Cell Biology Chapter on Membranes

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Questions and Answers

What effect does cholesterol have on membrane fluidity below its melting temperature?

Decreases fluidity

Increases fluidity (correct)

Causes cholesterol to solidify

Has no effect on fluidity

What primarily characterizes the 'flip-flop' diffusion of lipids in a pure lipid environment?

Constantly occurring

Extremely rapid

Moderately slow

Extremely slow (correct)

How does cholesterol affect membrane fluidity above its melting temperature?

Fluctuates fluidity

Increases fluidity

Decreases fluidity (correct)

Maintains fluidity

What factor influences whether cholesterol increases or decreases fluidity in membranes?

Ambient temperature relative to melting temperature Signup and view all the answers

Which type of lipid diffusion is characterized as being rapid?

Lateral diffusion Signup and view all the answers

How does increasing the number of carbon atoms in fatty acids affect the melting temperature?

It increases the melting temperature. Signup and view all the answers

What type of structures do phospholipids form when mixed with water?

Bilayers Signup and view all the answers

Which property of phospholipids is primarily determined by their fatty acid constituents?

Physical properties Signup and view all the answers

Which statement is true regarding NP-NP interactions in lipid-water mixtures?

They are effective in forming organized structures. Signup and view all the answers

What characterizes the most common structural motif of biological membranes?

Lipid bilayer Signup and view all the answers

What does the hydrophobic effect involve in lipid interactions?

Self-assembly into organized structures Signup and view all the answers

Which model was found to be energetically unfavorable in depicting membrane structure?

Danielli-Davison model Signup and view all the answers

What is the significance of the 'unit membrane' hypothesis?

It states all biomembranes share the same functional structure. Signup and view all the answers

What is a characteristic property of rats and caveolae when subjected to cold non-ionic detergents?

They resist solubilization. Signup and view all the answers

Which property allows caveolae to separate from other membrane domains during sucrose density ultracentrifugation?

Low buoyancy. Signup and view all the answers

What is a primary objective of subcellular fractionation?

Isolate organelle/membrane from cellular components. Signup and view all the answers

Which condition should be avoided to prevent protein aggregation in media used for disrupting tissues or cells?

High salt concentration. Signup and view all the answers

Why is it important to maintain iso-osmotic conditions in the media?

To prevent cellular dehydration. Signup and view all the answers

What is the ideal pH range for media used in the disruption of tissues or cells?

7.4 - 7.5. Signup and view all the answers

Why should Ca2+ be avoided in the media used for tissue disruption?

It activates proteases. Signup and view all the answers

What should be minimized to avoid excessive friction during cell disruption?

Membrane fusion. Signup and view all the answers

What is the primary reason for membrane compartmentalization in cells?

To enhance reaction efficiency Signup and view all the answers

Which of the following accurately describes prokaryotic cells?

They lack internal organelles. Signup and view all the answers

What characteristic do cell membranes possess that allows them to function effectively?

They are amphipathic. Signup and view all the answers

What component is primarily found in ribonucleoproteins (RNP)?

RNA combined with proteins Signup and view all the answers

Which part of the lipid structure is hydrophilic?

Polar head group Signup and view all the answers

How does membrane compartmentalization contribute to cellular function?

It improves metabolic efficiency. Signup and view all the answers

Which of the following statements about cytosol is true?

Cytosol is the largest compartment in the cell. Signup and view all the answers

Which structure is NOT typically found in cell membranes?

DNA Signup and view all the answers

What is the role of COP1 vesicles in the cell?

To retrieve ER-resident proteins using KDEL signals Signup and view all the answers

What initiates the disassembly of the COP2 coat on vesicles?

Conversion of GTP to GDP on Sar1 Signup and view all the answers

What characterizes the polarity of actin filaments?

The (+) end facilitates association of ATP-actin Signup and view all the answers

How are lysosomal enzymes activated?

