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The membrane bilayer is held together by hydrophobic forces. This is an entropy driven process. When a greasy or hydrophobic molecule is suspended in water, the water molecules form an organized "cage" around the hydrophobic molecule. When two hydrophobic molecules come into contact, they force the water between them out. This increases the entropy because ...


6

The original figure that Danielli and Davson proposed looks like this (from the original publication): It shows the phospholipid bilayer of the membrane (which is correct) embedded between two layers of globular proteins. The hydrophobic tails of the lipids are orientated towards each other, while the hydrophilic heads are oriented to the outside. ...


6

You may want to look into "Evolutionary - Developmental Biology", which deals with how an embryo develops into a grown organism. Thus, by combinatorial specifying the identity of particular body regions, Hox genes determine where limbs and other body segments will grow in a developing embryo or larva. A paragon of a toolbox gene is Pax6/eyeless, ...


5

Your thinking is correct based on typical carbohydrates, but glycerol, the backbone of the phospholipid, is a 3-carbon carbohydrate that is usually derived from glucose. It is not a sugar, but it does fall into the general class of polyols (aka sugar alcohols) that are a type of carbohydrate. A carbohydrate definitely is an important structural part of the ...


5

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 ...


4

Many cell components are not simply hydrophobic or hydrophilic, but have dual affinities. Proteins typically have structures which result in the interior of the protein being hydrophobic and the exterior, which is exposed to the water in the cytosol, being hydrophilic. Thus, differences in polarity between different regions allow proteins to be dissolved in ...


4

Some thoughts on this. First of all, the positive-inside rule, proposed by Gunnar von Heijne, is an empirical rule based upon observations, not one derived from theoretical considerations, so any explanation is simply an attempt at a rationalisation. Having said that, here are three of those rationalisations: the membrane potential is usually negative ...


4

The main difference is that memory B cells start an immune reaction much more effective and faster than naive B cells. The reaction is also specific towards the antigen. The memory B cell has a specific membrane receptor for an antigen. It produces specific antibodies only when exposed to the antigen. References: Tangye SG, Avery DT, Deenick EK, Hodgkin ...


4

In human cells it takes about 20 s to make a 20,000 dalton enzyme. Assuming that the cells concerned are already making mRNA for the enzyme, there will be two main factors: (1) The time taken to synthesize the polypeptide (2) Any time taken to fold the protein (If the enzyme is secreted from the cell there will also be the time taken for the protein to ...


4

There are several, but I guess the most well known is the neuron action potential, where the concentrations of Na+, K+, and Cl- ions determine the membrane potential of the cell. When the potential reaches a certain level, it triggers the action potential. You can read about this in much more detail on wikipedia, ...


4

Disclaimer: This is my understanding of the egg anatomy as a general biologist. There is most certainly better references and sources out there to explain this (please add better references if you know of any). If I understand you correctly, your question is why we do not see cell organelles in a cracked or boiled egg. If so, your question seems to stem ...


3

Yes. But it is incorrect to call mitochondria an organism now. Most of their genes were lost and are now encoded in the nuclear genome It gets most of its metabolites It is not known. See the other post for details. Why membrane: I guess you know that. Why folded: you guessed right. Only ovum donates mitochondria and other cytoplasmic factors. Sperm just ...


3

There's nothing wrong in your statements! Maybe your professor was talking about glycolipids, that are lipids (also phospholipids) with a carbohydrate attached; they can be found on the outer surface of all eukaryotic cell membranes. They are important because they work as a recognition site for specific chemicals or for antibodies.


3

Cyclin dependent kinase is the answer for the first question. Cyclin concentration increases during m phase and falls in g1 s and g2 phase as it is degraded. Cdk is always present in the cell but gets activated during m phase, when cyclin is present. (cyclin dependent) Cancer cells do not require growth factors to stimulate cell division. They have ...


3

Because cells are not only characterized by by their genetic material and other interior components, but also by the genes they express. Cells have to fulfill multiple different functions to be able to build complex multicellular organisms. Differently expressed genes lead to different proteins made in the cell, which leads to different morphology, shape or ...


