physics

Relative accessible surface area

Relative accessible surface area is a physics 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 Relative accessible surface area rather than just read about it. In short: Relative accessible surface area or relative solvent accessibility (RSA) of a protein residue is a measure of residue solvent exposure. It can be calculated by formula: RSA = ASA / MaxASA {\displaystyle {\text{RSA}}={\text{ASA}}/{\text{MaxASA}}} where ASA is the solvent accessible surface area and MaxASA is the maximum possible solvent accessible surface area for the residue.

Key takeaways

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

Reference excerpt

Relative accessible surface area or relative solvent accessibility (RSA) of a protein residue is a measure of residue solvent exposure. It can be calculated by formula:

RSA = ASA / MaxASA {\displaystyle {\text{RSA}}={\text{ASA}}/{\text{MaxASA}}}

where ASA is the solvent accessible surface area and MaxASA is the maximum possible solvent accessible surface area for the residue. Both ASA and MaxASA are commonly measured in Å 2 {\displaystyle {\mathrm {\AA} }^{2}} . To measure the relative solvent accessibility of the residue side-chain only, one usually takes MaxASA values that have been obtained from Gly-X-Gly tripeptides, where X is the residue of interest. Several MaxASA scales have been published and are commonly used (see Table).

In this table, the more recently published MaxASA values (from Tien et al. 2013) are systematically larger than the older values (from Miller et al. 1987 or Rose et al. 1985). This discrepancy can be traced back to the conformation in which the Gly-X-Gly tripeptides are evaluated to calculate MaxASA. The earlier works used the extended conformation, with backbone angles of ϕ = − 120 ∘ {\displaystyle \phi =-120^{\circ }} and ψ = 140 ∘ {\displaystyle \psi =140^{\circ }} . However, Tien et al. 2013 demonstrated that tripeptides in extended conformation fall among the least-exposed conformations. The largest ASA values are consistently observed in alpha helices, with backbone angles around ϕ = − 50 ∘ {\displaystyle \phi =-50^{\circ }} and ψ = − 45 ∘ {\displaystyle \psi =-45^{\circ }} . Tien et al. 2013 recommend to use their theoretical MaxASA values (2nd column in Table), as they were obtained from a systematic enumeration of all possible conformations and likely represent a true upper bound to observable ASA. ASA and hence RSA values are generally calculated from a protein structure, for example with the software DSSP. However, there is also an extensive literature attempting to predict RSA values from sequence data, using machine-learning approaches.

Prediction tools Experimentally predicting RSA is an expensive and time-consuming task. In recent decades, several computational methods have been introduced for RSA prediction.

References

Worked examples

Example 1 — a first encounter with Relative accessible surface area

Start with the simplest possible case. Write down what Relative accessible surface area claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Relative accessible surface area 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 Relative accessible surface area 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 Relative accessible surface area

In research: Relative accessible surface area appears in physics 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 Relative accessible surface area 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: Relative accessible surface area is common in secondary-school and first-year university syllabi. It links to neighbouring topics Molecular modelling, Protein structure, so understanding it makes those chapters shorter.
In everyday life: Look for Relative accessible surface area 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Relative accessible surface area in 20 minutes

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

Frequently asked questions

What is Relative accessible surface area in simple terms?

Relative accessible surface area or relative solvent accessibility (RSA) of a protein residue is a measure of residue solvent exposure. It can be calculated by formula: RSA = ASA / MaxASA {\displaystyle {\text{RSA}}={\text{ASA}}/{\text{MaxASA}}} where ASA is the solvent accessible surface area and…

Why does Relative accessible surface area matter?

Because it connects several physics 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 Relative accessible surface area?

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 Relative accessible surface area.