7

No, carriers are not the same as pumps. Carriers may or may not carry out active transport and pumps always use energy. Carriers, for example, can make use of the concentration gradient of a certain ion built up by pumps to transport other molecules actively against their gradient. For example, the glucose transporter uses the sodium gradient to transport ...


6

See this paragraph and image from The Cell: A Molecular Approach. 2nd edition.: During passive diffusion, a molecule simply dissolves in the phospholipid bilayer, diffuses across it, and then dissolves in the aqueous solution at the other side of the membrane...Passive diffusion is thus a nonselective process by which any molecule able to dissolve in the ...


6

Pyruvate is negatively charged and quite polar, which makes it unfavourable to diffuse directly through any membrane. The outer mitochondrial membrane contains porins, which allow small molecules, like pyruvate, to passively diffuse through. Specifically, pyruvate uses voltage dependent anion channels. The inner mitochondrial membrane lacks such channels and ...


6

You have one misconception about the endocytosis: In the process no hole in the membrane is generated. It works in principle like in the figure below (it is of course more complicated, but this should explain it): The membrane forms a vesicle around the particle which shall be integrated until it is completely surrounded by a membrane. At this point the ...


4

According to wikipedia, cardiolipin is found in two places, the inner mitochondrial membrane, and bacterial membranes. Given the endosymbiotic origin of mitochondria, it makes sense that they would retain some remnant of their bacterial ancestry. But more importantly, cardiolipin plays a role in the enzymatic functions of mitchondrial membranes. Cardiolipin ...


4

Wikipedia is your friend: Exocytosis... is the durable, energy-consuming process by which a cell directs the contents of secretory vesicles out of the cell membrane and into the extracellular space. and Endocytosis is an energy-using process by which cells absorb molecules (such as proteins) by engulfing them. Emphasis mine. Here's a nifty paper ...


4

"Concentration" is "how much stuff is there someplace?" "Concentration gradient" is "how much is concentration changing from point A to point B?" Imagine a terrain where concentration is represented by height. "Down" a concentration gradient means from high concentration to low concentration - this is the direction things would move via simple diffusion. "...


4

Under the right conditions, emulsions of lipids (fatty compounds) and water can cross cell membranes. If the emulsion is prepared correctly, a structure known as a liposome forms, which is essentially a "bubble" with a layer of fatty molecules on the outside and water at the center. This has been studied intensely in biotechnology, because such liposomes can ...


4

Short answer Facilitated diffusion is a passive process in which membrane channels mediate the transport of polar, or big molecules that are not solvable in the cell membrane. Co-transport, on the other hand, is active transport, as it depends on the electrochemical gradient of ions across the cell's membrane, particularly Na+. Because ATP or other energetic ...


4

The red cell membrane is highly permeable to gases because the molecules of gases are small, uncharged, and soluble in lipids, such as those of a bilayer.The effect of 4,4′-diisothiocyanato-stilbene-2,2′-disulfonate on CO2 permeability of the red blood cell membrane Remember red blood cells are cells like any other cells only that they have hemoglobin and ...


4

General Approach Although I am not an expert in this area, as an ex-chemist I find this topic one of the most fascinating and fundamental in chemical biology. I have constructed an answer starting from my copies of the 5th (available on line) and 6th editions of Berg et al. Biochemistry (2003 and 2007, respectively), and then searched the Protein Data Bank ...


3

In general the outer mitochondrial membrane is thought to be basically permeable (through porins) to small molecules such as OAA. As is typical in biology, the situation may actually be more complex -- see for example this paper. But I think the default assumption is that metabolites freely cross the mitochondrial outer membrane. You might also ask whether ...


3

Co-transport, also called secondary active transport, is a form of active transport because it is using the energy from one concentration gradient to transport another molecule across the membrane against its concentration gradient. The concentration gradient which drives this process requires energy to set up in the first place, which is why co-transport is ...


3

I don't know any-such continuous-membrane-material that can do so. But yes certain membrane-transport-proteins can do so. Carrier proteins are normally highly specific about in which-direction to transport which molecule; and in general, they are classified as uniporters, symporters and antiporters. * So an uniporter would be an accurate example of ...


