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Questions and Answers

What is primarily responsible for the protective barrier function of the plasma membrane?

  • Membrane proteins
  • Lipid bilayer (correct)
  • Cytoskeletal filaments
  • Hydrophilic channels

Which component of the extracellular matrix is most essential for providing structural support to cells?

  • Carbohydrates
  • Proteins
  • Phospholipids
  • Glycoproteins (correct)

What is the main function of integrins in cellular processes?

  • Facilitating cell membrane fluidity
  • Forming tight junctions between cells
  • Connecting extracellular matrix to cytoskeleton (correct)
  • Transporting ions across membranes

What role do gap junctions play in cell communication?

<p>They create channels for direct cytoplasm-cytoplasm contact. (D)</p> Signup and view all the answers

Gap junctions are critical for what specific intercellular communication?

<p>Allowing transfer of small molecules and ions (B)</p> Signup and view all the answers

Which protein is primarily responsible for cell-matrix adhesion?

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

Which feature characterizes the fluid mosaic model of the cell membrane?

<p>Dynamic and fluid nature of the membrane (D)</p> Signup and view all the answers

Which of the following describes the extracellular matrix (ECM)?

<p>It bears mechanical stress and is produced by cells. (B)</p> Signup and view all the answers

Selectins are primarily involved in which function?

<p>Traffic of immune cells in blood (B)</p> Signup and view all the answers

What is the primary function of integrins in cellular processes?

<p>Binding cells to the extracellular matrix. (C)</p> Signup and view all the answers

Which cell adhesion protein helps in maintaining epithelial integrity?

<p>Cadherin (C)</p> Signup and view all the answers

What is the role of the glycocalyx in cells?

<p>Providing a protective outer coat (D)</p> Signup and view all the answers

Which of the following is NOT a function of the plasma membrane?

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

Which component is NOT a typical feature of the extracellular matrix?

<p>Connexins (C)</p> Signup and view all the answers

What type of attachment is more common in connectives tissues?

<p>Direct attachments and structural support. (C)</p> Signup and view all the answers

Cell-matrix adhesion is primarily facilitated by which type of membrane proteins?

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

Which component primarily links cells to the extracellular matrix?

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

What is a primary function of gap junctions in epithelial cells?

<p>To create a passage for cell communication (D)</p> Signup and view all the answers

Which type of junction is most associated with cell-cell adhesion?

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

Which adherens molecule exists in various forms, such as E-cadherin and N-cadherin?

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

What role do intermediate filaments play in cell adhesion?

<p>They provide structural support (A)</p> Signup and view all the answers

Which structure prevents leakage across epithelial layers?

<p>Tight junctions (D)</p> Signup and view all the answers

How do integrins facilitate cell-matrix adhesion?

<p>By binding to proteins in the ECM (B)</p> Signup and view all the answers

Which type of junction is primarily responsible for linking adjacent epithelial cells against mechanical stress?

<p>Desmosomes (A)</p> Signup and view all the answers

Which molecule is directly involved in cell-cell adhesion in animal cells?

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

What is a key feature of tight junctions?

<p>They restrict paracellular permeability (B)</p> Signup and view all the answers

Which junction is most involved in communication between cells?

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

Which of the following is NOT a function of the extracellular matrix?

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

What role do cadherins play in cellular structures?

<p>Providing mechanical stability (B)</p> Signup and view all the answers

What form of cadherin is predominantly found in the placenta?

<p>P-cadherin (C)</p> Signup and view all the answers

Flashcards

Gap Junctions

Direct channels that connect the cytoplasm of adjacent cells, allowing for rapid communication.

Connexins

Protein components that form the channels of gap junctions.

Cell-cell adhesion molecules

Proteins that mediate adhesion between cells; include integrins, selectins, and immunoglobulin superfamily members.

Integrins

Cell-cell adhesion molecules that link cells to the extracellular matrix (ECM).

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Extracellular Matrix (ECM)

The meshwork of proteins and carbohydrates outside cells that provides structural support.

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ECM Components

The ECM is formed by cells and contains proteins like collagen and laminin.

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Cell-matrix adhesion

Adhesion of cells to extracellular matrix components.

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Selectins

Cell-surface carbohydrate-binding proteins, involved in cell traffic (e.g., white blood cell movement).

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Plasma membrane function

The plasma membrane acts as a protective barrier, controls transport, facilitates cell recognition, anchors the cytoskeleton, binds enzymes, allows cell junctions, and contains the cytoplasm.

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Cell membrane structure

The cell membrane is a thin film of lipids and proteins held together by weak bonds, creating a dynamic and fluid structure.

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Lipid bilayer

A double layer of lipid molecules (5 nm thick) forming the basic structure of the cell membrane. Impermeable to water-soluble molecules.

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Membrane proteins

Proteins embedded in the lipid bilayer, carrying out various functions, like transport, signaling, and enzymatic activity.

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Membrane proteins function

Membrane proteins are important for transporting substances and mediating chemical processes.

