Membranes and Receptors S3 Lecture 1

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Questions and Answers

What type of molecules are cerebrosides classified as?

Cholesterol derivatives

Oligosaccharides

Amphipathic lipids

Head group sugar monomers (correct)

What is the main reason for the spontaneous formation of lipid bilayers in water?

High temperature of the surrounding environment

Covalent bonding between lipids

Hydrophobic interactions between tails (correct)

Presence of cholesterol

Which of the following describes 'flip-flop' in lipid bilayers?

Movement of lipids from one half of the bilayer to another (correct)

Lateral diffusion within the same layer

Formation of kinks in fatty acyl chains

Rotation of lipid tails

What percentage of lipid content is Cholesterol typically found in tissues?

10-20% Signup and view all the answers

Which characteristic of the bilayer contributes to its low permeability to ions and polar molecules?

Hydrophobic tail interactions Signup and view all the answers

What effect do unsaturated fatty acids have on membrane fluidity?

Disrupt hexagonal packing and increase fluidity Signup and view all the answers

Which of the following is NOT one of the modes of mobility in a lipid bilayer?

Molecular transport mediated by proteins Signup and view all the answers

What is the primary force stabilizing the co-operative structure of a lipid bilayer?

Electrostatic and hydrogen bonding Signup and view all the answers

What is one of the main functions of biological membranes?

Selective permeability barrier Signup and view all the answers

Which type of lipid is primarily responsible for the formation of lipid bilayers?

Phospholipids Signup and view all the answers

How do unsaturated fatty acids affect membrane fluidity?

They enhance fluidity Signup and view all the answers

What characterizes amphipathic molecules in the context of membrane lipids?

They contain both hydrophilic and hydrophobic regions Signup and view all the answers

Sphingomyelin is unique among phospholipids because it is based on which structure?

Sphingosine Signup and view all the answers

Which of the following lipids may contain sugar components?

Glycolipids Signup and view all the answers

What is the predominant conformation of unsaturated fatty acids in membranes?

Cis Signup and view all the answers

What role do membranes play in cell communication?

They control the flow of information between cells Signup and view all the answers

Study Notes

Learning Outcomes

Recognize the main types of membrane lipids.
Understand properties of amphipathic molecules and lipid bilayer formation.
Describe movements in lipid bilayers and effects of unsaturated fatty acids and cholesterol on membrane fluidity.

Functions of Biological Membranes

Serve as a selective permeability barrier, regulating chemical environments.
Facilitate communication and information flow between cells and their environments.
Enable recognition through signaling molecules, adhesion proteins, and immune mechanisms.
Generate signals in response to stimuli (electrical and chemical).

Specialized Functions of Biological Membranes

Plasma membrane: encompasses all mentioned functions.
Mitochondrial membrane: crucial for energy conservation via oxidative phosphorylation.

Membrane Lipids

Amphipathic molecules: possess both hydrophilic and hydrophobic regions.

Types of Membrane Lipids

Phospholipids:
- Derived from glycerol-3-phosphate.
- Common types include phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, and phosphatidylinositol.
- Fatty acids typically range from 16-18 carbons; can be saturated or unsaturated (cis conformation).
Sphingomyelin:
- Unique as it is not based on glycerol, using sphingosine as a backbone.
Glycolipids:
- Sugars attached to lipids, with glycerol or sphingosine backbone.
- Subtypes include cerebrosides (sugar monomers) and gangliosides (sugar multimers).
Cholesterol:
- Integral to membrane fluidity and stability.

Lipid Distribution in Tissues

Phosphatidylcholine: 45-55%
Phosphatidylethanolamine: 15-25%
Phosphatidylinositol: 10-15%
Phosphatidylserine: 5-10%
Cholesterol: 10-20%

Lipid Bilayer Formation

Amphipathic molecules form micelles or bilayers in water, with bilayers being preferred for phospholipids and glycolipids.
Bilayer formation is spontaneous due to van der Waals forces among hydrophobic tails.
Stabilization occurs through non-covalent interactions (electrostatic and hydrogen bonds) between hydrophilic moieties and water.
Pure lipid bilayers exhibit low permeability to ions and most polar molecules.

Dynamics of Lipid Bilayers

Membranes exhibit fluidity with lipid molecules able to move in four ways:
- Lateral diffusion: Rapid movement within the bilayer plane.
- Flip-flop: Transfer of lipid molecules from one bilayer layer to the opposite in a one-for-one exchange.
- Intra-chain motion: Kink formation within fatty acyl chains.
- Axial rotation: Fast rotation around the lipid axes.

Importance of Unsaturated Fatty Acids and Cholesterol

Unsaturated fatty acids increase membrane fluidity by disrupting hexagonal packing of phospholipids, thereby enhancing flexibility and function.

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Description

This quiz covers the foundational concepts of membrane bilayers, including the types of membrane lipids, properties of amphipathic molecules, and the mechanisms behind lipid bilayer formation. You'll also explore the dynamics of movements within lipid bilayers and the role of unsaturated fatty acids and cholesterol in membrane fluidity.