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 ...


7

Reducing your question to its fundamental misunderstanding Similarly one could ask "Mammals and birds are vertebrates. Why are they grouped into two separate taxa?" (Bacteria and Archea include all procaryotes unlike my example). Or even better, one could ask "procaryotes and eukaryote are all alive. Why are they grouped into two separate taxa?" At the end ...


6

This question has been asked before: Is there an advantage to linear chromosomes? Firstly, I should state that the generalisation that ALL prokaryotes have circular genomes is incorrect. A growing number of prokaryotes have been discovered which have linear chromosomes, such as Borrelia burgdorferi ,which causes Lyme disease, members of the Streptomyces ...


5

This is an interesting question (I really mean this — see below), for which a straight answer is remarkably difficult to find on the web. When I googled for it I got pages with statements that obligate anaerobic bacteria still had the electron transport chain (ETC) and ATP synthase as there were different electron acceptors other than oxygen. Yes, we know ...


4

They did evolve, and they keep evolving every single day, like all other organisms. Let's take an example. Prokaryotes acquire antibiotic tolerance in hospitals, and have evolved resistance to pretty much every antibiotic available, within a few years of their discovery. More fundamentally, what is evolution (in a classic Darwinian definition)? Evolution ...


4

According to this Wikipedia article: "The Shine-Dalgarno (SD) sequence is a ribosomal binding site in bacterial and archaeal messenger RNA, generally located around 8 bases upstream of the start codon AUG.1 The RNA sequence helps recruit the ribosome to the messenger RNA (mRNA) to initiate protein synthesis by aligning the ribosome with the ...


3

Mitochondria pumps out the H+ perhaps just because there is no disadvantage of it. Once they've evolved such a machinery with complex network; they weren't threatened to evolve any opposite-system. Any opposite system too; would not plausibly disadvantageous; and really happens in case of chloroplast; another sort of cell-organelle. 1: image from Plant ...


3

Osmosis works across every cell membrane along a concentration gradient as its a physico-chemical principle. Water can cross the membrane (or cell wall), while the substance dissolved in it (for example salts) can not. Because eukaryotic cells only have a cell membrane, they will burst eventually, while bacteria (and also plant cells) have a more rigid cell ...


2

Animal cells Generally all (animal) cells have different shapes because they do different things. Each cell type has a specific role which it has to play in order to assist the body in working efficiently and functionally. Thus their shape supports them to carry out these roles effectively. Look at (animal cells): Neurones Photoreceptors Immune Cells ...


2

There are two ways of classification of Prokaryotes(on the basis of mode of nutrition) that you will generally come across: Way 1 Way 2 The First classification is very much based on a complete segregation between respiration and photosynthesis. In the first classification, anything that needs another animal to get food is a 'Heterotroph'. (Here, ...


2

Yes there are, though I had to dig a lot to find them. They are called strictly fermentative bacteria. Lactic acid bacteria (Lactobacillales (Firmicutes)) ferment glucose through pyruvate to lactate using the glycolytic pathway, and include the genera Streptococcus, Lactococcus, Lactobacillus, and Leuconostoc. From Madigan et al. 2014 Brock biology of ...


2

Several answers to this question: Much of the time what bacteria are doing to repair DSBs is actually non-homologous end-joining, which does not require strict homology. This is the more likely mechanism earlier in the cell cycle when copy number is more likely to be ~1. If cells have completed DNA replication (later in the cell cycle), there are at minimum ...


2

The mitochondrial genome is highly reduced; many mitochondrial genes have been transferred to the nuclear genome (see endosymbiotic gene transfer) and therefore the mitochondria are fully dependent on the nucleus to function. Bacteria need not necessarily have a plasmid. Usually, all the important genes are present in the chromosomal DNA. Since the ...


