biology

Glucose transporter

Glucose transporter 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 Glucose transporter rather than just read about it. In short: Glucose transporters are a wide group of membrane proteins that facilitate the transport of glucose across the plasma membrane, a process known as facilitated diffusion. Because glucose is a vital source of energy for all life, these transporters are present in all phyla.

Key takeaways

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

Reference excerpt

Glucose transporters are a wide group of membrane proteins that facilitate the transport of glucose across the plasma membrane, a process known as facilitated diffusion. Because glucose is a vital source of energy for all life, these transporters are present in all phyla. The GLUT or SLC2A family are a protein family that is found in most mammalian cells. 14 GLUTS are encoded by the human genome. GLUT is a type of uniporter transporter protein.

Synthesis of free glucose Most non-autotrophic cells are unable to produce free glucose because they lack expression of glucose-6-phosphatase and, thus, are involved only in glucose uptake and catabolism. Usually produced only in hepatocytes, in fasting conditions, other tissues such as the intestines, muscles, brain, and kidneys are able to produce glucose following activation of gluconeogenesis.

Glucose transport in yeast In Saccharomyces cerevisiae glucose transport takes place through facilitated diffusion. The transport proteins are mainly from the Hxt family, but many other transporters have been identified.

Glucose transport in mammals GLUTs are integral membrane proteins that contain 12 membrane-spanning helices with both the amino and carboxyl termini exposed on the cytoplasmic side of the plasma membrane. GLUT proteins transport glucose and related hexoses according to a model of alternate conformation, which predicts that the transporter exposes a single substrate binding site toward either the outside or the inside of the cell. Binding of glucose to one site provokes a conformational change associated with transport, and releases glucose to the other side of the membrane. The inner and outer glucose-binding sites are, it seems, located in transmembrane segments 9, 10, 11; also, the DLS motif located in the seventh transmembrane segment could be involved in the selection and affinity of transported substrate.

Types Each glucose transporter isoform plays a specific role in glucose metabolism determined by its pattern of tissue expression, substrate specificity, transport kinetics, and regulated expression in different physiological conditions. To date, 14 members of the GLUT/SLC2 have been identified. On the basis of sequence similarities, the GLUT family has been divided into three subclasses.

Class I Class I comprises the well-characterized glucose transporters GLUT1-GLUT4.

Classes II/III Class II comprises:

GLUT5 (SLC2A5), a fructose transporter in enterocytes GLUT7 (SLC2A7), found in the small and large intestine, transporting glucose out of the endoplasmic reticulum GLUT9 (SLC2A9), recently has been found to transport uric acid GLUT11 (SLC2A11) Class III comprises:

GLUT6 (SLC2A6), GLUT8 (SLC2A8), GLUT10 (SLC2A10), GLUT12 (SLC2A12), and GLUT13, also H+/myo-inositol transporter HMIT (SLC2A13), primarily expressed in brain. Most members of classes II and III have been identified recently in homology searches of EST databases and the sequence information provided by the various genome projects. The function of these new glucose transporter isoforms is still not clearly defined at present. Several of them (GLUT6, GLUT8) are made of motifs that help retain them intracellularly and therefore prevent glucose transport. Whether mechanisms exist to promote cell-surface translocation of these transporters is not yet known, but it has clearly been established that insulin does not promote GLUT6 and GLUT8 cell-surface translocation.

Discovery of sodium-glucose cotransport In August 1960, in Prague, Robert K. Crane presented for the first time his discovery of the sodium-glucose cotransport as the mechanism for intestinal glucose absorption. Crane's discovery of cotransport was the first ever proposal of flux coupling in biology. Crane in 1961 was the first to formulate the cotransport concept to explain active transport. Specifically, he proposed that the accumulation of glucose in the intestinal epithelium across the brush border membrane was [is] coupled to downhill Na+ transport cross the brush border. This hypothesis was rapidly tested, refined, and extended [to] encompass the active transport of a diverse range of molecules and ions into virtually every cell type.

See also Cotransport Cotransporter GLUT1 deficiency syndrome GLUT2 deficiency syndrome

References

External links Glucose+Transport+Proteins,+Facilitative at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

Illustrations

Worked examples

Example 1 — a first encounter with Glucose transporter

Start with the simplest possible case. Write down what Glucose transporter 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 Glucose transporter 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 Glucose transporter 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 Glucose transporter

In research: Glucose transporter 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 Glucose transporter 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: Glucose transporter is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbohydrate metabolism, Integral membrane proteins, Solute carrier family, so understanding it makes those chapters shorter.
In everyday life: Look for Glucose transporter 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 Glucose transporter in 20 minutes

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

Frequently asked questions

What is Glucose transporter in simple terms?

Why does Glucose transporter 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 Glucose transporter?

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 Glucose transporter.