BIO353: Exam 2 Short Answers Module 11: Actin Filaments

BIO353: Exam 2 Short Answers Module 11: Actin Filaments 1. Draw an actin monomer and an actin filament and label all the parts, molecular weights, etc.. 2. Explain the geography of actin filaments. Explain the geography of stress cable, filapodia and lamelliapodia in a cell, and locomoting in a culture plate. a. Actin filaments are located under the plasma membrane on the inside of the cell. Stress cables as well as filopodia and lamellipodia are located near the plasma membrane. 3. Focusing on actin monomers and actin filaments: explain what occurs when a cell reverses its direction by 180 degrees. a. When a cell reverses its direction by 180 degrees, there is a reverse displacement for the actin and myosin filament. There is an increase in the movement and contraction of the filaments in direction towards each other. Due to the complete 180 degree reversal and the presence of the extended N-terminus in the myosin, it will tend to block the complete 180 degree swing of other myosin and hence it might lead to interruption in the function of the muscles. Due to the reversal, the actin monomer tends to fall in the same direction and tends to make the muscle more polar. 4. Explain how the binding of ATP affects cytoskeletal monomers. Explain how the function of cytoskeletal networks can change depending on reversible binding of cytoskeleton associated proteins a. Hydrolysis of ATP to ADP helps identify the assembly vs disassembly end with an ATP “cap” on the assembly end and an ADP “cap” on the disassembly end. With ATP present, the monomer changes shape and promotes self-assembly into the actin filament. When ATP is hydrolyzed to ADP, it changes the conformation of the monomer making it less suited to fit into an actin filament. Position of ATP gives the monomer a polarity that steps up the polarity of the actin filament. 5. Describe how myosin II can be made into a tool to analyze the different polarities of actin filaments in the cell. a. Myosin II can be made into a tool by scientists using biotechnology to determine the orientation of an