Module 2 Wednesday: Cell Membrane components and passive diffusion

Flashcards on Membrane Structure and Function

What is the fluid mosaic model?

A model describing the membrane as a dynamic, flexible structure with proteins embedded like tiles in a mosaic.

What biomolecules make up the cell membrane?

Phospholipids, proteins, cholesterol, and carbohydrates.

What are phospholipids made of?

A phosphate group (hydrophilic head) and two fatty acid tails (hydrophobic).

What does amphipathic mean?

Molecules with both hydrophobic and hydrophilic regions (e.g., phospholipids).

What allows the membrane to be selectively permeable?

The structure of the phospholipid bilayer and embedded proteins.

How do phospholipids arrange in the membrane?

Hydrophilic heads face the water on both sides; hydrophobic tails face each other inside.

What is the effect of unsaturated vs. saturated fats on membrane fluidity?

Unsaturated fats increase fluidity; saturated fats decrease it.

How does cholesterol affect the membrane?

Reduces fluidity at moderate temperatures and prevents solidification at low temperatures.

Why do organisms in extreme climates need membrane adaptations?

To maintain membrane fluidity in cold or hot environments.

What are peripheral proteins?

Proteins on the membrane’s surface, not embedded.

What are integral proteins?

Proteins embedded in the membrane; transmembrane proteins span the whole bilayer.

Name 5 functions of membrane proteins.

Transport, enzymatic activity, signal transduction, cell recognition, intercellular joining.

What are aquaporins?

Channel proteins that specifically allow water to pass through the membrane.

What are glycoproteins and glycolipids?

Glycoproteins = protein + carbohydrate; Glycolipids = lipid + carbohydrate. Both assist in cell recognition.

What is passive transport?

Movement of molecules without energy input (down concentration gradient).

What is active transport?

Movement of molecules requiring energy (usually ATP), against a concentration gradient.

What is bulk transport?

Moving large particles using vesicles (endocytosis & exocytosis).

What is diffusion?

Passive movement of molecules from high to low concentration.

What is facilitated diffusion?

Passive transport of molecules using protein channels or carriers.

What is osmosis?

Diffusion of water across a selectively permeable membrane.

What do channel proteins do?

Provide open pores for specific molecules to pass through the membrane.

What do carrier proteins do?

Bind to specific molecules and change shape to shuttle them across the membrane.

How do carrier proteins ensure selectivity?

They have specific shapes and binding sites (lock-and-key model).

Why is protein structure important for function?

The 3D shape determines what molecule a protein can bind and transport.

Which molecules can diffuse directly through the membrane?

Small, nonpolar molecules like O₂, CO₂, and some hydrocarbons.

Which molecules cannot pass easily through the membrane?

Large, polar, or charged molecules like glucose and ions.

How does a cell regulate molecule entry?

Through selective permeability and transport proteins.

What analogy did the professor use to explain membrane selectivity?

A bouncer at a club—only certain molecules get in.

How does HIV enter cells?

It binds to the CD4 receptor and a co-receptor on T helper cells like a puzzle piece.

What makes some people immune to HIV?

Lack of the co-receptor needed for HIV to enter the cell.

What analogy was used for diffusion?

People spreading from a crowded room to a less crowded one through a doorway.

What is equilibrium in diffusion?

When molecules are evenly spread out and move equally in both directions.