AP Biology Membrane Structure and Function 2023/2024 verified to pass

AP Biology Membrane Structure and Function hydrophilic head - correct answer water loving, polar hydrophilic tail - correct answer hates water (nonpolar) Would the polar portion of the phospholipid mix well with water? - correct answer Yes because water is polar and tends to dissolve polar molecules Would the nonpolar portion of the phospholipid mix well with water? - correct answer No because water is polar and therefore does not mix well with nonpolar molecules What is the three-dimensional shape of a micelle? - correct answer spherical Phospholipids assemble in layers to make membranes for cell organelles. Why do phospholipids have water on the inside and outside of the membrane. - correct answer Since water is both inside and outside of the membrane, the polar head of the phospholipid must face both inside and outside because this is not possible with one molecular layer. How do phospholipid molecules lead to compartmentalization of a cell? - correct answer Since the phospholipids form bilayers and micelles, they form small areas and compartments where the inside and outside do not touch. The phospholipid molecules become boundaries between two fluids. Animal cells are bound by a cell membrane and plant cells are bound by a cell membrane and cell wall. Are cell membranes flexible (fluid)? - correct answer Cell membranes are flexible. An amoeba, appears to change its shape as it consumes food or makes about responding to its environment. Plants, which need a rigid cellular structure for support, require a cell wall because the membrane is not strong enough to support the plant. Why is a phospholipid bilayer flexible in terms of the strength of the forces that hold it together? - correct answer Phospholipids are held together by weak forces between the molecules making up the bilayer, the molecules can slide past each other and change position in the bilayer, allowing the membrane to be flexible. What happens to the shape of the hydrophobic tail in a phospholipid when a double bond is present in the carbon chain? - correct answer The carbon chain appears bent when a double bond is present. Why is the flexibility (fluidity) of a membrane increased when more of the phospholipid in the layers contains a double bond? - correct answer When the tail of the phospholipid is bent, the molecules cannot assemble as tightly. This will increase membrane flexibility. Is the cholesterol molecule in the diagram polar or nonpolar? - correct answer Cholesterol is mostly nonpolar because it consists of primarily C-C and C-H bonds, with only one polar O-H bond. Cholesterol in a phospholipid bilayer - correct answer Cholesterol forms weak attractive forces with multiple phospholipids in the bilayer. Would this increase or decrease flexibility of the membrane? - correct answer There would be a decrease in flexibility because more bonds are formed. The phospholipids would not be able to slide past one another when the membrane was bent. What sections of the embedded protein chain are most likely to contain amino acids with hydrophobic R-groups? - correct answer The sections of the protein that are embedded in the membrane are most likely to have hydrophobic R-groups. These R-groups would undergo hydrophobic interactions with the hydrophobic tails of the phospholipids and hold the protein in place. What sections of the embedded protein chain are most likely to contain amino acids with hydrophilic R-groups? - correct answer The sections of the protein that are on the surface of the membrane (the entrance and exit) are most likely to have hydrophilic R-groups. These R-groups would be in contact with the cytoplasm and extracellular fluid, which are mostly water. Some membranes have surface proteins on them which often serve a signaling function between cells. How do these proteins attach to the membrane? - correct answer The surface protein is most likely attached to the membrane by interactions between the hydrophilic heads of the phospholipids and hydrophilic R-groups in the protein. These interactions could be hydrogen bonds or ionic interactions.