Stem cells, telomeres and cancer
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Cells that can become anything
- What stem cells are
- Potency
Read the transcript of the teaching part
Last time
Before we start: last time, in Chromosomes, the cell cycle and mitosis, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Cells that can become anything
Your skin is replaced about every month, and your blood cells every few months. Something must keep supplying new cells of the right type. Stem cells do that job, and when the cell cycle goes wrong, the same dividing power produces a tumour.
What stem cells are
A stem cell is an unspecialised cell that can divide by mitosis again and again, to make more stem cells. Some of the daughter cells then differentiate, which means they switch on particular genes and become specialised cells, such as red blood cells or muscle cells. A stem cell cannot repair a damaged cell. It makes new cells to replace the damaged one. To do this a stem cell replicates its D N A, divides its nucleus and cytoplasm, and transcribes the genes it needs.
Potency
Totipotent stem cells can become any cell type in the organism, including the cells of the placenta. They are found in the very early embryo. Pluripotent stem cells can become almost any cell type in the body, but not the placenta. Embryonic stem cells are pluripotent. Multipotent stem cells can become only a limited range of cell types. Stem cells in bone marrow form the different blood cells, including phagocytes.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Stem cells.
The whole chapter: The Mitotic Cell Cycle, The Mitotic Cell Cycle.
Chapter 5: The mitotic cell cycle
- Chromosomes, the cell cycle and mitosis 6 min
- Stem cells, telomeres and cancer 5 min
Also for A Level Biology 9700
Which topics come up most in A Level Biology 9700 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency, Paper 4 topic frequency.