BIOB11H3 Lecture Notes - Lecture 19: Contact Inhibition, Telomerase, Aneuploidy
Lec 19- The Biology of Cancer
Lecture Notes
• Characteristics of Normal vs. Cancer Cells
• Normal cells →
• i) Density dependent growth
• ii) Exhibit contact inhibition- once cells contact neighbours cell cycle arrest occurs
• iii) Anchorage dependent growth
• iv) Require growth factors for cell proliferation
• v) Normal ploidy levels – Apoptosis (programmed cell death) induced in aneuploids
• vi) Low telomerase levels
• vii) Form gap junctions for intercellular communication
• viii) Normal proteinase secretion (breakdown of proteins)
• Cancer cells →
• i) Density independent growth
• ii) No contact inhibition
• iii) Anchorage independent growth
• iv) Often produce their own growth factors
• v) Aneuploidy (unusual chromosome number) common- apoptotic failure
• vi) High telomerase levels
• vii) Form few gap junctions
• viii) Elevated levels of secreted proteinases
o Proteinases break down extracellular matrix
o Loosens tissue so cancer cells can detach & invade adjacent tissues (metastasize)
• Fig 16-3: Normal cells grow in a monolayer but cancerous cells grow in multilayered
clumps
• Fig 16-4: Growth of normal cells levels off as the growth factors in the medium are
depleted whereas the growth of cancer cells continues regardless of presence or absence
of growth factors
• Normal cells either have i) finite # divisions → cell death or ii) altered states/aneuploidy
→ apoptosis
• Cancer cells have mutations (specific or multiple) that occur to deregulate the cell cycle
so that the cancerous cells become immortalized
• Benign tumour: unresponsive to growth controls but lack the ability to invade other
tissues (e.g. mole)
• Malignant tumour: unresponsive to growth controls & capable of invading other
tissues: secondary tumours
• Immortalization: cancer cells must either have the capacity for unlimited proliferation
or they must acquire it
o Cancers may arise from stem cells or progenitor (pluripotent) cells
o They acquire immortality by reactivation of telomerase expression which
increases lifespan/capacity to divide
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