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Module 3: Membrane Structure and Function

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How many different types of molecules are shown in Model 1?
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two: circle and triangle
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Number of triangles and circles on each side of membrane?
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14 triangles on left: 0 triangles on right 12 circles on left: 13 circles on right
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Which shape is larger?
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triangle
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Describe direction of movement of molecules in Model 1.
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Random-all directions
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Which molecules are able to pass through the semi-permeable membrane?
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Circles can fit through the gaps due to small size and are nearly equally distributed on both sides of the membrane.
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Would you expect the Model 1 system to change over time?
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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.
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What two major types of biological molecules compose the majority of the cell membrane in Model 2?
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Phospholipids and membrane spanning proteins.
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How many different protein molecules are found in Model 2?
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Four. Two small surface proteins and 2 membrane spanning proteins.
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What is the difference between the position of the surface proteins and the membrane-spanning proteins?
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Surface proteins do not span the cell membrane.
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When a carbohydrate chain is attached to a protein, what is the structure called?
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Glycoprotein; glyco = carbohydrate
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When a carbohydrate is attached to a phospholipid, what is the structure called?
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Glycolipid
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What types of molecules are shown moving across the membrane?
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Small nonpolar or small polar molecules.
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Where exactly in the membrane do these molecules pass through?
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Through the phospholipid bilayer.
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How does the concentration of the small molecules inside the cell compare to that outside the cell?
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Far fewer small molecules inside compared to outside cell. Concentration of small molecules greater outside compared to inside.
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Does Model 2 indicate that the molecules are moving in equal amounts in both directions?
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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.
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Looking at Models 1 and 2. Which particles are moving by diffusion across the membranes?
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Dots in both models are moving by diffusion across the membrane.
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Diffusion is the net movement of molecules from an area of (low/high) concentration to an area of (low/high) concentration.
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high low
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The molecules will continue to move along this (semi-permeable membrane/concentration gradient) until they reach (diffusion/equilibrium).
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concentration gradient equilibrium
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Once equilibrium is reached, molecules will continue to move across a membrane (randomly/in one direction).
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randomly
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Model 3, which part of the cell membrane is shown in more detail?
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Membrane-spanning proteins; also known as channel proteins
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What is the gap between the proteins called?
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“Gated” channel
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What type of molecules attach to the protein?
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Glucose (sugar)
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How do the glucose molecules pass through the channel protein?
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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.
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Why is the protein channel in Model 3 called a “gated” channel?
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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.
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Why is diffusion called “facilitated” diffusion?
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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.
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Why is facilitated diffusion necessary for the transport of charged ions such as Na+ and K+ across the cell membrane?
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Na+ and K+ are positively charged ions and would stick to the negatively charged polar heads of the phospholipids.
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Which part of the cell membrane is shown in more detail in Model 4?
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Membrane-spanning (channel) proteins.
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What shape represents the substance being transported across the membrane in Model 4?
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Diamond
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List two binding sites found on the protein.
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Ion and ATP binding sites
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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?
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Low concentration to high concentration. Fewer ions on the outside and more ions inside.
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How is ATP (energy) being used in Model 4?
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ATP provides the energy to change the shape of the channel protein.
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What happens to the ATP after it binds to the protein?
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ATP changes to ADP because it loses one phosphate group.
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Why does active transport require energy from the cell?
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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.
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Complete the Active Transport or Passive Transport Table
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Define active transport
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Movement of a substance against (up) a concentration gradient, which requires energy input from the cell and also requires membrane (channel) proteins.
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35. Which type of cell transport would be best to move substances into or out of the cell quickly?
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Active transport
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36. Which type of transport would be the best if the cell needs to respond to a sudden concentration gradient difference?
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Diffusion-the rate increases as the concentration gradient increases.
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37. Why would the line representing facilitated diffusion level off as the concentration gets higher, while the line representing diffusion continues to go up at a steady rate?
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Facilitated diffusion relies on channel proteins and ATP (energy)-so the number of channel proteins and amount of ATP will limit how fast the substance can be moved.
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38. Why does active transport start off with such a high initial rate compared to diffusion and facilitated diffusion?
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Active transport does not depend on a concentration gradient, only a supply of energy (ATP).