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17

EDIT: Thanks a lot to @abukaj for pointing out the mistake in my answer (and to @paracetamol for asking such a beautiful question). I am rewriting my answer to incorporate the (hopefully) correct background knowledge this time. NEW ANSWER: As @paracetamol and @AlanBoyd (in their answer) pointed out the lack of credible support for the claim that infants ...


15

Enzymes alter the rate of a reaction by lowering activation energy; they have no effect on the reaction equilibrium ($\ce{K_{eq}}$). Since $\ce{K_{eq}=\frac{k_f}{k_r}}$ and $\ce{K_{eq}}$ is constant, an increase in forward rate ($\ce{k_f}$) requires a corresponding increase in the reverse rate ($\ce{k_r}$). Intuitively it may help to think that the same ...


13

Enzymes can catalyze a thermodynamically unfavorable reaction by coupling it with a thermodynamically favorable reaction. Most often, enzymes use ATP hydrolysis reaction (energetically favorable) as a source of energy (in simple terms) to drive the unfavorable reaction forward. One important point to keep in mind here is that enzymes don't drive a reaction ...


12

While it's true that cellulose is full of calories, it's very difficult to get the calories out. Symbiotic bacteria take ages to digest cellulose, and as a result animals that digest cellulose with specialized symbiotic bacteria have a huge gut to house them in. It's likely that the reason humans can't digest cellulose is because mammals generally can't. ...


12

Short answer The direction of rotation depends on the viewing point of the observer and the reaction catalyzed by the ATP synthase. When synthesizing ATP, and viewed 'from the bottom' (observer faces the intermembrane space looking into the mitochondrial matrix) it rotates clockwise. Background ATP synthase is a membrane bound enzyme with two large subunits;...


12

Can enzymes catalyze thermodynamically unfavourable reactions? Enzymes don't change the equilibrium of a reaction, but the fact that an equilibrium exists means that the reaction proceeds in both the forward and reverse directions. Before equilibrium is attained, ΔG for the reaction is not 0. Thus, by definition, one direction is thermodynamically ...


11

No, not all enzymes (or other proteins for that matter) can be obtained in functional form by recombinant expression with today's methods. As you suspect, problems arise when complex post-translational modifications are necessary to obtain the correct function. Direct modifications to peptide is one potential problem. Some of these can be resolved by ...


11

This terminology is at least as old as September 1944 when Enzymatic Synthesis of Acetyl Phosphate Journal of Biological Chemistry 155, 55-70 was published by Lipmann, which says: Inorganic phosphate, referred to as Pi, was estimated colorimetrically See also the definition of "inorganic phosphate" and "orthophosphate" from this 1943 ...


11

What about the ATP synthase? https://en.wikipedia.org/wiki/ATP_synthase it uses proton flow to generate ATP but it can also burn ATP to generate proton flow. Like other enzymes, the activity of F1FO ATP synthase is reversible. Large-enough quantities of ATP cause it to create a transmembrane proton gradient, this is used by fermenting bacteria that do ...


9

You can certainly get massive differences between EC50 and affinity. This is especially true for cell-based assays and membrane protein systems. The reason why is because the appropriate time scales to achieve binding equilibrium (hrs for nM affinity, days for picomolar, feptomolar affinity according to back of the envelope calculations) may be and likely ...


9

This seems one form of a common question about evolution. That being: "Trait X would seem to be an advantage, so why can't organisms adapt to X? That is, why don't we have all traits that are advantageous at all? Why not just digest cellulose, but maybe why not lignin as well? Why shouldn't we photosynthesize our own food? What about sonar as well ...


9

The answer given by Sadegh gives a general correct broad view. But one part of the puzzle is missing, which is molecular recognition. Molecules bind to each other via physical/chemical interaction like forming hydrogen bonds, electrostatic interactions and other mechanisms. The sum of all interaction defines the strength of the binding. If molecules have ...


8

How are diabetes and obesity connected in light of low lipase activity? Short answer: There's more than one type of diabetes. (And to complicate things, there's also more than one type of lipase. It's unclear from the question which type were mentioned in what you read.) Diabetes mellitus is usually divided into Type 1 (insulin-deficient) and Type 2 (...


