Questions tagged [proteins]

For questions about proteins. Proteins are biopolymers consisting primarily of polycondensated amino acids.

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Can a protein complex be a machine? [closed]

Discussing an article with friends we began discussing whether a protein complex that punches holes in cells (membrane attack complex) would be considered a machine. Now, my friends are biochemistry ...
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Purifying cysteine containing peptides

I would like to purify my peptide having cysteine residue by using HPLC. It is known that thiol containing peptides undergo oxidation and form disulfide linkages. In order to prevent it I used proper ...
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Correct Generalization for Adair Equation?

I know how to derive the Adair Equation for n binding sites the long way, writing n+1 mini equations and linking them to relate all sub $K_b$ values to $K_{b-intrinsic}$. Tried to find a general ...
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What is the precise definition of Ramachandran angles?

The Wikipedia article Ramachandran plot is very schematic and doesn't even say when these angles are considered to be zero. It seems to assume that the peptide chain has no end, and always shows the ...
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Chemical Equilibria - Fraction Bound equation based on Kd, [R], [L], [RL], is actually an average?

Let's say 150 stem cells express exactly 150 copies of the same mebrane antigen X. While all differentiated cells express exactly 15 copies of X. To the cell mixture you add a large amount of 0.2 μM ...
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Which Flocculant/Coagulant is ideal for harvesting Algae?

While dealing with Algae fit for human consumption (as protein supplements), which is the most suitable coagulant/Flocculant available? Factors to consider: 1) Cost Effectiveness (for instance poly ...
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64 views

Why is casein hydrophobic?

According to this source hydrophobic behaviour occurs when a molecule does not have a charge or is neutral and therefore cannot be attracted to the negative nor positive parts of water. Casein has an ...
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47 views

Can glucose and insulin exist in the same container without reacting?

Someone asked if glucose and insulin could be mixed in the same container and used as an injection to provide a quick energy boost. I'm not interested about the medical part of this question, but just ...
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Developing a lab to identify the concentration of casein in organic milk

I am currently attempting to create a feasible lab design that will enable me to identify the concentration of casein protein in organic milk without having to use spectroscopy. Thus far I have ...
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132 views

Can =NH2+ in Arginine's side chain form hydrogen bonding at physiological pH?

I know that at physiological pH, Arginine will have its $\ce{=NH}$ protonated to $\ce{=NH2+}$. I was wondering if this $\ce{=NH2+}$ can still form a hydrogen bond by being a donor? And does the ...
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Molecular dynamics after modeling a protein loop. Necessary?

Firstly, I am postign this question to both chemistry and physics stacks exchange as I am not sure to which it belongs and to use the benefits from both sites. I have modeled missing loops in a PDB ...
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32 views

cluster of milk [closed]

I have a problem with milk when we are making yogurt in factory. When the milk pass through the machine it clogs the filter of the machine because the cluster that formed on the filter. My question is ...
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403 views

Is chitin actually protein?

Recently insects are featured as a protein rich source for human nutrition. That humans can really digest chitin through chitinase enzym has been only recently confirmed. But, does the chitin shell ...
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53 views

Why Greek yogurt has higher protein concentration?

During fermentation, no nitrogen is added and the number of amino acid molecules cannot increase. Why does it have a higher protein concentration than milk?
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247 views

Formating chemical equations for proteins binding in hugely complex configurations

In a previous question I asked about a simple case, I'm now trying to write equations for proteins that bind multivalently. In the simplest case proteins $A_1$ and $A_2$ can bind to up to two $L$ ...
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Why does the isoelectric range decrease as an Alanine chain grows longer?

The pK1 and 2 values for alanine are 2.3 and 9.7. In the dipeptide Ala-Ala, they are 3.1 and 8.3 and in tri-peptide Ala-Ala-Ala, they are 3.3 and 8.0. Why does this trend in pKa values exist? Why does ...
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283 views

How to dock aggregated structures comprised of “elementary” protein units like LEGO pieces?

