Lecture 3.3: Chapter 11 Membrane Structure Essential Cell Biology

A comprehensive set of flashcards based on lecture notes about membrane structure and functions in cell biology.

What do cell membranes act as?

Selective barriers that prevent molecules on one side from freely mixing with those on the other.

What is the role of receptor proteins in the plasma membrane?

They enable the cell to receive signals from the environment.

Which type of cells have internal membranes enclosing organelles?

Eukaryotic cells.

What are the main components of a cell membrane?

A lipid bilayer with embedded proteins.

What do membrane channels and transporters allow?

The import and export of small molecules.

What are phospholipids primarily composed of?

A hydrophilic head and two hydrophobic tails.

Which phospholipid is the most common in cell membranes?

Phosphatidylcholine.

What makes membrane lipid molecules amphipathic?

They contain both hydrophilic and hydrophobic regions.

What happens to phospholipids in water?

They spontaneously form bilayers.

How does cholesterol affect cell membranes?

It tends to stiffen cell membranes.

Where does membrane assembly begin?

In the endoplasmic reticulum (ER).

What is the function of scramblases in the ER?

They randomly transfer phospholipid molecules from one monolayer to the other.

What phospholipids are concentrated in the noncytosolic monolayer?

Phosphatidylcholine and sphingomyelin.

What role do flippases play in membrane composition?

They selectively flip certain phospholipids from one side of the membrane to the other.

What are the functions of plasma membrane proteins?

They transport molecules, act as anchors, detect signals, or catalyze reactions.

What structure do transmembrane proteins often form?

An alpha helix that spans the lipid bilayer.

What stabilizes the structure of the cytosolic half of membranes?

Spectrin, forming a cortex that gives shape.

How do cells restrict the movement of their membrane proteins?

Through tethering to the cytoskeleton or other extracellular structures.

What is unique about the orientation of membrane proteins during vesicle transport?

The original orientation of membrane lipids and proteins is preserved.

What is the fluidity of a lipid bilayer dependent on?

Its composition, including the types of lipids and presence of cholesterol.

How are sugars involved in eukaryotic cell membranes?

They are part of glycoproteins and glycolipids on the membrane surface.

What allows neutrophils to migrate from blood to tissue during an immune response?

Interaction with lectins on endothelial cells, recognizing cell-surface carbohydrates.

What are integral membrane proteins?

Proteins that extend across the lipid bilayer.

What do amphipathic phospholipids do when placed in water?

They form a bilayer by orienting their hydrophilic heads outward.

What are the consequences of phospholipid bilayers closing on themselves?

They form stable, sealed compartments.

What maintains the asymmetric distribution of lipids in cell membranes?

Specific transport proteins such as flippases and scramblases.

What is the typical length of an alpha helix required to span a cell membrane?

About 20 amino acids.

What is the role of glycoproteins on the cell surface?

They function in cell recognition and signaling.

What happens when mouse and human cells are fused regarding membrane proteins?

Initially, they remain in their own halves, then intermingle.

Why do phospholipid bilayers spontaneously close?

To avoid energy unfavorable exposure of hydrophobic tails to water.

What is a liposome?

A closed and spherical structure formed by phospholipid bilayers.

How does the structure of a membrane protein typically differ from the structure of an alpha helix?

Transmembrane proteins can form multiple α helices or β barrels.

What allows polypeptide chains to span lipid bilayers?

Hydrophobic interactions with lipid tails and hydrogen bonding in the helix.

What types of molecules can interact with the lipid bilayer?

Integral proteins, amphipathic proteins, and peripheral proteins.

How do membranes retain their orientation during intracellular transport?

By vesicle budding and fusing without rotating.

Where are glycolipids primarily found in the membrane?

Exclusively in the noncytosolic monolayer.

What happens to phospholipids in a closed bilayer during the assembly?

They achieve a balance of lipid composition and monolayer size.

Which type of membrane protein can form a water-filled pore?

Transmembrane proteins composed of multiple amphipathic α helices.

What is the primary reason for membrane fluidity?

The presence of unsaturated fatty acids and cholesterol.

How do cells create functional domains in their membranes?

By restricting protein movement through physical barriers.

What facilitates the movement of peripheral proteins?

Weak, noncovalent interactions with other membrane proteins.

What type of transmembrane protein primarily forms channels?

A collection of amphipathic α helices.

How do membrane proteins interact with the underlying cytoskeleton?

Anchored by attachment proteins linking spectrin networks.

What dictates the specific composition of membrane phospholipids?

Biosynthetic processes in the endoplasmic reticulum.

How are transmembrane proteins associated with the lipid bilayer?

Through hydrophobic interactions and sometimes covalent modifications.

What unique characteristic do neutrophil cell-surface carbohydrates provide?

They allow recognition and interaction with endothelial cells.