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Correct option is (a) True

Explanation: Cytoskeletal elements are dynamic PROTEINS which include microfilaments, intermediate FILAMENTS and microtubules. They maintain the shape of the CELL and any change in their orientation leads to change in cell shape.

Right ANSWER is (a) True

The explanation: According to the “SLIDING filament model of muscle CONTRACTION” shortening of sacromeres RESULTS from sliding of the FILAMENTS one over the other.

The correct choice is (c) nonmuscle MOTILITY

Easy explanation: CELLS like fibroblasts and neuronal cells usually OUTGROW the SPECIMEN, when ultured over a substratum. This behavior is an exhibition of nonmuscle motility.

Correct CHOICE is (C) microvilli

Easy EXPLANATION: Villin and fimbrin are GLOBULAR cross-linking proteins that promote the bundling of actin filaments into PARALLEL and tightly-knit arrays. Such arrays are found in microvilli of epithelial cells.

The correct choice is (a) True

The best EXPLANATION: The slowest step in the formation of actin FILAMENTS is nucleation. At least two or three actin monomers come together in PROPER ORIENTATION in this step.

Correct option is (a) True

For explanation I would say: Monomer-sequestering proteins such as thymosin β4 are RESPONSIBLE for HIGH concentration of G-actin in NONMUSCLE cells.

Correct choice is (d) plasma membrane

The best I can EXPLAIN: CORTEX of a CELL is located just beneath the plasma membrane. It is an active region of the cell that PARTICIPATES in ingestion of extracellular materials, cell division and MOTILITY.

The CORRECT OPTION is (c) 7

The best explanation: Tropomyosin is a 40 nm LONG ELONGATED molecule and it fits into the grooves of within the thin FILAMENTS. Each tropomyosin is associated with 7 actin subunits.

The correct CHOICE is (a) microfilaments

To EXPLAIN I would say: Microfilaments primarily constitute the cortex of a CELL and aid in the process of cell motility. All the ASSOCIATED process depends on the assembly of microfilaments in the cortex.

Correct CHOICE is (a) 1907

The explanation is: Ross Harrison of Yale UNIVERSITY performed a classic experiment in 1907 by culturing a piece of tissue from a frog’s developing nervous system. He cultured it in a TINY drop of lymphatic FLUID and OBSERVED that the axons grew by a process of active outgrowth and elongation.

The correct option is (a) True

Explanation: ACTINS are concentrated on the ADVANCING edge of the LAMELLIPODIUM because actin polymerization pushes the LEADING edge of a cell FORWARD.

Right option is (a) ACTIN filaments

The explanation: Lamellipodium is a cellular extension that occurs in MOTILE CELLS such as fibroblasts and keratinocytes. These PROJECTIONS are caused by actin filaments and are seen on the edges of the cells.

The correct answer is (d) cross-linking

The EXPLANATION is: FILAMIN is a cross-linking protein; such proteins have the ability to alter three-dimensional ORGANIZATION of a population of ACTIN filaments.

Correct option is (c) profilin

The best I can EXPLAIN: Profilin has the ROLE of binding to G-ACTIN and PROMOTING the growth of actin filaments rather than inhibiting (like thymosin).

The correct CHOICE is (a) formin

To elaborate: Formin is a nucleating protein that HELPS in the NUCLEATION of actin filaments. It helps in the generation of unbranched filaments such as those found in FOCAL adhesions.

The correct option is (d) keratocytes

To explain I would say: Keratocytes are CELLS DERIVED from epidermal COVERING of FISH’s scales. Locomotion is studying using keratocytes because they posses rapid gliding movement and broad lamellipodium.

The CORRECT choice is (C) vinculin

To elaborate: FIBROBLAST cells help in cellular adhesion which is aided by the protein Vinculin(a cell-cell adhesion molecule that interacts with fibroblasts). A fluorescently labelled Vinculin protein is used to locate the interaction of fibroblasts.

Right answer is (a) netrin

For explanation I would say: Advancing tip (growth CONE) of a cultured NEURON MAKES a DIRECT turn towards a DIFFUSIBLE protein called netrin. It acts as an attractant for axons growing in an early embryo.

The correct answer is (a) Arp2/3 COMPLEX

Easiest explanation: ActA is a surface protein found on one side of the BACTERIUM Listeria monocytogenes, when inside the HOST cell it activates the Arp 2/3 complex and other proteins that WORK together to DIRECT the process of actin polymerization.

