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First of all, let me make it clear that the heart is at the vertical centre of the body -- it is not shifted towards left (or right). However, it is slightly tilted towards the left in most cases. In some cases, it is tilted towards the right, and the condition is called Dextrocardia. For why it is so, lets look at what the heart does. Below is a diagram ...


108

One major problem with using uracil as a base is that cytosine can be deaminated, which converts it into uracil. This is not a rare reaction; it happens around 100 times per cell, per day. This is no major problem when using thymine, as the cell can easily recognize that the uracil doesn't belong there and can repair it by substituting it by a cytosine again....


79

I'm extremely skeptical of @leonardo's answer. I suspect that what would happen if you drank only distilled water is nothing perceptible. The only place where concentrations of distilled water would ever be high enough to conceivably matter is in the tissues of the mouth and throat, and even there, the effect would be temporary. Compare drinking 8 glasses ...


55

Brian Hayes wrote a very interesting article from a mathematical point of view: http://www.americanscientist.org/issues/pub/the-invention-of-the-genetic-code especially the "Reality intrudes" section. Basically people had created fancy mathematical reasons why it has to be exactly 20. Nature, being nature, does not follow the reasoning, but has its own ...


54

There are some cases, as hinted at by the comments. But these are relatively small amount of metal. Its not that there is no metal available, but I can think of several reasons you don't see iron exoskeletons on animals all the time. Firstly, fully reduced (oxidation state 0) metal has a high energetic cost to create in reduced form. Iron is the ...


53

The existence of thymine in DNA instead of uracil is apparently due to evolution process which made DNA more stable. Thymine has greater resistance to photochemical mutation, making the genetic message more stable. A rough explanation of why thymine is more protected then uracil, can be found in the article Arthur M, L., Why does DNA contain thymine and ...


52

blood clots inside the body have an unfortunate tendency to get into the bloodstream and cause blockages, leading to severe problems such as strokes or heart attacks This statement is primarily true only for blood clots within blood vessels, especially in the veins. When you are talking about bruising, you are talking about clots outside of the vasculature. ...


51

A few examples: Starch A polymer of glucose that can form a double helix and functions primarily as energy storage in plants. [image source] f-Actin Filamentous actin forms a helical structure with two strands of polymerized g-actin. This is a structural component of the cytoskeleton. [image source] Coiled Coil Protein motif with a helical structure ...


49

Interesting question! The cause of tears and itching is the chemicals produced by onion (Allium cepa). Lets go into some details. Onions, coming from the family Liliaceae (also containing garlic, chives, scallions and leeks) store compounds known as amino acid sulfoxides, and the one we are talking about here is S-1-propenyl-L-cysteine sulfoxide (...


44

One of the main reasons that modern(!) biology uses oxygen as an electron acceptor is availability. Around 2.45 billion years ago, oxygen (O$_2$) started being built up in the atmosphere (which actually killed off a lot of the lifeforms/bacteria at that point). Since then, oxygen consuming lifeforms were able to establish themselves. Before that, most ...


40

Nice question! Many vegetables taste bitter because they contain compounds known as phytonutrients (Greek phyto = "plant"). There are more than 2500 phytonutrients known, and the most important (and common) ones are categorized as1: Carotenoids: they are the ones that give red/orange/yellow color to some vegetables. They are mainly antioxidants, but some of ...


38

In 2010, Dr. Craig Venter actually used a bacterial shell and wrote DNA for it. Scientists have created the world's first synthetic life form in a landmark experiment that paves the way for designer organisms that are built rather than evolved. (Snip) The new organism is based on an existing bacterium that causes mastitis in goats, but at its ...


36

@Bryan Krause's answer is quite correct. I just want to clarify what a bruise is, because I think you have a misconception of what happens. There are bruises (blood leakage into tissue because of damage to capillaries) and there are hematomas (a collection of blood in a tissue caused by breakage of either many capillaries or normally a larger blood vessel.) ...


35

The phosphate group in NADPH doesn't affect the redox abilities of the molecule, it is too far away from the part of the molecule involved in the electron transfer. What the phosphate group does is to allow enzymes to discriminate between NADH and NADPH, which allows the cell to regulate both independently. The ratio of NAD+ to NADH inside the cell is high, ...


