11-cis-retinal has several conjugated ("neighboring") double bonds, which makes it easier to absorb photons in the visible range. The double bonds can share their electrons, which means there's a longer system for absorbing longer-wavelength (in this case visible) photons efficiently.

Once you add all this energy, the 11-cis double bond gets flipped into the trans conformation (the process is called photoisomerization). That removes the bend in the retinal molecule, which pushes on the protein, rhodopsin, around it to change its shape. With its new shape, the rhodopsin can bind to and activate a trimeric (three subunits) G protein. The trimer falls apart, and one part called G_alpha goes on to bind and activate a phosphodiesterase enzyme that destroys cyclic GMP. This affects ion channels that are opened by cyclic GMP.

Triglycerides consist of a small glycerol backbone with three fatty acids attached. The glycerol can be quite directly derived from sugars, but the fatty acids would require more complicated de novo lipogenesis. Simpler for the adipocytes just to use fatty acids from fat, but it's certainly possible to make fat from sugars.

No, CAR-T simply uses T cells extracted from an adult. Either the patient themselves or a donor. The cells are then gene edited to express the chimeric antigen receptor, and the successfully edited cells are put back in the patient.

Sperm has to swim to reach the egg, so it would be a disadvantage to be carrying a lot of cargo.

Bear in mind plenty of viruses do not have any DNA, using RNA instead. But there are other Cas proteins that cut RNA, so you can still apply that kind of approach.

It's not necessarily going to be all that effective for typical viral infections, as it's hard to deliver a lot of CRISPR-Cas machinery in vivo, whereas a viral infection can create huge numbers of viruses.

Where it could be exciting is in potentially permanently curing HIV infection. You use other drugs to knock the infection down, but some of the viruses have integrated into the DNA of host cells, where drugs do no good. But CRISPR-Cas9 could come along and destroy those viral DNA sequences.

Read your own source:

>This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations.

Your source does explain that it gets complicated when there are, for example, two different kinds of mutations in the two copies of the gene. That obviously goes beyond the simple categorization of recessive vs. dominant.

Other sources make the definition even clearer, like this:

>sickle cell anemia, which is defined as homozygosity for the sickle hemoglobin (HbS) gene (i.e., for a missense mutation [Glu6Val, rs334] in the β-globin gene [HBB])

Well no. Full-blown sickle cell disease only affects homozygotes, and as such is considered recessive. But the heterozygotes do still have a different phenotype than either homozygote in some ways. That means in those respects the allele is not recessive at all. When it comes to malaria resistance, it's more of a dominant allele.

That isn't turning a recessive allele into a dominant allele. That's turning a rare allele into a common allele.

> however at times just one recessive gene is enough to cause a disease or other phenotype problem (think a gene that produces a mutant protein that your body can't get rid of).

That's not a recessive gene. Firstly, it's not genes that are recessive, it's alleles. Secondly, what you're talking about there is a dominant allele.

It's not genes that are recessive or dominant, it's variants (alleles) of genes. A recessive allele is generally a gene that doesn't work, but if your other copy of the gene still works you still have enough activity to be unaffected. Changing that to a dominant allele isn't trivial. I can't come up with any examples of that happening quickly in evolutionary terms. On longer timescales it's easier, like if the gene product goes from acting as a monomer to a dimer and the broken allele then makes the dimer inactive - then the loss of activity can be enough to leave heterozygous individual affected.

We're also talking about humoral immunity, which relies on antibodies. There is no self recognition involved there. As for cell-mediated immunity, it's true that the self MHC is part of what's required for recognition, but MHC alone is not sufficient - you need the foreign antigen loaded into the self MHC for recognition.

As for MHC and HLA, they are not two different molecules. MHCs are HLAs.

> > > > > The reason it's important to know this is because your body recognizes your cells by recognizing the cell surface antigens on your cells.

Well, mostly they don't recognize your own cells, they recognize anything foreign.

There are a few exceptions like NK cells recognizing MHC I from your own cells. But that's not involved here.

The detector itself is technically part of the brain, as is all of the retina. It's true that the response of the cells that detect light is the opposite of normal neuron activation - hyperpolarization instead of depolarization. That gets swapped around before the signal leaves the retina though, along with some early processing taking place.

>I found out today that ethanol reacts with organic fats (carboxylics only?) to form esters, which do not appear to act like ethanol in the body.

An alcohol can form an ester with a carboxylic acid, such as a fatty acid. Ethanol is obviously an alcohol, so that can happen under the right circumstances.

