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The question is relatively broad and one should take into account that the brain not only consists of neurons, but also glial cells (supportive cells) and pre-mitotic neuronal stem cells. Furthermore, as critical fellow-scientists have indicated, developmental stage is very important, as the developing embryonic brain is very different from the adult brain. ...


32

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 relatively ...


29

First, tattoo pigment isn't injected into cells. If you were to puncture a cell with something the size of a tattoo needle, it would die - full stop. Many cells are destroyed in the process though, mostly by tearing, which initiates the wound healing process. So what actually happens is the particles lodge in between the cells of the dermis (the layer below ...


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.


25

Isn't there a possibility that cell division will result in a daughter cell with no mitochondria? Yes, there is always the possibility. However, there must be a strong negative selection pressure against eukaryotic life that cannot achieve the proper partitioning of mitochondria, so you can imagine that there are mechanisms in place to prevent this case. ...


23

Short Answer Myelination acts as an electrical insulator and allows saltatory propagation. By reducing membrane capacitance and increasing membrane resistance, myelination increases the velocity of signal (i.e., Action Potential) propagation. If you want to see a really wonderfully simplified explanation, see this Quora post by Edward Claro Mader. Four ...


23

Yes, plants for example! Autotrophs vs. heterotrophs Plants are autotrophs while animals and fungi are heterotrophs. Have a look at the Wikipedia articles. In short, autotrophs organisms are organisms that synthesize their own compounds from inorganic compounds. Heterotrophs organisms are organisms that synthesize their own compounds from organic compounds....


22

Welcome to Biology StackExchange. Am I remembering this incorrectly? No, you're remembering it correctly. I think you're talking about slime molds. You'll find more information on the wiki page Is this the video you saw? These images are pretty cool. Is this even possible? Yes (given that it exists). There is no way to correctly answer this ...


22

Yes, we are eating the DNA and proteins of an organism when we consume and digest its cells. However, consuming the "raw flesh of hen or fish" in your example would not cause harm strictly due to the consumption of their DNA. DNA has two basic components - a structural 'backbone' of alternating phosphate molecules and sugar molecules (called deoxyribose) ...


22

It depends what you mean by 'leg'. The instinctive way to define a 'leg' is based on its functional use: we use legs to walk on. But if we adopt that definition of 'leg' then there certainly are animals with odd numbers of legs: kangaroos, for instance, have a five-legged gait, functionally using their tail as a fifth leg. There is no developmental process ...


19

Mitochondria evolved before chloroplasts. We know this because Mitochondria form a monophyletic group: e.g. all life with mitochondria traces back to a single common ancestor (source). Since the group with chloroplasts groups within this clade, it must be the case that either (a) chloroplasts were obtained by an organism that already had mitochondria or (b) ...


19

Hemoglobin molecules used to manufacture these products are not contained by a red cell membrane, and when released into the vasculature, these molecules rapidly scavenge nitric oxide.This can result in systemic vasoconstriction, decreased blood flow, increased release of proinflammatory mediators and potent vasoconstrictors, and a loss of platelet ...


19

A tumour is simply a space-occupying lesion (something that should not be there, that is; a "lump") caused by abnormal cell replication. (In medicine, the word "tumour" literally means "swelling", and can sometimes refer to that instead, but that's a different story). Cancer is a disease in which cell replication is totally out of control. What causes ...


18

How did multicellularity evolved? It is an ongoing field of research - Some insights about the origin of multicellularity This is a big ongoing field of research. To start with an example, there was relatively recently (2012) an important article by Ratcliff et al. that shows that yeast can quickly evolve multicellularity under selection on the speed they ...


18

There is evidence that cells can exchange mitochondria. There are some donor cells that transfer mitochondria to recipient cells via cytoplasmic nanotubes (within the same species). This happens endogenously and triggering factors may include stress. References: Pasquier et al. 2013 Ahmad et al. 2014 Wang and Gerdes. 2015 Hayakawa et al. 2016 On ...


18

Do all bacterial cells have a double membrane? No. There are a number of bacterial membrane and cell wall structures. Some of them have a double membrane, some of them don't. In microbiology, we often make the initial distinction between two groups of bacteria based on whether or not they take up an iodine based stain called a Gram stain. Gram negative ...


17

Like all tough questions, this one has no well understood answer. Itching "is one of the most poorly understood sensations." The obvious facts: The urge to scratch part of your skin is the result of stimulus of the skin which causes some of the nerves to register an irritation (you can get an itch in internal organs too - which sounds excruciating). ...


17

There are two factors that need to be taken into account here: 1. Myelination decreases membrance capacitance. The rate at which sodium influx through a node can depolarize the axon at the next node is related to both the current and capacitance across the membrane (in addition to a few other factors). So while adding a new node to the axon would indeed ...


16

They are both right. Animal cells do have vacuoles, but they are smaller, larger in number (plant cells usually have just one or a few large vacuoles) AND serve a somewhat different purpose than those of plants. A vacuole is basically a membrane-covered compartment (vesicle) filled with molecules, that shouldn't, right now, be in the cytoplasm. For plants, ...


16

Since you chose kinesins as an example class of motor proteins, I will also stick to them. In general, the movement mechanisms of kinesins are well studied and the general structure of kinesin proteins, that is a dimer, is known by crystallography (see Kull et al. (1996) for the structure publication). Even before that, the movement of single kinesin ...


15

No. Nobody considers red blood cells to be prokaryotic, perhaps most importantly because they are part of a eukaryotic organism. Red blood cells begin life with the full complement of organelles, including a nucleus and mitochondria, but our RBCs shed their organelles during maturation. In actuality, though, only mammalian RBCs lack nuclei; other animals' ...


15

Ventricaria ventricosa (previously called Valonia ventricosa) is not exactly a single cell. It has a coenocytic structure with multiple nuclei and chloroplasts. As Jasand Pruski correctly guessed the organism possesses a large central vacuole which is multilobular in structure (lobules radiating from a central spheroid region). The entire cell contains ...


14

The definition of life is the main issue here. That is one of the great philosophical questions in Biology (and not only Biology) and is way beyond the simple Q&A format of this site. However, most definitions of life can be boiled down to1: A self replicating entity that interacts2 with its environment. Or, even more simply [1]: Life is self-...


14

This is one of the most intriguing questions of eukaryotic evolution. As far as I know and have read, the autogenous theory is not accepted. There are quite some reviews on this topic. Also there is a wonderful book by Nick Lane on mitochondria called Power Sex and Suicide. You would be interested to read it. There are no sufficient evidences for the ...


14

Wanted to give a one line answer some day!! Lens fiber cells and keratinocytes.


14

What should be the correct reason for bilayer arrangement? I'll answer your second question first, but there is an almost identical question on this site already: Why do cells have a bilayer? There is water on the extracellular and intracellular side of the membrane. What's actually happening at a molecular dynamics level is the self-association of the ...


14

IMO, the definitive answer to this question is given in a paper by J. S Clegg. He traced the origin of the term cytosol to a book chapter by H. A. Lardy, and confirmed by email that Lardy had indeed coined the term. Their definition of cytosol is as follows: ... that portion of the cell which is found in the supernatant fraction after centrifuging the ...


13

Bianconi et al. 2013 give an estimated lower bound of 3.72 × 10^13 (which, by the way, is approximately the geometric mean of 10^13 and 10^14). However, from the table in their Supplemental Information (where estimates for about fifty different types of cells are added up), it is clear that the vast majority of these are the erythrocytes, also known as red ...


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