biology

Mesosome

Mesosome is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mesosome rather than just read about it. In short: Mesosomes or chondrioids are folded invaginations in the plasma membrane of bacteria that are produced by the chemical fixation techniques used to prepare samples for electron microscopy. Although several functions were proposed for these structures in the 1960s, they were recognized as artifacts by the late 1970s and are no longer considered to be part of the normal structure of bacterial cells.

Key takeaways

Mesosome belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mesosome to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mesosome from memory before moving on to harder problems.

Reference excerpt

Mesosomes or chondrioids are folded invaginations in the plasma membrane of bacteria that are produced by the chemical fixation techniques used to prepare samples for electron microscopy. Although several functions were proposed for these structures in the 1960s, they were recognized as artifacts by the late 1970s and are no longer considered to be part of the normal structure of bacterial cells. These extensions are in the form of vesicles, tubules and lamellae.

Initial observations These structures are invaginations of the plasma membrane observed in gram-positive bacteria that have been chemically fixed to prepare them for electron microscopy. They were first observed in 1953 by George B. Chapman and James Hillier, who referred to them as "peripheral bodies." They were termed "mesosomes" by Fitz-James in 1960. Initially, it was thought that mesosomes might play a role in several cellular processes, such as cell wall formation during cell division, chromosome replication, or as a site for oxidative phosphorylation. The mesosome was thought to increase the surface area of the cell, aiding the cell in cellular respiration. This is analogous to cristae in the mitochondrion in eukaryotic cells, which are finger-like projections and help eukaryotic cells undergo cellular respiration. Mesosomes were also hypothesized to aid in photosynthesis, cell division, DNA replication, and cell compartmentalisation.

Disproof of hypothesis These models were called into question during the late 1970s when data accumulated suggesting that mesosomes are artifacts formed through damage to the membrane during the process of chemical fixation, and do not occur in cells that have not been chemically fixed. By the mid to late 1980s, with advances in cryofixation and freeze substitution methods for electron microscopy, it was generally concluded that mesosomes do not exist in living cells. However, a few researchers continue to argue that the evidence remains inconclusive, and that mesosomes might not be artifacts in all cases. Recently, similar folds in the membrane have been observed in bacteria that have been exposed to some classes of antibiotics, and antibacterial peptides (defensins). The appearance of these mesosome-like structures may be the result of these chemicals damaging the plasma membrane and/or cell wall. The case of the proposal and then disproof of the mesosome hypothesis has been discussed from the viewpoint of the philosophy of science as an example of how a scientific idea can be falsified and the hypothesis then rejected, and analyzed to explore how the scientific community carries out this testing process.

See also Cell membrane Organelle Lysosome

References

Illustrations

Worked examples

Example 1 — a first encounter with Mesosome

Start with the simplest possible case. Write down what Mesosome claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mesosome before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mesosome ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mesosome

In research: Mesosome appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mesosome in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mesosome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Membrane biology, Organelles, Prokaryotic cell anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Mesosome outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mesosome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mesosome means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mesosome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mesosome in simple terms?

Why does Mesosome matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mesosome?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mesosome.