Thing is, when you're talking about fat, usually you're talking about triglycerides or maybe phospholipids etc. In those cases, the fatty acids have already formed an ester with an alcohol. It just isn't ethanol, but instead glycerol. So there's nowhere for ethanol to "attack".

In the process of digestion, those esters in dietary fat are actually broken down by enzymes, but those same enzymes would also immediately break any esters that ethanol might try to form.

In any case, the reaction conditions to form an ester aren't really there in the human body (except when aided by enzymes).

> Is it like a child's toy where squares fit into squares and circles fit into circles?

That's pretty much how it works for putting things together. When the proteins have to do more, they have to change shape. But that still depends on how they're put together, they're like little machines with like springs, levers etc.

The information is stored in DNA. Proteins are made based on the DNA sequence, and the shape of those proteins dictates their function. Like how tubulin makes microtubules and so on.

The centrosome in an interphase cell uses its radiating microtubules to sense the peripheries of the cell and place itself roughly in the center. Like pushing rods out in every direction to end up in the middle. During mitosis, the centrosome divides and each new baby centrosome does something similar, except they're also pushing each other away. So they end up towards each side of the cell.

The microtubules projecting from each centrosome each bind a chromatid at the other end, at the kinetochore (a big protein complex that sits on a particular sequence of DNA). Microtubules can bind on each side, so both centrosomes get connected to one side of the pair of sister chromatids. They can then do the same pushing thing, and since they're equally good at pushing, the chromatids all end up roughly at the mid-line of the cell. Then it's just a matter of cell cycle regulation - once everything is ready, the anaphase-promoting complex is activated, and activates separase to cleave the proteins holding the sister chromatids together. Then each centrosome can pull its set of chromosomes to its side of the cell in preparation for cytokinesis.

It used to be we thought of just apoptosis and necrosis, with apoptosis being a clean and deliberate suicide, while necrosis was a messy and uncontrolled cell death.

While those are still very valid, it's turning out that there are a lot more ways for cells to die.

There's necroptosis which is controlled like apoptosis, but messy like necrosis. There's ferroptosis which is iron-reliant and happens in response to excessive oxidation. There's anoikis, which is very similar to apoptosis but initiated by lack of contact to extracellular matrix. There's NETosis, where a type of immune cell called neutrophils eject their DNA as a sticky net to capture pathogens. There's pyroptosis which is triggered by the inflammasome and strongly stimulates inflammation to combat mainly intracellular pathogens.

There are a few more I've left out, probably a few more I haven't heard of, and then all the ones we might not have discovered/characterized yet.

Mutations. Those can be caused by many things, most often either DNA damage from the cell's own metabolic byproducts or mistakes made when growing/dividing cells replicate their DNA.

On the other hand, we do talk about genes coding for stuff, so that kind of language is useful (but in a more basic manner - a gene codes for a protein, not a gene (or allele) codes for a big nose).

Your cells have, for example, some "programs" that tell them to grow and divide, and some programs that tell them to commit suicide. Those programs are normally only turned on when appropriate.

In a cancer cell, mutations cause one or more programs telling the cell to grow and divide to be constantly turned on, and the suicide programs to be broken (so even if it would be appropriate, they will not commit suicide).

There are some other programs that tend to be broken in cancer cells too, but those are two of the main ones.

Insulin is chiefly removed by receptor-mediated endocytosis and proteolysis (the receptor organizes a vesicle being pinched off from the cell membrane with the insulin inside, and then the contents of the vesicle can be digested).

Insulin acts by binding to the insulin receptor on the outside of cells, so it isn't otherwise "used up" when it acts. Since a homeostatic signal isn't much good if you can't turn it down/off again, that breakdown mechanism is important.

> > > > > How many proteins are made per transcript before degradation is also liable to be very different for reasons like, for example, codon usage (rarer codons tend to have smaller tRNA pools) so it will take longer to translate and thus there will be fewer proteins, and any number of other things.

On that note, codon optimality also influences the half-life of mRNAs.

https://doi.org/10.1016/j.cell.2015.02.029

They're almost always broken down, but there are exceptions. In our gut, there is for example a cell type that's taking small samples of the proteins and longer peptides, in order to feed "information" to our immune system about what might be lurking in our gut. Unfortunately that includes prions. Some of the prions end up in neurons rather than the immune cells, and that's where the problem can happen. In principle it only takes one single prion to trigger the disease.

> If I remember correctly, only single amino acids can cross into the bloodstream

Small oligopeptides can also cross, via transporters (eg. SLC15A1) that can accept peptides of about 2-4 amino acids.