32

You are correct in thinking that since the translation of mRNA begins with AUG, which codes for methionine, then all proteins should contain a methionine at their N-terminus (aka start site). But, it is indeed not so. First of all, I want to mention about variations in start codon. As you say, AUG is not the only, but actually the most common, start codon, ...


31

Proteins can move around the membrane. Most proteins do move within the membrane. The membrane is a liquid crystal and has fluid behaviour. Specifically, this is due to the membrane being in a gel-state. This gel state allows phase behaviour which means that the protein is able to move around on the surface. This results in an effect that is often referred ...


31

Availability and applicability. Availability. In the beginning, there was CO2. It was abundant in the atmosphere, and later, the oceans. Fluorine and neon weren't, and so respiration evolved around what was (and is) available. Ref.: Paeloclimatology / History of the Atmosphere. Applicability. The other point about oxygen is that it works rather ...


30

Ripening of bananas (and other fruits) is induced by acetylene and ethylene (Ethyne and Ethene) (see reference 1), which acts as a hormone and induces the ripening process. The incomplete combustion of the leaves produces ethylene, additionally the warmth of the process will help the enzymes as well. There is even a paper about this technique (although it is ...


30

The feeling of cold from mints is caused by menthol. Menthol affects the TRPM8 receptor on skin and also in the mouth. TRPM8 is also a general cold receptor: so if you are in contact with menthol the receptor reacts just like when you are exposed to cold (Bautista et al., 2007). The receptor is strongly activated at temperatures below 26 degrees Celsius (...


30

1. Synopsis I'd like to preface this by saying don't randomly use medicines without a doctor's advice. It's fairly unlikely antivenom would cause you any harm but in some cases, antivenom could be dangerous and even lethal. You have to consider possible allergic reactions and the route of administration. In any case, it would be a stupid idea to blithely ...


29

I really like this question as it is such a fundamental underpinning of all life on the planet, yet there is such sparsity of actual information on its origins and why selection rewarded ATP use over anything else. Here I am talking generally since no specific studies exist in ATP vs other candidates. A lot of the below information is taken from a ...


28

A reaction where the the free energy of a thermodynamically favorable transformation, such as the hydrolysis of ATP, and a thermodynamically unfavorable one, are mechanistically joined into a new reaction (or may be envisaged to be so joined) is known as a coupled reaction. To put it another way, two or more reactions may be combined mechanistically such ...


28

Because their shape reminded researchers of rolls of Sushi (Ichinose et al, 1990): These repeats were initially called GP-I structures because they were first identified in $\beta_2$-glycoprotein I. More recently, they have been called short consensus repeats or sushi structures because of their shape.


28

Short answer It has been shown that plants may already suffer from doubling the atmospheric CO2 concentration from 340 to 610 ppm, something that might happen during the next hundred years or so based on current emissions. Background A popular science website tells us that an excess of carbon dioxide (CO2) reduces the rate of transpiration of some plants. ...


27

In principle it is possible. Life doesn’t contain some divine or intrinsically spiritual element that we would have to add to our artificial organism potion to breathe life into it. At this moment we are limited by gaps in our knowledge and by the current state of technology. We first have to better understand fundamental principles of life on a multi-...


27

Oxygen is actually highly toxic to cells and organisms – reactive oxygen species cause oxidative stress, essentially cell damage and contributing to cell ageing. A lot of anaerobic organisms have never learned to cope with this and die almost immediately when exposed to oxygen. One classical example of this is C. botulinum. Oxygen is incorporated in several ...


27

This is not really a biological answer, but a psychological one: One important fact to consider is that the perception of time is essentially a recollection of past experience, rather than perception of the present. Researchers who study autobiographical memory have suggested that part of this effect may be explained by the number of recallable memories ...


26

Superoxide, O2− is created by the immune system in phagocytes (including neutrophils, monocytes, macrophages, dendritic cells, and mast cells) which use NADPH oxidase to produce it from O2 for use against invading microorganisms. However, under normal conditions, the mitochondrial electron transport chain is a major source of O2−, converting up to perhaps 5% ...


26

The image was not in the DNA as such, only as an abstract representation that could be converted into an image from knowledge of the code. Briefly, they encoded the image into DNA, using a couple of different strategies in which DNA represented pixels -- either with a single DNA base representing a pixel, or with a triplet representing a pixel. Knowing the ...


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