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My first thought was this: According to Wikipedia (citation provided) Between 50 and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day. For every cell that dies a new one must be born, so there must be at least between 50 ...


11

Morphological point of view Neurons cannot divide because they lack centrioles. Because centrioles function in cell division, the fact that neurons lack these organelles is consistent with the amitotic nature of the cell [1]. Functional point of view New cells in the nervous system wouldn't do any good. The whole nervous system is based on ...


10

Neurons do not divide due to the reasons mentioned in Cornelius's answer. However, some new neurons can be generated in adults (Ref: Neuroscience, 2nd edition). Generation of new neurons in adults was first demonstrated in birds, where labeled DNA precursors could be found in differentiated neurons. Experiments in mammals and humans demonstrated later that ...


9

There are many different ways to make a spindle in plant cells: Mitotic spindles may be organized at centriolar centrosomes (only in final divisions of spermatogenesis), polar organizers (POs), plastid MTOCs, or nuclear envelope MTOCs (NE-MTOCs). Of these, only the latter has been observed in angiosperms (flowering plants). For more info (and the source ...


9

First of all, in eukaryotes (as far as I'm aware), older cells can be distinguished from younger cells due to telomere shortening, so there is an ageing process. HeLa cells mentioned by @Gary Chou have a more active telomerase which mitigates telomere shortening, allowing cells to continue to divide indefinitely. I think it's a very interesting question ...


8

No, there was nothing special about Henrietta Lacks, apart from the fact that her cells have been used for so many years (without her knowledge or consent, by the way). She was not immortal, her tumor cells were. The HeLa cell line comes from her cervical cancer cells. The rest of the cells of her body were not immortal any more than yours or mine are. Such ...


7

So in mitosis, the cell has to split itself into two cells; each daughter cell has a functional genome that may again split into more daughter cells. The cell replicates the DNA before dividing, so the error in replicating 3x or 4x is that upon division, the daughter cells will have more DNA than the initial cell, and every generation will have more DNA than ...


7

You talk about memory loss. The hippocampus is involved in the formation and storage of memories and indeed one of the few places in the brain where new neurons are formed. The formation of new neurons here is indeed linked to the formation of memories (Coras et al., 2010). Hippocampal neurons do not lack centrioles (Dotti & Banker, 1991; Poppov & ...


6

The hematopoietic stem cells are quite rare, and each progenitor cell produced by a stem cell gives rise to a large number of red blood cells (and other blood cell types). I'm not sure if the precise number of offspring for the earliest progenitor cells is known in vivo, but recent cell culture models indicate that early progenitors can give rise to as many ...


5

The question is a bit vague but I will take it to mean the following Why does it (the body) stop in terms of height or physical mass when it can still keep on growing? The answer is physics, specifically the ability for a body of a specific shape and structure to support itself and move itself, followed by the energy requirement to feed all those cells. ...


4

In case of gametogenesis (let us talk about spermatogenesis) gametes are formed from meiotic division of Primary spermatocytes. In Primates Primary spermatocytes are cells that that are formed from mitotic division of B spermatogonia (which is another class of germ cells) which inturn are formed from mitosis of Ap spermatogonia which arise from mitotic ...


4

Amoebas undergo binary fission, which is a much more simplistic process than mitosis. In binary fission, the duplicated chromosomes simply separate as the cells is pulled apart. There are no spindle fibers used in this method of cell division.


3

Sperm can already be generated using stem cells http://blogs.discovermagazine.com/d-brief/2016/02/25/scientists-grow-working-sperm-from-stem-cells/#.V-UADBV94o8 Also, heart, liver and kidney cells as well. http://www.popsci.com/scientists-grow-transplantable-hearts-with-stem-cells http://www.ncbi.nlm.nih.gov/pubmed/26458176 Full organs are still far. The ...


3

You pretty much have answered your own question. It is a math problem. Cells are burning up their telomeres during fetal development onward but the cells are multiplying exponentially in number. But biology is a bit messy, embryonic stem cells do have telomerase activity and their telomerase are maintain. So the clock doesn't start counting down ...


3

As far as I know, the function is not truly known, although there are some seriously interesting guesses. Part of the problem seems, from scanning the literature, to be that it's not easy or obvious to disrupt centriole orientation. This paper in PLoS Biology presents some really interesting results, in particular two piece of evidence: Centriole ...


