Cell Membrane Structure and Cholesterol Effects

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the effect of cholesterol on membrane fluidity at body temperature?

It alters the permeability of the membrane.

It decreases fluidity by restraining the movement of phospholipids. (correct)

It has no effect on the fluidity of the membrane.

It increases fluidity by allowing phospholipids to pack closely together.

What are lipid rafts primarily enriched with?

Cholesterol and sphingolipids. (correct)

Phospholipids and proteins.

Fatty acids and nucleic acids.

Glycoproteins and glycolipids.

What portion of the proteins in living organisms do integral membrane proteins represent?

20-30% (correct)

40-50%

30-40%

10-20%

What is a characteristic of integral membrane proteins?

They penetrate entirely through the lipid bilayer. Signup and view all the answers

Which type of protein is permanently anchored within the membrane?

Integral membrane protein. Signup and view all the answers

What technique is used to visualize the surface of a specimen after preparing it with a carbon and platinum coating?

Scanning electron microscopy. Signup and view all the answers

How can integral membrane proteins normally be removed from the membrane?

By treatment with ionic detergents like SDS. Signup and view all the answers

What is a characteristic of integral polytopic proteins?

They can span across the membrane. Signup and view all the answers

What role do membrane rafts play in cellular processes?

They are involved in signal transduction and membrane trafficking. Signup and view all the answers

Which interaction allows integral monotopic membrane proteins to associate with membranes?

Covalently bound membrane lipid Signup and view all the answers

Which statement is true regarding the orientation of membrane proteins?

Membrane proteins have a distinct orientation in the lipid bilayer. Signup and view all the answers

What are helix bundle proteins primarily associated with?

All types of biological membranes Signup and view all the answers

Which type of integral membrane protein can only attach to one side of the membrane?

Integral monotopic proteins Signup and view all the answers

Which of the following is NOT a type of interaction between integral monotopic proteins and cell membranes?

Polar covalent bond with water Signup and view all the answers

What is the role of Triton X-100 in relation to proteins?

It generally does not alter protein's tertiary structure. Signup and view all the answers

What do transmembrane topology differences refer to?

Locations of the N- and C-termini of transmembrane proteins. Signup and view all the answers

How do lipid bilayers with high proportions of unsaturated fatty acid tails compare to those with lower proportions?

They are more fluid. Signup and view all the answers

What role does cholesterol play in animal cell membranes?

Stiffens the bilayer and reduces fluidity. Signup and view all the answers

What factor can bacteria and yeast cells adjust to maintain membrane fluidity?

Temperature and fatty acid composition. Signup and view all the answers

What does the FRAP technique specifically measure in a cell membrane?

The fluidity through diffusion of fluorescently tagged molecules. Signup and view all the answers

What is likely to happen to the diffusion of a membrane protein if it is anchored to the cytoskeleton?

It will not move at all. Signup and view all the answers

What distinguishes peripheral membrane proteins from integral membrane proteins?

Peripheral proteins are temporarily attached via non-covalent interactions. Signup and view all the answers

What treatment can cause peripheral membrane proteins to dissociate from the membrane?

Exposure to polar reagents with high salt concentrations Signup and view all the answers

Which type of integral membrane protein transports ions across the membrane?

Pumps Signup and view all the answers

How does the presence of double bonds in the hydrocarbon tails affect the fluidity of a lipid bilayer?

Double bonds prevent lipid molecules from aggregating closely. Signup and view all the answers

Which of the following is NOT a function of integral membrane proteins?

Synthesizing new membrane lipids Signup and view all the answers

What primarily determines the fluidity of a lipid bilayer at a given temperature?

Nature of the phospholipid hydrocarbon tails Signup and view all the answers

What is the role of structural proteins in the context of membrane proteins?

They form junctions between adjacent cells. Signup and view all the answers

Which factor contributes to a more viscous and less fluid lipid bilayer?

Longer hydrocarbon tails Signup and view all the answers

Where does the assembly of new membrane phospholipids begin?

In the endoplasmic reticulum Signup and view all the answers

What is the primary function of flippases in membrane asymmetry?

