Test: Cell Physiology and Membrane Potential- 2 - NEET PG MCQ

• Integrins - heterodimer
• Adhesion molecules from the IgG superfamily of immunoglobulins
• Cadherins - Ca²⁺ dependent molecules
• P-Selectins - bind carbohydrates

Integrins are proteins that play a crucial role in connecting cells to the extracellular matrix (ECM). They help anchor cells to their surroundings and facilitate communication between cells and the ECM.

Among the various components of the ECM, integrins specifically connect actin filaments to fibronectin. This connection is vital for maintaining cell shape, movement, and overall tissue integrity.

• Fibronectin is a glycoprotein that helps cells adhere to the ECM.
• It plays a key role in wound healing and cell migration.
• Integrins bind to fibronectin, allowing for the transfer of signals between the cell and its environment.

Zonula occludens refers to tight junctions. These structures are not present in cardiac muscle.

• For instance, the luminal membranes of mucosal cells within the small intestine possess a symport that facilitates the entry of glucose into the cell.
• This process occurs exclusively when Na⁺ attaches to the protein and is simultaneously transported into the cell.

Na-K-ATPase functions as an electrogenic pump, transferring three positive charges out of the cell for every two that it brings in. Consequently, it is described as having a coupling ratio of 3:2.

The β-subunit comprises a solitary membrane-spanning domain along with three extracellular glycosylation sites, each of which seems to have carbohydrate residues attached.

The region of fusion, which exists between the vesicle and the cell membrane, disintegrates, resulting in the vesicle's contents being released outside while the cell membrane remains undamaged. This aspect is part of the Ca²⁺ dependent mechanism of exocytosis.

The osmolarity refers to the quantity of osmoles in one litre of solution (for instance, plasma), while the osmolality denotes the quantity of osmoles per kilogram of solvent.

Relative permeability of different molecules: Hydrophobic molecules (CO₂, O₂, N₂, steroid hormones) >>> small uncharged polar molecules
(H₂O, urea, glycerol) >>> large uncharged polar molecules (glucose,
sucrose) >>> Ions (Na⁺, K⁺, Cl^–).

Among the options provided, the substance that can easily pass through a pure phospholipid bilayer is:

• Oxygen: This small, nonpolar molecule can diffuse freely across the bilayer.
• Na⁺: This ion is charged and cannot pass through the bilayer easily.
• Water: Although it can pass through, it does so less effectively compared to oxygen.
• None: This option does not apply since oxygen is permeable.

Therefore, the most permeable substance to a pure phospholipid bilayer is oxygen.

• Na⁺, K⁺, and glucose are key contributors to the creation of osmolality and osmotic pressure.

Fick's law is utilised to determine the rate of straightforward diffusion.

The pump is crucial for upholding the resting membrane potential, rather than for the generation of action potentials.

Reverse pinocytosis is an exocytosis mechanism that necessitates the presence of Ca²⁺.

The channel's diameter typically ranges from 0.8 to 1.4 nm, allowing for the movement of:

• ions
• sugars
• amino acids
• other solutes with molecular weights of up to approximately 1000.

The transport of neutral substances across the cell membrane can occur through several methods:

• Porins: These are proteins that form channels in the membrane, allowing specific molecules to pass through.
• Ionophores: These compounds facilitate the movement of ions across the membrane, but they are not primarily for neutral substances.
• Lipopolysaccharides: These molecules are part of the outer membrane of certain bacteria and do not directly assist in transport.
• Diffusion: This is the main process for transporting neutral substances. It involves the movement of molecules from an area of higher concentration to an area of lower concentration, allowing them to pass through the cell membrane naturally.

In summary, diffusion is the primary method for transporting neutral substances across the cell membrane.

Facilitated diffusion is a process that allows substances to cross membranes with the help of proteins. Here are the key points:

• Requires a carrier protein: Facilitated diffusion needs specific proteins to help move molecules across the cell membrane.
• Concentration gradient: The rate of transport increases when there is a higher concentration of the substance on one side of the membrane compared to the other.
• Passive process: It does not require energy, unlike active transport.

In summary, facilitated diffusion is crucial for moving substances in and out of cells efficiently.

Facilitated diffusion is a type of transport that helps molecules move across a cell membrane. Here are some key points about this process:

• Direction of movement: It occurs in the direction of the concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration.
• Energy requirement: This process does not require energy, making it a passive form of transport.
• Electrical gradient: It does not occur in the direction opposite to the electrical gradient; rather, it follows the concentration gradient.
• Facilitation: Molecules are assisted by specific proteins in the membrane, which help them cross without using energy.

Facilitated diffusion does not require energy. This process allows substances to cross membranes with the help of specific proteins, but it relies on the natural movement of molecules from areas of high concentration to low concentration, which does not require energy.

In contrast, active transport uses energy to move substances against their concentration gradient. This process is essential for transporting nutrients and ions into cells where they are needed.

Co-transport involves the use of carrier proteins to move two substances simultaneously across a membrane. This is a critical mechanism for the absorption of nutrients.

Lastly, glucose is not transported through passive diffusion; instead, it typically requires a specific transport mechanism, such as facilitated diffusion, to enter cells.

Active transport mechanisms can be classified into two categories: primary active transport (such as Na-K ATPase) and secondary active transport. Both categories are facilitated by carrier proteins.

Carrier-dependent transport adheres to saturation kinetics. In contrast, simple diffusion does not necessitate a carrier protein.

Fick's law describes how the flow of particles (flux) through a geomembrane is influenced by various factors. Here are the key points to consider:

• Concentration Gradient: The difference in concentration across the membrane plays a crucial role. A higher concentration difference leads to increased flux.
• Temperature: Higher temperatures generally increase particle movement, which can enhance the flux through the geomembrane.
• Molecule Size: Larger molecules may diffuse more slowly, reducing the flux compared to smaller molecules.
• Weight: Heavier particles tend to move less freely, potentially decreasing the flux.
• Area: A larger surface area of the geomembrane allows for more particles to pass through, increasing the overall flux.

In summary, the flux of a geomembrane increases significantly with a greater concentration difference and temperature, while it may decrease with larger molecule size and weight.

The sodium-potassium pump is a vital protein in cell membranes that helps maintain proper ion balance. It works by moving ions across the membrane against their concentration gradients, using energy.

The coupling ratio refers to how many sodium ions are pumped out of the cell compared to potassium ions pumped in. For the sodium-potassium pump, the coupling ratio is:

• 3 sodium ions are exported from the cell
• 2 potassium ions are imported into the cell

This means the correct coupling ratio is 3:2. This action is essential for various cell functions, including maintaining cell volume and electrical excitability.

The extracellular binding site on the Na⁺-K⁺ pump is primarily associated with the molecule known as quabain. Quabain is a specific inhibitor that binds to this site and affects the pump's function.

• The Na⁺-K⁺ pump is crucial for maintaining cell membrane potential.
• It transports sodium ions out of the cell and potassium ions into the cell.
• Quabain's binding disrupts this process, leading to increased sodium levels inside the cell.

Understanding the role of quabain helps in studying the pump's mechanisms and its importance in cellular physiology.

The Na⁺-K⁺ pump is important for maintaining the balance of sodium and potassium in cells. Here are the key points about its function:

• ATPase activity: The pump uses ATP, which is energy, to function.
• Movement of sodium: It can transport Na⁺ both into and out of the cell.
• Electrical neutrality: The pump does not maintain electrical neutrality as it moves ions.
• Pumping ratio: It pumps out three Na⁺ ions for every two K⁺ ions it brings in.
• Ion transport: It effectively pumps three Na⁺ ions out and two K⁺ ions into the cell.