biology

Methylglyoxal pathway

Methylglyoxal pathway 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 Methylglyoxal pathway rather than just read about it. In short: The methylglyoxal pathway is an offshoot of glycolysis found in some prokaryotes, which converts glucose into methylglyoxal and then into pyruvate. However unlike glycolysis the methylglyoxal pathway does not produce adenosine triphosphate, ATP.

Key takeaways

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

Reference excerpt

The methylglyoxal pathway is an offshoot of glycolysis found in some prokaryotes, which converts glucose into methylglyoxal and then into pyruvate. However unlike glycolysis the methylglyoxal pathway does not produce adenosine triphosphate, ATP. The pathway is named after the substrate methylglyoxal which has three carbons and two carbonyl groups located on the 1st carbon and one on the 2nd carbon. Methylglyoxal is, however, a reactive aldehyde that is very toxic to cells, it can inhibit growth in E. coli at millimolar concentrations. The excessive intake of glucose by a cell is the most important process for the activation of the methylglyoxal pathway.

The Methylglyoxal pathway

The methylglyoxal pathway is activated by the increased intercellular uptake of carbon containing molecules such as glucose, glucose-6-phosphate, lactate, or glycerol. Methylglyoxal is formed from dihydroxyacetone phosphate (DHAP) by the enzyme methylglyoxal synthase, giving off a phosphate group. Methylglyoxal is then converted into two different products, either D-lactate, and L-lactate. Methylglyoxal reductase and aldehyde dehydrogenase convert methylglyoxal into lactaldehyde and, eventually, L-lactate. If methylglyoxal enters the glyoxylase pathway, it is converted into lactoylguatathione and eventually D-lactate. Both D-lactate, and L-lactate are then converted into pyruvate. The pyruvate that is created most often goes on to enter the Krebs cycle.

Enzymes and regulation The potentially hazardous effects of methylglyoxal require regulation of the reactions with this substrate. Synthesis of methylglyoxal is regulated by levels of DHAP and phosphate concentrations. High concentrations of DHAP encourage methylglyoxal synthase to produce methylglyoxal, while high phosphate concentrations inhibit the enzyme, and therefore the production of more methylglyoxal. The enzyme triose phosphate isomerase affects the levels of DHAP by converting glyceraldehyde 3-phosphate (GAP) into DHAP. The usual pathway converting GAP to pyruvate starts with the enzyme glyceraldehyde 3-phosphate dehydrogenase. Low phosphate levels inhibit GAP dehydrogenase; GAP is instead converted into DHAP by triosephosphate isomerase. Again, increased levels of DHAP activate methylglyoxal synthase and methylglyoxal production.

The oscillation of Methylglyoxal concentration in feast concentrations Jan Weber, Anke Kayser, and Ursula Rinas, performed an experiment to test what happened to the methylglyoxal pathway when E. coli was in the presence of a constantly high concentration of glucose. The concentration of methylglyoxal increased until it reached 20 μmol. Methylglyoxal concentration then began to decrease, once it reached this level. The decrease in the concentration of methylglyoxal was connected to the drop in respiratory activity. When respiration activity increased the concentration of methylglyoxal increased again, until it reached the 20 μmol concentration.

Why does the Methylglyoxal pathway exist? This pathway does not produce any ATP, this pathway does not replace glycolysis, it runs simultaneously to glycolysis and is only initiated with an increased concentration of sugar phosphates. One believed purpose of the methylglyoxal pathway is to help release the stress of elevated sugar phosphate concentration. Also when methylglyoxal is formed from DHAP, an inorganic phosphate is given off which can be used to replenish a low concentration of needed inorganic phosphate. The methylglyoxal pathway is a rather dangerous tactic, both because less energy is produced and a toxic compound, methylglyoxal is formed.

References

Further reading Saadat, D., Harrison, D.H.T. "Methylglyoxal Synthase From Escherichia Coli." RCSB Protein Data Base. 24 Apr. 2007. RCSB Protein Data Base. 25 Apr. 2007 <http://www.pdb.org/pdb/explore.do?structureId=1B93>. "Methylglyoxal Synthase From Escherichia Coli." RCSB Protein Data Base. 24 Apr. 2007. RCSB Protein Data Base. 25 Apr. 2007 <http://www.pdb.org/pdb/explore.do?structureId=1B93>. Yun, M., C.-G. Park, J.-Y Kim, and H.-W. Park. "Structural Analysis of Glyeraldehyde 3-Phosphate Dehydrogenase from Escherichia coli: Direct Evidence for Substrate Binding and Cofactor-Induced Confromational Changes. RCSB Protein Data Base. 24 Apr. 2007. RCSB Protein Data Base. 30 Apr. 2007 <http://www.pdb.org/pdb/explore.do?structureId=1DC4>.

Worked examples

Example 1 — a first encounter with Methylglyoxal pathway

Start with the simplest possible case. Write down what Methylglyoxal pathway 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 Methylglyoxal pathway 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 Methylglyoxal pathway 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 Methylglyoxal pathway

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

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

Frequently asked questions

What is Methylglyoxal pathway in simple terms?

Why does Methylglyoxal pathway 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 Methylglyoxal pathway?

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 Methylglyoxal pathway.