1. Which of the following statements about actin is correct? Polymerization of a
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Question
1. Which of the following statements about actin is correct?
Polymerization of an actin filament will only occur at the plus end.
2. Which one of the following statements about actin is incorrect?
When both ends of an F-actin molecule are polymerizing, both ends are referred to as plus ends.
3. Hypothetically, the plus end of an actin filament has a critical concentration of 60 and the minus end has a critical concentration of 90. If the concentration of available, ATP-bound G-actin in the cell is 75, which of the following is true? Choose all that apply.
4. Which of the following statements about the cytoskeleton is correct? Choose all that apply.
5. Which of the following statements about actin filaments is/are correct? Choose all that apply.
If the actual amount of available ATP-bound G-actin is below the critical concentration at both ends of a filament, then the actin filament will depolymerize. Actin monomers are called G-actin because they have a nucleotide binding site that accommodates a molecule of GTP. The plus end of an actin monomer has a net positive charge. Actin generally polymerizes more rapidly at the pointed end.Polymerization of an actin filament will only occur at the plus end.
2. Which one of the following statements about actin is incorrect?
Some G-actin molecules in the cell is not available for use to make F-actin because actin binding proteins are bound to that G-actin. G-actin monomers and F-actin polymers both exhibit directionality (polarity). A typical F-actin molecule has a diameter of 7 nm. Actin polymerization requires a concentration of G-actin above the critical concentration.When both ends of an F-actin molecule are polymerizing, both ends are referred to as plus ends.
3. Hypothetically, the plus end of an actin filament has a critical concentration of 60 and the minus end has a critical concentration of 90. If the concentration of available, ATP-bound G-actin in the cell is 75, which of the following is true? Choose all that apply.
Depolymerization will be favored at the minus end. Polymerization will be favored at the plus end. No net growth will be exhibited at the plus end. No net growth will be exhibited at the plus end. Polymerization will be favored at the minus end. Depolymerization will be favored at the plus end.4. Which of the following statements about the cytoskeleton is correct? Choose all that apply.
The cytoskeleton is made of a mixture of protein and carbohydrate. The cytoskeleton provides shape and support to eukaryotic cells, particularly animal cells. Cytoskeletal elements can be found in the cytoplasm and in at least one organelle. The cytoskeleton forms the cell wall of plant cells. Cytoskeletal elements are rigid, and once established are not easily changed. The cytoskeleton is made of a mixture of protein and lipid.Explanation / Answer
1. Which of the following statements about actin is correct?
If the actual amount of available ATP-bound G-actin is below the critical concentration at both ends of a filament, then the actin filament will depolymerize
2. Which one of the following statements about actin is incorrect?
When both ends of an F-actin molecule are polymerizing, both ends are referred to as plus ends.
3. Hypothetically, the plus end of an actin filament has a critical concentration of 60 and the minus end has a critical concentration of 90. If the concentration of available, ATP-bound G-actin in the cell is 75, which of the following is true? Choose all that apply
Depolymerization will be favored at the minus end.
Polymerization will be favored at the plus end.
[ the difference in the Cc values for the (+) and () ends of a filament, can predict the following: at G-actin concentrations below Cc+, no filament growth occurs; at G-actin concentrations between Cc+ and Cc, growth occurs only from the (+) end; and at G-actin concentrations above Cc, growth occurs at both ends, although it is faster at the (+) end than at the () end. Once the steady-state phase is reached at G-actin concentrations intermediate between the Cc values for the (+) and () ends, subunits continue to be added at the (+) end and lost from the () end ]
4. Which of the following statements about the cytoskeleton is correct? Choose all that apply.
The cytoskeleton provides shape and support to eukaryotic cells, particularly animal cells.
Cytoskeletal elements can be found in the cytoplasm and in at least one organelle.
The cytoskeleton forms the cell wall of plant cells. (Cytoskeleton is used as a template, helps cell wall formations. )
5. Which of the following statements about actin filaments is/are correct? Choose all that apply.
F-actin has polarity.
ATP-bound G-actin has higher affinity for other actin than does ADP-bound G-actin.
Actin filaments are made up of two separate strands of polymerized G-actin wrapped together in a helix.
The critical concentration of the plus end is lower than the critical concentration of the minus end.
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