23

The answer to this question lies in the pharmacokinetics of these two drugs: the acetyl groups cause Heroin to be 200 times more lipid soluble than Morphine1. Another example of a common drug would be Fentanyl, which is 580 times more lipid soluble than morphine, with a structure very similar to that of Morphine. Increased lipid solubility allows these drugs ...


9

It is important to remember that the purine scaffold is one of the most fundamental organic structures in all lifeforms. From an evolutionary standpoint, this means that there must have been a simple, effective way for this scaffold to be prepared in the pre-biotic earth. After all, the first organisms to contain purine scaffolds did not have "access&...


9

It almost certainly refers to the amino acid (residue) serine. The numbers (300, 333, 351) refer to the residue numbers. The COOH at the end signifies the C-terminus of the protein (subunit). The black P's next to it are phosphate groups; both protein kinase A and C ("PKA" and "PKC") are involved in control of protein activity precisely ...


8

all 10 steps in glycolysis require an enzyme We count it as 10 steps because there are 10 enzymes. There might be other steps that are fast (like a product acting as an acid or base) that we don't count because they don't need an enzyme. I’d have thought that evolution would have selected for “simpler” pathways. What is simple is that everything is ...


8

The identification of urolithins as products of human metabolism of ellagic acid was reported by Cerda et al. in the European Journal of Nutrition in 2004. The full reference is Cerda, B., Espin, J.C., Parra, S., Martinez, P. and Tomas-Barberan, F.A. (2004) The potent in vitro antioxidant ellagitannins from pomegranate juice are metabolised into bioavailable ...


7

A double bond between 2 carbon atoms means there is a $\pi$ bond with the side orbital overlaps in 1 plane, in parallel to the axial $\sigma$ bond. The consequence is, free rotation would need to break this $\pi$ bond, making the double bond just a single bond, what would require a strong torque and a lot of energy. By other words, particular rotation ...


7

Isoelectric point of an amino acid is the $\mathrm{pH}$ at which the molecule carries no net charge[1]. It can be calculated by the average of the relevant $\mathrm pK_\mathrm a$ values as you have mentioned. Your confusion seems to stem from choosing the relevant $\mathrm pK_\mathrm a$ values. For this we should refer to the titration curve of the amino ...


7

transported electrons in $\ce{NADH}$ have a higher energy than those in $\ce{FADH2}.$ This is jargon describing the redox potential of the electron carrier $\ce{NADH}/\ce{NAD+}$ vs the electron carrier $\ce{FADH2}/\ce{FAD}.$ So if you compare the two reduction half reactions $$ \begin{align} \ce{NAD+ + H+ + 2e- &-> NADH} &\quad E^{\circ '}_\...


6

Enzymes act as catalysts to increase the rate of reactions. In the absence of enzymes, most biological reactions would be incredibly slow, in some cases many many orders of magnitude slower than when catalyzed. Given the large number of biological reactions that require enzymes, it seems that there might be an advantage to reactions that are slow in the ...


5

The vicinal-glycols can be cleaved to corresponding aldehydes and/or ketones in high yield by the action of periodic acid ($\ce{HIO4}$) or lead tetraacetate ($\ce{Pb(OAc)4}$). This oxidative cleavage of a carbon-carbon single bond provides a two-step involving cyclic intermediate reaction mechanism with high-yield. A generally accepted equation for these ...


5

The authors mention three residues that they consider "second shell", 12, 77, and 102. They are shown in the figure below in green: Residues Trp50 and Glu101 are directly involved in ligand binding, shown as space-filling in yellow. As you can see, they are part of the central beta barrel. The residues in green are also part of the beta barrel, but the side ...


5

How does gefitinib impede the proliferation and apoptosis pathway? Does it in effect "ace out" the binding of EGF? If this is correct, how does it accomplish that? If not, I would appreciate a brief explanation as to what the successful mechanism is. No, EGF binds on the extracellular side (to the ectodomain), and gefitinib binds on the intracellular side (...


5

We speak of reactions that build complex molecules or break complex molecules at a specific position they must happen at constant 37°C all of which must be rather low energy or be very well controlled, like photosynthesis no fancy other reagents are available many would never happen at all without stringent control and/or the result could only be achieved ...


5

As @Zhe says, the name urolithin A seems to have derived from the word urolith which is basically kidney stone. Quoting from here1: The name urolithin was first given to two metabolites isolated from the renal calculus of sheep (Trifolium subterraneum has been reported as the cause of clover stone and might be a relevant source of ellagitannins) that were ...


5

OP's request: I am curious as to how it (urolithin) was discovered but cannot find the story. 3,8-Dihydroxybenzo[c]chromen-6-one or 3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one (CAS #: 1143-70-0), now known as urolithin-A is first discovered as a metabolite of ellagic acid from mice in 2003 (Ref.1) by the same research group who also discovered that in as a ...


