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Cell membrane is a phospholipid bilayer that regulates the entry and exit of molecules. Diffusion, osmosis and active transport are some forms of transport seen across the cell membrane. Here, let’s learn about them in detail.
- Phospholipids
- Proteins
- Carbohydrates
The main fabric of the membrane is composed of amphiphilic phospholipid molecules. Recall from chapter 4 that a phospholipid is a molecule consisting of glycerol, two fatty acids, and a phosphate-linked head group (Figure 8.3) . The hydrophilic “head” of these molecules are in contact with the aqueous fluid both inside and outside the cell. The hyd...
Proteins make up the second major component of plasma membranes. Integral proteins are, as their name suggests, integrated completely into the membrane structure, and their hydrophobic membrane-spanning regions interact with the hydrophobic region of the the phospholipid bilayer (Figure 8.2). Single-pass integral membrane proteins usually have a hy...
Carbohydrates are the third major component of plasma membranes. They are always found on the exterior surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids) (Figure 8.2). These carbohydrate chains may consist of 2–60 monosaccharide units and can be either straight or branched. Along with periph...
- Katherine Mattaini
- 2020
There are two major ways that molecules can be moved across a membrane, and the distinction has to do with whether or not cell energy is used. Passive mechanisms like diffusion use no energy, while active transport requires energy to get done.
- Sorry for the late answer (you might've already become a doctor), but for reference, pH dictates concentration of H+ ions, so it directly affects p...
- I just read about this. I believe larger nonpolar molecules (such as benzene) can cross via simple diffusion. Even though these have large ring str...
- This is wrong. Endocytosis and Exocytosis are examples of active transport as they require energy in order to work.
- Injection of insulin leads to fat and muscle cells to dock more GLUT-4 in their cell membranes. This allows for greater import of glucose into thes...
- Yes! Insulin signals for GLUT4 to be moved as necessary. I believe GLUT4 is just contained in vesicles in the cell.
- The plasma membrane. Learn about the amazing and versatile barrier that surrounds all of your cells: the plasma membrane! Learn. Fluid mosaic model of cell membranes.
- Diffusion and osmosis. Ever wonder why plants wilt if you don't water them? Find out here, and learn more about the basic principles of probability that underlie movement of water and other molecules in biological systems.
- Passive transport. Sometimes it pays to go with the flow! Learn about passive transport mechanisms, in which molecules travel across the plasma membrane by moving down their concentration gradients (no energy expenditure required).
- Active transport. In active transport, the cell has to pay (often, in the form of ATP) to move molecules against their gradients. Learn more about the amazing protein machines that make this possible.
- A. Passive Diffusion. Passive diffusion is the movement of molecules over time by random motion (also called Brownian motion) from regions of higher concentration to regions of lower concentration.
- B. Facilitated Diffusion of Solutes and Ions. Like passive diffusion, facilitated diffusion is the spontaneous (downhill) passage of molecules or ions across membranes through specific transmembrane proteins.
- C. Osmosis. Osmosis, the diffusion of water across membranes from lower to higher solute concentrations, is an essential activity. It allows cells to use water to maintain cellular integrity or to adapt to changes in the solute composition in the extracellular environment.
- 1. Osmosis in Plant and Animal Cells. We could present this section in the context of free water concentrations, but we will do so in the more familiar terms of solute concentrations.
Let's explore cell transport mechanisms that regulate what can go into or out of a cell. You'll examine the distinctions between passive and active transport, and learn how ions like potassium and sodium, along with glucose, traverse cell membranes.
- 12 min
- Raja Narayan
6.2: Transport Across Membranes. Plasma membranes act not only as a barrier, but also as a gatekeeper. It must allow needed substances to enter and cell products to leave the cell, while preventing entrance of harmful material and exit of essential material.
