Cell Membranes and Proteins Quiz
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Questions and Answers

What is the main function of the plasma membrane as a barrier?

It maintains essential differences between the cytosol and the extracellular environment.

Describe the fluid-mosaic model of membrane structure.

The fluid-mosaic model describes the membrane as a bilayer of phospholipids with embedded proteins forming a mosaic pattern.

What are the two general classes of membrane proteins based on their association with the membrane?

Integral and peripheral membrane proteins.

What role does the glycocalyx play in cellular function?

<p>The glycocalyx is involved in cell-cell adhesion and regulating material exchange between the cell and its environment.</p> Signup and view all the answers

What characteristic do amphipathic transmembrane proteins possess?

<p>They have hydrophilic portions exposed to the aqueous environment on both sides of the membrane.</p> Signup and view all the answers

What distinguishes phospholipids from other membrane lipids?

<p>Phospholipids are amphipathic molecules with hydrophobic fatty acid tails and a hydrophilic phosphate head group.</p> Signup and view all the answers

What is the role of channel proteins in the plasma membrane?

<p>Channel proteins allow the free passage of small ions, molecules, and water across the membrane.</p> Signup and view all the answers

Identify the two non-membranous organelles within eukaryotic cells.

<p>Ribosomes and centrioles are the two non-membranous organelles.</p> Signup and view all the answers

Explain how membranes contribute to the selective transport of molecules.

<p>Membranes are selectively permeable, allowing certain molecules to pass while preventing others, thus regulating transport.</p> Signup and view all the answers

How do carrier proteins differ from channel proteins?

<p>Carrier proteins selectively bind and transport specific molecules, while channel proteins allow free passage of substances.</p> Signup and view all the answers

How do the proteins in the membrane contribute to its function?

<p>Membrane proteins facilitate communication between cells and assist in the transport of molecules.</p> Signup and view all the answers

What type of amino acid regions are typically found in the membrane-spanning portions of transmembrane proteins?

<p>Nonpolar amino acid regions, usually forming α-helical structures.</p> Signup and view all the answers

What is the significance of membrane organization for cell structure and function?

<p>Membrane organization is critical because it defines the boundaries and functional compartments of the cell, enabling distinct cellular processes.</p> Signup and view all the answers

Explain the function of membrane proteins that act as receptors.

<p>Receptor proteins bind specific molecules and initiate cellular responses.</p> Signup and view all the answers

What modifications are commonly found on eukaryotic transmembrane proteins?

<p>They are often modified with carbohydrates.</p> Signup and view all the answers

What is the significance of the selective permeability of cell membranes?

<p>It allows cells to regulate the internal environment and maintain homeostasis.</p> Signup and view all the answers

What did Robert Hooke observe in 1663 that led him to name cells?

<p>He observed the thick cell walls of cork using a primitive microscope.</p> Signup and view all the answers

How do the cell walls of plant cells differ from those of animal cells?

<p>Plant cell walls are generally thicker, stronger, and more rigid than the extracellular matrix of animal cells.</p> Signup and view all the answers

What is the primary component of the primary cell wall in plant cells?

<p>The primary component is cellulose polymers united into thread-like microfibrils.</p> Signup and view all the answers

What role does pectin play in plant cell walls?

<p>Pectin acts as a sticky substance that binds adjacent plant cells together.</p> Signup and view all the answers

What additional component is often found in the secondary cell walls of woody plants?

<p>Lignin is the additional polymer commonly found in the secondary walls.</p> Signup and view all the answers

During which cellular process do cell walls originate in plant cells?

<p>Cell walls originate during cytokinesis when the cell plate forms.</p> Signup and view all the answers

What characteristic do primary cell walls exhibit to support plant cell growth?

<p>Primary cell walls are thin and extensible to accommodate growth.</p> Signup and view all the answers

When and how does a secondary cell wall typically form in plant cells?

<p>A secondary cell wall forms after growth stops by depositing new layers inside the primary wall.</p> Signup and view all the answers

What is the primary role of anchoring junctions in animal tissues?

<p>Anchoring junctions form strong membrane-spanning structures that connect cells to each other and to the cytoskeleton, allowing for the transmission of mechanical forces.</p> Signup and view all the answers

Describe the structure and function of adherens junctions.

