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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 ...


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 ...


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", ...


11

The answer to this question emerges from an examination of the structure of tyrosine — or, more strictly, the tyrosyl residue, which is how it exists in proteins, the concern of the question: It has both hydrophobic and hydrophilic features and can exhibit both behaviours depending on the circumstances. The ring is aromatic and hydrophobic, but the ...


9

A very interesting example are the cohesin molecules holding sister chromatids together in the oocytes (so only applicable to females, sorry!). Cohesion is established in utero, and these molecules are not recycled throughout life (AFAIK only shown directly for mice, not humans - https://www.ncbi.nlm.nih.gov/pubmed/20971813, https://www.ncbi.nlm.nih.gov/...


8

Chaperone proteins are still proteins and they can certainly misfold just like any other. If that happens, it will either be assisted by another chaperone and given time to fold successfully or it will be destroyed. If this is happening too often and the amount of chaperones drops too low or the number of unfolded or incorrectly folded proteins becomes ...


8

Dr. Bailey wrote a short piece that hints at the reasons behind why she expected what she expected: Telomeres are the ends of chromosomes that protect them from damage and from “fraying” – much like the end of a shoestring. Telomeres are critical for maintaining chromosome and genome stability. However, telomeres naturally shorten as our cells divide, and ...


7

Let’s first consider what the Central Dogma[1] actually says. It is precisely summarised in the following figure[2]: solid arrows represent transfer of information that has been observed directly; dashed arrows represent potential, not yet observed, transfer of information In the time since the original formulation of the Central Dogma in 1958, we ...


7

Your question is rooted in a misundertsanding of the hydrophobic effect. Hydrophillic and hydrophobic molecules do not repel but, rather, attract one another through van der Waals interactions. The tendency of hydrophobic molecules to aggregate in aqueous solution (ie the hydrophobic effect) is, instead of some repulsive force, actually driven entropically. ...


6

Human genome is 3.2Gbp (giga=billions of basepairs). If you assume there are 100k genes, this yields around 32kbp (kilo=thousands base pairs) per gene. Before human genome project, let's say before 1990, people were isolating a lot of genes from human-derived tissues. You can use google scholar to find relevant papers. From quick search, you can see that ...


6

It is standard IUPAC nomenclature to write bases that are not uniquely defined. For example, "N" means "any base", but "V" means "A, C or G, but not T". See the full list here


6

Short answer Some genes on the X chromosome escape X-inactivation. Two copies of these genes are needed for normal development. These genes are also present on the Y chromosome. Hence, healthy males and females both have two copies of these genes. In Turner's, the SHOX gene seems to be one of the culprits, which is needed for normal skeletal development. ...


6

It doesn't make sense to set volumes of decimals of microliters with a P200, since usually the accuracy of these pipettes is in the order of a few microliters. So even if you set your pipette at 190 uL, you may still dispense a volume ranging from 187 to 193 uL. For a P1000, due to higher volumes the inaccuracy is of course higher, usually +/- 10 uL or more. ...


6

The PubChem format description is not that easy to find: https://www.ncbi.nlm.nih.gov/IEB/ToolBox/CPP_DOC/asn_spec/pcsubstance.asn.html And the ASN file linked here: https://pubchemdocs.ncbi.nlm.nih.gov/data-specification I am correct in saying that the numbers in the 'element' array are corresponding to Atomic Numbers? Yes, 1 is hydrogen, 6 is carbon, ...


5

There's actually no need to speculate on the answer to this question since scientists have published their estimates and methodology, as is their way. The following paper is a good review: Fields C, Adams MD, White O, Venter JC. 1994. How many genes in the human genome? Nature Genetics 7:345-346. Below are some truncated excerpts from the paper but, if ...


5

I found this paper, which goes very deep into the molecular details of the individual steps of this reaction and also discusses how this is coupled to nucleotide selectivity. The 'basic' details about the reaction (quoted from this section, which also has a nice figure): The polymerization reaction proceeds by a simple nucleophilic attack of the 3'OH ...


