8. Individual cell development. Cell senescence. Elements of cellular ageing. Apoptosis and necrosis

Question 1

Individual development of cells

Answer 1

The life cycle of animal cells:
- Involves growth, development, and reproduction.
- Follows instructions encoded in DNA inherited from parent cells.

The life cycle of bacteria:
- Coincides with the cell cycle.
- Consists of continuous alternation of growth and division.

Question 2

Telomeres

Answer 2

Telomeres
- Regions of repetitive DNA sequences (TTAGGG) at the ends of chromosomes.

• Protect chromosome ends from being recognized and processed by DNA break repair systems, preventing damage and fusion with other
  chromosomes.
• Telomeres shorten with each cell division.
• Telomere length is an important indicator of cell lifespan.
• For cells to survive indefinitely (become “immortalized”), they must activate a mechanism to maintain telomere length.

Question 3

Telomerase

Answer 3

Mechanism is an enzyme called TELOMERASE

• It adds repeated nucleotide sequences to telomere ends
• Expression of telomerase extends the lifespan of cells.
• Activation of telomerase in somatic cells may lead to cancer.

Question 4

Cell Death (senescence)

Answer 4

Cell death:

• Observed throughout life of individual, including embryonic development.
• Two types of cell death:

1. Necrosis:
   - Non-physiological process.
   - Caused by external factors such as physical and chemical trauma or infections.
2. Programmed cell death - Apoptosis:
   - Normal physiological process.
   - Guided by the genetic program of the cell.

Question 5

Necrosis

Answer 5

Necrosis

Results from:
- Toxic effects
- Mechanical damage
- -Lack of oxygen (O2)
Disturbances in nutrient transport

Process:
- Begins with damage to cell membrane, allowing water to enter dying cell.
- Membrane-bound organelles are destroyed, leading to total destruction of cytoplasm.
- Cells swell, burst, and release their contents into the intercellular space.
- Fragments of the destroyed cell cause local inflammation.
- Phagocytic cells invade the area, triggering an inflammatory response from immune system.

Morphological changes of nucleus:
- Shrinkage of nucleus
- Fragmentation of chromatin
- Loss of nuclear structure

Question 6

Apoptosis

Answer 6

Genetically programmed cell death:
- Cell is not damaged by an external agent.

Process:
- Starts with changes in nucleus and DNA fragmentation:
-> DNA breaks down by nuclear endonucleases – an irreversible process.
->Nuclear chromatin aggregates, and nucleus divides into several discrete fragments bounded by nuclear envelope.

• Decrease in cell volume due to cytoplasm shrinkage and disorganization of the cytoskeleton, ER, and other organelles.
• Membrane blebbing occurs due to changes in its physical and chemical properties.
• Cells disintegrate into membrane-bound compartments containing nuclear material and cytoplasm (apoptotic bodies), which are phagocytosed by neighboring cells or macrophages.

Importance of apoptosis for the body:
- Clears body of damaged or dangerous cells, such as:
->Lymphocytes reacting against own antigens in autoimmune processes.
-> Degenerate cells in tumor processes.
->Infected cells in some viral infections.

• Involved in some pathological processes, such as:
  ->Death of nerve cells in diseases of the nervous system, like Alzheimer’s and Parkinson’s diseases.