Cell Biology: Structure of Cell Membrane

Study Notes

Surface of the Cell

Initially described as trilaminar (three layers), later corrected to bilayer due to reevaluation.
Cell membranes consist mainly of lipids, forming a lipid bilayer.

Composition of the Cell Membrane

Comprised predominantly of phospholipids.
Phospholipids feature a polar head (glycerol and phosphate) and non-polar tails (unsaturated fatty acids).
Polar heads face outward while non-polar tails orient inward, creating distinct internal and external environments.

Membrane Environment

Internal membrane environment is non-polar and hydrophobic, while the external surface is polar and hydrophilic.
Polar substances cannot easily diffuse through the membrane, necessitating controlled movement.
Sodium ions present significant concentration differences: low inside the cell and high outside, maintaining the cell's polar nature.

Membrane Functionality

The lipid bilayer serves as a selective barrier for substances, but is enhanced by embedded proteins.
Specialized proteins in the bilayer facilitate the movement of large and polar molecules, enhancing membrane functionality.

Cell Specialization

Cell membranes reflect the specific needs of the cell’s function (e.g., liver cells vs. red blood cells).

Integral and Transmembrane Proteins

Transmembrane proteins span the lipid bilayer, protruding from both sides.
These proteins can function interchangeably with integral proteins.

Classification of Transmembrane Proteins

Pumps: Maintain specific concentrations using ATP (e.g., sodium pumps).
Channels: Allow ions/molecules passage along concentration gradients without ATP (e.g., calcium channels).
Gap Junctions: Facilitate fast ion signaling between adjacent cells.
Receptors: Bind ligands to elicit cellular responses, often triggering the secretion of hormones.

Other Membrane-Bound Structures

Glycoproteins and Glycolipids: Carbohydrate-associated proteins/lipids found on extracellular vesicles, contributing to cell-cell recognition.
Cholesterol: Present in all cell membranes, enhances rigidity while reducing flexibility; higher cholesterol lowers membrane fluidity.
Cell Coat (Glycocalyx): A glycoprotein and glycolipid covering that surrounds cell membranes, allowing for enzyme secretion.

Description

This quiz explores the composition and structure of cell membranes, focusing on the concept of the lipid bilayer. It discusses the characteristics of phospholipids, including their polar head structure and the implications of membrane composition. Test your understanding of these fundamental concepts in cell biology.