The frozen sample is cracked or fractured with a microtome, which is a knife-like instrument for cutting thin tissue slices. This causes the cell membrane to split apart precisely between the two layers because the attraction between the hydrophobic lipid tails represents the weakest point.
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When a membrane is freeze fractured the bilayer splits down the middle between the two layers?
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are: Integral proteins.
What happens to cell membranes when frozen?
At the molecular level, freezing affects membrane lipids, proteins and nucleic acids by changing the hydrophobic and hydrophilic interactions determining structure and function. It is well established that cooling alters the physical state of lipids, thus altering lipid organization and fluidity [9].
What do freeze fracture techniques reveal about the involvement of proteins in membranes?
Explain what freeze-fracture techniques reveal about the arrangement of proteins in membranes. The freeze fracture method splits a membrane along the middle of the phospholipid bilayer. When it is viewed through an electron microscope, protein particles are interspersed in a smooth matrix.
What is the freeze-fracture technique in biology?
The freeze-fracture technique consists of physically breaking apart (fracturing) a frozen biological sample; structural detail exposed by the fracture plane is then visualized by vacuum-deposition of platinum-carbon to make a replica for examination in the transmission electron microscope.
How does freeze fracturing work?
In the freeze fracturing process, a specimen is frozen rapidly and cracked on a plane through the tissue. This fracture occurs along weak portions of the tissue such as membranes or surfaces of organelles. After cleaving, both surfaces are shadowed with a platinum film. This coating produces a replica of the surfaces.
When biological membranes are frozen and then fractured They tend to break along the middle of the bilayer Why does this happen?
When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that. C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing. You just studied 63 terms!
Which of the following would likely move through the lipid bilayer of a plasma membrane most quickly?
Of these molecules, it is likely that CO2 moves by far faster than any other molecule through the lipid bilayer.
Which of the following would you expect to be a problem for someone with nonfunctional chloride channeling *?
(Cystic fibrosis is a genetic disease in humans in which chloride ion channels in cell membranes are missing or nonfunctional.)
Does freezing break cell walls?
When you freeze a fruit or vegetable, you are freezing the water contained in the cells. As the water freezes, it expands, and ice crystals cause the cells walls to rupture.
Why can freezing damage cells?
All living things are made of cells. Living cells generally contain water along with all the raw materials and structures that make the cell work. Freezing usually damages cells because water expands when it freezes.
How does cold temperature affect cell membranes?
Low temperatures also slow down cell growth. Sub-freezing temperatures or prolonged exposure to temperatures much below the physiological normal can cause the liquid in the cells to freeze and form into sharp crystals that are capable of piercing the cell membrane and potentially killing the cell.
What does freeze-fracture reveal about cell structure?
Freeze fracturing is a process where a frozen specimen is cracked to reveal a plane through the tissue. The fracture occurs along weak hydrophobic planes such as membranes or surfaces of organelles. The technique is extremely powerful when applied to the study of membrane structure and organisation.
What do you mean by freeze-fracture and freeze drying?
Freeze fracture describes the technique of breaking a frozen specimen to reveal internal structures. Freeze etching is the sublimation of surface ice under vacuum to reveal details of the fractured face that were originally hidden.
What eventually happens to the concentration of a substance that moves across a membrane due to diffusion?
Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes “down the concentration gradient.” The end result of diffusion is an equal concentration, or equilibrium, of molecules on both sides of the membrane. At equilibrium, movement of molecules does not stop.
What is facilitated diffusion simple?
Facilitated diffusion is the passive movement of molecules along the concentration gradient. It is a selective process, i.e., the membrane allows only selective molecules and ions to pass through it. It, however, prevents other molecules from passing through the membrane.
When a plant cell is submerged in a very hypotonic solution what is likely to occur?
When a plant cell, such as one from an elodea, is submerged in a very HYPOTONIC solution, What is likely to occur? The cell with become turgid.
What will happen to the cell if placed in a hypotonic solution?
A cell placed into a hypotonic solution will swell and expand until it eventually burst through a process known as cytolysis.
Which of the following substances would be most likely to pass through the plasma membrane without the help of a transport protein?
Which one of the following molecules is most likely to diffuse freely across the lipid bilayer of the plasma membrane without the involvement of a transport protein? Carbon dioxide. Hydrophobic molecules, such as hydrocarbons, carbon dioxide, and oxygen, can dissolve in the membrane and cross it with ease.
Which of the following processes moves a substance that can freely pass through the cell membrane?
Diffusion. Diffusion is a passive process of transport. A single substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. You are familiar with diffusion of substances through the air.
Which of the following disorders is due to a defect in membrane proteins that normally function in chloride ion transport?
Cystic fibrosis is the most common and best-known genetic disease involving a defect in transepithelial Cl– transport. It affects several epithelial organs, i.e., the lungs, pancreas, and intestine, among others.
What is the major interaction responsible for stabilizing plasma membrane?
Once the bilayer forms, hydrogen bonds, electrostatic attractions and van der Waals contacts further stabilize the membrane.
Which of the following factors would tend to increase membrane fluidity?
High temperature increases membrane fluidity.
What happens to tissue when it is frozen?
During freezing, the overall volume of tissue cells is reduced due to cell shrinkage, but the total tissue volume cannot shrink because it is extended by the hard ice crystals. Thus, a mechanical stress results that may disrupt cell-to-cell connections.
What causes cell membrane damage?
Causes of multifactorial membrane damage include the accumulation of free fatty acids inside and outside the ischemic cells and increased amounts of potentially toxic fatty acid metabolites, such as acyl CoA and acyl carnitine.