13

Isn't it illogical to give more of insulin for a deficit amount of receptors? Seems like there is some confusion in the definition of type-2 DM itself. According to the American Diabetes Association: If you have type 2 diabetes your body does not use insulin properly. This is called insulin resistance. At first, your pancreas makes extra insulin to make ...


11

As said by @dblyons, there has not been a lot of research (biochemical) on chameleons. So, the exact part of mechanism that you're looking for is still not understood. However, we have recently caught the broad end of the stick. Chameleons don't have special cells for color, their complete skin has a layer of pigments (dermal iridophores) which helps them in ...


10

Steroid hormones are transported in an inactive form bound to proteins in the bloodstream. Androgens and estrogen are bound to Sex hormone-binding globulin (SHBG), while glucocorticoids and progestins are bound to transcortin. References: Transport of steroid hormones: binding of 21 endogenous steroids to both testosterone-binding globulin and ...


9

This is true for the beginning of the disease. As a reaction to the reduced sensitivity of the cells in the body to insulin (and thus less uptake of glucose from the blood and a resulting hyperglycemia) the body produces more and more insulin to cope with this problem. At some point the insulin producing beta cells cannot increase the production anymore and ...


9

The answer given by Sadegh gives a general correct broad view. But one part of the puzzle is missing, which is molecular recognition. Molecules bind to each other via physical/chemical interaction like forming hydrogen bonds, electrostatic interactions and other mechanisms. The sum of all interaction defines the strength of the binding. If molecules have ...


8

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 provided ...


8

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 ...


8

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 ...


7

Parts of the answer are in the text that you provide yourself. But I shall try to add where i can. What do each of these three terms [hormone, cytokine and protein hormone] mean and how are they different? Both cytokines and hormones are a class of signalling molecules that are secreted by cells. Cytokines are a group of small protein that have a ...


7

It's both simple and complex. The simple answer is Brownian motion. All the particles in the cell do have mobility which is related to their mass. A small particle like a soluble enzyme undergoes random walks through the cytoplasm or nucleoplasm. Thus by having a grand number of a certain molecule you can be sure that at some point it interacts with the ...


6

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 ...


6

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 not ...


6

There is one main reason: Amplification of the signal. You can start a signal downwards the cascade with relatively few receptors which need to be activated which allows even for weak signals to be translated into the nucleus. This figure shows this for G protein coupled receptors (from here): For example one molecule of cAMP can activate many molecules ...


6

A perfectly reasonable definition of a ligand from Wikipedia: In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. A ligand can be anything, so long as it binds to a biomolecule. Often, the ligand is a small molecule or peptide, and the thing that it binds to is a protein. On the ...


6

Insulin is a "last resort" treatment for people with Type 2 diabetes—partly due to the unpleasantness of injections, but partly due to the fact that high insulin levels can worsen insulin resistance. People with Type 2 diabetes are generally started on Metformin and/or advised on diet and exercise, and progress to other oral medication, before insulin ...


6

All the body does is produce a ton of cells that can recognize single antigens. Each time you encounter pathogens, some of these naïve cells contact antigen that can activate them. The activated clone replicates itself, forming effector cells that can deal with pathogens. As the infection is cleared and the population of effector cells begins to contract (...


6

The breakdown and reassembly of proteins is a ubiquitous process within cells, and yes this is expensive but transport is expensive, too, and recycling has the added benefit of dealing with proteins that become misfolded or otherwise damaged as well as allowing for transcription and translation to regulate overall protein levels. The Toyoma & Hetzer 2013 ...


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 definitions for ...


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

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 and ...


5

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, ...


5

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 ...


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

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. ...


5

In biology ligand is a very broad term. Everything is called a ligand that has a receptor for it, regardless whether it is free or membrane-bound. There is very much sense in membrane bound ligands, because many cells in our body are capable of actively moving around (for example T-cells). Cells can use signal transduction by direct cell-to-cell contact - ...


5

All biomolecules are eventually broken down. This process is called turnover. Since inositol is a signalling molecule it is necessary to remove in order to terminate the signal, despite adaptive mechanism in the ER calcium channels. IP3 is generally dephosphorylated by a family of phosphatase enzymes called inositol polyphosphate phosphatases. After ...


5

is every neurotransmitter receptor also an ion channel? No. There are two general types of receptors for neurotransmitters, ligand gated ion channels and receptors that activate second messenger systems, for example, G protein coupled receptors. They are sometimes referred to as ionotropic and metabotropic receptors. This figure from Principles of Neural ...


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 ...


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

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):  &...


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