How do phospholipids move in the bilayer?

Phospholipids in the lipid bilayer can either move rotationally, laterally in one bilayer, or undergo transverse movement between bilayers. Lateral movement is what provides the membrane with a fluid structure. Phospholipids stay in one region for a short while before hopping to another location.

Why can lipid molecules move across the bilayer?

Because of the chemical and structural nature of the phospholipid bilayer (hydrophobic core), only lipid-soluble molecules and some small molecules are able to freely pass through the lipid bilayer. Therefore, the passage of most molecules and ions is aided by the presence of specific membrane transport proteins.

Is it possible to move directly through the phospholipid bilayer?

Gases, hydrophobic molecules, and small polar uncharged molecules can diffuse through phospholipid bilayers. Larger polar molecules and charged molecules cannot.

Why can’t all substances directly pass through a phospholipid bilayer?

Large polar or ionic molecules, which are hydrophilic, cannot easily cross the phospholipid bilayer. Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are repelled by the hydrophobic tails in the interior of the phospholipid bilayer.

Why can phospholipid molecules move laterally but they rarely flip sides of a lipid bilayer?

Phospholipids can flip-flop but do so at a much lower rate than lateral diffusion. Proteins cannot flip flop at all. Phospholipids have smaller polar regions and so can occasionally flip flop. Special proteins found in the membrane called flippases can actually help the phospholipids move across the membrane.

Why does a phospholipid on the cytoplasmic side of the cell membrane rarely flip to the extracellular side if both environments are polar?

Why does a phospholipid on the cytoplasmic side of the cell membrane rarely flip to the extracellular side if both environments are polar? The two sides have different functions and thus the phospholipid would not function properly.

Which molecules can move across the phospholipid bilayer by simple diffusion?

Simple diffusion occurs when the molecules are either very small or lipid soluble and pass through the phospholipid bilayer of the cell membrane. Some examples of substances that use this process are oxygen (O2), carbon dioxide (CO2), and lipids.

Why are some substances able to pass through the membrane?

The membrane is selectively permeable because substances do not cross it indiscriminately. Some molecules, such as hydrocarbons and oxygen can cross the membrane. Many large molecules (such as glucose and other sugars) cannot. Others actually bind to the molecules and move them across the membrane.

What property of the phospholipid bilayer allows protein to move laterally in the membrane?

An important property of lipid bilayers is that they behave as two-dimensional fluids in which individual molecules (both lipids and proteins) are free to rotate and move in lateral directions (Figure 2.46). Such fluidity is a critical property of membranes and is determined by both temperature and lipid composition.

Why do phospholipids tend to organize into a bilayer in an aqueous solution?

Being cylindrical, phospholipid molecules spontaneously form bilayers in aqueous environments. In this energetically most-favorable arrangement, the hydrophilic heads face the water at each surface of the bilayer, and the hydrophobic tails are shielded from the water in the interior.

Why the hydrophobic tails of phospholipid molecules are towards inner side of the cell membrane?

The fatty acid chains are the uncharged, nonpolar tails, which are hydrophobic. Since the tails are hydrophobic, they face the inside, away from the water and meet in the inner region of the membrane. Since the heads are hydrophilic, they face outward and are attracted to the intracellular and extracellular fluid.