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Phycoerythrobilin

Phycoerythrobilin is a science 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 Phycoerythrobilin rather than just read about it. In short: Phycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of which it is the terminal acceptor of energy.

Phycoerythrobilin — main illustration
Phycoerythrobilin — illustration

Key takeaways

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

Reference excerpt

Phycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of which it is the terminal acceptor of energy. The amount of phycoerythrobilin in phycoerythrins varies, depending on the organism. In some Rhodophytes and oceanic cyanobacteria, phycoerythrobilin is also present in the phycocyanin, then termed R-phycocyanin. Like all phycobilins, phycoerythrobilin is covalently linked to these phycobiliproteins by a thioether bond.

Chemical structure Phycoerythrobilin is a tetrapyrrole formed in nature by the catabolism of heme B via biliverdin. Two geometric isomers of the compound have been reported, which differ only in the configuration of one sidechain. The stereochemistry of the compounds were confirmed by total synthesis of their methyl esters.

Biosynthesis (E) and (Z)-phycoerythrobilin are products of porphyrin biosynthesis beyond heme B. They arise from its oxidation which cleaves the macrocyclic ring, giving biliverdin:

Biliverdin is then reduced to give either the (E) or (Z) isomers of phycoerythrobilin, for example by phycoerythrobilin synthase:

There is evidence that in some organisms it is the (3Z) form that is produced first and that this is converted into the (3E) isomer.

Biological role Phycoerythrobilins are components of phycobilisome protein complexes, the light-harvesting antennae that transmit the energy of photons to photosystem II and photosystem I in cyanobacteria and in the chloroplasts of red algae and glaucophytes. The absorption spectrum of phycoerythrobilins in the 500–650 nm range where chlorophyll absorbs poorly allows organisms such as Galdieria sulphuraria which use them to be more efficient. The tetrapyrrole is covalently attached to the phycobiliprotein through a bond between the sulfur of a cysteine amino-acid and the (3E) or (3Z) ring-C=CCH3 sidechain, as a thioether.

Uses Phycoerythrobilins, in the form of phycobiliproteins, are widely used in foodstuffs and cosmetics as colourants. They are mainly obtained from Spirulina species.

References

Illustrations

Phycoerythrobilin illustration
Phycoerythrobilin illustration
Phycoerythrobilin illustration
Phycoerythrobilin illustration

Worked examples

Example 1 — a first encounter with Phycoerythrobilin

Start with the simplest possible case. Write down what Phycoerythrobilin claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Phycoerythrobilin 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 Phycoerythrobilin 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 Phycoerythrobilin

In research
Phycoerythrobilin appears in science 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 Phycoerythrobilin 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
Phycoerythrobilin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fluorescent dyes, Photosynthetic pigments, Tetrapyrroles, so understanding it makes those chapters shorter.
In everyday life
Look for Phycoerythrobilin 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 Phycoerythrobilin in 20 minutes

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

Frequently asked questions

What is Phycoerythrobilin in simple terms?

Phycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of which it is the terminal acceptor of energy.

Why does Phycoerythrobilin matter?

Because it connects several science 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 Phycoerythrobilin?

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 Phycoerythrobilin.

Tags

  • Fluorescent dyes
  • Photosynthetic pigments
  • Tetrapyrroles

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