Membrane Structure and Function: POGIL Answer Key

Membrane Structure and Function POGIL Answer key two: circle and triangle How many different types of molecules are shown in Model 1? Number of triangles and circles on each side of membrane? 14 triangles on left: 0 triangles on right 12 circles on left: 13 circles on right Which shape is larger? triangle Describe direction of movement of molecules in Model 1. Random-all directions Which molecules are able to pass through the semi-permeable membrane? Circles can fit through the gaps due to small size and are nearly equally distributed on both sides of the membrane. Would you expect the Model 1 system to change over time? No. The triangles will remain on the left side because they are too big to pass through membrane. Circles will remain evenly distributed on both sides due to size and random movement. Phospholipids and membrane spanning proteins. What two major types of biological molecules compose the majority of the cell membrane in Model 2? Four. Two small surface proteins and 2 membrane spanning proteins. How many different protein molecules are found in Model 2? Surface proteins do not span the cell membrane. What is the difference between the position of the surface proteins and the membrane-spanning proteins? When a carbohydrate chain is attached to a protein, what is the structure called? Glycoprotein; glyco = carbohydrate 1/5 Glycolipid When a carbohydrate is attached to a phospholipid, what is the structure called? Small nonpolar or small polar molecules. What types of molecules are shown moving across the membrane? Through the phospholipid bilayer. Where exactly in the membrane do these molecules pass through? Far fewer small molecules inside compared to outside cell. Concentration of small molecules greater outside compared to inside. How does the concentration of the small molecules inside the cell compare to that outside the cell? Does Model 2 indicate that the molecules are moving in equal amounts in both directions? No. Three molecules (small polar/small nonpolar) are moving into the cell and one molecule (small polar/small nonpolar) moving out of the cell. Arrows show direction of movement. Looking at Models 1 and 2. Which particles are moving by diffusion Dots in both models are moving by diffusion across the membrane. across the membranes? Diffusion is the net movement of molecules from an area of (low/high) concentration to an area of (low/high) concentration. high low 2/5 concentration gradient equilibrium The molecules will continue to move along this (semi-permeable membrane/concentration gradient) until they reach (diffusion/equilibrium). randomly Once equilibrium is reached, molecules will continue to move across a membrane (randomly/in one direction). Membrane-spanning proteins; also known as channel proteins Model 3, which part of the cell membrane is shown in more detail? What is the gap between the proteins called? "Gated" channel Glucose (sugar) What type of molecules attach to the protein? Hormone (insulin) attaches to "binding" site on channel protein causing channel to begin to open by changing its shape, which allows glucose (sugar) molecule to pass into the cell. How do the glucose molecules pass through the channel protein? 3/5 Channel acts like a gate; when the hormone (insulin) binds with the protein, it acts like a key that opens the locked gate, allowing the glucose (sugar) t pass through. Why is the protein channel in Model 3 called a "gated" channel? Glucose needs help from the hormone insulin, which causes the channel to widen. The process is still diffusion because the glucose moves from an area of higher to lower concentration. Why is diffusion called "facilitated" diffusion? Na+ and K+ are positively charged ions and would stick to the negatively charged polar heads of the phospholipids. Why is facilitated diffusion necessary for the transport of charged ions such as Na+ and K+ across the cell membrane? Membrane-spanning (channel) proteins. Which part of the cell membrane is shown in more detail in Model 4? What shape represents the substance being transported across the membrane in Model 4? Diamond Ion and ATP binding sites List two binding sites found on the protein. Low concentration to high concentration. Fewer ions on the outside and more ions inside. In which direction is the transported substance moving-from an area of high concentration to low or from an area of low concentration to high? 4/5 ATP provides the energy to change the shape of the channel protein. How is ATP (energy) being used in Model 4? ATP changes to ADP because it loses one phosphate group. What happens to the ATP after it binds to the protein? Active transport requires energy because the molecules were moved against (up) the concentration gradient; molecules moved from area of LOW concentration to HIGH concentration. Passive transport does not require energy because molecules move from HIGH to LOW concentration or with (down) the concentration gradient. Why does active transport require energy from the cell? Complete the Active Transport or Passive Transport Table Define active transport Movement of a substance against (up) a concentration gradient, which requires energy input from the cell and also requires membrane (channel) proteins. 35. Which type of cell transport would be best to move substances into or out of the cell quickly? Active transport 36. Which type of transport would be the best if the cell needs to respond to a sudden concentration gradient difference? Diffusion-the rate increases as the concentration gradient increases. 37. Why would the line representing facilitated diffusion level off as Facilitated diffusion relies on channel proteins and ATP (enerthe concentration gets higher, while the line representing diffusion gy)-so the number of channel proteins and amount of ATP will limit continues to go up at a steady rate? how fast the substance can be moved. 38. Why does active transport start off with such a high initial rate Active transport does not depend on a concentration gradient, only compared to diffusion and facilitated diffusion? a supply of energy (ATP). 5/5