There are proteins with intrinsic symmetries. For example: I was wondering how to use transformations such as: rotations, translation, replications to construct possible structures using 2 types of ...
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71 views

How to unify all the subunits in a PDB file?

A PDB may contain a TER token. For example, hemoglobin has 4 subunits separated by a TER identifier. If we take hemoglobin's ...
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190 views

How to write an entire trajectory into a single PDB file?

I have a trajectory (few frames) that I want to stack together and build a single PDB. I thought either to use VMD or MDAnalysis library. With VMD if I do ...
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178 views

How to visualize a crystal from a unit cell PDB and how to draw the unit cell's axes? [closed]

I am looking at the following PDB experimental data: Length (Å) Angle (°) a = 155.72 α = 90.00 b = 155.72 β = 90.00 c = 106.16 γ = 120.00 I find it hard to ...
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90 views

Biomolecular energy functions and entropy

From what I've been reading, it seems that entropy (rather than enthalpy) is the biggest driver of protein folding (especially the burying of hydrophobic residues). However, popular energy functions ...
3
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1answer
3k views

What happens to the t-butyl cation in the TFA deprotection of a t-butyl ester?

I am a first-year chemistry graduate student and I am currently learning how to synthesize proteins. I have reached a stage in the process where I need to deprotect a carboxylic acid moiety protected ...
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76 views

Calcium concentration in NMDARs e Nitric Oxide Synthase

My question is related to calcium $\ce{Ca^{2+}}$ concentration in NMDA receptors and nitric oxide synthase. I've found a very simple model that describes how the time change of calcium can be related ...
2
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1answer
390 views

What is the difference in the effect of DTT (Dithiotreitol) and SDS (sodium dodecyl sulfate) for PAGE?

In class, we have studied that when running a polyacrylamide gel with our protein sample to separate the proteins by molecular size, we can use several techniques, among which we have denaturing PAGE ...
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72 views

How to read these graphs and what are they called?

How does one interpret/read the following graph (found here) as well as on wikipedia or What are these called?
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56 views

Formating chemical equations for proteins binding in multiple configurations

I am working on problems involving protein-protein binding, particularly ones in which two proteins may bind in two or more configurations, and where some of the resultant structures may also bind ...
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316 views

Mono-oxidized and dioxidized tryptophan

I'm translating a Russian text in which there is the following diagram of tryptophan degradation: Further on in the text, hydroxytryptophan is called "the mono-oxidized form" (моноокисленная ...
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502 views

Why aren't chaperones considered to be catalysts?

I'm reading about protein folding on Wikipedia and I stumbled on a bit about a class of proteins called chaperones that aid in the folding of proteins by: ...reducing possible unwanted aggregations ...
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1k views

What is the nature of the Fe–O2 binding in oxymyoglobin and oxyhemoglobin?

Deoxymyoglobin ($\ce{Mb}$) is known to have iron in the +2 oxidation state; I believe this was deduced from its magnetic moment, which corresponds to four unpaired electrons in high-spin $\mathrm{d^6}$...
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1answer
636 views

Is protein folding thermodynamically favourable? If yes.. why? [duplicate]

The second law of thermodynamics dictates that the sum of entropy of the universe is always increasing. Is the process of protein folding a spontaneous process which is increasing the entropy? Is this ...
4
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1answer
189 views

How to measure a distance along the surface of a protein in a PDB

I would like to measure the distance between two active sites in a protein complex (pdb), but I do not find a straightforward way to do it. To be more precise I need the distance along the surface ...
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1answer
606 views

Using baking soda paste (alkaline) to “neutralize” honeybee venom (acidic). Is this scientifically sound?

I recall reading (courtesy: my 9th grade Chemistry text-book, chapter Acids, Bases and Salts), something along the lines of: Bee venom is acidic. This is why the area of skin (stung by a bee) is ...
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2answers
147 views

Why is the E2 protein important for protein degradation?

