Context
The recent death of Leonard Hayflick, a leading biomedical researcher, has renewed focus on his discovery of the Hayflick limit.
About Hayflick Limit
- It states Somatic (non-reproductive) cells can only divide approximately 40-60 times before stopping, a phenomenon called cellular senescence.
- Impact on Ageing: Cessation of cell division leads to the accumulation of senescent cells, contributing to ageing and bodily decline.
- Inherent Cellular Clock: The Hayflick Limit suggests an internal clock in organisms that determines the maximum lifespan (estimated at 125 years for humans).
- Species Comparison:
- Galapagos turtles (lifespan over 200 years) have a Hayflick limit of 110 divisions.
- Laboratory mice (short lifespan) reach senescence after only 15 divisions.
About Telomeres:
- Repetitive DNA sequences at chromosome ends that protect during cell division.
- Telomere Shortening: With each division, telomeres shorten, signaling the end of cell division and contributing to ageing.
- Telomere-Lifespan Correlation: Not straightforward; e.g., mice have longer telomeres but shorter lifespans than humans.
- Telomerase: is a protein that produces new telomeres.
- Cancer Cells: Telomerase is active in cancer cells, allowing them to bypass the Hayflick limit and divide indefinitely.
About Cell Division
- Parent cell divides to form two or more daughter cells.
- Critical for growth, repair, and reproduction in living organisms.
- Mitosis: Process where somatic (body) cells divide.
- Results in two daughter cells with the same number of chromosomes as the original cell.
- Highly regulated to ensure genetic consistency in somatic cells.
- Meiosis: Specific to the formation of gametes (sperm and egg cells).
- Reduces chromosome number by half, creating four non-identical daughter cells with 23 chromosomes each.
- Maintains species’ chromosome number across generations.
- Introduces genetic variation through crossing over and independent assortment.
Source:
IE
Previous Year Question
Which one of the following statements best describes the role of B cells and T cells in the human body?
[UPSC Civil Services Exam – 2022 Prelims]
(a) They protect the environmental allergens. body
(b) They alleviate the body’s pain and inflammation.
(c) They act as immunosuppressants in the body.
(d) They protect the body from diseases caused by pathogens.
Answer: (d)
