Question 1

Which protein is responsible for anchoring the plus ends of actin filaments to the Z line in skeletal muscle sarcomeres?

Accepted Answer

CapZ

Question 2

During skeletal muscle contraction, what is the role of calcium ions ($\mathrm{Ca^{2+}}$) in the regulation of the actin-myosin interaction?

Accepted Answer

Calcium binds to troponin C (TnC), causing tropomyosin to move and expose myosin-binding sites on actin.

Question 3

Which of the following best describes the sliding-filament model of muscle contraction?

Accepted Answer

Thin filaments slide past thick filaments, causing sarcomere shortening without changing the length of either filament.

Question 4

A patient presents with a genetic defect in desmoplakin. Which tissue is most likely to be affected?

Accepted Answer

Cardiac muscle

Question 5

Which G protein is primarily responsible for the formation of lamellipodia during cell migration?

Accepted Answer

Rac

Question 6

What is the main function of tight junctions in epithelial tissues?

Accepted Answer

Seal adjacent cells to prevent movement of molecules between them

Question 7

Which of the following proteins is NOT a component of the thin filament in skeletal muscle?

Accepted Answer

Myosin

Question 8

In smooth muscle contraction, which enzyme is activated by the calcium-calmodulin complex to initiate contraction?

Accepted Answer

Myosin light-chain kinase (MLCK)

Question 9

Which type of cell junction allows the direct passage of ions and small molecules between adjacent cells, facilitating electrical and chemical communication?

Accepted Answer

Gap junctions

Question 10

Which protein is the largest single-chain polypeptide in muscle, contributing to elasticity and connecting the Z line to the M line?

Accepted Answer

Titin

Question 11

A mutation in claudin proteins would most likely disrupt which cellular function?

Accepted Answer

Paracellular transport and tight junction sealing

Question 12

Which process is directly responsible for the detachment of myosin from actin during the muscle contraction cycle?

Accepted Answer

Binding of ATP to myosin

Question 13

Which cell adhesion molecule is a member of the immunoglobulin superfamily and is involved in transient cell-cell adhesion?

Accepted Answer

CAM (Cell Adhesion Molecule)

Question 14

Which of the following best explains why smooth muscle contraction is slower and more sustained than skeletal muscle contraction?

Accepted Answer

Smooth muscle contraction is regulated by phosphorylation of myosin light chains rather than troponin-tropomyosin.

Question 15

Which of the following correctly matches the junction type with its primary cytoskeletal linkage?

Accepted Answer

Adherens junctions — actin filaments

Question 16

Which event occurs first during the cross-bridge cycle in skeletal muscle contraction?

Accepted Answer

Release of $\mathrm{Ca^{2+}}$ from the sarcoplasmic reticulum

Question 17

Which protein is responsible for stabilizing the length of thin filaments in skeletal muscle?

Accepted Answer

Nebulin

Question 18

Which of the following is TRUE regarding integrins in cell migration?

Accepted Answer

Integrins attach cells to the extracellular matrix and connect to actin filaments inside the cell.

Question 19

Which of the following statements about desmosomes is CORRECT?

Accepted Answer

Desmosomes provide strong adhesion by linking intermediate filaments between cells.

Question 20

Which of the following best describes the role of selectins in leukocyte adhesion during inflammation?

Accepted Answer

Selectins bind to specific sugars on the cell surface to mediate transient adhesion of leukocytes to endothelial cells.

Muscle Contractile Mechanisms and Cell Junctions in Cell Biology

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