Volume 30, Number 3, February 2018
Teachernotes
Cell death
Martin Rowland
Introduction
Apoptosis is subject content in only one of the Ofqual-accredited A-level biology specifications— OCR’s biology A (H420).
The indicative content of this specification is covered in slides 2–6 and slide 12 of this presentation.
The process of apoptosis, however, provides a context for other biological concepts common to all specifications. Slides 7–11 include some of these aspects.
The pronunciation of apoptosis is problematic.The word is derived from two Greek words: apo, meaning falling off, and ptosis, meaning falling towards. As with other English words derived from Greek, the second ‘p’ in apoptosis is often silent (as in, e.g., pterodactyl).The pronunciation, thus, becomes a-po-tosis.In the USA, however, the second ‘p’ is often pronounced, so the word becomes a-pop-tosis. To add to the confusion, many pronounce the initial ‘a’ as in ‘apple’, while others pronounce it as in ‘acorn’.
The presentation
Slide 1 is the title slide.
Slide 2 contrasts two types of cell death — necrosis and apoptosis. The inflammation resulting from necrosis can be linked back to what students have learnt about the non-specific immune response.
The importance of apoptosis shown in this slide is that cells are destroyed in a way that does not lead to inflammation or further injury. The method will become clearer in slides 5 and 6.
Slide 3 shows apoptosis in a context that will be familiar to students — the loss of a tadpole’s tail as it develops into a frog.
Slide 4 shows examples of apoptosis in humans, demonstrating how common it is.
Slide 5 introduces caspases: a family of proteases. The advantage of producing caspases as inactive procaspases can be discussed with students and, if you have covered this topic, linked to the inactive precursors of digestive proteases, such as pepsinogen.
The family contains many different procaspases and caspases. For the sake of simplicity, this has not been introduced here. You might, however,choose to introduce this concept. Your more able students might, for example, use their knowledge of enzyme specificity to ask how ‘a caspase’ is able to hydrolyse so many different proteins.
You can also link the content of this slide to the cytoskeleton of cells and to the structure of chromosomes.
Slide 6 contains a photograph from Andrew Gilmore’s article. It will help students to visualise the content of the final two bullet points of slide 5.
You might like to remind students of a comment in slide 2, i.e. that, unlike necrosis, apoptosis does not lead to inflammation. Phagocytosis of membrane-bound apoptotic bodies prevents leakage of cytoplasm into the surrounding tissues. The ability of phagocytes to engulf these bodies depends in part on a change in the chemical nature of their cell-surface membranes. Again, this has been omitted from the slide for the sake of simplicity, but could be introduced by you.
Slide 7 represents the activation of procaspase to produce active caspase (left) and the caspase cascade (right). There is an opportunity here to link the cascade to arithmetic versus logarithmic increases in number. Implicit in this increase, of course, is the concept that enzymes are not changed by the reaction they catalyse, so old and newly activated caspase remain.
Slide 8 provides a quick summary of the two pathways by which the caspase cascade is initiated.
Slide 9 describes the intrinsic pathway in more detail. This pathway provides an excellent opportunity for synopsis, linking to the structure of mitochondria, to membrane structure and to the role of cytochromes in electron transport during aerobic respiration.
Slide 10 shows two effects of cytochrome c that lead to activation of caspases during the intrinsic pathway.Both involve aggregated proteins, providing an opportunity to remind students of the quaternary structure of proteins.
Slide 11 describes the extrinsic pathway. Like the intrinsic pathway, an aggregation of proteins is involved. There is also an opportunity to remind students of the role of proteins as receptors in cell-surface membranes.
Slide 12 provides a link between apoptosis and human health. This gives students an anchor to topics of current interest, including cancer, which is a topic common to all A-level biology specifications.
Opportunities to add video links
You can find accessible videos from the following sites:
For a noisy video of both the extrinsic and intrinsic pathways and of bleb formation:
For a simple cartoon summary followed by a more complex breakdown of the process:
This resource is part of Biological Sciences Review, a magazinewritten for A-level students by subject experts. To subscribe to the full magazine go to
Hodder & Stoughton © 2018