<p>Adherens junctions consist of cadherins that hold adjacent epithelial cells together and are connected to actin filaments via intracellular anchor proteins.</p> Signup and view all the answers

What types of intermediate filaments are typically associated with desmosomes in different cell types?

<p>Desmosomes typically link keratin filaments in epithelial cells and desmin filaments in heart muscle cells.</p> Signup and view all the answers

How do focal adhesions facilitate cell interaction with the extracellular matrix?

<p>Focal adhesions enable cells to attach to the extracellular matrix via integrins, which link to actin filaments inside the cell.</p> Signup and view all the answers

What role do catenins play in adherens junctions?

<p>Catenins anchor actin filaments to the plasma membrane at adherens junctions, maintaining cell shape and stability.</p> Signup and view all the answers

Explain the significance of the adhesion belt in tissues.

<p>The adhesion belt provides a continuous layer of adherence between adjacent epithelial cells, contributing to tissue strength and integrity.</p> Signup and view all the answers

Discuss the difference between cadherins and integrins in cell junctions.

<p>Cadherins are used in cell-cell junctions such as adherens junctions and desmosomes, while integrins are involved in cell-matrix junctions like focal adhesions.</p> Signup and view all the answers

In what way do anchoring junctions contribute to mechanical stability in tissues?

<p>Anchoring junctions link cells to the cytoskeleton and to each other, providing structural support and resistance to mechanical stress.</p> Signup and view all the answers

What is the primary function of gap junctions in animal tissues?

<p>Gap junctions primarily mediate the passage of chemical or electrical signals between neighboring cells.</p> Signup and view all the answers

Describe the structure and components of gap junctions.

<p>Gap junctions are formed by connexins, which are four-pass transmembrane proteins that assemble into hexameric structures called connexons.</p> Signup and view all the answers

How does the permeability of gap junctions change in response to cellular conditions?

<p>The permeability of gap junctions decreases rapidly when cytosolic pH drops or when free Ca^2+^ concentration increases significantly.</p> Signup and view all the answers

Explain the role of connexons in cellular communication.

<p>Connexons facilitate direct transfer of inorganic ions and small water-soluble molecules between the cytoplasm of adjacent cells.</p> Signup and view all the answers

What happens to gap junctions when a cell experiences a large influx of Ca^2+^?

<p>A large influx of Ca^2+^ causes gap junction channels to close, isolating the damaged cell from its neighbors.</p> Signup and view all the answers

What is unique about the gap between cells in a gap junction?

<p>The gap between cells in a gap junction is uniform and measures about 2--4 nm.</p> Signup and view all the answers

In which embryonic stage do vertebrate embryos primarily utilize gap junctions?

<p>Gap junctions are predominantly utilized in the late eight-cell stage of mouse embryos.</p> Signup and view all the answers

What type of cells are exceptions to the general use of gap junctions for intercellular communication?

<p>Terminally differentiated cells such as skeletal muscle cells and blood cells do not primarily use gap junctions for communication.</p> Signup and view all the answers

What is the main component of bacterial cell walls and how does it differ from plant cell walls?

<p>The main component of bacterial cell walls is peptidoglycan, which differs from plant cell walls that primarily contain cellulose.</p> Signup and view all the answers

Explain the process of gram staining and its significance in bacterial classification.

<p>Gram staining involves staining bacteria with gentian violet, applying iodine, and washing with alcohol; it helps classify bacteria as gram positive or gram negative based on their cell wall characteristics.</p> Signup and view all the answers

What characteristic of gram positive bacteria allows them to retain the violet color during gram staining?

<p>Gram positive bacteria have a thick peptidoglycan layer in their cell wall that traps the violet color during staining.</p> Signup and view all the answers

How do the cell walls of gram negative bacteria differ from those of gram positive bacteria?

<p>Gram negative bacteria have a thinner peptidoglycan layer and higher lipid content, along with an additional outer membrane.</p> Signup and view all the answers

What substance in the cell wall of gram positive bacteria contributes to its structural integrity?

<p>Teichoic acids contribute to the structural integrity of the cell wall in gram positive bacteria.</p> Signup and view all the answers

Describe the structure of the outer membrane in gram negative bacteria.

<p>The outer membrane of gram negative bacteria contains a high concentration of lipids, polysaccharides, and proteins.</p> Signup and view all the answers

What role does the periplasmic space play in gram negative bacteria?