3

All the receptors I know about are integral, transmembrane proteins. It would certainly be possible for a receptor domain to exist on a peripheral protein that interacted with a transmembrane protein, but I don't know of any examples of this: an extracellular peripheral protein would tend to float away, which is a bit of a problem if they aren't intended for ...


3

Just to extend the answer from @Amory slightly, I think that the terms active and passive transport are best kept for describing transmembrane movement of molecules. In the case of exocytosis the only transmembrane event is when a secreted protein is first inserted (usually cotranslationally) across the endoplasmic reticulum membrane. I'm not aware of any ...


3

Normally, epithelial cells of mucous membranes express a chloride ion channel that allows movement of Cl- down its electrochemical gradient and out of the cell. This increase in extracellular electrolytes draws water out of the cells by osmosis, hydrating the mucus. In cystic fibrosis, this protein is defective, most commonly caused by misfolding and ...


3

Would it not then make more sense for the latter substance to simply be actively transported to its destination, as opposed to involving another substance which has no net movement at the end of the process? But where would the energy for the transport come from! Thermodynamics tells us that the universe tends to increase the amount of disorder (Entropy). ...


2

Since posting, I did some more research using background refs from the intro (who knew?). The trick seems to be that when protons are pumped out, the cell regenerates them from water in order to maintain pH. So the solute concentration DOES increase inside the cell with more Na/H transport.


2

Osmotic pressure: pressure applied by a solution to prevent the inward flow of water across a semi-permeable membrane. Osmotic potential: the potential of water molecules to move from a hypotonic solution to a hypertonic solution across a semi-permeable membrane. Osmotic pressure can be calculated using the following formula: $$Π = iMRT$$ where $Π$ is ...


2

The molecule won't "stick" to the polar amino-acids for at least three reasons : The amino-acids might not all be on the same plan, so their is always a force pulling the molecules transiting trough the channel in one direction (in or out the cell) When a flux is established, the repulsion forces between the molecules will force them to go in a direction, ...


2

Below is the structure of a Na+/K+ ATPase, i.e., the sodium/potassium pump shown on the left in your figure: (image from here) Compare to the structure of a potassium leak channel (the type of channel depicted on the right in your question): (see this publication; image from here) It's clear they are quite different beasts, without much similarity at all ...


2

The plasma membrane consists of hydrophobic and hydrophillic characteristics. Towards the outsides, they are hydrophillic, so they can create bonds with water. The insides are hydrophobic, allowing no water inside and keeping them tight together due to the polar forces. An non-polar particle (if small), can pass through this because it does not interfere ...


2

From my initial reading on this, the SGLT1 does not itself directly use energy in the form of ATP. https://en.wikipedia.org/wiki/Sodium-glucose_transport_proteins It appears the uptake of the sugars by this protein are achieved by cotransport. In this case, they "hitch a ride" into intestinal epithelium by following the flow of sodium ions back into the ...


2

Interesting question. The term anterograde refers to movement in the forward direction. In the context of vesicular trafficking, anterograde refers to (1) movement from the site of protein synthesis in the rough endoplasmic reticulum (RER) towards the Golgi and then (2) movement from the Golgi towards the final destination in the cell. Both processes rely ...


2

Sort of a "magic trick" that biology does. With facilitated transport, the movement is passive. That is, you have a protein that certain molecules/ions can pass through, but you aren't doing any pumping or using energy to move molecules. That means that the molecules are free to move in either direction, according to concentration (and electrical) gradients....


2

It isn't neurons that are charged, it is their membranes. From the distance of other cells, they "see" both the charges inside and outside the membrane, so there isn't any substantial repulsion on that scale. The charge across a membrane comes mostly not from the Na+/K+ pump directly, but due to differential permeability of the membrane to different ions. ...


2

All enzymes can theoretically catalyze the reverse reaction. Researchers have driven the Na+/K+ ATPase to synthesize ATP with artificial ion concentrations: We have studied the apparent affinity for K at its intracellular discharge sites by measuring the rate of ATP synthesis as a function of the internal K concentration in resealed red blood cell ghosts,...


2

That sentence is located in a paragraph titled "Stages 5-7: Endocytosis and recycling": it's talking about recycling exocytosed membrane which is necessary for making vesicles for further exocytosis. The sentences before the part you quoted are: Synapses possess highly efficient mechanisms for retrieving SVs from the plasma membrane of the presynaptic ...


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