biology

Hemidesmosome

Hemidesmosome 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 Hemidesmosome rather than just read about it. In short: Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy; however, desmosomes attach to adjacent cells.

Key takeaways

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

Reference excerpt

Hemidesmosomes are very small stud-like structures found in keratinocytes of the epidermis of skin that attach to the extracellular matrix. They are similar in form to desmosomes when visualized by electron microscopy; however, desmosomes attach to adjacent cells. Hemidesmosomes are also comparable to focal adhesions, as they both attach cells to the extracellular matrix. Instead of desmogleins and desmocollins in the extracellular space, hemidesmosomes utilize integrins. Hemidesmosomes are found in epithelial cells connecting the basal epithelial cells to the basement membrane. Hemidesmosomes are also involved in signaling pathways, such as keratinocyte migration or carcinoma cell intrusion.

Structure Hemidesmosomes can be categorized into two types based on their protein constituents. Type 1 hemidesmosomes are found in stratified and pseudo-stratified epithelium. Type 1 hemidesmosomes have five main elements: integrin α6β4, plectin in its isoform 1a, i. e. P1a, tetraspanin protein CD151, BPAG1e, or bullous pemphigoid antigen isoform e, and BPAG2 (also known as BP180 or type 17 collagen). Type 1 hemidesmosomes are found in stratified and pseudostratified epithelial tissue. Type 2 hemidesmosomes contain integrin α6β4 and plectin without the BP antigens. Hemidesmosomes have two membrane-spanning components: Integrin α6β4 and BPAG2. Integrin α6β4 operates as a laminin-332 receptor. Integrin α6β4 is composed to two α and β subunit dimers. The larger β4 subunit has domains that bind to fibronectin III and calcium. The α6 subunit binds to extracellular BP180, CD151 and laminin-322. When integrin α6β4 binds to Plectin 1a and BPAG1, it associates with the keratin intermediate filaments in the cytoskeleton. Hemidesmosomes are linked to keratin by plectin isoform 1a from the plakin protein family. Plectin is a 500 kDa protein with a long, rod-like domain and a domain at the end that contains an intermediate filament binding site. BPAG2, or (bullous pemphigoid antigen 2), is a transmembrane protein that exists adjacent to integrins, BPAG2 has domains that bind to plectin, integrin β4 subunit in the cytoplasm and integrin α6 and laminin-332 in the extracellular space. CD151, a protein of the tetraspanin superfamily, resides on the cell surface of keratinocytes and vascular endothelium. CD151 aids in hemidesmosome formation. BPAG1e is an antigen with multiple isoforms that binds to integrin α6β4, BPAG2 and keratin 5 and 14. The main role of BPAG1e is for hemidesmosome stability.

Diseases Keeping the basal epidermal keratinocytes attached to the basal lamina is vital for skin homeostasis. Genetic or acquired diseases that cause disruption of hemidesmosome components can lead to skin blistering disorders between different layers of the skin. These are collectively coined epidermolysis bullosa, or EB. Typical symptoms include fragile skin, blister development, and erosion from minor physical stress. However, the disease also can manifest as erosions on the cornea, trachea, gastrointestinal tract, esophagus, muscular dystrophy and muscular deformity. Mutations in 12 different genes that code for parts of the hemidesmosome have led to epidermolysis bullosa. There are three types of EB: EB simplex (EBS), dystrophic EB (DEB) and junctional EB (JEB). In epidermolysis bullosa simplex, layers of the epidermis separate. EBS is caused by mutations coding for keratin, plectin and BPAG1e. With junctional epidermolysis bullosa, layers of the lamina lucida (part of the basal lamina) separate. This is caused by mutations in integrin α6β4, laminin 322 and BPAG2. In dystrophic epidermolysis bullosa, the layers of the papillary dermis separate from the anchoring fibrils. This is caused by mutations in the collagen 7 gene.

See also Desmosome Epidermolysis bullosa Focal adhesion

References

Illustrations

Worked examples

Example 1 — a first encounter with Hemidesmosome

Start with the simplest possible case. Write down what Hemidesmosome 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 Hemidesmosome 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 Hemidesmosome 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 Hemidesmosome

In research: Hemidesmosome 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 Hemidesmosome 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: Hemidesmosome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cell anatomy, Skin anatomy, so understanding it makes those chapters shorter.
In everyday life: Look for Hemidesmosome 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 Hemidesmosome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hemidesmosome 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 Hemidesmosome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hemidesmosome in simple terms?

Why does Hemidesmosome 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 Hemidesmosome?

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 Hemidesmosome.