Biology Last Class: Membrane Structure

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Questions and Answers

Which statement best represents the mechanisms of lipid mobility in membranes?

Lateral diffusion and thermal movement both contribute to lipid mobility. (correct)

Lipids only move through flip-flop movements.

Lipids are fixed in place and do not move within the membrane.

Lipid movement is entirely dependent on carrier proteins.

What experimental evidence most strongly supports the Fluid Mosaic Model?

Physical studies using X-Ray diffraction.

Chemical studies indicating lipid permeability.

The presence of a trilaminar structure.

The observation of integral proteins floating in the lipid bilayer. (correct)

How does the transition temperature affect lipid behavior in membranes?

It causes lipids to become permanently solid.

It enhances the fixation of lipids in one position.

It defines the shift between gel-like and liquid states in lipids. (correct)

It has no effect on lipid movement.

What role does flippase play in lipid diffusion across the membrane?

Flippase accelerates the flip-flop movement of lipids. Signup and view all the answers

What is the impact of fatty acid saturation on membrane fluidity?

Saturated fatty acids enhance rigidity and decrease fluidity. Signup and view all the answers

In what way does the architecture of the membrane contribute to its functionality?

The asymmetric orientation of proteins facilitates selective permeability. Signup and view all the answers

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

Cholesterol increases membrane flexibility and regulates fluidity. Signup and view all the answers

How does lipid aggregation occur when mixed with water?

It spontaneously forms liposomes as a result of hydrophobic interactions. Signup and view all the answers

What is one of the key characteristics of the fluid mosaic model?

Membrane components can diffuse laterally. Signup and view all the answers

How does the saturation of fatty acids in phospholipids affect membrane fluidity?

Saturated fatty acids decrease membrane fluidity. Signup and view all the answers

What experimental evidence supports the characteristics of the fluid mosaic model?

Structural analysis through X-ray diffraction. Signup and view all the answers

What impact does an increase in transition temperature have on membrane properties?

It may lead to membrane rigidification. Signup and view all the answers

What role does flippase play in cellular membranes?

It assists in the asymmetric distribution of lipids. Signup and view all the answers

Which of the following biological processes is NOT directly related to membrane fusion?

Protein synthesis Signup and view all the answers

Which feature defines the trilaminar appearance of biological membranes?

The distinct layers of lipid bilayers. Signup and view all the answers

What is a consequence of having phospholipid membranes with a similar composition to natural membranes?

They mimic natural membrane behavior. Signup and view all the answers

What does the presence of flippase influence in the membrane?

The time of flip-flop diffusion Signup and view all the answers

How do saturated fatty acids affect transition temperature?

They decrease fluidity and increase transition temperature. Signup and view all the answers

Which statement accurately reflects the effects of unsaturated fatty acids on membrane fluidity?

They interfere with packing, enhancing membrane fluidity. Signup and view all the answers

What role do sterols play in membrane fluidity?

They restrict the movement of fatty acid tails. Signup and view all the answers

What experimental evidence supports the lateral diffusion of lipids and proteins in membranes?

Fusion of cells and mixed fluorescence patterns Signup and view all the answers

What does transition temperature specifically refer to?

The temperature at which a paracrystalline solid becomes fluid Signup and view all the answers

What discovery did David Frye and Michael Eddidin make in 1970 regarding membrane proteins?

Membrane proteins undergo lateral diffusion. Signup and view all the answers

Which characteristic affects the transition temperature of membrane lipids?

The degree of fatty acid saturation Signup and view all the answers

Study Notes

Membrane Structure and Composition

Acyl chain angularity contributes to membrane fluidity.
Cholesterol plays a significant role in modulating membrane properties.
The fluid mosaic model describes the dynamic nature of membranes as first proposed by Singer and Nicolson in 1972.

Lipid Composition in Hepatocytes

Lipid proportions vary across different organelles within hepatocytes.
The most common lipid in plasma membranes is phospolipid, essential for membrane integrity.

Trilaminar Structure of Membrane

Membrane appears trilaminar under electron microscopy, characterized by two electron-dense lines.
Experimental evidence includes chemical permeability studies and physical analyses via X-ray diffraction.

Protein and Lipid Interaction

Integral proteins reside in a lipid bilayer, held by hydrophobic interactions with non-polar amino acids.
Carbohydrate motifs on proteins extend into the extracellular space, forming glycoproteins and glycolipids.
Protein orientation within the membrane is asymmetric, influenced by functional requirements.

Lipid Mobility and Dynamics

Lipids exhibit constant movement within the membrane, including flip-flop and lateral diffusion.
Flip-flop movement between bilayer sides is slow, accelerated by the enzyme flippase.
Factors affecting lipid mobility include:
- Thermal movement of fatty acid groups.
- Lateral diffusion influenced by temperature.
- Transition temperature marks the shift from a solid to a fluid state.

Transition Temperature

Critical temperature where membranes shift from paracrystalline to liquid state, dependent on lipid composition.
Saturated fatty acids promote tighter packing and higher transition temperatures, whereas unsaturated fatty acids introduce fluidity through double bonds.
Sterols modulate transition temperatures by restricting fatty acid movement.

Experimental Evidence of Membrane Dynamics

FRAP (Fluorescence Recovery After Photobleaching) allows measurement of lateral diffusion.
Fusion experiments using different species (mouse and human cells) showcase the mobility of membrane components.
The study by Frye and Eddidin demonstrated protein mixing via fluorescence labeling.

Characteristics of Biological Membranes

Flexible structures capable of undergo shape change and self-sealing.
Participate in membrane fusion processes relevant to exocytosis, phagocytosis, fertilization, and infection routes.

Physical Properties of Membrane Structure

Phospholipid membranes closely mimic natural membranes.
Mixtures achieving comparable proportions lead to spontaneously forming bilayers or liposomes.
X-ray diffraction supports bilayer structure evidence.
Membranes possess selective permeability, particularly to polar solutes.

Membrane Thickness and Composition Specifics

Membranes typically measure 5 to 8 nm in thickness and exhibit a trilaminar appearance.
Composed primarily of lipids and proteins, with specific lipid-protein ratios varying by membrane type.
Contains receptors for extracellular signals and molecules facilitating cell adhesion.

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Description

This quiz covers the architecture of cell membranes, emphasizing the fluid mosaic model and the role of lipids and cholesterol in membrane fluidity. Additionally, it explores the lipid composition of different organelles in a hepatocyte and discusses experimental evidence supporting the trilaminar structure. Test your understanding of these key concepts in cell biology!