2

MitoSOX looks pretty cool. I've never used it myself, but I'm sure you could see some cool mitochondrial dynamics going on. Its a bit pricey though, but all dyes are going to be. Even at only 8 hours you should probably be able to see a few divisions, which would be cool with hoechst.


2

groups of cells A normal light microscope. 4x-20x magnification individual cell Lo resolution: Light microscope with 40x magnification. High resolution: Confocal microscope with 40-100x magnification. cell organelles Low resolution: Confocal microscope with >=60x magnification. Note: some organelles are easier to visualize while others ...


2

There is a wide continuum from "cancer" in the sense of uncontrolled cell division (this could include even things like 2-3 extra cells making an imperceptible, microscopic bulge in your colon) to cancer in the sense of huge lumps of meat growing on your body and killing you painfully within X months. For the latter kind, many "stages" of "evolution" must be ...


2

My understanding is that telomeres are linked to cell senescence, which is not necessarily the same thing as organism senescence. So even if you could track down a method to slow cell division, it would more likely mess with organ function now rather than extend life. Here's a nice summary of cell senescence: ...


2

Flagella in prokaryotets is very different from that of eukaryotes. The main structural protein in a prokaryotic flagellum is flagellin. The flagellar motion is caused by a molecular motor similar to Mitochondrial ATP-synthase; molecular motion generated by the chemiosmotic energy. Eukaryotic flagella or cilia are made of microtubules with dynein attached ...


2

What may be confusing is that the myelin is wrapped around the membrane of the axon. The easiest way to see this is in cross-section: From here. The axon is indicated by #1 in the diagram and the myelin sheath is #4 The intracellular space (as represented by the horizontal resistors in the case of your model of the axon) is the fluid, replete with ...


2

The central dogma of molecular biology states that DNA encodes the information for building proteins, the information is copied to messenger RNA through transcription, and messenger RNA is used to build proteins through translation. DNA is also copied through replication. So while it's true that DNA contains the information needed to build a living ...


2

Embryonic cells "know" where they are relative to each other by chemical signals, same as in adults. These molecules are known as morphogens (specific examples include the sonic hedgehog and β-catenin). The amount of morphogen in a region of cells determines which gene gets turned on and thus what it develops into. And the amount varies by how far they are ...


2

I wanted to add some helpful references. The 6th edition of the Gilbert Developmental Biology textbook is available on NCBI bookshelf. It's a bit old (2000), but much of the information is still relevant. You can search this textbook for specific terms but not browse. There is also a collaborative science/fashion project between the Storey sisters, called ...


1

yea the hox genes are essential for the the specification of the location but the actual growing of the limbs are determined by a series of protein and other factors. proximal limb contains fgf(fibroblast growth factors) wnt(look up wnt pathway) and high levels of retonic acid where distal limbs shows high fgf's high wnt and little to none RA. the sonic the ...


1

I don't think the microtubules shorten. The disassembly of tubulin (dynamic catastrophe) happens from its + end which in this case is protected by the kinetochore proteins. The separation of chromatids, I guess, happens via a kinesin mediated movement. I have to revise my basics now :P


1

Your hypothesis is incorrect. You must be assuming that lactamase destroys the antibiotic with perfect efficiency. This is incorrect. You must be assuming that the population will remain genetically stable. This is doubly incorrect. Firstly the penicillin will select highly resistant bacteria which suffer a greater fitness burden from expressing the ...


1

activation energy - there is an energy barrier that must be crossed by supplying energy for a chemical reaction to proceed - enzymes bring substrates and reagents into close proximity so the amount of energy needed to initiate, sustain and complete the reaction is reduced in the process.


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This answer doesn't add anything to the others, but is an attempt to explain using different language. "my question is why the water of cytosol doesn't dissolve the ionic part of the lipid bilayer" In a sense, it does. See my diagram below The bilayer is composed of phospholipids, classic amphiphiles with a polar head group and a nonpolar tail group. The ...


1

ADDENDUM Water can disrupt the intramolecular hydrogen bonds by bonding to the donors/acceptors. However, water in many cases can also act like a bridge and stabilize the protein structures. As already pointed out by jarlemag, the hydrophobic residues can push the water out of the pockets where intramolecular hydrogen bonds are to be formed. You may notice ...



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