Cellular Membranes structure and functions: L3

What are the four major components of cellular membranes

Phospholipids, glycolipids, sterols, and proteins.

What is membrane asymmetry

Membrane asymmetry means that the two sides (leaflets) of a membrane have different compositions, including differences in lipid types, degree of lipid saturation, and proteins.

Why can the composition of cellular membranes differ between cells and organisms

The lipid and protein composition of membranes varies greatly among different organisms, within individual cells, and between the two sides of the same membrane.

What is the fundamental structure of a cellular membrane

The fundamental structure is a lipid bilayer consisting of two layers, or leaflets, of lipids.

What types of movement can phospholipids perform within a membrane

Phospholipids can rotate around their long axis and diffuse laterally within the same leaflet. These movements occur frequently, freely, rapidly, and randomly.

What is lateral diffusion

Lateral diffusion is the movement of a membrane lipid or protein sideways within the same leaflet of the membrane.

What is transverse diffusion (flip-flop)

Transverse diffusion, or flip-flop, is the movement of a phospholipid from one leaflet of the membrane to the other. It occurs much less frequently unless phospholipid translocases, or flippases, are involved.

What does the fluid mosaic model describe

The fluid mosaic model describes a membrane as a fluid lipid bilayer in which membrane lipids and proteins can move laterally within the membrane.

What evidence demonstrates that membrane proteins can move laterally

When mouse and human cells containing species-specific membrane proteins were fused, the proteins became mixed throughout the hybrid cell over time. This demonstrated that membrane proteins can laterally diffuse within the membrane.

Why is membrane fluidity important

Membrane fluidity allows membrane lipids and proteins to move within the membrane and is critical for proper membrane function.

What is the transition temperature (Tm) of a membrane

The transition temperature (Tm) is the temperature at which a membrane changes from a more rigid, gel-like state to a more fluid state.

How does temperature affect membrane fluidity

Increasing temperature generally increases membrane fluidity, while decreasing temperature generally decreases membrane fluidity.

What happens to a membrane when its temperature decreases below its transition temperature (Tm)

The membrane becomes more rigid because the phospholipids have less movement and pack more tightly together.

What happens to a membrane when its temperature increases above its transition temperature (Tm)

The membrane becomes more fluid because the phospholipids have greater movement and diffuse more freely.

What factors determine the fluidity of a membrane

Membrane fluidity is determined largely by the membrane's lipid composition and temperature.

What does cholesterol do in eukaryotic membranes

Cholesterol acts as a fluidity buffer, helping prevent the membrane from becoming too rigid at low temperatures or too fluid at high temperatures.

How does cholesterol affect membrane fluidity when temperature decreases

The rigid hydrophobic steroid rings of cholesterol prevent phospholipids from fitting tightly together, reducing the membrane's transition temperature (Tm) and helping maintain fluidity.

How does cholesterol affect membrane fluidity when temperature increases

The rigid hydrophobic steroid rings of cholesterol reduce the rate of phospholipid lateral diffusion, helping prevent the membrane from becoming excessively fluid and increasing the membrane's transition temperature (Tm).

What is homeoviscous adaptation

Homeoviscous adaptation is the ability of most organisms to regulate membrane fluidity by changing the lipid composition of their membranes.

Why is regulating membrane fluidity important for cells

Cells need to maintain an appropriate level of membrane fluidity because membrane function depends on the proper movement and organization of membrane lipids and proteins.

What are lipid rafts

Lipid rafts are regions within a membrane monolayer that have a different lipid composition from the surrounding membrane and can sequester specific membrane proteins.

Is lipid composition homogeneous throughout a membrane monolayer

No. Different regions of a membrane monolayer can have different lipid compositions, including specialized regions called lipid rafts.

What are membrane domains

Membrane domains are specialized regions of a membrane where particular lipids and proteins are concentrated or where protein movement is restricted.

What can restrict the lateral movement of membrane proteins

Protein aggregation, tight junctions, and anchoring to the cytoskeleton or extracellular matrix can restrict the lateral movement of membrane proteins.

What is the apical surface of an epithelial cell

The apical surface is the side of an epithelial cell that contains microvilli and is specialized for the absorption of nutrients.

What is the basolateral surface of an epithelial cell

The basolateral surface transfers absorbed nutrients toward the underlying connective tissue.

How do tight junctions maintain separate membrane domains in epithelial cells

Tight junctions separate the apical and basolateral domains and prevent membrane proteins from diffusing from one domain to the other.

What is the glycocalyx

The glycocalyx is a sticky surface coat formed by carbohydrate groups from plasma membrane glycoproteins and glycolipids that protrude from the cell surface.

Where is the glycocalyx found

The glycocalyx is found on the surface of animal cells and bacterial cells.

What are the functions of the glycocalyx

The glycocalyx participates in cell-cell recognition, adhesion, protection, and the creation of a permeability barrier.

What are the five major functions of cellular membranes

Cellular membranes define the boundaries of cells and internal compartments, regulate transport, detect and transduce signals, participate in cell-to-cell communication, and produce or interact with external structures.

How do cellular membranes define the boundaries of cells and internal compartments

Membranes separate the inside of a cell or organelle from its surrounding environment, allowing different compartments to maintain their own internal conditions.

How do cellular membranes regulate transport

Cellular membranes regulate the movement of materials into and out of cells and organelles.

What does it mean that cellular membranes detect and transduce signals

Membrane proteins can detect signals from outside the cell and convert those signals into changes or responses inside the cell.

How do cellular membranes participate in cell-to-cell communication

Membrane components allow cells to recognize, interact with, and communicate with other cells.

How do cellular membranes interact with external structures

Cellular membranes can produce or interact with external structures such as cell walls and the extracellular matrix.

Why is membrane asymmetry important

Membrane asymmetry allows the two sides of the membrane to have different lipids and proteins, giving each side specialized properties and functions.

Why is membrane fluidity important for cellular membrane function

Membrane fluidity allows lipids and many proteins to move within the membrane, which is important for processes such as transport, signaling, and cell communication.

How does membrane lipid composition affect membrane fluidity

The types and proportions of lipids in a membrane influence how tightly the lipids pack together, which affects membrane fluidity and its transition temperature.

How do the structure and composition of cellular membranes allow them to perform their functions

The fluid lipid bilayer provides a flexible boundary, while membrane proteins perform specialized functions such as transport and signaling. Differences in lipid and protein composition allow different membranes and membrane domains to perform specialized functions.