Test: Cell Physiology and Membrane Potential- 1 - NEET PG MCQ

There is lateral movement of proteins and lipids within the membrane.

The cell membrane comprises proteins and lipids in a ratio of 55:45. This is roughly equivalent to 1:1.

Cholesterol is a lipid that possesses both hydrophilic and hydrophobic properties. As a vital structural element of membranes, it plays a significant role in:

• Maintaining appropriate permeability
• Ensuring fluidity

It is also a crucial component of the outer layer of plasma lipoproteins.

• Channels (or pores)
• Carrier proteins (pumps)
• Receptors (enzyme receptors)

The Na-K-ATPase pump plays a crucial role in:

• Regulating cell volume
• Maintaining membrane integrity

Integral proteins serve as a structural element of the membrane, functioning as:

• Channels (or pores)
• Carrier proteins (pumps)
• Receptors (enzyme receptors)

The mass ratio of protein to lipid in human erythrocytes is 1.1.

The mass ratio of protein to lipid is as follows:

• 3.2 in the inner mitochondrial membrane
• greater than 2.0 in the sarcoplasmic reticulum
• 1.1 in the outer mitochondrial membrane
• 0.23 in the myelin sheath

Resistance of intracellular fluid 10² Ohm.cm². Resistance of the extracellular fluid is very low compared to ICF. The resistance across the cell membrane may be high up to 10⁵ Ohm/cm² (Average membrane resistance is 3,450 Ohm/cm²).

Ankyrin is a peripheral protein that attaches to the inner side of the integral protein known as ‘band 3’ in the erythrocyte membrane.

Spectrin, a cytoskeletal component found within the erythrocyte, is connected to ankyrin, thus significantly contributing to the preservation of the biconcave shape of the erythrocyte.

Microtubule is a cytoskeletal protein that helps to preserve the size and form of the cell. It may also contribute to the precise regulation of locomotion.

• Tubulins serve as the structural subunits of microtubules, playing a role in regulating cell motility.
• Motilin is a polypeptide hormone composed of 22 amino acids in humans that governs intestinal motility.
• Laminin is a protein found in the extracellular matrix that influences cell development and growth. Other matrix proteins with comparable functions include collagens, fibronectin, tenascin, and various proteoglycans.
• Tactilin: This term is not found in medical dictionaries.

The diameter of the pores within the channel is estimated to range from 0.8 to 1.4 nm. This size allows for the movement of:

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

Gap junctions can be found in electrically excitable cells, including neurons, heart tissue, and smooth muscle. In fact, gap junctions, also known as electrical synapses, were initially identified in the myocardium and nervous tissue due to their ability to facilitate electrical transmission between neighbouring cells.

The plasma membrane of eukaryotic cells is composed of various components, but it does not include:

• Carbohydrates - These are present on the surface for cell recognition.
• Lecithin - This is a type of phospholipid that is part of the membrane structure.
• Cholesterol - This stabilises the membrane and maintains its fluidity.

However, triglycerides are not a component of the plasma membrane. They are primarily used for energy storage in fat cells.

The uncharged, hydrophobic segments of the proteins are typically found within the membrane's interior, while the charged, hydrophilic segments are positioned on the surfaces.

Membrane carbohydrates are typically found associated with lipids, forming glycolipids. Examples include gangliosides and cerebrosides.

The lipid bilayer of the cell membrane has several important characteristics:

• Asymmetrical arrangement: The components of the membrane are not arranged equally on both sides.
• Lateral diffusion: Ions and molecules can move sideways within the membrane.
• Amphipathic lipids: The bilayer is primarily made up of lipids that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts.

Therefore, the correct understanding of the lipid bilayer is essential for grasping how cells function.

• A higher proportion of saturated fatty acids results in a stiffer membrane, leading to reduced fluidity and an increased T_m.
• Conversely, unsaturated fatty acids, such as linoleic acid, enhance membrane fluidity, which lowers T_m.

An increase in Tm indicates a rise in rigidity, leading to a reduction in membrane fluidity.

The inner mitochondrial membrane contains the greatest amount of protein, while the myelin sheath has the highest lipid concentration.

• Both hydrophobic and covalent interactions are significant.
• Covalent bonds play a crucial role.
• Electrostatic and hydrogen bonds exist between peripheral and integral proteins, but not between proteins and lipids.

Integral proteins serve as essential structural elements of the membrane, functioning as:

• Channels (or pores)
• Carrier proteins (pumps)
• Receptors (enzyme receptors)