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6

The reason for this is the oxidation of phenol residues in the banana (for example in the yellow color) which get oxidized by the enzyme Polyphenol oxidase (PPO) to melanins. The scheme (the image is from this website on food browning) looks like this (you can of course also use more complicated substrates): For further information, see these references: ...


5

The term "irreversible" means that the reverse reaction occurs so rarely that it is considered negligible. This means that you do not have to consider equilibrium, as you have to for reversible reactions. Instead, you can assume that all of the reactants will eventually become product. As you stated, this is true for reactions that have a very negative ...


5

See here. Histones are basic proteins (cationic, high pI) because they are required to interact with polyanionic DNA at physiological pH. Heparin and dextran are polyanions which form insoluble salts with the cationic histones.(Dextran is a polymer of glucose. In dextran sulphate it is derivatised with sulphonate groups creating a polyanionic material.) ...


4

Membranes are built from a specific class of lipids, namely phospholipids, whose key property is that they are amphiphilic and so can self-organise to form bilayers. Not all amphiphiles do this, some prefer to adopt a micellar organisation. A bilayer composed of phospholipids produces the ideal combination of a hydrophobic barrier with a hydrophilic surface. ...


4

Some thoughts on this. First of all, the positive-inside rule, proposed by Gunnar von Heijne, is an empirical rule based upon observations, not one derived from theoretical considerations, so any explanation is simply an attempt at a rationalisation. Having said that, here are three of those rationalisations: the membrane potential is usually negative ...


4

The lipopolysaccharide layer of the Gram-negative bacterial cell wall is stabilised by divalent cations. Most recipes for disrupting E. coli cells include Tris-EDTA for this reason. I seem to just know this, so no reference at the moment. All nucleases require Mg2+, which is why there is EDTA in the stop buffer added to restriction digests. Carry-over of ...


3

A lot of enzymes need metal ion in their active center (it is actually the metal ion which is taking part in the catalyzed reaction). These are manganese, magnesium, copper and so on. For DNAses the metal in the active center is magnesium and EDTA simply chelates this ions, making them unavailable for the enzyme and thus hinders the enzyme from working. ...


3

"Let's say and acidic solution triple what you would find for a "corn", with and alcohol content of 14% by volume and salt 3.6% by volume of the two liquids?" cell death and tissue death, person death. All 3 of these conditions you cite are fatal to cells under the skin. A blood Alcohol level of 0.5% w/v is fatal. In the digestive tract its okay and on ...


2

Creatine is an important energy source for body, especially for the muscles, so it is no wonder you can finde it there. I don't think it has a special role besides that. See the Wikipedia article for more information. For bilirubin this is different, this substance is a breakdown product of the heme metabolism (basically hemoglobine). It is not water ...


2

What you are asking about is the precipitation of DNA (or any other nucleic acid) by isopropanol (or ethanol, which is more common). To do so, you add salt (usually slightly acidic sodium acetate) which makes sure that the phosphate backbone of the DNA is saturated with sodium ions to make it less soluble. Then you add the organic solvent, which precipitates ...


2

The free energy change that you quote for the phosphoglycerate kinase (PGK) forward reaction is, of course, the standard free energy change (ΔG0') for the overall reaction. The standard free energy change is defined for all reactants at a concentration of 1M. Note that this value includes the formation of ATP - the free energy of hydrolysis of 1,3-BPG ...


1

You have to look at the complete reaction including the cofactors. In general, you can drive a chemical reaction into directions which are not favorable by: removing products from the environment (if they are gaseous for example or react further) having a huge excess of substrates (and thus making the back reaction less likely to happen) and by coupling ...


1

The main regulatory input into erythrocyte production is hypoxia. The response to elevated CO2 levels in the blood (hypercapnia) is mainly to increase ventilation (i.e. more and/or deeper breaths) so that the excess can be "blown off". I think that some carbon dioxide could pass into the bloodstream from the stomach since gases tend to be quite good at ...


1

The problem with this is something called the structure-function relationship. The function of a protein or enzyme is completely dependent on its structure. For example, take a look at this representation of the active site of chymotrypsin: The side chains of D102, H57, and S195 all need to be in a perfect conformation in order for the enzyme to function ...


1

First thing to make clear is that net $6$ $H_2O$ go out of the reaction.($12$$H_2O$ $-$ $6$$H_2O$) Let me tell you my calculation, you should then be able to figure out what went wrong. For the Left hand Side, $6$ $H_2O$ are accounted here : $2$ $H_2O$ go in conversion of 2-Phosphoglycertae to phosphoenolpyruvate. $2$ $H_2O$ in TCA from conversion of ...


1

Lewis & Engelman (1983) Lipid bilayer thickness varies linearly with acyl chain length in fluid phosphatidylcholine vesicles. J. Mol. Biol. 166: 211 - 217. Table 1 and Figure 3 have the information that you need. For C14:0 the thickness of the hydrocarbon bilayer is given as 23 Å. Just in case this is homework, I'll leave you to convert that to ...


1

The process is described here. This is my summary, plus a few extra details: The primary gene product of the INS gene is preproinsulin. As the N-terminal signal sequence (pre-) emerges from the ribosome during polypeptide elongation the signal sequence binds to a signal recognition particle which arrests elongation until the nascent chain has engaged with ...


1

First of all lets have a look, what these guys want to accomplish: They want to use bacteria to make certain products. To do so, they want to exploit the bacterial metabolism at steps where no alternative pathways are available. One of these steps is the first step of glycolysis, when Glucose gets phosphorylated to glucose-6-phosphate (G6P). In bacteria the ...


1

In the beta-Lactamase test, an inhibitor of beta-Lactamase is added to a sample of the culture medium. The inhibitor binds to the enzyme and changes its color, which is in direct correlation to the concentration of the beta-Lactamase. More b-lactamase means more inhibitor binding and this results in more color development leading to a higher absorption. So ...



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