5

Unlike that in organic chemistry, polar and non-polar compounds determination is done differently in biochemistry, probably because most biochemical reactions are done in aqueous medium. Therefore, the classification of them as polar and non-polar is somewhat different from source to source. In general, amino acids, which can make hydrogen bonding in aqueous ...


4

It is good practice to avoid vortex mixing any protein solutions, especially vigorously. Vigorous vortex mixing can produce foaming and proteins can denature (unfold and lose activity) when they are present at an air/liquid interface (as in a foam). This is because the hydrophobic regions of the protein will want to be in the air region and the hydrophilic ...


4

Interesting reverse question. I could figure out three questions: Why milk changes from a liquid to a gel when it turns into yoghurt? Why venous blood has lower pH than arterial blood? Why do we get tired on intense physical exertion? The answer to the first one would be because the metabolite of lactose fermentation in the lactobacilli cells is lactic ...


4

Aldehydes are easier to oxidize via radical mechanisms because of the ease with which one can break the C-H bond. The resulting radical is stabilized via delocalization of an oxygen lone pair. Such stabilization is absent in an alcohol. The alcohol shows a similar moiety, but I think the stabilization in the aldehyde is greater because of the shorter C-O ...


4

The illustration is likely taken from a later edition of Baum's Introduction to organic and biological chemistry. The first edition [1, p. 292] presents nearly identical illustration under a different number alongside with a note that the image was adapted from Bennett's Graphic Biochemistry [2]: Unfortunately, at the moment (2020-10-16) [1] is available on ...


4

@KarstenTheis made it clear by using E0 values of each half reaction. Here I describe what they actually mean by using the phrase "high energy electrons" in biochemistry texts. Consider Ethyne and Ethane. Therefore Ethynide has a high energy electron compared to Ethanide Another Example : H- , OH- , SH- . H- is stronger than OH- and OH- is ...


3

The statement is correct. The most common method for the esterification of amino acids is with anhydrous acid in alcohol. The most convenient way of doing this is with thionyl chloride example procedure or chlorotrimethylsilane example procedure as a source of anhydrous HCl. The original procedures with HCl gas or conc. sulfuric acid are slower and lower ...


3

Larger concentration of $\ce{CO2}$ directly affects only organisms with metabolism involving $\ce{CO2}$. Killing is indirect as humans and animals fall into unconsciousness and stop breathing. $\ce{CO2}$ is used, in mixture with $\ce{N2}$, as protective gas for packed food. It may not necessary kill bacteria, rather stops their growth. A virus does not ...


3

For the "shotgun" approach, saliva samples ($\pu{1 mL}$) were pre-fractionated with the use of Millipore ultracentrifuge filters (Millipore Corp., Billerica, MA, USA). Individual fractions were treated with $\pu{10 mM}$ dithreitol for $\pu{30 min}$, and then $\pu{50 mM}$ iodoacetamide for $\pu{30 min}$. This reaction sequence in Ref.1 has a clear intention: ...


3

Which biological and chemical processes underlie the effect of antiperspirants that make metal salts so effective? Aluminium-based complexes present in the antiperspirants react with the electrolytes in the sweat to form a gel plug in the duct of the sweat gland. The plugs prevent the gland from excreting liquid and are removed over time by the natural ...


3

Based on the discussion in comments, the OP is interested in the equilibrium concentration of the species ABC in this reaction scheme: $$\ce{A + B + C <=>[k_1][k_2] AB + C <=>[k_3][k_4] ABC}$$ Equilibrium is reached when the rates of the forward and backward reactions of each step are equal. Thus, we have have two equations describing the ...


3

Acetylcholinesterase is important enzyme and its mechanism of function is well known. In active site, it has two pockets: anionic pocket (to attract positively charged Quaternary nitrogen of choline) and esteric pocket. The esteric pocket consists of a serine side chain (a $\ce{-CH2-OH}$ function) as depicted in following cartoon, which pacilitate the ...


3

I dont know about HPLC column tolerance to various reducing agents, this would need to be checked. However, in biochemistry we routinely add reducing agents to avoid disulphide-bridge formation in the proteins. Overall there are three main reducing agents used, to avoid this problem. The choice of which one to use depends on your needs. They include: TCEP: ...


3

Lactic acid and lactate are part of an equilibrium reaction in aqueous solution. Even when the pH is far away from the pKa, there is still a small fraction of the minor species, and protonation/deprotonation reactions occur. If lactate were a bunny and the hydrogen ions in solutions were hats, lactic acid would just be the bunny after putting on the hat. If ...


3

There are multiple types of collagen variants, so the answer here is somewhat non-specific. Pepsin is an endo type of serine protease and it has low specificity. Proteolysis depends on residues upstream (P1’) and downstream (P1) of the recognition site. Hydrophobic residues at P1’ and P1 increase the likelihood of successful proteolysis. An aromatic residue ...


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