8

Yes, something can be both a hormone and an enzyme. There are a group of hormones known as peptide hormones. These are proteins (such as enzymes) that act as hormones indirectly (and maybe directly too?). A hormone is a chemical secreted by a cell that has some effect on another cell elsewhere in the body. In this case, the chemical just happens to be an ...


8

As @Chris commented, when assayed in vitro with a single substrate (which may not even be the physiological one) most enzymes can catalyse a reaction in either direction. And enzymes such as pyruvate kinase were discovered before the pathways they are constituents of were worked out in full. Furthermore, the ways of naming enzymes only became more ...


7

This refers to the turnover number (a.k.a kcat or k2) of an enzyme and is usually calculated using Michaelis-Menten kinetics. Jump to the summary at the end if you want a simple answer. If you want a more thorough answer, consider the following chemical equation: [E] + [S] ⇌ [ES] → [E] + [P] This says that a certain concentration of enzyme mixed with a ...


7

In what follows I am going to attempt to answer your question using a specific example of (competitive) reversible activation, and I hope to show what a misleading parameter EC50 can be. (Rate law derivation is an area of interest, hence the long-winded answer). It can of course give information, but IMO it needs to be used with extreme care. I am ...


7

Examples of enzymes working in reverse? Except three enzymes of Glycolysis (Hexokinase, PFK-I and Pyruvate kinase) all catalyse reversible reactions. As these enzymes catalyse the backward reactions too they are part of Gluconeogenesis pathway. (A comparison between the two pathways)


7

Until the late 1980's all enzymes* were believed to be proteins, and were often defined as protein catalysts, often in textbooks which are often not perfect representations of science. At that point every macromolecular biological catalyst known was a protein so they thought all macromolecular catalysts were proteins. But the discovery of ribozymes (RNA ...


7

It's both simple and complex. The simple answer is Brownian motion. All the particles in the cell do have mobility which is related to their mass. A small particle like a soluble enzyme undergoes random walks through the cytoplasm or nucleoplasm. Thus by having a grand number of a certain molecule you can be sure that at some point it interacts with the ...


6

Why don't we have any enzyme to digest cellulose? Why should we? We don't use it as a source of energy so why bother? Even animals that do "digest" cellulose, like ruminants, only do so because of symbiotic bacteria; it would be a poor system indeed in which every organism utilized the same resource. We occupy enough of the food chain as it is.


6

Have you heard of something known as "Occam's Razor" ? It says when you have multiple possible explanations/hypotheses then select the one which is simplest (i.e least number of assumptions) Same with mathematical models. Chemical kinetics models usually assume first order unless there is some evidence against it. Similarly, for enzyme kinetics, as long ...


6

Having done an inordinate number of rather mind-numbing A.S. practicals involving milk and enzymes the year before last, in my experience lactase always began breaking down the lactose immediately and converting a boiling tube worth of milk in less than 50 minutes at below room temperature. To further allay your concerns, this website suggests that most ...


6

The mechanism of aconitase classifies it as a lyase, even if (under most physiological conditions), the relative concentrations of substrates results in it catalysing the conversion of citrate to isocitrate. In short, it is not an isomerase because the substrate is released after each step. As the mechanism of aconitase shows, it catalyses the conversion of ...


6

Competitive inhibitor competes for the active site. Therefore it will interfere with the binding of the substrate thereby increasing the apparent KM. A strictly non-competitive inhibitor does not compete for the active site. It however inhibits the catalysis by reducing the available molecules of active enzyme, E0 (if it is a perfect inhibitor), thereby ...


6

You mention nucleases and proteases, but if you turn these processes around and think about the actual nucleic acid or protein synthesis reactions an interesting point emerges: These synthetic processes involve the production of pyrophosphate — not orthophosphate — from ATP (etc.). (In the case of nucleic acid synthesis this should be obvious; in the ...


6

Is there a difference in the gene encoding for the protease? This paper by Wu et al. annotates the SARS-CoV-2 genome and compares its divergence from other coronaviruses, which may help answer your second question. This annotation includes 16 genes for non-structural protein ("nsp"). Supplemental materials for this paper indicate that all but two of these ...


5

Early histochemical work indicated that the internal surface of the lysosomal membrane has a glycocalyx - a layer of polysaccharide, presumed to have a protective role. Neiss, W. F. (1984) A coat of glycoconjugates on the inner surface of the lysosomal membrane in the rat kidney. Histochemistry 80, 603–608 Subsequently it was found that major membrane ...


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