. End product: 2 diploid cells, both genetically identical.
Stem Cells
Stem cells in Plants meristems:
- These are unspecialised cells that have the ability to differentiate into specialised cells.
- Human stem cells are found in human embryos and in some adult tissue called bone marrow.
- Bone marrow is a bone tissue that contains all blood stem cells.
Stem cells are undifferentiated cells found in multicellular organisms. Characterised by two features:
1) Self-renewal: The ability to undergo numerous cycles of cell division while maintaining an unspecialised state.
2) Potency: The ability to differentiate into specialised cells.
- Stem cells divide, and some of your body's specialised cells make up your various tissues and organs.
- Stem cells remain in your organs (in small quantities in the brain, heart, muscle, and liver) for many years until diseases injure or affect your tissues.
- Embryonic stem cells can differentiate into any cell body type.
- Humans can treat paralysis (spine injury), leukaemia, dementia, and diabetes using this treatment. The spare embryos from IVF/aborted embryos, as well as the umbilical cord of newborn babies, provide the embryonic stem cells for this research.
- However, some human embryos cannot give permission, so using them is a violation of human rights; religious implications don't mess with potential life.
- Treating medical conditions with stem cells can cause cancer and is also very slow, expensive, and hard.
Therapeutic Cloning:
- The process involves using one of your (adult) body cells to create a cloned, early embryo (32 cells) that serves as a source of perfectly matched embryonic stem cells.