In the ubiquitination process, the E2 protein transfers ubiquitin from E1 to E3. Why can't E1 work with E3 directly to tag some protein with ubiquitin? Going further, why can't one of the E(1-3) ...
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128 views

Positive charge on a zwitter ion at pH=7?

I faced this question. But I am having some problems understanding the solution to this: How can the negative charge on the peptide vanish on $\pu{pH = 7}$? Suppose, we have some $\ce{H+}$ donor on ...
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How to make a sephadex slurry

I want to purify crude alpha-amylase with column chromatography. I am using a spehadex 75, But for some reason I can't find any information on how to make the slurry. I can quickly find tons of ...
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83 views

Collagen: similarity of human to fish and meat amino acids [closed]

I am looking for a collagen supplement for my partner who has joint pain, bone pain, fatigue associated with ligaments, flaccid skin problems, and is just over 40. As she does not eat fish or meat, ...
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362 views

proteolysis - how to determine the partial or completeness of the cleavage reaction?

Though the question is about biomolecules, we agree the underlying functions, formation, degradation etc come down to chemistry, (then physics and maths). I am posting it here to receive an ...
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Do proteins have a smell?

Proteins are heavy and not so volatile. Does it mean that pure proteins do not have a smell?
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Is it known for sure that bases feel slippery because of the production of soap/surfactant?

Discussion around the question Why does bleach feel slippery? has started me thinking about the saponification explanation for the slippery feeling of basic solutions. According to Wikipedia: ...
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Antiprion effectiveness of phenol

I am investigating ways to reliably decontaminate instrumentation that has come into contact with mammalian prions. Chaotropic salts and extreme pH are good at inactivating prions by disaggregating ...
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Terminology: what's the difference between “monomer” and “protomer”?

Using definitions from Wikipedia, a protomer is defined as "the structural unit of an oligomeric protein. It is the smallest unit composed of at least two different protein chains that form a larger ...
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652 views

Using electronegativity and atomic size to compare acidity of cysteine with serine

In proteins, the alcohol group of serine is generally more difficult to deprotonate than the thiol group of cysteine. Serine and cysteine respectively: In the literature, the explanation given is ...
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1answer
4k views

Why is % yield in a purification table measured using activity instead of total protein?

I'm trying to understand why % yield is measured with activity instead of total protein in mg. According to my biochemistry notes, activity is "1.0 units of enzyme activity = 1.0 μmol of substrate ...
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Is there a pH at which all proteins are negatively charged? How can it be determined?

I know that depending on the amino-acid-composition of the peptide the distance to the isoelectric point determines the charge. Is there a universal point at which all proteins are definitely ...
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1answer
201 views

How can absolute binding free energies be calculated?

In the calculation of binding free energies, such as between a protein and a ligand, I learned that absolute values cannot be obtained from simulation (such as taught in this lecture, slide 2). Rather,...
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Why do the physical properties of an egg shell change when the egg shell is exposed to vinegar for a week?

When an egg is kept in vinegar for one week, its hard calcium carbonate shell changes into a soft rubbery membrane. As vinegar is weak acetic acid, how does vinegar change calcium carbonate into a ...
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305 views

The definition of peptide, peptide bond and protein

According to what I understand the difference between peptide and peptide bond is that peptide is two or more amino acids (up to 19 -inc.) which linked together, while the term "peptide bond" refers ...
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309 views

Which is more stable chemically: DNA or peptide

Assuming enzyme-free environment, and the DNA and peptide are lyophillized, and then stored in vials under the same conditions (temperature and humidity). On average, which would be more chemically ...
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What makes heat resistant proteins heat resistant?

We were doing the chapter Biomolecules in class the other day, and a doubt popped up once we reached the section on proteins. We were taught that the stuff that keeps proteins together are: Ionic ...
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What aspects of a macromolecule/protein do the various contributions to its entropy relate to?

I've come across a few different contributions to entropy in macromolecules such as proteins: configurational, conformational and vibrational. The problem is that I can't seem to find a consistent ...