Quiz 2/Exam 2 Cell Membranes

selectively permeable

A barrier in which some materials are capable of crossing while others cannot. The plasma membrane's phospholipid bilayer's hydrophobic inner region forms a barrier that cannot easily be crossed by hydrophilic molecules. It therefore contributes to the selective permeability of the membrane.

sterols

A lipid in the membrane that maintains a necessary degree of fluidity in the membrane. The membrane's permeability is altered if it becomes either too stiff or too pliable. Sterols hinder the membrane from solidifying because they are wedged into the hydrophobic interior of the membrane next to the fatty acid tails of the phospholipids, preventing the phospholipids from packing too tightly in the solid state. Sterols also reduce the permeability of the membrane because the steroid rings are large and densely packed. At moderate temperatures, sterols hinder phospholipid movement in the membrane.

Amphipathic

A phospholipid is amphipathic — a molecule containing both hydrophobic and hydrophilic regions.

fluid mosaic

Being made of many separate and distinct components not bonded to each other so as to retain fluid properties; the currently accepted model of cell membrane structure. Like a tile mosaic, the plasma membrane is created from many individual units. And, also like a tile mosaic, the plasma membrane is a whole that is greater than the sum of its parts. The properties of the plasma membrane as a whole require all the components to play their part. But unlike in a tile mosaic, the plasma membrane's components are in constant motion.

Sterols

Components of plasma membranes. Sterols help the plasma membrane maintain the proper fluidity and stability.

Enzymes and plasma membrane

Enzymes are bound to membranes. A suite of membrane-bound enzymes facilitates cellular respiration, which requires the build-up of a concentration gradient across a membrane, so the enzymes must be attached to the membrane. Some of these enzymes pump protons across the membrane to create the concentration gradient; others use the concentration gradient of protons to synthesize ATP, which stores energy that can be used to drive other processes.

Fluorescent labeling

Fluorescent labeling is one of the most useful techniques for the study of membranes. Frye and Edidin's fluorescent labeling experiments, in which they labeled antibodies specific to membrane proteins with fluorescent tags, demonstrated membrane fluidity. Fluorescent labeling uses antibodies to the target protein to image the protein's location.

Carbs and the plasma membrane

How do carbohydrates attach to the membrane? To stay attached, they are bound to a molecule that is embedded in the membrane. If such a carbohydrate is bound to a protein, the whole molecule is called a glycoprotein. If the carbohydrate is bound to a lipid, the resulting molecule is a glycolipid. The immune system uses carbohydrates to recognize a cell as "self." It can also recognize carbohydrate messages that indicate a foreign or unhealthy cell, allowing the immune system to dispose of cells with incorrect carbohydrate tags

phospholipid bilayer

Major portion of the cell membrane; composed of two layers of phospholipids oriented such that the hydrophobic regions face each other and are sandwiched between the hydrophilic regions on the outside. the hydrophilic, globular-shaped heads of the phospholipids are located on the membrane's inner and outer surface and are in contact with aqueous solutions.

How cells interact with each other?

Membrane proteins facilitate cell-to-cell interactions. Membrane proteins can link two cells together. These linkages may be structural; for example, tight junctions hold skin cells together to keep molecules from leaking in or out between the skin cells. Proteins also help cells communicate. Some cellular linkages, such as gap junctions, open communication channels between the cells they connect. glycoproteins can be used to identify cells via receptor proteins.

Mesophilic organisms

Mesophilic organisms are those adapted to medium temperatures. The proportion of unsaturated versus saturated fatty acids in their phospholipids is somewhere between those of the extremophiles (i.e., psychrophiles and thermophiles).

transmembrane protein

Part of a transmembrane protein; one or more stretches of hydrophobic amino acids in a protein that cross the phospholipid bilayer when intact and in a cell membrane.

Peripheral membrane

Peripheral membrane proteins are also attached to either the inside or outside of the membrane. Like carbohydrates, they are bound to molecules embedded within the membrane. Sterols, such as the cholesterol in animal membranes, are also components of plasma membranes. Sterols help the plasma membrane maintain the proper fluidity and stability.

Integral Proteins

Proteins that are embedded in the phospholipid bilayer have unique functions that contribute to the overall use of the plasma membrane. These molecules are amphipathic; they contain hydrophobic regions to span the inner membrane, and they contain hydrophilic regions on the surface of the membrane. Proteins that span the membrane are called integral proteins because they are integrated across the membrane bilayer. Integral proteins have various functions, most of which are related to gatekeeping, allowing materials to pass in and out of the cell.

Receptor protein function

Receptor proteins bind to outside signal molecules. They also start a signal transduction pathway so the cell can respond to these signals. Receptor proteins can recognize all kinds of signals from the environment and from other cells.

plasma membrane

Serves as barrier between the living cell and outside environment; composed of phospholipid bilayer containing proteins and other components. The plasma membrane serves three primary functions: protecting the cell, controlling the cell's cytoplasmic contents, and sensing molecules and other cells in the environment.

Protein functions in Plasma membrane

Some proteins are mainly structural, serving to anchor the plasma membrane to the cytoskeleton and the extracellular matrix (ECM). They transport (transport protein/enzymes), signal transduction and communication.

Active vs Passive Transport

Some proteins open a pore or channel that lets the target diffuse across the membrane. These passive transport proteins do not require energy to function. Other transport proteins move materials against a concentration gradient. This active transport requires ATP, the chemical form of energy that cells can use to do work.

Kinds of carbohydrates found in plasma membrane and function?

The carbohydrate components of the membrane (the glycolipids and glycoproteins) are used mainly in cellular identification. These molecules are hydrophilic, so they need to be anchored to the membrane via bonds with the membrane's hydrophobic molecules.

cytoskeletal and protein and membrane connection?

The cytoskeleton is an internal network of proteins that helps ANIMAL cells in particular maintain their shape. The cytoskeleton also allows for the organization and transportation of materials inside the cell. It also interacts with membrane proteins to keep them in a specific location. The shape of plant cells, on the other hand, is maintained by the cell wall, which is a type of ECM. In multicellular animals, the ECM acts as a guide for cells to move to new locations, such as cell migration during embryonic development and wound healing.

What can and connot cross phophlipid bilayer

The membrane serves as an effective barrier for large, polar, or charged molecules. These molecules cannot cross through the hydrophobic interior of the bilayer. Only small, nonpolar molecules can cross the membrane unaided. Gases such as carbon dioxide and oxygen freely diffuse across the membranes of the cell.

Transport proteins

Transport proteins facilitate the movement of materials into and out of the cell. Some chemicals diffuse across the membrane without assistance, but many cannot do so due to their polarity or charge. Transport proteins serve as a GATE or opening across the membrane. Transport protein interactions are very specific/SELECTIVE, so only the target, or those very similar to the intended target, can move through the protein gate in the cell membrane.

Glycoproteins

are carbohydrate-protein complexes that can be used to identify cells. The glycoproteins serve as markers that other cells can "read" and recognize via receptor proteins

psychrophilic organisms

psychrophilic organisms are adapted to cold temperatures, below 20°C. Phospholipids in psychrophilic plasma membranes have a greater proportion of unsaturated fatty acid tails than saturated fatty acid tails on their phospholipids compared with other organisms. Unsaturated fatty acids have bends in their carbon chains and they do not pack together as tightly in the bilayer.

thermophilic organisms and membrane fluidity

thermophilic organisms are adapted to hot temperatures, above 60°C. Thermophiles have more saturated fatty acids in their phospholipids, to keep the membrane from becoming too fluid. Extreme thermophiles thrive in temperatures above 90°C.