17

Your reasoning is sound and correct. The answer key is wrong. An unclotted blood sample needs something to prevent clotting. Extracellular calcium is required for both the coagulation cascade and platelet activation. It even has its own name in this context, Factor IV. This why EDTA, a calcium chelator, is used in some blood collection tubes to delay ...


15

In both humans and animals, the body fat stores appear as triglycerides, which can be composed of different fatty acids, but they all have about 9 kilocalories per gram (USDA). There can be different amounts of fat in different fat cells, so there can be slightly different amounts of fat in 100 grams of different types of fat tissue. Calories in 100 g of ...


8

The short answer is no, there currently aren't any visible macroscopic asymmetries in some organisms traceable to DNA's handedness. The long answer is still no, but I want to clarify that this "no" is more of a "not really". This is because there can be potentially drastic consequences when left-handed DNA is present in a cell in addition to the ...


6

Whenever you see a percentage, you should think "Percentage of what?". Not doing this is usually at the root of the trouble people get into with percentages. The water and fat percentages mentioned in the question are certainly not percentages of the same thing. The sources of the figures should make clear what the percentage is of, but non-scientific ...


6

Arrowhead interpretation As I said in my comment and to add to @AlwaysConfused's answer, the arrowhead is a promotion, and flathead is an inhibition. Typically, any other notation such as dotted lines would be explained in the figure legend of the illustration. The below definitions are generally accepted and widely used. But don't take these ...


6

As far as I am aware, there is no known requirement for Cd in mammalian systems, but it is extremely toxic (Waalkes & Goering). It would seem that cadmium is required to get crystals of RBP, and its presence is an artifact of the crystallization process (ref): Pig holoRBP crystals were obtained at 277 K by the sitting-drop vapor- diffusion method, ...


5

The fundamental 'problem' with acetyl-CoA is that it cannot be converted to glucose via the tricarboxylic acid (TCA) cycle: a two-carbon compound (acetyl-CoA) enters the TCA cycle, but two carbons are lost as CO$_2$ during each round of the cycle (in the two decarboxylation steps, ie in the reactions catalyzed by isocitrate dehydrogenase and by the alpha-...


5

There are a number of ways to address this, and the other answers are certainly correct. Another strategy, especially if you already have the sample in PBS, is just to dilute it in the low salt ion exchange buffer. This works because you don’t need to completely remove the phosphate or salt, just get it low enough so that it doesn’t interfere with binding to ...


5

Assuming that your protein can handle being in the new buffer, you have multiple options. Dialysis will work although you might want to consider using a centrifuge spin filter with a suitable MW cutoff to gradually switch buffer and concentrate the sample. Be aware that some of your protein will stick to the filter, giving a loss of sample. Alternatively ...


5

There is the classic potato starch/iodine/amylase experiment: http://dailynexus.com/2016-08-31/chemistry-101-the-classic-potato-iodine-blueblack-experiment-finally-has-an-explanation/ From memory, when you add iodine to a small piece of potato, the potato starch reacts to produce a dark blue/black colour. The amylase enzyme in human saliva can break down ...


5

This is a question I also remember wondering about when I was younger in school. Now as a professional it's way too obvious to even explain. But i think it's an important and common question, which warrants an example or two from common daily lab practice. Preface You have to understand that DNA is a molecule. It's really tiny. It's not trivial to work ...


5

The blunt head arrow means inhibition i.e. suppression. i. e. A -----------| B means A suppressing B. the factor at the arrowhead is being supressed. The factor at arrowtail is an suppresor for the other factor. The pointed head arrow means activation or increasing activity. A -------------> B means A is increasing activity of B. Factor at ...


5

Many invertebrates possess myelin. It is a misconception that invertebrates lack myelin. The world speed record for a traveling bioelectric signal is held by the myelinated axons in the abdomen of the Penaeus shrimp! Please take a look at this website or this review to find a highly recommended comprehensive website about invertebrate myelin from about a ...


5

The common scientific belief around 1900 was that the only dietary components needed to support life were protein, fats, carbohydrates, and salts.[1] In 1912 Hopkins reported on experiments showing that "accessory factors" seemed to be needed.[1] In 1916, some of the factors began to be characterized in the paper "The Relation of the Unidentified Dietary ...


5

I have also been frustrated by use of percentages in protocols when making dilutions of stock bleach. It's helpful to look at the product labels, as they often have dilution factors for different uses as well as concentrations in parts per million. I have a bottle of Clorox brand concentrated bleach sitting next to me, and the label says this solution is ...


