Biomolecules And Membranes II

disaccharide

Carbohydrate

monosaccharide

polysaccharide

4. a polysaccharide found in animals Animals store energy in the form of glycogen.

3. maltose + water ... dehydration synthesis Maltose is the disaccharide formed when two glucose molecules are linked by dehydration synthesis.

5. milk Lactose is the sugar found in milk.

1. cellulose Cellulose is a carbohydrate composed of many monomers.

3. cellulose Cellulose, a component of plant cell walls, is the most abundant organic compound found on earth.

5. (a), (b), and (c). Good choice! Polymers that contain sugars do all the named functions and more. For example, they also lubricate the path of roots through soil and they glue plant cells together.

1. (always) 2. (only before equilibrium is reached) 3. (only before equilibrium is reached) 4. (never) 5. (only at equilibrium) Each dye molecule and the water molecules that surround it are in constant motion due to their thermal energy. Any individual molecule's motion is random because of the frequent collisions among all of the molecules. If a concentration gradient exists for a population of molecules, the motion of the individual molecules in that population will result in a net (directional) movement from higher to lower concentration. For example, in the initial condition, there is a concentration gradient for the orange dye. As a result, the orange dye molecules diffuse down the concentration gradient, with net movement from side A to side B. Once diffusion has eliminated the concentration gradient and equilibrium is reached, net movement stops, but the random motion of each molecule continues (as indicated by the red arrows in the image below).

3. lipids, 4. carbon dioxide, 5.water, 7. oxygen Some solutes pass readily through the lipid bilayer of a cell membrane, whereas others pass through much more slowly, or not at all. Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer. Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer.Polar molecules such as glucose and sucrose have very limited permeability.Large molecules such as proteins cannot pass through the lipid bilayer.Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane. http://session.masteringbiology.com/problemAsset/1119629/22/1119629_006.jpg

-Only channels: -Provide a continuous path across the membrane, -Allow water molecules and small ions to flow quickly across the membrane -Only carriers: -Undergo a change in shape to transport solutes across the membrane, -Transport primarily small polar organic molecules -Both channels and carriers: -Transport solutes down a concentration or electrochemical gradient, -Are integral membrane proteins, -Provide a hydrophilic path across the membrane Carrier proteins and channels are both transport proteins involved in facilitated diffusion, the passive transport of solutes across a membrane down their concentration or electrochemical gradient. As integral membrane proteins, both carriers and channels protect polar or charged solutes from coming into contact with the hydrophobic interior of the lipid bilayer. Furthermore, all transport proteins are specific for the solutes they transport, owing to the specificity of the interactions between the solute and the transport protein. Channels are protein-lined pores across the membrane. A channel may be open at all times (non-gated), or may be gated such that the channel opens and closes under specific conditions. Channels transport inorganic ions or water http://session.masteringbiology.com/problemAsset/1119629/22/1119629_008.jpg In contrast, carrier proteins do not have a pore. Binding of the transported solute to the carrier protein on one side of the membrane induces a conformational change in the protein that exposes the solute binding site to the opposite side of the membrane, where the solute is released. Carriers transport small polar solutes such as sugars and amino acids. http://session.masteringbiology.com/problemAsset/1119629/22/1119629_009.jpg

A). Glucose low B). v glucose v Na+ C). Glucose high D). 1.down 2.against In cotransport, the energy required to move one solute against its concentration or electrochemical gradient is provided by an ion moving into the cell down its electrochemical gradient. The ion that moves into the cell down its gradient is usually the same ion that is pumped out of the cell by an active transport pump: for example, Na+ in animal cells using the sodium-potassium pump, or H+ in plants and prokaryotes using the proton pump. In the case of the glucose-sodium cotransporter in animals, Na+ moves back into the cell down its electrochemical gradient, providing the energy for glucose to move into the cell against its concentration gradient. The energy for glucose transport into the cell is supplied indirectly by the sodium-potassium pump's hydrolysis of ATP, and directly by the Na+ electrochemical gradient created by the pump. http://session.masteringbiology.com/problemAsset/1125908/12/1125908_007.jpg

B.[Na+]high [K+]low C. excess + charge A. 3 Na+ ^ 2 K+ v D. [Na+]low [K+]high E. excess - charge -Active transport by the sodium-potassium pump follows this cycle. 1. Three Na+ ions from the cytosol bind to the pump. 2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. 3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. 4. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. 5. Release of the phosphate group causes another conformational change in the pump. 6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol. http://session.masteringbiology.com/problemAsset/1119630/24/1119630_009.jpg The net result is that the concentration of Na+ is higher outside the cell and the concentration of K+ is higher inside the cell. In addition, one more positive charge has been transported out of the cell than into the cell, leaving the outside of the cell with an excess positive charge and the inside with an excess negative charge. Thus, the sodium-potassium pump creates both chemical gradients and charge differences across the plasma membrane. The function of the sodium-potassium pump in animal cells (and the proton pump in bacteria and plant cells) is essential to many cell functions. It prevents chemical and electrical gradients across the plasma membrane from reaching equilibrium (at which point the cell would be dead) and powers many types of active transport across the plasma membrane.

1. The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. 4. The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. 5.The electrochemical gradient is larger for Na+ than for K+. -The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell. The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell. The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.

-Exocytosis: 7. secretes large molecules out of the plasma membrane, 6. increases the surface area of the plasma membrane, 3. requires fusion of vesicles with the plasma membrane -Endocytosis: 4. decreases the surface area of the plasma membrane, 2. forms vesicles from inwards folding of the plasma membrane Both: 5. requires cellular energy, 1. transported substances never physically cross the plasma membrane -In exocytosis, substances are transported to the plasma membrane in vesicles derived from the endomembrane system. These vesicles fuse with the plasma membrane, releasing the enclosed substances outside the cell. In endocytosis, substances are taken into the cell by folding in of the plasma membrane and pinching off of the membrane to form a vesicle. Notice that in both exocytosis and endocytosis, the transported substances never actually cross the plasma membrane as they leave or enter the cell. http://session.masteringbiology.com/problemAsset/1125909/10/1125909_001.jpg