4. (20 pts) Short answer and multiple guess a) (10 pts) Describe the composition

Question

4. (20 pts) Short answer and multiple guess a) (10 pts) Describe the composition of the plasma membrane and the role of 5 of the components of the system. b) (5 pts) Generally speaking, the contrast between metals and ceramics: (a) ceramics are less durable chemically than metals (b) most metals are more brittle than most ceramics (c) most ceramics are more brittle than most metals (d) none of the above c) (5 pts) A common mechanism for ceramics to failure is: (a) movement of dislocations (b) propagation of cracks (c) ductile failure (d) creep (e) none of the above

Explanation / Answer

Composition

Plasma membranes contain a variety of biological molecules, notably lipids and proteins. Material is incorporated into the membrane, or deleted from it, by a variety of mechanisms:

Lipids:

Lipid bilayers form through the process of self-assembly. One important role is to regulate the movement of materials into and out of cells. The phospholipid bilayer structure (fluid mosaic model) with specific membrane proteins accounts for the selective permeability of the membrane and passive and active transport mechanisms

Carbohydrates

Plasma membranes also contain carbohydrates, predominantly glycoproteins, but with some glycolipids (cerebrosides and gangliosides). For the most part, no glycosylationoccurs on membranes within the cell; rather generally glycosylation occurs on the extracellular surface of the plasma membrane. The glycocalyx is an important feature in all cells, especially epithelia with microvilli. Recent data suggest the glycocalyx participates in cell adhesion, lymphocyte homing, and many others. The penultimate sugar isgalactose and the terminal sugar is sialic acid, as the sugar backbone is modified in the golgi apparatus. Sialic acid carries a negative charge, providing an external barrier to charged particles.

Protiens:

The cell membrane has large content of proteins, typically around 50% of membrane volume[11] These proteins are important for cell because they are responsible for various biological activities. Approximately a third of the genes in yeast code specifically for them, and this number is even higher in multicellular organisms

Lipid vesicles

Lipid vesicles or liposomes are circular pockets that are enclosed by a lipid bilayer. These structures are used in laboratories to study the effects of chemicals in cells by delivering these chemicals directly to the cell, as well as getting more insight into cell membrane permeability.

Sialic acid

Sialic acid carries a negative charge, providing an external barrier to charged particles.

2)

most ceramics are more brittle than more metals

3) propogation of cracks

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