Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange
218

Short answer Blue color is not only rare in edible organisms - Blue color is rare in both the animal and plant Kingdoms in general. In animals, blue coloring is generated through structural optic light effects, and not through colored pigments. In the few blue-colored plants, the blue color is generated by blue pigment, namely anthocyanins. The reason for ...


109

Although @AliceD's answer is a great simple demonstration of the paucity of blue in our natural world, there's likely a more nuanced/technical reason. Short answer Blue light was the most available wavelength of light for early plants growing underwater, which likely led to the initial development/evolution of chlorophyll-mediated photosytems still seen in ...


69

Crystallin proteins are found in the eye lens (where their main job is probably to define the refractive index of the medium); they are commonly considered to be non-regenerated. So, your crystallins are as old as you are! Because of this absence of regeneration, the accumulate damage over time, including proteolysis, cross-linkings etc., which is one of ...


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 ...


40

I'll keep this short and simple. The direction of transcription (which determines which strand is used as the template) is controlled by the promoter, which is a region of specific DNA motifs at the 5' end of a gene. RNA polymerase binds to the promoter, which orients it on the correct strand and in the correct direction, after which it can proceed to ...


36

Unfortunately, we are all still "confuzzled" by how memory works. We are far from a complete understanding of how memory is stored and recalled. Nonetheless, we do know a little, so read on. Your understanding of basic neural function is almost correct. First, an individual neuron will signal through its single axon onto the dendrites of many downstream ...


34

HIV was identified as an infectious disease through classical epidemiology, and the virus was identified through classical virology. I won't get into the epidemiology, but briefly it went pretty much as you'd expect -- a cluster of symptoms were identified, patient characteristics were analyzed, the contagious nature of the symptoms were recognized, all ...


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

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.


27

Chart of C-values (the mass of DNA in a single haploid cell); there is no logical order to the groups: [source] Base pairs in haploid genome (some examples): Escherichia coli (bacterium): ~4.5 million Caenorhabditis elegans (nematode worm): ~100 million Homo sapiens (we all know what these are): ~3 billion Pinus taeda (coniferous tree): ~22 billion ...


26

I know that you are referring to the commonly ribosome-translated L-proteins, but I can't help but add that there are some peptides, called nonribosomal peptides, which are not dependent on the mRNA and can incorporate D-amino acids. They have very important pharmaceutical properties. I recommend this (1) review article if you are interested in the subject. ...


22

Usually in biology (and being ATP, it most probably is biology), it's one of two things. The gamma-phosphate (the third one, the one farthest from the adenosine) is very unstable, meaning the phosphoanhydride bond is easy to break. The cell "allows" it to break, but only at the cost of moving the phosphate to some other molecule, such as a serine or ...


22

Nice question! It is actually very difficult to do so because humans, obviously, are far more complex than some animal species which naturally show parthenogenesis. Just to mention, there are female-only animals also present in nature, such as New Mexico whiptail, which reproduce only by parthenogenesis, meaning that it is not as impractical as one might ...


22

The terms intron and exon were coined by Walter Gilbert in a renowned 'News and Views' article, Why Genes in Pieces, published in the journal Nature in 1978. Introns are the intragenic regions and exons are the regions which are expressed. This is the relevant passage in full: The notion of the cistron, the genetic unit of function that one thought ...


22

I like Mowgli's answer, because it is a non-obvious example. However I would also point out that there are many, many protein-based structural components in the body that we know do not regenerate due to associated pathologies; so presumably these structural proteins are as old as from when they first arose in developemnt. Take the stereocilia on hair cells ...


21

There is a recent paper that introduced the first molecular-level whole-cell simulation. Karr, J.R., Sanghvi, J.C., Macklin, D.N., Gutschow, M.V., Jacobs, J.M., Bolival, B., Assad-Garcia, N., Glass, J.I., & Covert, M.W. (2012). A whole-cell computational model predicts phenotype from genotype. Cell 150:389-401 DOI: 10.1016/j.cell.2012.05.044 The ...


20

The role of the salt is to neutralize the charge of the DNA's sugar phosphate backbone. This makes the DNA less hydrophilic (less soluble in water). Ethanol has a lower dielectric constant than water so it's used to promote ionic bonds between the Na+ (from the salt) and the PO3- (from the DNA backbone) causing the DNA to precipitate.


20

Summary: The idea that primary sexual determination defaults to female was proposed several decades ago and is primarily based on the observation that, in the absence of Sry, ovarian development takes hold. However, more recent models suggest that both ovary and testis development require complex genetic regulation and neither can really be said to occur by ...


19

It does fold on to itself. There are secondary structures in RNA and some of these secondary structures also have regulatory functions (for example, riboswitches). Some of these structures can also inhibit translation (by different mechanisms such masking of the ribosome binding site or equivalent eukaryotic sequences, or stalling of ribosome etc). Other non-...


19

Experimental protein structure determination is hard: the most common method is X-ray crystallography, which can be done in a few months if you are lucky and can take years if you're not. The problem with X-ray crystallography is that you need good protein crystals, and in most cases, proteins don't crystallize very well, so it takes a lot of time (and a lot ...


19

(my comment reiterating the answer seemed useful, so I've reproduced it here) There are "NMDA receptors" in our body. There is not NMDA naturally in our body*. "NMDA receptor" is just a name people gave to one of the receptors that normally binds glutamate. They could have called it something else, like the "slow glu receptor", or "Glutamate Receptor A", ...


18

The cost of transcribing and translating a hypothetical average gene in yeast has been calculated as 551 activated phosphate bonds ~P per second (Wagner, 2005). The median length of a yeast RNA molecule is 1,474 nucleotides, and the median cost of precursor synthesis per nucleotide (derived from the base composition of yeast-coding regions) is 49.3 ∼...


17

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) ...


17

I am restricting the answer to only $Na^+$ and $K^+$ channels, assuming similar mechanism for other channels. In these 2 channels, such high level of specificity is achieved because of two main differences between $Na^+$ and $K^+$: difference in size of $Na^+$ and $K^+$ ions. difference in chemical properties of $Na^+$ and $K^+$ ions. Lets discuss these ...


16

The ribosome holds the peptide-bound tRNA and aminoacyl-tRNA in the right orientation to catalyze the peptidyltransferase reaction. http://www.pnas.org/content/103/36/13327/F1.expansion.html If the incoming aminoacyl-tRNA was the other enantiomer, the amino acid moiety would not fit properly into the ribosome active site. In other words, the shape of the ...


16

According to Gleick, Feynman spent the summer of 1960 in Delbrück's lab at Caltech and discovered intragenic supression. This is where the expression of a gene which has been knocked out by a mutation may be restored by a second mutation within the same gene. Fenynman worked with the rII mutant of phage T4 and was looking for back mutations in E.coli ...


16

There are several concepts to understand: Alternative splicing From one gene, several proteins can be constructed depending on which introns are spliced. Tissue-specific genetic expression Genes are differentially expressed (and differentially spliced) depending on the tissue. Post-transcriptional modifications Those are modifications that are made ...


16

To add to canadianer's answer, in fact genes can be found on both strands of the DNA in most eukaryotic cells, in the sense that the sense and anti-sense strands are not always the same strand. The direction is therefore completely determined by the promoter. Furthermore, there are bidirectional promoters.


Only top voted, non community-wiki answers of a minimum length are eligible