Correct OPTION is (a) 1954

For explanation I would say: The “Sliding filament model of muscle CONTRACTION” was PROPOSED in the year 1954 by TWO groups of British INVESTIGATORS, Andrew Huxley and Rolf Niedergerke, and Hugh Huxley and Jean Hanson.

Correct OPTION is (c) LISTERIA monocytogenes

To elaborate: In the bacterium Listeria monocytogenes which INFECTS the macrophages and causes food poisoning, cell motility is facilitated SOLELY by the polymerization of ACTIN.

Correct option is (C) cofilin

The EXPLANATION: Cofilin is a FAMILY of proteins that include ADF, depactin. These proteins can fragment actin filaments and can PROMOTE depolymerization at the pointed END.

The CORRECT option is (B) A band

To elaborate: The A band of sacromeres REMAINS CONSTANT in length whereas H and I bands decrease in length and DISAPPEAR altogether.

The correct option is (a) True

For EXPLANATION: Titin is an abundant protein found in SKELETAL muscles and is the largest protein discovered in any organism. The gene encoding for titin contains approximately 38000 AMINO acids.

The correct ANSWER is (a) thymosin

For explanation I WOULD SAY: Thymosins are the proteins that BIND to G-actin and prevent their polymerization. Actin-ATP monomers are referred to as G-actin.

Correct option is (a) shortening

To explain: The skeletal muscles OPERATE by the process of shortening, SACROMERES are the units of shortening WHOSE combined decrease in length account for decrease in length of entire muscle.

The correct ANSWER is (d) motile

The explanation: Microfilaments are skeletal filaments involved in PROCESSES INVOLVING cellular MOTILITY; such as movement of vesicles, phagocytosis and CYTOKINESIS.

Correct choice is (b) keratin

For explanation I would say: ‘Epidermolysis bullosa simplex’ is a genetic disorder that associated with extremely fragile skin that blisters easily. The DISEASE is caused by mutations in the gene ENCODING K14, a TYPE I keratin POLYPEPTIDE.

Correct option is (d) kinesin

Easiest explanation: Kinesins are the smallest MOTOR PROTEINS that use microtubules as their tracks. These were discovered in 1985 from the cytoplasm of squid giant axons. Kinesin is a tetramer CONSISTING of two light and two heavy CHAINS.

The CORRECT OPTION is (b) 5

The best I can explain: Depending upon the cell TYPE, intermediate filaments are composed of different polypeptide SUBUNITS. The polypeptide subunits found in intermediate filaments are DIVIDED into 5 major subclasses.

Right option is (c) nucleus

The explanation: Microtubules are hollow, rigid and tubular structures found in all eukaryotic cells. They are associated with the MITOTIC spindle and the core of CILIA and FLAGELLA.

Right OPTION is (c) XI

To elaborate: The myosin superfamilies are divided into two TYPES, conventional and UNCONVENTIONAL. Type VIII and XI BELONG to the latter type and are found only in the plant cells.

Correct choice is (a) True

Best explanation: The internal framework of a cell (the cytoskeleton) is RESPONSIBLE for POSITIONING the various ORGANELLES. This is particularly evident in POLARIZED epithelial cells where organelles are specifically ORDERED from apical to the basal end of the cell.

Right choice is (b) CYLINDRICALLY shaped

The explanation: Muscle cells are cylindrically shaped, 10 to 100 μm thick and 100 mm long. DUE to these DISTINCTIVE properties a skeletal muscle cell is CALLED muscle fiber.

Correct OPTION is (b) False

Explanation: The plus-end of the microtubule is terminated by a ROW of beta-tubulin SUBUNITS and the opposite, minus-end of the microtubule is terminated by a row of alpha-tubulin subunits.

Right ANSWER is (a) Laser beams

Explanation: MICROSCOPIC beads attached to specific proteins can be placed DIRECTLY on a specific cell organelle using laser beams. This grasps microscopic objects and is REFERRED to as OPTICAL tweezers.

Right option is (b) False

The best explanation: Fluorescently LABELED PROTEINS are microinjected or expressed in living CELLS in the technique of fluorescence speckle microscopy. All the proteins of the cytoskeletal filaments are not UNIFORMLY labeled.

Correct ANSWER is (B) False

To explain I would say: INTERMEDIATE filaments are strong, flexible, UNBRANCHED structures, found only in ANIMAL cells. These provide mechanical strength to the cells.

Correct OPTION is (c) isoforms

The best explanation: In fluorescence microscopy, proteins can be labeled using antibodies and it is possible to distinguish between closely RELATED variants of proteins CALLED the isoforms.