Eukaryotic Cell Membrane Overview
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Questions and Answers

What primarily determines the specialized function of a particular membrane?

  • The set of membrane proteins it contains (correct)
  • The interactions between integral and peripheral proteins
  • The overall thickness of the membrane
  • The type of lipids present in the membrane

How are integral membrane proteins typically solubilized?

  • Through gentle shaking
  • By disrupting the lipid bilayer with detergents (correct)
  • By applying high temperatures
  • Using saline solutions

What characteristic is true for peripheral membrane proteins?

  • They are embedded within the lipid bilayer
  • They are easily extracted with gentle methods (correct)
  • They cannot interact with lipid membranes
  • They require extreme conditions for extraction

What is a common feature of transmembrane proteins in the lipid bilayer?

<p>They often form amphipathic structures (A)</p> Signup and view all the answers

What type of proteins can be referred to as GPI-anchored proteins?

<p>Integral membrane proteins that are covalently attached to lipids (B)</p> Signup and view all the answers

Which statement accurately describes how transmembrane proteins interact with the lipid bilayer?

<p>They consist of multiple alpha helices that maximize hydrogen bonding. (C)</p> Signup and view all the answers

What extraction method would be suitable for isolating peripheral membrane proteins?

<p>Applying gentle methods to disrupt non-covalent interactions (C)</p> Signup and view all the answers

Which statement is incorrect regarding the structure of integral membrane proteins?

<p>They exclusively perform intracellular signaling roles. (B)</p> Signup and view all the answers

What does lateral diffusion of membrane proteins refer to?

<p>Movement of proteins within the same layer of the membrane (C)</p> Signup and view all the answers

How can membrane proteins become immobilized?

<p>Through attachment to surface molecules of adjacent cells (C)</p> Signup and view all the answers

What is the biological significance of the cell cortex?

<p>It regulates morphological changes or motility. (D)</p> Signup and view all the answers

Which of the following best describes lipid rafts?

<p>Transiently formed, relatively ordered membrane domains (B)</p> Signup and view all the answers

What structural component is essential for the stabilization of the plasma membrane?

<p>A meshwork of filamentous intracellular proteins (C)</p> Signup and view all the answers

What role do lipid interactions play in the formation of lipid rafts?

<p>They facilitate weak protein-protein, protein-lipid, and lipid-lipid interactions. (C)</p> Signup and view all the answers

What is one function of membrane domains within a cell?

<p>They segregate membrane components to maintain cell polarity. (A)</p> Signup and view all the answers

Which type of lipids are typically enriched in lipid rafts?

<p>Cholesterol, sphingolipids, and glycolipids (B)</p> Signup and view all the answers

What is the primary role of phosphatidylserine in the plasma membrane?

<p>It recruits enzymes involved in signal transduction. (B)</p> Signup and view all the answers

Which lipid is known for its role as an indicator for apoptotic cells?

<p>Phosphatidylserine (B)</p> Signup and view all the answers

What distinguishes glycolipids from other membrane lipids?

<p>They contain sugar groups that form glycocalyx. (B)</p> Signup and view all the answers

Which of the following statements is true regarding lipid distribution in the plasma membrane?

<p>Phosphatidylinositol is important for recruiting signaling proteins. (D)</p> Signup and view all the answers

What is one of the biological significances of lipid asymmetry in the plasma membrane?

<p>It influences cell signaling pathways. (B)</p> Signup and view all the answers

Which enzyme is known to modify phosphatidylinositol for signaling purposes?

<p>Lipid kinase (D)</p> Signup and view all the answers

What function does the glycocalyx serve for the cell?

<p>It provides physical protection to the cell. (B)</p> Signup and view all the answers

Which of the following is a characteristic of phosphatidylinositol?

<p>It is modified by lipid kinases for signaling. (B)</p> Signup and view all the answers

Flashcards

Membrane protein diffusion

Membrane proteins can rotate (rotational diffusion) and move laterally (lateral diffusion).

Immobilized membrane proteins

Membrane proteins can be immobilized by their attachment to structures outside/inside the cell or to surface molecules of adjacent cells.

Cell cortex

Reinforces the plasma membrane and is stabilized by a meshwork of proteins that are linked to membrane proteins.

Lipid rafts

Transiently formed, ordered membrane domains enriched in cholesterol, sphingolipids, glycolipids, GPI-anchored proteins, and transmembrane proteins.

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Cell polarity

Formation of functionally specialized regions, on the cell surface, that restrict membrane components to specific domains. Example: Epithelial cells.

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Membrane Domains

Functionally specialized regions on the cell or organelle surface.

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Extracellular Matrix (ECM)

Part of the cell's environment that interacts with the plasma membrane.

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Membrane protein immobilization

Membrane proteins can be immobilized by attachments outside or inside the cell, and to the surface of adjacent cells.

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Membrane protein function

The specific role of a membrane is determined by the proteins it contains.

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Integral membrane proteins

Membrane proteins embedded within the lipid bilayer, needing detergents to remove.

