CHAPTER 8 MEMBRANE STUCTURE AND FUNCTION Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section A: Membrane Structure 1.Membrane models have evolved to fit new data 2. Membranes are fluid 3. Membranes are mosaics of structure and function 4. Membrane carbohydrates are important for cell-cell recognition

The plasma or cell membrane is a ________ layer that separates the living cell from its nonliving surroundings. Like other membranes, the plasma membrane is ___________________, allowing some substances to cross more easily than others. Introduction Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The main macromolecules in membranes are _____________. Phospholipids are ______________ molecules. Amphipathic molecules have both __________ regions and ___________ regions. The plasma membrane is described by the _______ ____________________ A membrane is a fluid structure with proteins embedded or attached to a double layer of phospholipids. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Most of the lipids and some proteins can ________ laterally in the plane of the membrane, but rarely flip- flop from one layer to the other. 2. Membranes are fluid Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.4a

Membrane fluidity is influenced by _________ As temperatures cool, membranes switch from a fluid state to a solid state as the phospholipids are more closely packed. Membranes rich in ________________ fatty acids are more fluid that those dominated by saturated fatty acids because the ______ in the unsaturated fatty acid tails prevent tight packing. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.4b

The steroid ____________ is wedged between phospholipid molecules in the plasma membrane of animal cells. At warm temperatures, it __________ the movement of phospholipids and reduces fluidity. At cool temperatures, it maintains fluidity by ___________ tight packing. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.4c

A membrane is a collage of different __________ embedded in the fluid matrix of the lipid bilayer. 3. Membranes are mosaics of structure and function Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.6

Proteins determine most of the membrane’s specific functions. There are two populations of membrane proteins. ___________ proteins are not embedded in the lipid bilayer at all. Instead, they are loosely bounded to the _______ of the membrane __________ proteins penetrate the hydrophobic core of the lipid bilayer, often completely spanning the membrane (a _________________ protein). Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The proteins in the plasma membrane may provide a variety of major cell functions. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.9

The ______________ attached to the membrane play a key role in _________________________. Cell-cell recognition is the ability of a cell to distinguish one type of neighboring cell from another. This attribute is important in cell sorting and organization as tissues and organs in ___________. It is also the basis for rejection of foreign cells by the __________ system. 4. Membrane carbohydrates are important for cell-cell recognition Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

CHAPTER 8 MEMBRANE STRUCTURE AND FUNCTION Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Section B: Traffic Across Membranes 1.A membrane’s molecular organization results in selective permeability 2. Passive transport is diffusion across a membrane 3. Osmosis is the passive transport of water 4. Cell survival depends on balancing water uptake and loss 5. Specific proteins facilitate the passive transport of water and selected solutes: a closer look 6. Active transport is the pumping of solutes against their gradients 7. Some ion pumps generate voltage across membranes 8. In cotransport, a membrane protein couples the transport of two solutes 9. Exocytosis and endocytosis transport large molecules

A steady traffic of small molecules and ions moves across the plasma membrane in both directions. However, substances do not move across the barrier indiscriminately; membranes are selectively permeable. 1. A membrane’s molecular organization results in selective permeability Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Permeability of a molecule through a membrane depends on the interaction of that molecule with the ____________ of the membrane. ___________ molecules, like hydrocarbons, CO 2, and O 2, can dissolve in the lipid bilayer and cross ________. Ions and polar molecules pass through with _________. This includes small molecules, like water, and larger critical molecules, like glucose and other sugars. Ions, whether atoms or molecules, and their surrounding shell of water also have difficulties penetrating the hydrophobic core. __________ can _______ and regulate the transport of ions and polar molecules. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Specific ions and polar molecules can cross the lipid bilayer by passing through _____________ that span the membrane. Transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane. Each transport protein is ___________ as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, a similar sugar. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

__________ is the tendency of molecules of any substance to spread out in the available space If we start with a permeable membrane separating a solution with dye molecules from pure water, dye molecules will cross the barrier randomly until both solutions have ______ concentrations At this dynamic ________________ as many molecules pass one way as cross in the other direction. 2. Passive transport is diffusion across a membrane Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

In the absence of other forces, a substance will diffuse down its ______________________. Each substance diffuses down its _____ concentration gradient, ______________ of the concentration gradients of other substances. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.10b

The __________ of a substance across a biological membrane is ________________ because it requires _________ from the cell to make it happen. However, because membranes are selectively permeable, the interactions of the molecules with the membrane play a role in the diffusion rate. Diffusion of molecules with limited permeability through the lipid bilayer may be assisted by transport proteins. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

_______ in a solution also moves to reach equilibrium. The solution with the higher concentration of solutes is _____________. The solution with the lower concentration of solutes is ____________. These are ______________ terms. Tap water is hypertonic compared to distilled water but hypotonic when compared to sea water. Solutions with equal solute concentrations are _________. 3. ________ is the passive transport of water Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Water molecules will move from _________ to _______________ This diffusion of water across a selectively permeable membrane is a special case of passive transport called ________. Osmosis continues until the solutions are _________. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.11

The direction of osmosis is determined by ________ solute concentration. The _______ of solutes in the solutions do not matter. When two solutions are isotonic, water molecules move at equal rates from one to the other, with no ____ osmosis. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The chart below demonstrates the reactions of animal and plant cells to varying tonicities 4. Cell survival depends on balancing water uptake and loss Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Some transport proteins can move solutes ________ their concentration gradient This is _______________ and requires the cell to expend its own metabolic energy. Active transport is critical for a cell to maintain its internal concentrations of small molecules that would otherwise diffuse across the membrane. 6. Active transport is the pumping of solutes against their gradients Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The __________________________ actively maintains the gradient of sodium (Na + ) and potassium ions (K + ) across the membrane. This pump plays a critical role in the ________ system The sodium-potassium pump uses the energy of one _____ to pump ______ Na + ions out and ____ K + ions in. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 8.15

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig Both diffusion and facilitated diffusion are forms of passive transport of molecules down their concentration gradient, while active transport requires an investment of energy to move molecules against their concentration gradient.

Large molecules, such as polysaccharides and proteins, cross the membrane via ________. During __________, a transport vesicle budded from the _______ apparatus is moved by the cytoskeleton to the plasma membrane. When the two membranes come in contact, the bilayers ______ and _______ the contents to the outside. 9. Exocytosis and endocytosis transport large molecules Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

During __________, a cell brings in macromolecules and particulate matter by forming new vesicles _______ the plasma membrane. Endocytosis is a _________ of exocytosis. A small area of the palsma membrane ______ inward to form a ________ As the pocket into the plasma membrane deepens, it pinches in, forming a vesicle containing the material that had been outside the cell Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

One type of endocytosis is ____________, “cellular __________.” In phagocytosis, the cell engulfs a particle by extending pseudopodia around it and packaging it in a large vacuole. The contents of the vacuole are _________ when the vacuole fuses with a ____________. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.19a

In ___________, “cellular _________,” a cell creates a vesicle around a droplet of extracellular fluid. This is a non-specific process. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 8.19b