5

I wouldn't really say RNA polymerase is "creating" the hydrogen bonds so much as it's thermodynamics that creates them. When we talk about an enzyme "creating" a bond, what we're generally referring to is an enzyme facilitating a reaction by lowering its activation energy so that it can proceed. However, in the hydrogen bonding between base pairs, there's ...


5

The textbook is asserting that translation could function without redundant codons, not that it does. In reality, all possible codons are used. See this answer on the interchangeability of codons.


5

It sounds a bit like chem exam question to be honest... Or at least the answer does... namely that O2 being paramagnetic creates a "spin barrier" that prevents most organic compounds from reacting fast with atmospheric oxygen: The magnetic properties of O2 are not just a laboratory curiosity; they are absolutely crucial to the existence of life. Because ...


4

This sort of question is easily answered by consulting and carefully reading an introductory biochemistry text, like this section of Berg et al. on line. However, as the diagrams of β-sheets can be confusing, I will summarize. The amino acids linked by covalent peptide bonds produce a protein molecule in the form of a single polypeptide chain. This ...


4

Contrary to my belief, it may be possible. The main concern we must look at is Protein to RNA, as we know RNA to DNA can be done through reverse transcription. Some evolutionary scientist believe that reverse translation may be a process that could have occurred naturally during the process of evolution to create the central dogma we know today. Hence, ...


4

Thiol-Based Reducing Agents The instability of thiol-based reducing agents in solution is due to their propensity to form disulfide bonds by the following half reaction: $$\ce{2RSH -> RSSR + 2H+ + 2e-}$$ It is clear that disulfide formation requires: Deprotonation of the thiols to form thiolates (RS-). An electron acceptor. Therefore, solutions of ...


4

For any question regarding volume and concentration, you should consider the equation $C_1V_1=C_2V_2$. We can use it to derive a general equation for the addition of concentrated stock solutions. We want to find the volume of stock solution ($V_1$) to add so that its final concentration is 1X. Here's what we know: The initial concentration of stock solution,...


4

Candianer's answer is a generally correct way of solving these problems but, in my opinion, overkill for this situation. All Nx buffers are mixed to make your life easier, and you will generally encounter 10x, 6x, and 5x buffers. 10x and 5x seem obvious, you just put them in so they make up a tenth or a fifth of your solution, but 6x seems to confuse people....


4

I don't know much about the evolution of thoughts on the subject but I would suppose that the estimate of 100,000 genes is probably caused by the one gene - one enzyme/protein ideas The one gene–one enzyme hypothesis is the idea that genes act through the production of enzymes, with each gene responsible for producing a single enzyme that in turn affects ...


4

The problem statement says all the proteins have the same molecular weight but does not say how many amino acids they have. It does say how many cysteine amino acids each has, but not how many other kinds they have. Cysteine forms disulfide bonds, holding bends in the protein structure. BiteSizeBio says: SDS is a detergent that is present in the SDS-...


4

The term ‘redundant’ is not ideal in this respect, as that implies a redundancy in reality rather than theory, as @canadianer points out. Redundancy and Degeneracy However I would mention that there is another term more usually applied to the fact that certain amino acids are encoded by more than one codon — degeneracy. There is a Wikipedia entry on ...


4

@AliceD's answer is excellent, but I thought it would be helpful to include an additional perspective. The issue here isn't that monosomy X shouldn't be a problem because the majority of one X chromosome is inactivated. It is that monosomy X isn't as big a problem as any other monosomy because the majority of one X chromosome is inactivated. Monosomies ...


4

If you look at the Google ngram for the term ‘Molecular Biology’ you will see that it first appears just before 1960, and it is relevant that the Journal of Molecular Biology was founded in 1959. It is not biochemistry — indeed the name was meant to indicate its difference from biochemistry, and I heard second-hand (so I cannot vouch for its truth) that Hans ...


4

This DSSP page makes it clear that: Helix-3 = 3-10 helix Helix-5 = π-helix The α-helix) is described in every biochemistry text book and widely on the web. It has 3.6 residues per helical turn and has 13 atoms in the ring formed by the hydrogen bond and so can also be called a 3.6-13 helix. The 3-10 helix is less common than the α-helix, but is ...


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