42. Actin exists in two forms, a globular G form and a filamentous F form. a. Tr
ID: 253560 • Letter: 4
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42. Actin exists in two forms, a globular G form and a filamentous F form. a. True b. False 43. Formation of actin filaments requires energy in the form of ATP a. True b. False 44. In muscle, every myofibril lis organized as a chain of contractile units called myoytes. a. True b. False 45. Microtubules are approximately 1/3 the diameter of actin filaments. a. True b. False 46. The cycle of alternating growth and shrinkage of microtubules is referred to as dynamic instability rescue and catastrophe. a. True b. False 47. Kinesins and dyneins are molecular motor proteins. a. True b. False 48. Desmosomes are a. True specialized junctions that help hold cells together, while their counterpart hemidesmosomes prevent cell-to-cell contact b. False bullosa simplex is a skin disease caused by a mutation in the gene encoding keratin. 49. Epidermolysis a. True b. False the main component of brain lesions found in Alzheimer's patients? is a MAP that forms 50. Omega a. True b. False 2096 Siner Associates, BExplanation / Answer
42. True. Filamentous actin (F-Actin) are linear polymers of globular actin (G-actin) subunits. F actin are found in cytosketon.
43. True. Actin polymerization (nucleation) starts with the self-assembly of three G-actin monomers to form a trimer. ATP-bound actin then binds the end of the trimer, and the ATP is subsequently hydrolyzed. This is how the elongation continues and actin filaments are formed.
44. False. In muscles, every myofibril is organized as chain of contactile units in muscles called scaromeres. The sacromeres give straited appearance to skeletal and cardiac muscles.
45. False. Microtubules have a diameter of 23 nm while actin is 7 nm. Actin is 1/3 diameter of microtubules.
46. True. The cycle of alternating growth and shrinkage of microtubules is called dynamic instabilty. Rescue is growth after a pause and catastrophe is shrinkage after a pause.
47. True. Kinesins move along microtubules and are powered by ATP hydrolysis. They support mitosis and meiosis and also carry cargo such as organelles and vesicles from the center of a cell to its periphery. Dyneins too move along microtubules utilizing ATP and are function in sliding microtubules relative to one other during the beating of cillia and flagella in eukaryotic cell surface.
48. True. are a type of junctional complex. They are also known as a macula adhaerens provide the cells with adhesion to one another. They are randomly arranged on the lateral sides of plasma membranes. Hemidesmosomes are specialized adhesive structure found in keratinocytes of the epidermis of skin that attach cells to the underlying basement membrane (extracellular matrix).
50. Epidermolysis bullosa simplex is a genetic skin disorder that cause skin to blister fom mechanical trauma. It can result from mutations in either the KRT5 or KRT14 gene. These genes encode for keratin 5 and keratin 14.
51. False. Omega is not a MAP (microtubule associated protein). It is a fatty acid. Omega-3 fatty acid are known to benefit the brain by lowering the risk of Alzheimer's disease.
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