2

These resources may help. This book, “Plasmids of Eukaryotes”, explains that... “The possession of plasmids was for a long time recognized only in the bacteria. It is now evident that plasmids, or replicative forms of DNA structurally and experimentally comparable to bacterial plasmids, exist in eukaryotic organisms as well. Such plasmids are in fact common ...


1

The diagram is a composite of all 16S RNA structures. It has a summary with it that explains all. "16S rRNA secondary structure, showing conserved parts for Prokaryotes (IUPAC letters) and amongst Archea/Bacteria (asterisks) all others as dots. Adapted (in SVG!) from Woese Bacterial evolution 1987" The base pairs that are marked with A,U,C,G are ...


1

This paper suggests the opposite in mammalian cells. Obviously, gene regulation is quite different in prokaryotes, so don't know how much confidence you want to put into that one. This paper suggests more of the same, but includes some caveats related to prokaryotes that may pique your interest. They do a pretty in-depth dive of GC content near genes from ...


1

This is a great question. I decided to research it and here is what I found. For some reason the GOE is not on lists of the "big 5" mass extinctions. The question is why? I think it's due to the pace of the event. The event is described as happening 2.45–2.32 billion years ago. This is a timescale in billions of years. So it isn't really a proper mass ...


1

If you mean "why do we have mitochondria instead of our cells doing the work themselves" Then I can think of several answers. First, oxidative phosphorylation must take place within an organelle, and requires specialized cellular machinery to occur. So either a prokaryote can wait a couple million years to evolve these structures, or it can ask its friend ...


1

I don't know if this is a proper answer... and this answer is really late... but if I remember correctly, the mitochondria pump H+ out to better compartmentalize the activities of the TCA and other oxygen-dependent metabolic processes within the mitochondria. This compartmentalization helps further minimize the possibility of a process or reaction to take ...


1

Probably someone can dig up an answer that answers this question, but I'll just repeat it here shortly: You'll get the same gradient if you pump protons out or in. You're not specifically decreasing the outside pH when you pump protons, you're mainly increasing the inside pH. As long as there is a gradient that can be used to achieve other things for the ...


1

This is a very late answer, but many Mycoplasmas lack most major metabolic pathways beyond glycolysis; so no electron transport chain, and no tricarboxylic cycle (refer Pollack et a. 2002).


1

As you note, "Monera" includes both Bacteria and Archaea -- but genetic analysis and molecular comparisons reveal without a shadow of a doubt that Archaea share a more recent common ancestor with Eukaryota than they do with Bacteria. Consequently, "Monera" is a paraphyletic group, not a proper taxonomic category. Thus the term has been abandoned in favor of ...


1

I'm surprised this term shows up much anymore. Though it's a part of history now, the following paper by Woese demonstrated the three domain system long ago. This, however, is the net result of the sequenced genomes of eukaryotes, archaea and bacteria: Source: Toward automatic reconstruction of a highly resolved tree of life. The phylogenetic differences ...


1

I wonder whether it is just some sort of functionless drift. I don't know about bacteria, but think the example of some human viruses may be instructive. The human herpes simplex 1 virus (causes cold sores) has a very high GC content, whereas the quite closely related (in terms of gene repertoire and organization) human varicella zoster virus (causes ...


1

Interesting question. I think that bacterial GC content diversity boils down to a mix of mutational biases, such as using different polymerase and replication/repair gene isoforms, and environmental pressures, such as temperature and salinity, that have placed different selection pressures on the various microbes. I would read over the linked papers for ...


1

The force driving osmosis exists in any system with an imbalance of solute molecules across a semipermeable membrane. Think of a concentration gradient as an electrical potential, where high concentration is negative charge and low concentration is positive charge. In the case of electricity, its the magnetic force which causes the interactions leading to ...


1

The processes that occur at the ER membrane in eukaryotic cells take place directly at the bacterial plasma membrane. Phospholipids are synthesised and inserted at the plasma membrane, and there is a protein translocation apparatus for translocation of proteins into the periplasmic space and insertion of transmembrane proteins into the plasma membrane.


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