<p>The periplasmic space in gram negative bacteria contains enzymes and other proteins crucial for nutrient processing and cell wall maintenance.</p> Signup and view all the answers

Why might gram negative bacteria be more resistant to certain antibiotics compared to gram positive bacteria?

<p>Gram negative bacteria are more resistant to antibiotics due to their outer membrane which acts as a barrier, limiting drug penetration.</p> Signup and view all the answers

Flashcards

Plasma Membrane Function

The cell membrane that separates the inside of the cell from the outside environment and controls what enters and exits.

Membrane Composition

Membranes are made up of a phospholipid bilayer with proteins and carbohydrates embedded.

Phospholipid Structure

A phospholipid has a hydrophilic head (likes water) and two hydrophobic tails (hates water).

Fluid-Mosaic Model

The model that describes the cell membrane as a fluid structure with proteins embedded in a phospholipid bilayer.

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Glycocalyx Function

A carbohydrate layer on the cell surface involved in cell-cell recognition and interaction.

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Membrane Proteins

Proteins embedded in the cell membrane that perform various functions like transport, signaling, or adhesion.

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Membrane Lipid Types

Phospholipids, sphingolipids, glycolipids, and cholesterol are major types of lipids found in cell membranes.

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Non-Membraneous Organelles

Ribosomes and centrioles are organelles that do not have a membrane.

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Integral Membrane Proteins

Proteins embedded directly within the lipid bilayer of the cell membrane, often spanning the membrane.

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Peripheral Membrane Proteins

Proteins not directly inserted into the lipid bilayer, but are associated with the membrane.

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Transmembrane Proteins

Integral membrane proteins that span the entire lipid bilayer.

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Channel Proteins

Membrane proteins forming open pores for molecules to pass through the membrane.

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Carrier Proteins

Membrane proteins that bind and selectively transport specific molecules across the membrane.

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Membrane Protein Functions

Membrane proteins perform various tasks including transporting (channels & pumps), signaling (receptors), linking cells and providing structure.

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Selective Permeability

The ability of the cell membrane to control which molecules pass through, due to the interactions between molecules and membrane proteins.

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Cell Wall Function

Provides structural support, protection, and aids in fluid transport within the plant.

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Primary Cell Wall

The first cell wall formed in plant cells, thin and flexible, allowing for growth.

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Secondary Cell Wall

A rigid, thicker layer formed inside the primary cell wall, often containing lignin for extra strength.

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Cellulose

A complex sugar that forms long, strong fibers, the main component of plant cell walls.

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Lignin

A rigid substance that reinforces secondary cell walls, adding strength and rigidity, found in woody tissues.

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Middle Lamella

A sticky layer between adjacent plant cells, holding them together, composed of pectin.

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Cell Plate

A new partition wall formed during cell division, separating daughter cells, eventually becomes the cell wall.

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What makes plant cells different from animal cells?

Plant cells have a rigid cell wall made of cellulose and lignin, giving them structural support and a more sedentary lifestyle compared to animal cells.

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Bacterial Cell Wall

A protective outer layer surrounding bacterial cells, distinct from plant cell walls. Composed primarily of peptidoglycan, a unique molecule made of sugars and peptides.

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Peptidoglycan

A complex molecule found in bacterial cell walls, composed of sugars and peptides. It provides structural support and rigidity.

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Gram Staining

A technique used to classify bacteria based on their cell wall structure. It utilizes dyes and a decolorizing agent to reveal differences in cell wall composition.

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Gram-Positive Bacteria

Bacteria that retain the violet dye during gram staining, indicating a thicker peptidoglycan layer in their cell wall.

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Teichoic Acid

A polymer found in gram-positive bacterial cell walls, attached to peptidoglycan. It helps with cell wall structure and may be involved in immune recognition.

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Gram-Negative Bacteria

Bacteria that lose the violet dye during gram staining, revealing a thinner peptidoglycan layer and the presence of an outer membrane.

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Outer Membrane

An additional membrane found in gram-negative bacteria that lies outside the peptidoglycan layer. 富含有机物，可以阻挡一些抗生素.

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Periplasmic Space

The space between the inner cell membrane and the outer membrane in gram-negative bacteria, where peptidoglycan is found.

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Communicating Junctions

Specialized connections between cells that allow the passage of signals (chemical or electrical) from one cell to another. Examples are gap junctions in animals and plasmodesmata in plants.

