Skip to main content
16 votes
Accepted

Why can't H3O+ ions pass through aquaporins?

This question has been directly addressed by the paper The Mechanism of Proton Exclusion in the Aquaporin-1 Water Channel. I think it's a pretty good one too! I paste the abstract below: Aquaporins ...
S Pr's user avatar
  • 6,262
7 votes
Accepted

How do lipid-soluble substances diffuse through the cell membrane?

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 ...
another 'Homo sapien''s user avatar
7 votes
Accepted

Difference between going against and going down a concentration gradient

"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 ...
Bryan Krause's user avatar
  • 46.1k
6 votes
Accepted

Why do ion leak channels exist?

Check the parameters that go into the Goldman equation... it shows that permeability of ions is as important as their concentrations. If the permeability is zero, there is no potential. Because other ...
Bryan Krause's user avatar
  • 46.1k
5 votes
Accepted

How does carbon dioxide diffuse into red blood cells?

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,...
Moyo Freeman's user avatar
4 votes
Accepted

Is co-transport within a cell active or passive transport?

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 ...
canadianer's user avatar
  • 17.8k
4 votes
Accepted

How are lipid-coated mRNA-based vaccines transported into cells for expression?

I can't give an authoritative answer on this because my PhD work was based on mRNA delivery using peptides instead of lipids, but many of the concepts are the same. I also don't have time to provide ...
user137's user avatar
  • 5,348
4 votes
Accepted

Which complexes physically pump protons in photosynthesis?

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 ...
David's user avatar
  • 26.2k
4 votes

Examples of passive membrane transport proteins that only transport in one direction and their mechanism

Voltage-gated proton channels are passive transmembrane transport proteins that will only transport protons in one direction. These channels will be open when there is a lower pH in the cytoplasm, ...
Eonema's user avatar
  • 878
4 votes
Accepted

Are channel proteins considered a type of integral protein or peripheral protein?

Channel proteins are located on the peripheral surface of the cell, however, they have the function of integral proteins. Is my understanding correct? No. In this case of nomenclature, the context/...
S Pr's user avatar
  • 6,262
3 votes
Accepted

How does exercising/starved muscle import glucose (released by liver)?

GLUT4 is the major glucose transporter in muscle even in exercise. However, during exercise, it is translocated to the cell surface by contraction-triggered, insulin-independent mechanisms, such as ...
Adhish's user avatar
  • 1,307
3 votes

Does osmosis require a protein channel?

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 ...
canadianer's user avatar
  • 17.8k
3 votes

What is the purpose of co-transport?

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 ...
Jam's user avatar
  • 1,506
3 votes
Accepted

Can Oxaloacetate cross the outer mitochondrial membrane?

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 --...
Victor Chubukov's user avatar
3 votes

Are receptors integral membrane proteins or peripheral membrane proteins?

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, ...
Bryan Krause's user avatar
  • 46.1k
3 votes

Membrane Potential Question

Usually we use the Goldman Equation when calculating membrane potential with multiple ions and the Nernst equation for calculating reversal potentials for individual ions. Try out the Goldman Equation ...
Bryan Krause's user avatar
  • 46.1k
2 votes

Why do cell membranes let small non-polar molecules through but won't let small polar molecules through?

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 ...
GH05T's user avatar
  • 53
2 votes

Transport mechanism in absorption of monosaccharides in small intestine

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 ...
bpedit's user avatar
  • 1,351
2 votes
Accepted

Are Na+/K+ active pumps and K+/Na+ "Leak" channels same as given in the figure?

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 ...
Bryan Krause's user avatar
  • 46.1k
2 votes

Are cells electrically neutral or charged to setup the membrane potential across them?

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 ...
Bryan Krause's user avatar
  • 46.1k
2 votes
Accepted

How does 'phosphorylation of glucose' maintain concentration gradient in membrane transport (facilitated diffusion)?

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 ...
Bryan Krause's user avatar
  • 46.1k
2 votes
Accepted

COPI/COPII proteins and kinesins/dyneins

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 ...
canadianer's user avatar
  • 17.8k
2 votes
Accepted

Can the Na+/K+ pump backwards to generate ATP?

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 ...
canadianer's user avatar
  • 17.8k
2 votes
Accepted

Exocytosis of synaptic vesicles

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. ...
Bryan Krause's user avatar
  • 46.1k
2 votes
Accepted

Giving a sign to Pressure Potential, Osmotic Potential And Other Similar Quantities

I think you already know the sign convention in calculating the water potential: the addition of solutes lowers the potential (negative vector), while an increase in pressure increases the potential (...
Bipasha's user avatar
  • 964
2 votes

What would happen to the membrane potential if a cell didn't have developed relative refractory period?

" If the Na+ voltage gated channels remain open instead of getting deactivated during the re-polarization period, would the membrane potential become 0 ? " No, if Na+ channels remain open ...
program's user avatar
  • 208
2 votes
Accepted

Understanding the general dynamics of protein diffusion in cell plasma membrane

You might want to go to the library and have a look at Alberts „Molecular Biology of the Cell“, an older edition of which is also available on the NCBI Bookshelf. Publication-grade knowledge might be ...
markur's user avatar
  • 1,779
1 vote

What are the (evolutionary) advantages of secondary transport?

I think an easy analogy for why this approach evolves is to think of how humans use electricity (or energy more broadly). Although it is feasible to have localized electricity generators (for example,...
Bryan Krause's user avatar
  • 46.1k

Only top scored, non community-wiki answers of a minimum length are eligible