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Peripheral membrane proteins

Membrane proteins loosely bound to the membrane, removed by gentler methods.

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Transmembrane proteins

Proteins spanning the lipid bilayer, often with alpha-helices.

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Membrane protein orientation

Transmembrane proteins' structure maximizes hydrogen bonding between polar amino acids (on the outside) and hydrophobic amino acids (in the lipid bilayer).

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Alpha-helices

Common structure in transmembrane proteins, maximizing hydrogen bonds and hydrophobic interactions.

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Detergents

Agents that disrupt lipid bilayers, used to isolate integral membrane proteins.

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Membrane protein isolation

Essential for understanding membrane function; requires methods to maintain their structure during extraction.

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Membrane asymmetry

Different lipid compositions on the inner and outer layers of the cell membrane.

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Glycolipids

Membrane lipids with sugar groups attached, forming the glycocalyx.

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Phosphatidylcholine

A common membrane phospholipid.

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Phosphatidylserine

A negatively charged phospholipid, important for signaling and apoptosis.

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Phosphatidylinositol

A membrane lipid modified by enzymes for signaling pathways.

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Apoptotic cell

A cell undergoing programmed cell death (apoptosis).

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Membrane trafficking

The process of moving molecules across the cell membrane.

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Study Notes

Eukaryotic Cell Membrane

  • Eukaryotic cell membranes are selective barriers, preventing the mixing of contents from different sides
  • Plasma membranes and internal membranes share a similar structure, but their individual characteristics are primarily determined by the composition of their membrane proteins
  • Membrane proteins have key functions in cell signaling, cell metabolism, cell movement, and cell division

Learning Outcomes

  • Students should be able to describe the composition and properties of eukaryotic cell membranes after completing the lecture
  • Understanding how membrane lipids and proteins influence membrane properties is essential
  • The importance of the cell membrane in cell biology should be recognized
  • The specialized function of cell membranes is dependent on membrane proteins

Lecture Outline

  • Membrane structure
  • Membrane properties
  • Membrane assembly
  • Membrane proteins

Membrane Lipid Composition

  • Cell membranes are composed of ~50% lipids and proteins
  • Membrane lipids are amphiphilic (having both hydrophilic and hydrophobic regions), which spontaneously form bilayers in aqueous environments
  • Phospholipids are a major component, along with glycolipids and sterols
  • Phosphoglycerides are crucial in mammalian cells, comprising phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine
  • Sphingolipids, particularly sphingomyelin, are the other main lipid component in mammals
  • Membrane lipids help maintain membrane fluidity and flexibility
  • Cholesterol is an important sterol as its hydrophobic portion fills gaps in the membrane and its rigid shape restricts movement of lipid tails

Membrane Lipid Bilayer Flexibility

  • The membrane spontaneously forms a sealed compartment in an aqueous environment (e.g., vesicles, organelles, cells)
  • Self-healing is a key feature allowing the repair of small tears in the bilayer
  • The flexibility of the lipid bilayer is essential for cell functionality
  • Lipid packing and order dictates membrane fluidity: a greater degree of unsaturated hydrocarbon chains = greater membrane fluidity.
  • Shorter hydrocarbon tails also increase membrane fluidity
  • Cholesterol reduces membrane lipid mobility and modifies membrane permeability

Lipid Asymmetry

  • Membrane lipids are highly distributed in the non-cytosolic or cytosolic layers due to cell functions, e.g. signaling molecules.
  • Glycolipids make up the glycocalyx, protecting the cell and facilitating cell-cell interactions
  • Phosphatidylserine is crucial for apoptosis and signal transduction

Membrane Proteins

  • Membrane proteins carry out specialized functions within the membrane
  • Membrane proteins have diverse ways of interaction with the cell membrane, including: transmembrane, monolayer associated, lipid-linked, and protein attached
  • Types of membrane proteins include integral membrane proteins (transmembrane), peripheral membrane proteins, and GPI-linked proteins
  • Integral membrane proteins are crucial in determining membrane functionality

Membrane Protein Diffusion

  • Membrane proteins can rotate and move laterally
  • Membrane protein diffusion can be restricted via cell structures (e.g., cell cortex, extracellular matrix) that interact with the proteins
  • Membrane protein immobilization is influenced by proteins structure, location, and the cell structure
  • Membrane protein restriction is essential for cellular functions

Membrane Protein Organization: Lipid Rafts

  • Lipid rafts are transiently formed, relatively ordered domains within the membrane
  • Lipid rafts are typically enriched with cholesterol, sphingolipids, glycolipids, and GPI-anchored proteins
  • Lipid rafts support cellular signaling and interactions

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Eukaryotic Cell Membrane Lecture Notes PDF

Description

This quiz explores the structure and properties of eukaryotic cell membranes, focusing on their lipid and protein composition. Students will learn how these components influence cell functions such as signaling, metabolism, and movement. Understanding these concepts is crucial for grasping the role of membranes in cell biology.

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