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Gap Junctions

Specialized cell-to-cell junctions in animal tissues that allow the direct passage of small molecules and ions between the cytoplasm of adjacent cells.

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Connexins

Proteins that form the channels in gap junctions, allowing communication between cells.

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Connexons

The channel formed by the assembly of six connexin proteins in a gap junction, allowing the passage of small molecules and ions between cells.

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What makes gap junctions dynamic?

Gap junctions can reversibly open and close in response to changes in cellular conditions, such as pH or calcium levels.

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How do gap junctions protect cells?

When a cell is damaged, its gap junctions close, preventing the spread of damage to neighboring cells.

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Why are gap junctions important in development?

Gap junctions play a vital role in early development by enabling communication and coordination between cells during embryogenesis.

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Besides gap junctions, how else do cells communicate?

Cells can also communicate indirectly using signaling molecules that diffuse through the extracellular space or via specialized receptors on the cell membrane.

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Anchoring Junctions: Function

Anchoring junctions, like adherens junctions and desmosomes, connect cells to each other or to the extracellular matrix, providing structural integrity and resistance to mechanical stress.

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Adherens Junctions: Location

Adherens junctions are often found in epithelial tissues, where they form a continuous adhesion belt, encircling cells and providing a tight seal.

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Cadherins: Role in Adherens Junctions

Cadherins are transmembrane proteins that act as the glue in adherens junctions. They bind to cadherins on adjacent cells, holding them together.

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Actin Filaments: Connection to Adherens Junctions

Actin filaments are linked to adherens junctions through intracellular anchor proteins, providing structural support and allowing for cell movement.

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Desmosomes: Structure

Desmosomes resemble 'rivets' that connect cells together. Inside each cell, they are linked to intermediate filaments, forming a strong network that extends throughout the tissue.

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Intermediate Filaments: Role in Desmosomes

Intermediate filaments, like keratin filaments in epithelial cells or desmin filaments in muscle cells, attach to desmosomes, providing structural support and tensile strength.

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Focal Adhesions: Function

Focal adhesions are cell-matrix junctions that link cells to the extracellular matrix through integrins. These junctions connect actin filaments to the matrix, allowing cells to move and adhere to their surroundings.

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Integrins: Role in Focal Adhesions

Integrins are transmembrane proteins that link the intracellular cytoskeleton (actin filaments) to extracellular matrix components. They play a crucial role in cell adhesion, migration, and signaling.

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Study Notes

Cell Membranes

  • Cell membranes are vital for cell life, particularly the plasma membrane. They act as barriers, maintain internal environments, and regulate interactions.
  • The membrane's structure is a fluid mosaic model, a phospholipid bilayer with proteins embedded.
  • Carbohydrates form a glycocalyx on the cell surface, impacting cell-cell adhesion and material exchange.
  • Phospholipids are the fundamental building blocks, with hydrophobic tails and hydrophilic heads forming a stable barrier.
  • Cholesterol further influences the membrane's fluidity and permeability.
  • Glycolipids are similar to phospholipids but with a carbohydrate head group, playing roles in cell recognition and interactions.
  • Membrane proteins come in two types: integral (embedded in the lipid bilayer) and peripheral (associated with the membrane).

Membrane Protein Function

  • Membrane proteins are responsible for most specific functions, varying in amount and type across membranes.
  • They can act as transporters, receptors, enzymes, and structural components.
  • Channel proteins form pores for ion and other small molecule passage.
  • Carrier proteins bind and transport specific molecules.
  • Receptor proteins bind ligands, triggering intracellular signaling events.
  • Enzymes catalyze specific chemical reactions on the membrane.
  • Structural proteins provide support and link cells together

Cell-Cell Interactions

  • Specialized junctions link cells mechanically and functionally.
  • Tight junctions seal adjacent cells, preventing leakage.
  • Gap junctions form channels between cells, allowing communication.
  • Adherens junctions link cells mechanically, using actin filaments.
  • Desmosomes provide strong mechanical connections using intermediate filaments.
  • Hemidesmosomes connect cells to the extracellular matrix using integrins

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Cell Membranes: Structure and Function PDF

Description

Test your knowledge on cell membranes, their structure, and the crucial functions of membrane proteins. This quiz covers the fluid mosaic model, phospholipid bilayers, and the role of cholesterol and carbohydrates in membranes. Explore how these components contribute to cell life and interactions.

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