They move phospholipids from the outer leaflet to the inner leaflet Signup and view all the answers

Why is membrane asymmetry important for the function of membrane proteins like the Na+-K+ pump?

It preserves the electrochemical gradient necessary for cellular activity Signup and view all the answers

Which phospholipids are predominantly transported by flippases?

Phosphatidylethanolamine and phosphatidylserine Signup and view all the answers

How does asymmetry arise in membranes after new membranes emerge from the ER?

Through the action of enzymes called flippases Signup and view all the answers

What is the role of floppases in membrane transport?

To transport phospholipids from the inner leaflet to the outer leaflet Signup and view all the answers

What characterizes the composition of biological membranes?

It contains different sets of phospholipids on each side Signup and view all the answers

What happens to membrane proteins during their synthesis and insertion into the membrane?

They are inserted asymmetrically according to their function Signup and view all the answers

Study Notes

Cholesterol and Membrane Fluidity

Cholesterol reduces fluidity at body temperature by stabilizing phospholipid movement.
At lower temperatures, it increases fluidity by preventing tight packing of phospholipids.

Membrane Heterogeneity

Cellular membranes exhibit lateral heterogeneity with dynamic domains, including lipid rafts enriched in cholesterol and sphingolipids.
These lipid rafts play crucial roles in signal transduction, membrane trafficking, cytoskeletal organization, and pathogen entry.
Membrane domains are conserved across various life forms, indicating their functional significance.

Types of Membrane Proteins

Integral membrane proteins represent about one-third of proteins in living organisms, permanently anchored within the membrane.
Peripheral membrane proteins attach temporarily to the lipid bilayer or integral proteins through non-covalent interactions.
Lipid-anchored proteins are also present as a specialized class of membrane proteins.

Integral Membrane Proteins

Integral proteins penetrate the lipid bilayer; transmembrane proteins cross entirely, with extracellular and cytoplasmic domains.
Integral proteins comprise 20-30% of encoded proteins; difficult to isolate due to hydrophobic domains.
Removal typically requires detergents like SDS (ionic) or Triton X-100 (non-ionic).

Types of Integral Membrane Proteins

Integral monotopic proteins attach to one side of the membrane; interactions with the bilayer include α-helices, hydrophobic loops, or covalently bound lipids.
Varieties include bitopic and polytopic transmembrane proteins with unique orientations or structural arrangements.

Membrane Fluidity

Fluidity is defined by the ease of lipid movement within the bilayer; dependent on hydrocarbon tail composition.
Shorter fatty acid chains and higher unsaturation increase fluidity; longer chains and fewer double bonds decrease fluidity.
Cholesterol maintains membrane fluidity in animal cells by stiffening the bilayer while balancing permeability.

Studying Membrane Fluidity

Fluorescence Recovery After Photobleaching (FRAP) method assesses membrane fluidity by tagging and bleaching fluorescent molecules, tracking their recovery.
Membrane proteins are generally less mobile than phospholipids; anchoring to the cytoskeleton restricts protein movement.

Membrane Assembly and Asymmetry

New phospholipids are created in the endoplasmic reticulum (ER) and are initially deposited on the cytosolic side of the membrane.
Membrane asymmetry originates in the Golgi apparatus through specific enzymes (flippases and floppases) that redistribute phospholipids between leaflets.
Phosphatidylserine is primarily moved inward, whereas floppases transport choline-derived phospholipids and cholesterol outward.

Functional Importance of Membrane Asymmetry

Membranes display structural and functional asymmetry; outer and inner surfaces have distinct compositions and functions.
This asymmetry is vital for electrochemical gradients relevant to processes like the Na+-K+ pump, which maintains cell ion concentrations.
The orientation of membrane proteins is crucial for their function, as seen in energy-dependent processes involving ATP and ion transport.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the role of cholesterol in cellular membrane fluidity. It examines how cholesterol influences phospholipid movement at different temperatures and the overall structure of membranes. Understand the importance of cholesterol in maintaining membrane integrity and functionality.