Must be in paragraph form complete sentences Not too complex Free-Response Quest
ID: 150206 • Letter: M
Question
Must be in paragraph form complete sentences Not too complex Free-Response Question 1. The selectively permeable plasma membrane is composed of phospholipids and protein, which allow for its unique functions (a) Describe the structure and properties of phospholipids and explain the important roles of phospholipids in the plasma membrane. (b) Predict how the normal function of the plasma membrane would be altered if all phospholipids were saturated, resulting in fatty acid tails without kinks or bends. Explain the effect this would have on plants located in very cold regions. scribe two specific functions of proteins in the membrane. on the structure and properties of a protein. (c) Proteins are an important component of the cell membrane. De- (d) Explain the role of each type of protein you select for part (c) basedExplanation / Answer
1. Phospholipids are major components of the lipid bilayer. They are amphipathic molecules. They contain a polar head and a non-polar tail. So, they assemble into macromolecular assemblies to form membranes. Their polar groups face the aqueous external environment while the non-polar tail groups are buried inside. They are responsible for fluidity and semi-permeability of the membrane.
2. If all lipids are saturated, the membrane would be rigid.
Explanation: Biological membranes are mainly composed of lipids and proteins (protein molecules float in the sea of lipids) and provide selective permeability for various molecules into the cell. They are sheet-like noncovalent assemblies. The lipid molecules of the membrane prevent the free flow of polar molecules whereas proteins serve as receptors for signaling cascades and components of transport systems. Membrane structure and composition is dynamic i.e., it changes according to the environmental conditions. They are asymmetric and fluid in nature i.e., all the lipids and several proteins can easily diffuse rapidly in the plane of the membrane.
The fluidity of the membrane depends on its chemical composition and temperature. Lipids with longer fatty acid chains have more interactions between the hydrophobic fatty acid tails, stabilizing the crystal-like state and making the membrane less fluid. Saturated fatty acids also strengthen membranes and reduce fluidity.
3. Membrane proteins can perform various functions.
Ex: Receptors and carrier proteins
4. Membrane proteins can be peripheral or integral. Integral membrane proteins contain hydrophobic regions in their sequence which span the membrane.
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