4.3 Control of Cell Growth and Reproduction

• Which cells grow and reproduce continuously?

  Blood-forming cells of the bone marrow
• Why do some cells not reproduce for many years?

  They are specialized and have low turnover
• Which cells do not reproduce during a person's life?

  Neurons and most striated muscle cells
• What happens when there is an insufficiency of certain cell types?

  Cells grow and reproduce rapidly to compensate
• What occurs when seven eighths of the liver is removed in young animals?

  The remaining liver cells grow and divide
• Which types of cells do not undergo rapid reproduction after tissue loss?

  Highly differentiated cells like nerve and muscle cells
• What is poorly understood regarding cell growth?

  The mechanisms that maintain cell numbers
• How can growth be controlled in cells?

  Through growth factors, space limitations, and secretions
• What do growth factors do?

  They stimulate cell growth from other body parts
• What happens when cells run out of space for growth?

  They stop growing
• What is the effect of secretions in tissue culture on cell growth?

  They can cause cells to stop growing
• What is a telomere?

  A protective cap on chromosome ends
• What is the role of telomeres during cell division?

  They prevent chromosome deterioration
• What happens to DNA during cell division regarding telomeres?

  A small section is lost with each division
• How many base pairs are lost with each cell division?

  30 to 200 base pairs
• What is the telomere length in human blood cells at birth?

  Approximately 8000 base pairs
• What happens when telomeres shorten to a critical length?

  Chromosomes become unstable and cells die
• What is believed to be a reason for physiological changes associated with aging?

  Telomere shortening
• What can cause telomere erosion besides aging?

  Diseases related to oxidative stress and inflammation
• What does telomerase do in certain cells?

  Adds bases to the ends of telomeres
• Why is telomerase activity usually low in most body cells?

  To prevent uncontrolled cell replication
• What happens to descendant cells after many generations without telomerase activity?

  They inherit defective chromosomes and cease dividing
• How does telomerase activity relate to cancer cells?

  It is abnormally activated, allowing uncontrolled replication
• What is proposed about telomere shortening in relation to diseases?

  It protects against cancer and proliferative diseases
• What primarily determines cell size?

  Amount of functioning DNA in the nucleus
• What happens if DNA replication does not occur?

  The cell grows to a certain size and remains there
• How does colchicine affect cell division?

  It prevents formation of the mitotic spindle
• What occurs to the nucleus when colchicine is used?

  The nucleus contains greater quantities of DNA
• What is the result of increased DNA in the nucleus?

  The cell grows proportionately larger
• What is assumed to cause cell growth when DNA replication continues without mitosis?

  Increased production of RNA and cell proteins
• What is the relationship between RNA production and cell size?

  Increased RNA production causes the cell to grow larger
• What role do cell proteins play in cell growth?


  They contribute to the cell growing larger