3

It can actually on very rare occasions however, it is also highly problematic and generally creates deleterious mutations and can inactivate genes. Depending on the location of the cell and the cross-over within the genome, it can also contribute to the formation of cancer. For instance, in the case of retinoblastoma, if there is one mutated copy of RAS on ...


3

"How are germ cells not reduced in number?" It does happen. Germ cells do eventually run out. It is called menopause in women. And age related infertility in men. As for your question of where do germ cell come from? Much like were do muscles cells come from?, you have to be specific. Germ cells comes from the gonads (ovaries and testis) would be a simple ...


3

The common phrase I've heard is "DNA isn't a blueprint, it's a recipe". More specifically, the nucleotides in DNA correspond to which proteins get made (coding DNA) and when and where (regulatory DNA). Just like a recipe doesn't specify the exact color of a cake or the position of each raisin, but does say "cook the cake for this long" (which will, in ...


3

Biological nomenclature can be impenetrable. Almost certainly, at some point in history, there were cyclins designated with these letters. Researchers would have discovered apparently novel cyclins which were subsequently determined to be part of an existing family and renamed. For example, this paper reports the discovery of: a new cyclin, cyclin M, ...


2

You have a few misconceptions about stem cells, I will try to explain where they are. First of all, cells are not independent. They influence each other with signals and secreted messenger substances. If you look at a human embryo the state of totipotency (where all cells can differentiate into each cell type of the body) ends after 3-4 days when the ...


2

Short answer: No. Eukaryotes have more ways of maintaining telomere length than via telomerase alone and all organisms with circular genomes do not need to worry about telomere length anyway. Long answer: Firstly, the telomerase system is not the only observed mechanism in Eukaryotes that elongates telomeres. Other mechanisms such as the transposition of ...


2

Here is a study of planarian worms, which are immortal in asexual reproduction and mortal in sexual reproduction. Hydras also become mortal after they reproduce sexually. Relevant to your question: Cells within planarian worm differ in expression of telomerase active subunit depending on body part. Immortal (asexual) worms have more expression in the area ...


2

I believe your question is unclear, but if am I am understanding the question as: If H.L., or anyone, did not develop cancer, was never introduced to any physical insult, would they be immortal? The answer is no, they would not. When we talk about aging in biology, we use the technical term senescence. Without a cancerous influence normal aging would ...


2

Plant cells without centrioles build special vesicles from their Golgi apparatus which are important for cell division. This website has a nice comparison of different modes of cell division. Look for "Cytokinesis by Phragmoplasts" to get to the relevant part. Phragmoplasts are not exactly a replacement for centrioles, but the whole process is a little ...


2

The mechanism is straightforward: in Metaphase I of Meiosis, chromosomes line up in two lines, with homologous across from each other, which allows them to interact by crossing over. In Metaphase of Mitosis, the chromosomes are all lined up single file, so the homologous chromosomes cannot interact.


2

Molecules like complex lipids and carbohydrates are all synthesized by a special class of proteins that catalyze chemical reactions, called enzymes. Since the information of these proteins is coded for in the nucleus, you can imagine that ultimately the synthesis of these molecules does boil down to the genome. The basic building blocks that the enzymes use ...


2

Couldn't fit in a comment... To me, your question sounds like "what are the possible advantages of sexual reproduction over asexual reproduction?" but in the meantime you're saying that you're not interested neither in the advantage of recombination nor in the advantage of "independent assortment". I don't quite see what you mean by "independent assortment" ...


2

I am presuming this a Blue Green Algae(BGA) Identify your algae Growth rate for N1, N2 biomass at t1 and t2 time respectively, can be give as, Growth rate: $K'$ = $\ln \frac{(N_2 / N_1)}{(t_2 - t_1)}$ (source: csiro.au) So, by this equation it is easy to calculate the doubling time of your algae. For BGA normal doubling time is 6-8 hours.$^2$ ...


2

Another PLOS One article gives evidence of change both in volume and in surface area, but it is across mitosis phases. It could still be considered constant during cytokinesis only. It seems that cell shape and size have important function during mitosis, according to this research. It would be interesting to investigate different models from your advisor'...


2

We need to make a distinction between the genetic map of a chromosome, which is usually built up from meiotic recombination frequencies between linked genetic markers, the physical map of a chromosome, which used to be made up of clones and contigs, but is now usually derived from the reference genome sequence, and the cytological map of a chromosome, which ...


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