3. Cells

Membrane Structure

Plasma Membrane

Cell Membrane Structure, Function, and The Fluid Mosaic Model

 Even though water is highly polar, it passes via osmosis through the lipid bilayer. This is surprising because you’d expect water to be repelled by the hydrophobic lipid tails. One hypothesis is that random movements of the membrane lipids open small gaps between their wiggling tails, allowing water to slip and slide its way through the membrane by moving from gap to gap. 

 Water can pass via osmosis through the lipid bilayer. 

Cell Transport

Structure of the Cell Membrane - Active and Passive Transport

Active Transport: Primary & Secondary

Diffusion

 a lipid bilayer with protein molecules dispersed within it 

 a single layer of lipids surrounding a layer of proteins 

 The fluid mosaic model of the plasma membrane is composed of two layers of lipid molecules with protein molecules dispersed within. 

 a single layer of proteins with lipid molecules dispersed within 

 a single layer of proteins surrounding a single layer of lipids 

 a protein bilayer sandwiching a layer of lipids 

 Which of the following statements best describes the fluid mosaic model of the plasma membrane? 

 moving actively against a concentration gradient 

 In simple diffusion, substances move passively down a concentration gradient. 

 moving passively against a concentration gradient 

 moving actively down a concentration gradient 

 moving passively down a concentration gradient 

 Simple diffusion is best described as substances __________. 

 perform a function known as signal transduction 

 Carrier proteins bind to a substance and move the substance through the membrane. 

 Transmembrane proteins provide channels through the membrane. 

 Antigens are peripheral proteins in the cell membrane that provide cell identification. 

 Proteins in the cell membrane that bind hormones and relay messages into the interior of the cell __________. 

Passive and Active Transport

 Tight junctions are impermeable junctions between cells that prevent substances from traveling between adjacent cells. 

 Gap junctions are communicating junctions between adjacent cells. 

 Which of the following are considered anchoring junctions? 

 The plasma membrane is primarily made of phospholipids. Glycolipids, proteins, and cholesterol are all important components of animal cell membranes. In fact, cholesterol is important for keeping the plasma membrane of animal cells fluid. Nucleic acids are DNA and RNA; these molecules are not found in the plasma membrane. 

 Which of the following would NOT be found in the plasma membrane of a human cell? 

Cell Junctions

Membrane Receptors

 Cholesterol stabilizes the plasma membrane while decreasing the mobility of the phospholipids and the fluidity of the membrane. 

 A glycoprotein is a sugar bound to a protein and is part of the glycocalyx. 

 Integral proteins are firmly implanted into the plasma membrane and have a variety of functions, such as reception or transport. 

 A glycolipid is a sugar bound to a fat and is part of the glycocalyx. 

 Which of the following molecular components of the lipid bilayer of the plasma membrane possesses a charged polar phosphate "head" and uncharged nonpolar fatty acid "tails"? 

Osmosis

 Endocytosis is an active membrane transport process. Phagocytosis (“cell eating”) and pinocytosis (“cell drinking”) are examples of different types of endocytosis. 

 Facilitated diffusion does not use ATP. 

 Which type of membrane transport process uses ATP as a source of energy? 

 facilitated diffusion: active membrane transport process 

 Facilitated diffusion and osmosis are passive membrane transport processes. Endocytosis and exocytosis are active membrane transport processes. 

 endocytosis: passive membrane transport process 

 exocytosis: active membrane transport process 

 osmosis: active membrane transport process 

 Which of the following pairs is a correct match? 

 the diffusion of a solute across a membrane 

 Osmosis is the unassisted diffusion of a solvent, such as water, through a selectively permeable membrane. Osmosis is a passive transport process; it does not require the expenditure of energy. 

 the diffusion of water across a membrane 

 a form of facilitated diffusion across a membrane 

 a form of active transport across a membrane 

 Blood cells have no membrane junctions with other cells and are therefore said to be "footloose." 

 Sperm cells have no membrane junctions with other cells and are therefore said to be "footloose." 

 Phagocytic cells have no membrane junctions with other cells and are therefore said to be "footloose." 

 All of the following cells are considered "footloose," as they lack cellular junctions, EXCEPT __________. 

Cell Membrane Structure

 Proteins are involved in joining adjacent cells. 

 Transport of solutes is a function of some plasma membrane proteins. 

 Proteins serve as attachment sites for the cytoskeleton.  

 receptor for chemical messenger molecules 

 Some plasma membrane proteins are receptors for chemical messenger molecules. 

 Which item below is NOT a function or role performed by proteins found in the plasma membrane? 

 Receptor-mediated endocytosis is the main mechanism for the selective endocytosis of macromolecules. 

 Cells of the body mainly use __________ for the selective endocytosis of most macromolecules. 

Passive Transport

 Osmosis is the movement of water from a region of higher concentration to a region of lower concentration. 

 Which of the following transport mechanisms specifically involves the movement of water? 

 Primary and secondary active transport both require energy. In primary active transport, the energy comes directly from the hydrolysis of ATP. This hydrolysis results in the phosphorylation of the transport protein. The most investigated example of a primary active transport system is the sodium-potassium pump.Primary active transport pumps, such as the Na<sup>+</sup>-K<sup>+</sup> pump, can indirectly drive the secondary active transport of several other solutes. 

 Primary active transport is driven by secondary active transport. 

 Vesicular transport in which macromolecules are transported out of the cell is known as exocytosis. 

 Vesicular transport in which macromolecules move into the cell is known as endocytosis. 

 Vesicular transport in which macromolecules are transported in, across, and then out of the cell is known as transcytosis. 

 Vesicular transport is involved in all of the following transport processes EXCEPT __________. 

 Contact signaling is the function of membrane receptors that allows cells to recognize each other. 

 Chemical signaling is the function of membrane receptors that allows target cells to respond to hormones and neurotransmitters. 

 Some membrane receptors bind G protein and then produce their effect indirectly by their action on enzymes inside the cell. 

 All of the following are functions of membrane receptors EXCEPT __________. 

Cell Transport - Endocytosis, Exocytosis, Phagocytosis, and Pinocytosis

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