Cell Biology: Membrane Fluidity and Structure

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Questions and Answers

What characteristic of transmembrane proteins is determined by the orientation of hydrophobic side chains?

They are primarily composed of charged amino acids.

They are water-soluble.

They can easily permeate the aqueous environment.

They interact with the lipid bilayer. (correct)

How many amino acids typically span the hydrophobic regions of transmembrane proteins?

20-30 amino acids (correct)

10-15 amino acids

30-40 amino acids

5-10 amino acids

What visual tool is used to predict which amino acids span a membrane?

Electrophoresis mapping

Hydropathy plot (correct)

Chromatographic profiling

Spectrophotometry analysis

What structure do transmembrane proteins form when arranged as a β-barrel?

Water-filled pores Signup and view all the answers

What type of interaction allows membrane-associated proteins to cling to the lipid bilayer without covalent bonding?

Hydrophobic interactions Signup and view all the answers

What is the primary role of phosphatidylserine being translocated to the outside of a dying cell?

To serve as a signal for macrophages Signup and view all the answers

Which of the following best describes the arrangement of nonpolar and polar amino acids in a β-barrel structure?

Polar amino acids line the interior, while nonpolar amino acids project outward. Signup and view all the answers

What role does saturation of fatty acids play in lipid attachments to proteins?

Saturated fatty acids provide stability in protein anchoring. Signup and view all the answers

What characteristic is unique to glycolipids in cellular membranes?

They are exclusively located on the non-cytosolic side Signup and view all the answers

Which statement accurately describes transmembrane proteins?

Many are amphiphilic and possess alpha-helices Signup and view all the answers

In multipass transmembrane proteins, how do the α-helices interact after being inserted into the membrane?

Using noncovalent interactions Signup and view all the answers

What mechanism leads to the translocation of phosphatidylserine in dying cells?

Overactivation of a scramblase Signup and view all the answers

What role do glycolipids play in membranes?

They facilitate cell-recognition processes Signup and view all the answers

Which feature is typical of single-pass transmembrane proteins?

The polypeptide chain crosses the bilayer only once Signup and view all the answers

How do glycolipids primarily self-associate within membranes?

Via hydrogen bonds between sugars Signup and view all the answers

What is the approximate protein mass contribution in a cell membrane?

About one half Signup and view all the answers

What is the primary reason lipids rarely flip from one monolayer to another?

The polar head must move through the hydrophobic center. Signup and view all the answers

Which proteins facilitate the flipping of phospholipids across the bilayer?

Flippases Signup and view all the answers

What property primarily affects the fluidity of a lipid bilayer?

The length of the fatty acid tails Signup and view all the answers

How do cholesterol levels affect lipid rafts?

They increase the thickness and aid protein recruitment. Signup and view all the answers

What happens to membrane fluidity at lower temperatures?

It becomes less fluid. Signup and view all the answers

What role does phase segregation play in lipid bilayers?

It can lead to the recruitment of specific proteins. Signup and view all the answers

What characteristic defines lipid rafts within a membrane?

A specific composition of lipids and proteins. Signup and view all the answers

Why do human red blood cells exhibit asymmetry in monolayer composition?

Because of the presence of glycolipids. Signup and view all the answers

What role do detergents play in the study of membrane proteins?

They disrupt hydrophobic associations in the lipid bilayer. Signup and view all the answers

What is the significance of micelles in the context of detergents?

They associate with and protect hydrophobic regions of membrane proteins. Signup and view all the answers

Which statement correctly describes the movement of proteins in membranes?

Proteins diffuse laterally but do not generally flip-flop. Signup and view all the answers

What does the technique FRAP measure in membrane proteins?

The mobility of proteins within membranes. Signup and view all the answers

What are 'protein corrals' in membrane structures?

Restricted zones that limit protein diffusion. Signup and view all the answers

How does the cortical cytoskeleton impact protein movement in membranes?

It restricts the diffusion of proteins not directly linked to it. Signup and view all the answers

What property of sperm cell membranes allows for unique protein localization?

Tethering to other molecules like the extracellular matrix. Signup and view all the answers

What feature is created by spectrin in the cortical cytoskeleton?

Geometric arrangements that help restrict protein diffusion. Signup and view all the answers

What effect do hydrophobic groups have on a lipid bilayer?

They cause the bilayer to bend. Signup and view all the answers

Which statement accurately describes the permeability of a lipid bilayer?

