Sterols in Plasma Membranes Quiz

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Questions and Answers

Which characteristic of the cell membrane makes it a highly dynamic system?

Amphipathic property

Fluidity (correct)

Asymmetric nature

Mosaic structure

Why are transmembrane proteins important in the context of plasma membrane structure?

To provide energy for lipid flip flop

To anchor the protein in the bilayer (correct)

To facilitate lateral movements of phospholipids

To transport ions across the membrane

How do sterols impact the fluidity of the plasma membrane?

Decrease fluidity as they fill the spaces between hydrocarbon chains of phospholipids (correct)

Have no impact on fluidity

Increase fluidity as they intercalate between phospholipids

Cause random movement of molecules

What is the effect of increasing sterols on membrane fluidity?

Membrane fluidity decreases Signup and view all the answers

What type of fatty acid would most likely result in higher membrane fluidity?

Polyunsaturated fatty acids Signup and view all the answers

Which feature distinguishes lipid rafts from the rest of the plasma membrane?

Distinct lipid composition Signup and view all the answers

How does cholesterol act as a regulator of membrane fluidity?

It stabilizes the membrane at high temperatures and prevents clustering at low temperatures Signup and view all the answers

What is the composition of lipid rafts?

Glycosphingolipids, cholesterol, and proteins Signup and view all the answers

In freeze-fracturing technique, what is the main purpose of freezing and fracturing the cell membrane?

To observe the structural organization of the lipid bilayer Signup and view all the answers

How do saturated fatty acids impact membrane fluidity compared to unsaturated fatty acids?

Saturated fatty acids decrease fluidity by forming straight chains Signup and view all the answers

What role do lipid rafts play in cell signaling?

They facilitate cell signaling by clustering signaling molecules Signup and view all the answers

What is the impact of sterols on the transport of ions and small molecules across membranes?

Block transport by filling spaces between hydrocarbon chains of phospholipids Signup and view all the answers

Which technique is commonly used to visualize membrane proteins and reveal the asymmetrical nature of the phospholipid bilayer?

Freeze fracturing technique Signup and view all the answers

What is the main function of lipid rafts in the cell membrane?

Assisting in signaling processes Signup and view all the answers

According to Davson & Danielli model, how are proteins arranged in the cell membrane?

Present as a protein sheet on both sides of the membrane Signup and view all the answers

In terms of structure, what do membrane proteins visualized by electron microscopy appear as?

Discrete particles Signup and view all the answers

What is the primary reason for using hydrogenated oil in baking?

To increase the shelf life of baked products Signup and view all the answers

What does the freeze fracturing technique reveal about the phospholipid bilayer?

The layers are asymmetrical in composition Signup and view all the answers

Study Notes

Sterols

Sterols are 4-ring structures, such as cholesterol, found in animal plasma membranes
Sterols affect fluidity of plasma membranes by intercalating into the membrane, filling spaces between hydrocarbon chains of phospholipids
Sterols impact permeability of membranes to ions and small polar molecules, blocking transport if present
Cholesterol acts as a bidirectional regulator of membrane fluidity, stabilizing the membrane at high temperatures and preventing clustering at lower temperatures
As sterol levels increase, membrane fluidity decreases, and Tm (melting point) increases

Lipid Rafts

Lipid rafts are dynamic microdomains consisting of glycosphingolipids, cholesterol, and proteins, playing a crucial role in membrane signaling and protein trafficking
Lipid rafts are clusters of lipids in the cell membrane, involved in signaling and protein trafficking

Davson & Danielli Model of Cell Membrane

Protein sandwich model: proteins present as a protein sheet between two phospholipid bilayers
However, protein-to-lipid ratio is not constant, making the model incomplete
Phospholipid bilayer is asymmetrical, with differing constituents in the top and bottom layers (glycoproteins and glycolipids in the top layer, peripheral proteins in the bottom layer)

Freeze Fracturing Technique

Lipid bilayer is frozen quickly and then fractured with a diamond knife to visualize the membrane structure
E face (exoplasmic face) is on the exterior of the cell, and P face (protoplasmic face) is on the interior, showing the asymmetry of the bilayer
Freeze fracture electron microscopy reveals discrete particles representing membrane proteins in each layer

Membrane Proteins

Membrane proteins are long polypeptide chains consisting of amino acids, with alpha-helical structures
They can be integral membrane proteins, transmembrane proteins that cross the membrane by single pass or multi-pass methods
Flip-flop movement of membrane proteins is important for molecule transport, but occurs rarely

Phospholipid Bilayer

The bilayer is asymmetric, fluid, and mosaic, with embedded proteins
It is amphipathic, with a polar head and non-polar tail
The composition of phospholipids influences the fluidity of the membrane

Fatty Acids and Membrane Fluidity

The type of fatty acid affects membrane fluidity, with unsaturated fatty acids increasing fluidity and saturated fatty acids decreasing it

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Description

Test your knowledge about the role of sterols, such as cholesterol, in animal plasma membranes. Explore how sterols can impact membrane fluidity and permeability to ions and small molecules.