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7

The author is likely referring to the mechanosensory behavior of bone (reviewed in Huang and Ogawa, 2010; lots of Google Scholar citations). Bone loading produces very tiny mechanical deflections (strain) which are translated into biochemical signals that promote bone growth through the action of osteoblasts. Burger and Klein-Nuland (1999) review possible ...


6

The quick answer is that only certain cell types express the required steroid hormone receptors that are necessary to induce signaling and gene regulation when bound to their target steroid hormones, like estrogen, testosterone, cortisol, etc. If no receptor is present, the steroid doesn't effect any change. The second part of the answer involves the ...


5

This is mostly because of the nature of the amino acids. You need to have a Hydroxy-group in the sidechain of the amino acid which is the point where the phosphogroup is attached. Since this process needs to be reversible, this can only happen here. See the image below (from here) about the chemical structure: In eukaryotes not only these three are ...


5

Phosphorylation requires a nucleophile and hydroxyl oxygen acts like one. Serine, theronine and tyrosine get phosphorylated on the free $OH$ group in their side chains. Nitrogen, in some cases also can act as a nucleophile. In case of histidine, the imidazole nitrogen is phosphorylated during bacterial chemotaxis signaling. As far as I know eukaryotes do ...


5

The G-coupled protein receptors (GPCR) transmit signals from outside of the cell into the cell and activate downstream signalling pathways. These change for example the expression of certain genes. The whole process is a coorperation between the receptor, a G-protein, GTP as a co-factor and the ligand of the receptor (which starts the whole process). An ...


5

Brain's main energy source is glucose. It uses about 20% of total glucose [1]. Brain hypoglycemia causes depressive-like behaviors in mice through adrenergic pathways [2]. When it comes to humans, here is a study that claims low glucose leads to increased aggression in married couples (see this too): Self-control requires energy, part of which is ...


5

The answer is b, as the mutation constantly activates the RAS protein. RAS is part of the MAP-Kinase pathway, constant signaling of it permanently activates this pathway and leads to changes in gene expression. See the image below: If you are interested in more details, have a look at these papers: RAS oncogenes: weaving a tumorigenic web RAS mutations ...


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

Receptor tyrosine kinases are proteins which float around in the cellular membrane. Upon binding of their ligand, the dimerize (two units form a dimer). This releases the kinase domains and the proteins start phosphorylating themselves over cross (meaning part a phosphylates part b and vice versa). This looks like in this figure below (from here, it is an ...


4

It may be important to consider the developmental stage of the "female body" as well. For instance, organizational vs. activational hypothesis--injecting testosterone during a critical period during development (it can be pre-natal, or during puberty) could produce permanent changes in secondary sexual characteristics and sex-specific behaviors; however, ...


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

A tumor suppressor is an essential gene that regulates the cell cycle at different checkpoints. If one allele is lost due to a mutation then the function of that gene can be carried out by the other allele (There might be a less expression of that gene because of copy number reduction but it is not necessary in all cases- cases where there are feedback ...


3

Those residues are phosphorylated because they have a free hydroxyl group available to be bonded to a phosphate. Many other resides can be modified, like acetylation of lysines, but only those residues are chemically compatible with reversible phosphorylation.


3

For this specific question, let's divide the cells into two categories: Cells that rarely "navigate" are the cells that are connected to give the tissue its mechanical properties. How do these avoid an "adverse stimulus"? Well, they don't avoid it. But if that stimulus "harms" cells they react in some way: if the cell is destructed by the pathogen, it ...


3

Polar amino acids in this case stabilize the helical structure within the apolar milieu of the membrane by making intra- and inter-helical connections. Thus the side chains of polar amino acids turn to one another while apolars face the apolar membrane. This would be definitely supported if you could find alternating apolar - polar segments in the sequence ...


3

Steroid hormones produce a slow response because they do not have secondary messenger It's true that steroids don't have secondary messengers because they don't need them - they can go directly into a cells nucleus and affect transcription there. This wouldn't slow down the response by much, however. Slow response is due to lack of cell membrane receptors ...


3

There are two reasons for the asymmetry for the lipid composition of membranes in cells usually. The first which was mentioned by @Superbest is proteins which are called 'flippases' which describes three broad categories of proteins which facilitate the translocation of the lipids through the membrane, despite the fact that they all have polar or even ...


3

Mast cells contain a number of large, granular structures that are regarded as “secretory lysosomes,” yet they share several features in common with large dense-core vesicles, particularly with respect to the mechanisms of exocytosis. Upon activation, mast cells "degranulate" and exotcytose the contents of granules. SNARE-dependent mechanism mediates ...


3

According to wikipedia, cardiolipin is found in two places, the inner mitochondrial membrane, and bacterial membranes. Given the endosymbiotic origin of mitochondria, it makes sense that they would retain some remnant of their bacterial ancestry. But more importantly, cardiolipin plays a role in the enzymatic functions of mitchondrial membranes. Cardiolipin ...


2

@Alexandria Jak/Stat are two families of proteins which mediate signals through phosphotyrosines. JAK is a tyrosine kinase which binds to cell receptors and STAT is dimerized by JAK action. JAK specificity seems to be your question. A specific JAK protein (e.g. JAK1 or JAK2..) may mediate for different receptors in different cells. There may be ...


2

I found this paper[1], which might be relevant; it uses is a more chemically inspired approach. Another paper[2] also might be interesting, it takes a more dynamical systems approach. My personal instinct would be to use ordinary differential equations: generate a population of cells in random positions, assign each cell levels of any relevant molecular ...


2

It simply means after and before with respect to the flow of information in a given pathway. For example, consider this schematic representation of a pathway: TF1 ==activates==> gene1 ==produces==> Kinase1 ==phosphorylates==> ProtA In this schema, Kinase1 is downstream of TF1 and upstream of ProtA. Or, to take a classic example (source): ...


2

EDITED ANSWER Based on comments and responses my original answer to this question received I have decided to edit the answer and respond to some questions. Since I work on proteins, I tend to favour protein based approaches specially when wondering about the presence of a protein. This is simply the case because protein is what is important functionally ...


2

This is a short review about the issue and not complete. This and the earlier answer are not proofs of the link between the two proceses. To investigate this better, I think it would be much easier first to narrow the case to testosterone and energy homeostasis (Embryology; or better formulated research case) catabolism and anger anger and aggressive ...


1

those are phosphorylated because they are the present in consensus sequences and enzyme are specific to phosphorylate the specific target that's why other are not phosphorylated and also because of the OH group of these amino acids


1

Polarity essentially means a plus end (growing/polymerising) and a minus end (depolymerising). Look at microtubule (MT) (http://en.wikipedia.org/wiki/Microtubule). So molecules such as Kinesin-1 (http://en.wikipedia.org/wiki/Kinesin) use the hetero-dimeric nature of MT (alpha and beta subunits) and its polarity to orient themselves and move directionally ...


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

Here is a paper reviewing PKC action in exocytosis. Although it dates from several years ago it should be a good start for accessing the literature on this topic since it has been cited 90 times. Morgan A. et al. (2005) Regulation of exocytosis by protein kinase C. Biochem Soc Trans. 33:1341-4. PKC (protein kinase C) has been known for many years to ...


1

You've already learned much more than I know about cellular cascades in mast cells, but I wanted to be sure you knew about this handy resource - a free, searchable "Molecular Biology of the Cell" textbook: http://www.ncbi.nlm.nih.gov/books/NBK21054/ For general explanations about cell biology, it's thorough and readable. For instance: Transport from the ...



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