5

The World Health Organization states[*]: 1:100 dilution of 5% sodium hypochlorite is the usual recommendation. Use 1 part bleach to 99 parts cold tap water (1:100 dilution) for disinfection of surfaces. They say most household bleach solutions contain 5% sodium hypochlorite (50 000 ppm available chlorine), which does seem to be the typical concentration ...


5

For a direct reference on the contribution of these two forces see here. If it helps, think of the double helix of dsDNA as a more rigid structure than ssDNA, which flops around and generally is capable of a lot of steric freedom that dsDNA doesn't have. This freedom means that the bases of the ssDNA backbone may not always be in the correct orientation for ...


4

It's worth considering how many high energy electrons are actually released compared to the number of molecules in the tube. For instance, I routinely work with $^{32}P$-labeled DNA, and measure the specific activity of samples by scintillation counting. For me, a very hot stock sample of labeled DNA (~1000x more concentrated than I would use in an ...


4

You would not expect the same enzyme from different tissues to have different Km values if the enzymes are truly identical. In addition, you would not expect the Km value to change during purification: the Michaelis constant for the purified enzyme should be the same as that determined with a crude sample. If this is not true, it might mean that the ...


4

Summary Glycolysis and the tricarboxylic acid cycle (TCA cycle) are distinct processes which are not necessarily linked sequentially. It is therefore not surprising that their modes of regulation are not identical and, in fact, involve far more complex regulation than mentioned in the question. The use of AMP rather than ADP as sensor of energy deficit ...


4

It seems canadianer's intuition is correct -- Base stacking still occurs in ssDNA, so I suspect that is why you see a temperature dependence -- based on this paper: Conformational Changes in Single-Strand DNA as a Function of Temperature by SANS Motivation -- UV absorption-based measurement of DNA melting temperature is reliant on the assumption that ...


4

The ability of bacteria to take up intact environmental DNA is called natural competence. One problem with trying to take advantage of this in a therapy is that it is not very efficient. Importantly, natural competence is regulated and tends to be activated when bacteria are already stressed. This is also likely part of the answer as to why a bacterium ...


4

According to PeaceHealth: The vitamin B-complex refers to all of the known essential water-soluble vitamins except for vitamin C. Vitamin B was once thought to be a single nutrient. Researchers later discovered these extracts contained several vitamins. Each member of the B-complex has a unique structure and performs unique functions in ...


4

If you're interested in the biological or health effects of various chemicals, try to look up the Safety Data Sheet, or "SDS" or "MSDS", for that chemical compound. Going to your favorite search engine and plugging in your chemical of interest to the search term "SDS" or "MSDS" will almost always get you to some kind of answer — either what you're looking ...


4

Short Answer I do not believe that CO2 will become less available to phytoplankton on a global scale in the foreseeable future. Instead, I believe that rates of increasing concentrations of CO2 (and resulting chemical products) will not remain sustained at their current levels. There are two global change phenomenon occurring that are relevant : ...


3

"Cortex" is a more general anatomical term for the outermost layer of a structure. It applies to both the cerebral and cerebellar cortex gray matter, as these are gray matter structures on the outsides of their respective parts of the brain. Nucleus is also a more general term; in the context of neuroanatomy, it refers to a cluster of cell bodies. Typically ...


3

Two accepted methods of 'desalting' a protein and/or changing the buffer are dialysis and gel-filtration. Dialysis is time-consuming, and gel-filtration usually requires a concentrated sample (It is difficult to gel-filter a 250 ml sample unless a very large column is available, for example, but dialysis of such a volume is relatively easy). You do not say ...


3

Your guess is correct: glucose is not the sole source of energy in the cell! While cellular respiration is the classic mechanism for energy production (in the form of ATP) in the cell, there's another process that's equally important and a little less well-known: beta oxidation. Beta oxidation is how fats and other lipids in the cell can be broken down to ...


3

It sounds like you are asking about what are commonly referred to as "multifunctional enzymes". For a reasonably recent article covering this subject — see: Cheng, X. Y., Huang, W. J., Hu, S. C., Zhang, H. L., Wang, H., Zhang, J. X., ... & Ji, Z. L. (2012). A global characterization and identification of multifunctional enzymes. PloS one, 7(6), ...


3

Does the ingestion of alcohol, when taking (racemic) methylphenidate can actually make it more potent? It is the 2011 study you've mentioned that answers most of the question. In the study, ethanol co-ingestion with racemic MPH elevated maximal plasma levels of d-MPH by up to 40%. The participants reported greater stimulant effect after alcohol + MPH than ...


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