Small nonpolar molecules diffuse more quickly than charged molecules. Signup and view all the answers

How do channels differ from transporters in membrane transport?

Channels form a continuous pore, while transporters bind and release solutes. Signup and view all the answers

What drives passive transport of uncharged small molecules?

Concentration gradients of the molecules. Signup and view all the answers

What distinguishes active transport from passive transport?

Active transport can occur uphill against gradients. Signup and view all the answers

What role do electrical gradients play in the transport of charged molecules?

They combine with concentration gradients to influence the direction of transport. Signup and view all the answers

Which type of transport protein only facilitates active transport?

Transporters. Signup and view all the answers

What is the nature of membranes as described in the summary?

Membranes exist as two-dimensional fluids. Signup and view all the answers

What can induce positive curvature in lipid bilayers?

Accumulation of particular lipids in regions. Signup and view all the answers

What is the primary role of membrane proteins?

They play a crucial role in defining the concentrations of molecules on both sides of the membrane. Signup and view all the answers

Study Notes

Membrane Fluidity

Lipids in a membrane are in constant lateral motion and can rotate and flex.
Lipids rarely flip from one side of the membrane to the other because their polar head would need to pass through the hydrophobic center.
Flippases are proteins that allow lipids to flip from one side to the other.
The fluidity of a lipid bilayer is impacted by temperature and composition.
In general, membranes are less fluid at lower temperatures.
Short, unsaturated hydrocarbon tails oppose a phase transition (from liquid to gel).

Membrane Structure

Different phases can segregate based on lipid composition.
Lipid rafts are specialized lipid domains enriched with certain lipids and proteins.
Lipid rafts can be thicker than other membrane regions due to high cholesterol content.
The two monolayers of a lipid bilayer have different compositions
The non-cytosolic side of the membrane often has glycolipids, which are sugar-containing lipids.

Membrane Asymmetry

The asymmetry of the membrane contributes to its function.
In a dying cell, phosphatidylserine, which is usually on the inner monolayer, translocates to the outer monolayer.
This translocation serves as a signal to macrophages for the engulfment and digestion of the dead cell.
Glycolipids are found exclusively on the non-cytosolic side of membranes.
Glycolipids contribute to membrane protection, cell-recognition processes, and cell-environment interactions.

Membrane Proteins

Approximately half the mass of a membrane is protein.
Many proteins are transmembrane and span the lipid bilayer.
Transmembrane proteins are amphiphilic, with hydrophobic regions embedded in the membrane and hydrophilic regions exposed to the aqueous environment.
Transmembrane proteins often have alpha-helices that span the membrane.
Transmembrane proteins can also have strands arranged as a beta-barrel, which forms water-filled pores.
Some membrane proteins are anchored by lipid attachments.
Membrane-associated proteins can be attached to the membrane by non-covalent bonds.
Detergents can be used to purify and study membrane proteins by disrupting hydrophobic associations.

Membrane Protein Mobility

Proteins within a membrane can diffuse in the plane of the membrane.
Fluorescent Recovery After Photobleaching (FRAP) can measure the movement of proteins in a membrane.
Proteins can be corralled within a membrane due to interactions with the cytoskeleton or other molecules.

Membrane Shape

Membrane proteins can help give the membrane its shape.
Proteins can induce membrane curvature by inserting hydrophobic groups, forming rigid scaffolds, or influencing lipid distribution.

Membrane Transport

Lipid bilayers are highly impermeable to many types of molecules.
Small, nonpolar molecules, such as oxygen, can diffuse rapidly across a membrane.
Small uncharged polar molecules, such as water, can diffuse more slowly across a membrane.
Large uncharged polar molecules and charged molecules cannot easily diffuse across a membrane.

Transport Proteins

Two types of transport proteins are channels and transporters.
Channels allow solutes to passively diffuse across a membrane by forming a continuous pore.
Transporters bind to solutes, undergo a conformational change, and release the solutes to the other side of the membrane.
Both channels and transporters can facilitate the passive transport of molecules down their electrochemical gradients.

Active Transport

Active transport is the movement of molecules against their concentration gradient and requires energy.
Active transport is often coupled to ATP hydrolysis.

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Description

This quiz explores the concepts of membrane fluidity and structure in cell biology. It covers the movement of lipids within the membrane, the role of flippases, and factors affecting fluidity such as temperature and lipid composition. Additionally, it delves into the unique characteristics of lipid rafts and the composition of the lipid bilayer.