Through proteolytic cleavage Signup and view all the answers

Which of the following describes the functions of the cytoskeleton?

Maintains cell shape and facilitates cellular motility Signup and view all the answers

What is the primary limiting factor for the rate of actin filament dissociation?

Availability of actin monomers Signup and view all the answers

What type of structures assist with the fusion of vesicles?

V-SNAREs and T-SNAREs Signup and view all the answers

Which type of oligosaccharides are characterized as high-mannose?

Oligosaccharides with predominantly mannose residues Signup and view all the answers

What effect does ATP hydrolysis have on actin filaments?

It occurs after the polymerization process Signup and view all the answers

Study Notes

Cellular Compartmentalization

Cells utilize membranes to compartmentalize both anatomically and functionally.
Membrane compartmentalization enhances efficiency in reactions and avoids futile cycles.
Prokaryotes lack internal organelles, while organelles like ribonucleoproteins (RNPs) lack membranes.

Membrane Structure and Lipids

Membranes are amphipathic, comprising a hydrophilic (polar, charged) head and a hydrophobic (non-polar, non-charged) tail.
Cell membranes consist of various lipids, including phospholipids, sterols, and sphingolipids.
Physical properties of phospholipids are influenced by fatty acid (FA) composition, including carbon chain length and degree of unsaturation.

Phospholipid Behavior in Solution

In aqueous environments, phospholipids spontaneously self-assemble due to the hydrophobic effect, forming bilayers rather than micelles.
Molecular geometry of phospholipids determines the structure of organized formations, such as bilayers and vesicles.

Mechanisms of Endocytosis

Non-clathrin-mediated endocytosis involves lipid rafts and caveolae, which resist solubilization by non-ionic detergents.
These structures are low buoyancy, allowing them to be separated from other membrane domains during fractionation.

Objectives of Subcellular Fractionation

Preserve integrity and isolate organelles/membranes from cellular components to minimize friction.
Optimal conditions for media include maintaining low salt concentrations, avoiding calcium (Ca2+), ensuring isotonic conditions, and maintaining a pH of 7.4-7.5.

Role of Cholesterol in Membrane Fluidity

Cholesterol serves as a "fluidity buffer," altering membrane fluidity in response to temperature changes relative to lipid melting points.
Below the melting temperature, cholesterol increases fluidity; above it decreases fluidity, maintaining membrane stability.

Lipid Diffusion Dynamics

Lateral and rotational diffusion of lipids are rapid, while transverse ("flip-flop") diffusion is extremely slow in lipid bilayers.
Complex oligosaccharides can enhance the rate of lipid movement within membranes.

Protein Trafficking in Vesicular Transport

COP2 proteins are recruited through GTP-bound Sar1, which undergoes conformational change to assist in vesicle formation.
Retrieval of ER-resident proteins occurs via COP1-coated vesicles, utilizing KDEL sequences for targeting.

Cytoskeletal Structure and Function

V-SNAREs and T-SNAREs facilitate vesicle fusion with target membranes, which is crucial for intracellular transport.
Lysosomes contain hydrolytic enzymes that activate in acidic environments, essential for cellular degradation processes.
The cytoskeleton maintains cell shape, provides mobility, and supports intracellular transport.
Microfilaments (actin) are smaller than microtubules (tubulin) and play a critical role in cell dynamics, with polarity influencing assembly and disassembly rates.

Actin Dynamics

ATP-bound actin associates at the barbed (+) end while ADP-bound actin dissociates at the pointed (-) end.
Free monomer concentration has a significant impact on polymerization and stability of actin filaments, emphasizing the importance of availability for cellular functions.

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Description

Explore the intriguing world of cellular compartmentalization and membrane structures in this quiz. Understand how membranes enhance efficiency in cellular reactions and learn about the unique properties of various lipids, including phospholipids. Test your knowledge on the behavior of phospholipids in different environments and their role in forming biological membranes.