Please answer the 3 following question and provide a short reason why you chose
ID: 11346 • Letter: P
Question
Please answer the 3 following question and provide a short reason why you chose your answer.
40. Which of the following statements about the role of actin binding proteins in controlling microfilament
organization, assembly and motility is INCORRECT.
A) Profilin directs actin monomer assembly specifically towards the plus end of a microfilament.
B) Both myosin I and myosin II translocate towards the plus end of a microfilament.
C) Fimbrin is an actin binding protein that bundles microfilaments in parallel bundles in filopodia and
microvilli, while filamen organizes microfilaments into loosely woven networks in lamellipodia.
D) Interactions between microfilaments and transmembrane proteins called integrins are important in
allowing cells to assemble focal contacts involved in attaching to the extracellular surface.
E) In the absence of Ca++, tropomyosin binds tightly within the groove of actin thin filaments in the muscle
sarcomere, and this binding promotes interactions between actin filaments and myosin II heads in the
thick filaments.
41. You discover a protein that increases the rate at which GTP is hydrolyzed after tubulin-GTP assembly
into polymer. Which would you expect to be true in cells expressing this protein?
A) Microtubules will more frequently display curved protofilaments at the plus end.
B) Microtubules will be prone to catastrophic disassembly more frequently.
C) Microtubules will be shorter and more dynamic.
D) Microtubules will have reduced GTP caps at their plus ends.
E) All are true.
42. Normally, vimentin filaments disassemble when cells are plated onto a new surface. As the cells
flatten, vimentin filaments reform through a “squiggle” intermediate. You are studying a vimentin mutant
that does not disassemble after re-plating. Which of the following is a reasonable hypothesis?
A) The mutations may disrupt “squiggles” from interacting to form filaments.
B) The mutations may disrupt formation of the vimentin tetramer.
C) The mutations may prevent vimentin from hydrolyzing ATP and thus stabilize the filaments.
D) The mutations may disrupt amino acids that are phosphorylated by a protein kinase.
E) Now the vimentin filaments just wiggle.
Explanation / Answer
40. Which of the following statements about the role of actin binding proteins in controlling microfilament
organization, assembly and motility is INCORRECT.
A) Profilin directs actin monomer assembly specifically towards the plus end of a microfilament.
B) Both myosin I and myosin II translocate towards the plus end of a microfilament.
C) Fimbrin is an actin binding protein that bundles microfilaments in parallel bundles in filopodia and
microvilli, while filamen organizes microfilaments into loosely woven networks in lamellipodia.
D) Interactions between microfilaments and transmembrane proteins called integrins are important in
allowing cells to assemble focal contacts involved in attaching to the extracellular surface.
E) In the absence of Ca++, tropomyosin binds tightly within the groove of actin thin filaments in the muscle
sarcomere, and this binding promotes interactions between actin filaments and myosin II heads in the
thick filaments.
41. You discover a protein that increases the rate at which GTP is hydrolyzed after tubulin-GTP assembly
into polymer. Which would you expect to be true in cells expressing this protein?
A) Microtubules will more frequently display curved protofilaments at the plus end.
B) Microtubules will be prone to catastrophic disassembly more frequently.
C) Microtubules will be shorter and more dynamic.
D) Microtubules will have reduced GTP caps at their plus ends.
E) All are true.
42. Normally, vimentin filaments disassemble when cells are plated onto a new surface. As the cells
flatten, vimentin filaments reform through a “squiggle” intermediate. You are studying a vimentin mutant
that does not disassemble after re-plating. Which of the following is a reasonable hypothesis?
A) The mutations may disrupt “squiggles” from interacting to form filaments.
B) The mutations may disrupt formation of the vimentin tetramer.
C) The mutations may prevent vimentin from hydrolyzing ATP and thus stabilize the filaments.
D) The mutations may disrupt amino acids that are phosphorylated by a protein kinase.
E) Now the vimentin filaments just wiggle.