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17

One of the main points of contention in the study of virus evolution is whether or not they appear before the last universal cellular ancestor (LUCA) or afterwards (commonly accepted: genes that "escaped" from host organisms aka the escape hypothesis or vagrancy hypothesis). Basically though, the LUCA is the most recent ancestor that all organisms living on ...


11

Th reason for this is that for the third base of the tRNA non-Watson-Crick pairing is allowed. This phenomenon is called "Wobble base pairing". See the figure (from here) for illustration (from here): If you have a look at the codon table for amino acids, than the variation in the code for one amino acid mostly happens on the third position (from here): ...


7

Great question. There are several hypotheses, but in reality no one really "knows" because this is incredibly difficult to prove. We may never know for certain. Anyway, on to the three main hypotheses, I got this from http://en.wikipedia.org/wiki/Viral_evolution, I think you'll find it to be helpful. "There are three classical hypotheses on the origins of ...


6

The human skin is indeed made off a number of different layers, the three most important are epidermis, dermis and hypodermis (also called subcutaneous fat), see the figure (from here) for details: All three layers can be subcategorized further, I'll only give a few details here. More can be found for example in the Wikipedia article on skin. Epidermis: ...


5

Multiple RNA Polymerase transcription complexes engaged on the lacZ gene at the same time, staggered along the gene.


5

Okay, so for introduction the 4 levels of protein structure (each level influences the levels after it): primary (1st): the order of amino acids. secondary (2nd): alpha-helicies and beta-sheets tertiary (3rd): complex 3d structure quaternary (4th) : 3rd+ non-protein elements (ions, co-factors etc) and / or multple subunits interact. Not every protein has ...


4

Short answer. It was discovered pretty early (late 1800's). It is easy to get (you probably know where it comes from), purify, grow and is not virulent. E.coli spreads very rapidly (30 minutes division rate). Why this one in particular and not another similar bacteria? Well you have to choose something at some stage and usually the more an organism is used ...


4

Well there is the common Bloodworm (Glycera dibranchiata)which people use for fishing bait. The animals are unique in that they contain a lot of copper without being poisoned. Their jaws are unusually strong since they too contain the metal in the form of a copper-based chloride biomineral, known as atacamite. ...


4

According to this study, model data shows a maximum pressure of 110 kPa, that's 16 psi and only 1.086 atm: The three-phase process involved in the beetles explosive secretory discharge (ESD) process. The inlet size is shown as a proportion of the inlet radius. During the first phase of refill and heating (blue), only the inlet valve is open. ...


4

Either the gene is present in multiple copies (especially possible if it is in a plasmid) or multiple RNA polymerases are transcribing it, each beginning from the start site one after the other with some amount of time delay, much like multiple ribosomes translate the same mRNA to increase rate of protein production.


3

Short answer (A) is a possible answer and is indeed cause for fatigue, as pyruvate is needed for the Krebs cycle to run. The krebs cycle is an essential step in the generation of ATP in aerobic organisms. (B) is incorrect because NADH is never transported into the mitochondria in any organism (it is a nonsense answer). Background NADH is not transported ...


3

Not in human but you can use this technique with genetically modified model organisms as described here. The procedure is quite simple, you express the luciferase enzyme under the control of a specific promoter (specific for your cell type, like cancer) and provide luciferin via intravascular or intraperitoneal injection. The targeted cell type (for example ...


3

Watson-Crick base pairing can be violated by wobble base pairing. The 5' of the anticodon has more freedom in binding, that is why, for many amino acids, the last part of the codon has more possible characters.


3

There are two antipodes: The molecular (or makromolecular) biology, which has the concept of large macromolecules which fulfill one task. This can for example be an enzyme which breaks down its subtrate. The properties and the structure of all molecules of the enzyme are the same and the factor determining the function of the enzyme. The coloidal biology ...


3

The lac repressor act as a tetramere molecule and requires all 4 of the subunit to be able to bind DNA to act on the operon and repress β-galactosidase expression. The "all 4" is the key here, if any of the 4 subunits is unable to bind DNA then the whole complex cannot attach to the operon. The lacId mutation produces a repressor subunit that cannot attach ...


3

According to Kroeker WD, Kowalski W, Laskowski M. 1976. Mung Bean Nuclease I. Terminally Directed Hydrolysis of Native DNA. Biochemistry 15(20):4463-4467 It was concluded that the products of the terminally directed hydrolysis of native DNA possess 5’-phosphoryl groups because: (1) greater than 99% of acid-soluble activity applied to the column was ...


3

The short answer is that the Edman degradation is a multi-step process. The Wikipedia page has a decent picture of the mechanism. In practice, the peptide is reacted with phenylisothiocyanate (PTH) under mildly basic conditions to give a thiourea, which is stable. The excess PTH is separated from the thiourea intermediate. The thiourea is then treated with ...


2

Allergies are often caused by the immune system reacting to a part of a specific protein, therefore it is in fact a specific protein in the food that is causing the allergic reaction to occur. Milk allergies are caused by casein and whey (Source: Mayo Clinic) Oat allergies can be caused by avenin (Source: EJCI) Soy and egg allergies are caused by their ...


2

Concerning the difference between dominant vs. recessive mutations, in general, recessive, or loss-of-function mutations, are much more frequent than dominant, or gain-of-function, mutations, because there are many different ways to "break" or inactivate a protein. For example, not every amino acid site has the potential to mutate to a residue with dominant ...


1

The change in gel migration distance is due to the conformational changes due to the binding of the ion, and have nothing (detectable) to do with the ionic radius of the ion. The left image shows calmodulin with no ligand bound, and the right image shows it with calcium and peptide bound to it. As you can clearly see, the unbound calmodulin is ...


1

The two main chemical processes in the human body that generate carbon dioxide (CO2) are: Basal metabolic process of CO2 (CO2m) produced by the combustion of sugar in organs and tissues of the body. Bacterial decay processes occurring as a result of activity of the microbial fauna in the colon. This forms CO2 (CO2c), H2, CH4 and higher hydrocarbons, NH3, ...


1

I would suggest following: take any one-dimensional process that is described by gaussian function. If you integrate such process along variable, you will get a sigmoidal curve. For details see normal and cumulative distribution. Now, the question is: how many biological processes are described/modeled by Gaussian distribution and dependencies? A lot! ...


1

Rubisco is an enzyme that is involved in the biochemical process of carbon fixation in photosynthesis, but also has an economically important error (photorespiration) which incorporates the wrong molecule (oxygen) into RuBP, therefore wasting the energy captured by the plant and producing toxic downstream products. Rubisco's error rate in carbon fixation ...


1

First it is important to define what actually an error is. What you call misproduct is actually a right product for a different substrate. The enzyme has a low specificity; but you won't say hexokinase is error prone because it has wide substrate specificity. The question is — is specificity critical? Coming to the example of DNA polymerase, you should note ...



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