Plasma Membrane – Fluid Mosaic Model Essentials

Twenty question-and-answer flashcards covering key concepts of the plasma membrane and the fluid mosaic model.

What is another name for the plasma membrane (PM)?

Plasmalemma.

Which model is the central dogma of membrane biology, and who proposed it in 1972?

The Fluid Mosaic Model, proposed by S. J. Singer and G. L. Nicolson.

According to the fluid mosaic model, how is the membrane best described?

A dynamic, quasi-fluid lipid bilayer in which proteins freely float, move, and interact.

How does fatty-acid chain length and unsaturation affect membrane fluidity?

Shorter chains and higher unsaturation increase fluidity; longer chains and saturation decrease it.

What type of interactions mainly hold membrane lipids and proteins together?

Weak, non-covalent hydrophobic interactions (with some ionic and hydrogen bonds).

Which type of diffusion is common for membrane lipids and proteins, and which is restricted?

Lateral diffusion is free; vertical (flip-flop) diffusion is highly restricted.

How are phospholipid molecules oriented within the bilayer?

Polar heads face the aqueous exterior/interior, while non-polar fatty-acid tails face inward toward each other.

Which phospholipids dominate the outer versus inner monolayers of the PM?

Outer monolayer: mostly acidic phospholipids; inner monolayer: mostly neutral phospholipids.

What structural role does the phospholipid bilayer play in the membrane?

It forms the basic structural framework of the plasma membrane.

How is cholesterol distributed across the two lipid monolayers?

Almost evenly between the outer and inner monolayers.

What is the primary function of cholesterol in the plasma membrane?

It regulates membrane fluidity, preventing the bilayer from becoming too fluid or too rigid.

Approximately what percentage of membrane proteins are integral proteins?

Roughly 70–80 %.

What distinguishes peripheral (extrinsic) from integral (intrinsic) membrane proteins?

Peripheral proteins reside completely outside the bilayer, whereas integral proteins penetrate it.

What is a transmembrane protein?

An integral protein that spans the entire lipid bilayer from one side to the other.

Name two key functions of integral (especially transmembrane) proteins.

They form pores/channels and transmit signals across the membrane.

In the fluid mosaic analogy, how do intrinsic proteins behave within the lipid matrix?

They float and drift like icebergs in the open sea.

Where are carbohydrates located in the fluid mosaic organization, and what do they form?

Entirely on the outer surface; they bind to lipids/proteins forming glycolipids and glycoproteins.

What is the purpose of carbohydrate cross-linking on the membrane surface?

To create a network that anchors membrane components and restricts their lateral movement.

Which forces link the two lipid monolayers together?

Hydrophobic interactions between their fatty-acid tails.

State one major feature of the fluid mosaic model regarding molecular arrangement and movement.

The membrane exhibits a mosaic arrangement of molecules with free lateral movement within a quasi-fluid state.