Cell Biology Membranes I: Structure and function of biological membranes by Nathan H Lents, Ph.D., Donna Hesterman Reading Quiz Teach with this A cell membrane is said to be a bilayer. What forms the two layers? Proteins and carbohydrates with electron affinities. Aquaporins and proteins with opposite charges. Phospholipid molecules that self-arrange tail-to-tail. Phospholipid molecules that self-arrange head-to-head. The membrane itself is hydrophobic in the inner layers and doesn't allow water-soluble molecules to pass, yet water itself can permeate cells. Why? Channels called aquaporins in the membrane allow water molecules to pass through freely. Water molecules cannot pass through the membrane. The water that is inside a cell stays in it throughout its life. The membrane is fallible and sometimes water leaks through. Sometimes the membrane will mistake water molecules for lipids. When scientists at Johns Hopkins University fused human cells with mouse cells that had been dyed blue and red respectively, they made an important breakthrough regarding cell membranes. What was it? Cell membranes from mice were very different than those in human cells. Human cell membranes did not hold the dye as well. The fused cells grew and reproduced pink cells. The proteins in the cell membranes were moving around as if in a fluid mosaic. It can be said that some proteins in the cell membrane are like "icebergs floating in a sea of lipids." These embedded proteins that span the whole width of the membrane and “poke out” on the inside and the outside are called cholesterol. transmembrane proteins. glycoproteins. peripheral membrane proteins. The cell membrane is formed of phospholipids and proteins only. true false How does the cell membrane on the exterior of the cell differ from the membranes that envelope organelles inside the cell? Organelle membranes are not semipermeable. Organelle membranes have a different signature of proteins floating in the bilayer. Organelle membranes are not composed of a phospholipid bilayer. Organelle membranes aren't really membranes at all. What is meant by semipermeable with regards to describing the cell membrane? The cell membrane allows water-insoluble molecules to pass freely, but severely restricts the flow of water-soluble molecules and ions. The bilayer is single-ply in some cell membranes. The cell membrane allows water-soluble molecules to pass, but restricts the flow of lipids. Proteins in the membrane float freely as if in a fluid mosaic. The author mentions that a group of scientists in Romania published an article on the aquaporin protein long before the scientists who won the Nobel Prize for discovering aquaporins. What explanation does the author offer for the Romanian group's contribution being overlooked? The Romanians' experiments were not scientifically sound. The Romanians did not publish the article in a peer-reviewed journal. No one believed the Romanians had seen what they described. The Romanians work was not as well-publicized. The cell membrane could best be described as a skin that provides a barrier between the interior and exterior of the cell. sieve that lets fluids passively flow back and forth between the interior and exterior of the cell. an active and responsive part of the cell that controls what does or doesn't enter and leave the cell. a thin but strong physical wrapper that protects the cell despite its obvious fragility. Peripheral membrane proteins are often used by the cell to respond to signals from other cells. true false Score Quiz