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Fill in the blanks. Movement of materials in and out of cells is controlled by the_________________. The sites of protein synthesis are______________________. Glycerol and fatty acids combine to form___________________. Breakdown of organic nutrients in cells to release energy and form ATP is called_________________. In a__________________reaction, smaller molecules are combined to form a larger molecule. The building units of proteins are____________________. Choose the correct answer. Which of the following are functions of nucleic acids? They pass instructions from parents to offspring. They help make proteins. They contain instructions for proteins. all of the above. Types of lipids include: polysaccharides. amino acids. nucleotides. triglycerides. According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly spread in a continuous layer over the inner and outer surfaces of the membrane. confined to the hydrophobic int...
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Membrane Lipids

The plasma membrane contains several different types of lipids including phospholipids, cholesterol, and glycolipids.
The plasma membrane is composed of two layers of phospholipid molecules with scattered embedded protein and cholesterol molecules. The hydrophilic heads of the phospholipids face the extracellular and intracellular fluids, and the hydrophobic tails form the internal layer of the membrane.
The plasma membrane is composed of two layers of phospholipid molecules with scattered embedded protein and cholesterol molecules. The hydrophilic heads of the phospholipids face the extracellular and intracellular fluids, and the hydrophobic tails form the internal layer of the membrane. Cholesterol and proteins scattered throughout and associated with its surface.

Phospholipids

In a cell membrane, phospholipids are arranged in two layers - lipid bilayer, a double layer of phospholipid molecules, because they have a polar head and a nonpolar (uncharged) tail. The polar heads are attracted to water molecules, so they are also called hydrophilic (water-loving) heads. The polar, hydrophilic heads are exposed to the aqueous extracellular and intracellular fluids of the cell. The tails of the phospholipids are nonpolar and are not attracted to water molecules, so the tails are also called hydrophobic (water-fearing). The nonpolar tails face one another in the interior of the plasma membrane. The fluid-mosaic model of the plasma membrane describes the plasma membrane as being neither rigid nor static in structure. Instead, the plasma membrane is highly flexible and can change its shape and composition through time. The lipid bilayer functions as a dense liquid in which other molecules, such as proteins, are suspended. The fluid nature of the lipid bilayer has several important consequences: It provides an important means of distributing molecules within the plasma membrane. In addition, slight damage to the membrane can be repaired because the phospholipids tend to reassemble around damaged sites and close them. The fluid nature of the lipid bilayer also enables membranes to fuse with one another.

Cholesterol

Phospholipids are not the only lipid of the plasma membrane. Cholesterol is the other major lipid. It is interspersed among the phospholipids. The hydrophilic hydroxyl (–OH) group of cholesterol extends between the phospholipid heads to the hydrophilic surface of the membrane, whereas the hydrophobic part of the cholesterol molecule lies within the hydrophobic region of the phospholipids. The amount of cholesterol in a particular plasma membrane is a major factor in determining the fluid nature of the membrane. Cholesterol limits the movement of phospholipids, providing stability to the plasma membrane.

Glycolipids

Glycolipids are lipids with attached carbohydrate groups. They can be placed only on the outer phospholipid layer of the membrane, where they are exposed to the interstitial fluid. Together, the carbohydrate portion of the glycolipid molecules and the glycoprotein molecules help to form the glycocalyx, a coating sugar on the cell’s surface.

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