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Phospholipids

Major components of the lipid bilayer, with hydrophilic heads and hydrophobic tails.

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Glycocalyx

A carbohydrate-rich layer coating the cell membrane, involved in cell-cell recognition.

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Cell membrane fluidity

The cell membrane is not rigid but can move and change shape due to weak bonds between its components.

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Cytoskeleton's role in cell adhesion

The cytoskeleton, composed of actin and intermediate filaments, is crucial for cell-cell and cell-matrix interactions and provides structural support.

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Cell-matrix junctions

Cytoskeletal elements like actin and intermediate filaments connect cells to the extracellular matrix, providing structural integrity and cell movement.

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Actin-linked cell-matrix junctions

Junctions anchored using actin filaments, enabling cell anchoring and signal transmission.

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Cadherins

Calcium-dependent cell-adhesion molecules that connect cells.

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Desmosomes

Cell-cell junctions composed of cadherins linked to intermediate filaments, providing strong mechanical support.

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Tight junctions

Cell-cell junctions that prevent leakage across the epithelium.

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Epithelial tissues

Sheets of cells that line surfaces and cavities in the body.

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Desmosomes vs. adherens junctions

Differences in cadherin types and cytoskeletal connections lead to distinct mechanical strengths and roles.

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Intermediary filaments

Structural components of the cytoskeleton, used in various cell to cell junctions.

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N-cadherin

Specific type of cadherin, often found in nervous tissue and muscle, contributing to cell adhesion.

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Mechanical junctions

Specialized cell-matrix joins that offer structural strength.

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Study Notes

Cell Membrane

  • Functions of the plasma membrane:
    • Protective barrier
    • Selective transport
    • Cell recognition
    • Anchoring sites for cytoskeletal filaments
    • Binding sites for ligands
    • Interconnecting cells (junctions)
    • Contains cytoplasm

Structure of Cell Membrane

  • Thin film of lipids and proteins
  • Held together by non-covalent interactions
  • Dynamic and fluid
  • Lipid bilayer (5nm)
    • Impermeable to water-soluble molecules
  • Membrane proteins span the bilayer and mediate functions, including transport and catalysis.

Cell Membrane Components

  • Phospholipids
    • Two fatty acid chains
    • Polar head (with phosphate group, glycerol, and other groups)
    • Nonpolar tails (hydrophobic)
  • Cholesterol: embedded within the bilayer
  • Proteins (integral and peripheral): embedded within or on top of the bilayer.
  • Glycocalyx (cell coat): carbohydrate-rich layer, with glycoproteins and proteoglycans.

Membrane Transport

  • Simple diffusion: movement of molecules across the membrane from higher to lower concentration, without energy input.
  • Passive transport: movement of molecules across the membrane from higher to lower concentration, with the help of membrane proteins (e.g., channels, carriers).
  • Active transport: movement of molecules against their concentration gradient, requiring energy input.

Types of Transport

  • Simple diffusion
  • Facilitated diffusion (using transport proteins):
    • Channels: allow specific ions to pass through a pore.
    • Carriers: bind to the transported molecule and undergo a conformational change to move it across the membrane.
  • Active transport: uses energy to move molecules against their concentration gradient.
    • Coupled transporters: use the energy from one molecule's movement down its concentration gradient to move another molecule up its gradient.
    • ATP-driven pumps: use ATP hydrolysis to move molecules against their concentration gradient.
    • Light-driven pumps: use light energy to move molecules against their concentration gradient (e.g., in some bacteria).

Endocytosis and Exocytosis

  • Endocytosis: cellular uptake of materials via vesicles formed from the plasma membrane.
    • Pinocytosis: intake of dissolved substances.
    • Phagocytosis: intake of particulate substances.
    • Receptor-mediated endocytosis: intake of specific molecules bound to receptors.
  • Exocytosis: secretion of substances from the cell via vesicles fusing with the plasma membrane.

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic cells:
    • No membrane-bound organelles
    • No true nucleus
    • Unicellular
  • Eukaryotic cells:
    • Contain membrane-bound organelles
    • Contain a true nucleus
    • Uni- or multicellular

Organelles

  • Nucleus: DNA and RNA processing
  • Endoplasmic Reticulum (ER): lipid and protein synthesis
  • Golgi apparatus: modification, sorting, and packaging of proteins and lipids
  • Lysosomes: cellular waste removal
  • Peroxisomes: fatty acid breakdown
  • Mitochondria: energy production (ATP)
  • Ribosomes: protein synthesis, free in cytosol or associated with ER
  • Cytoskeleton: structural support and cell movement.

Protein Import and Export

  • Proteins destined for other organelles or secretion are often directed by signal sequences
  • Signal sequences direct proteins to the specific destination.
  • Proteins may require modification inside their destination
  • Proteins may be transported by vesicles to the target location.

Chromosomes

  • DNA is packaged with proteins into chromosomes
  • Unique structure and sequence
  • DNA forms the backbone.

Cell Cycle

  • A series of stages the cell undergoes for growth and reproduction
  • Specific stages necessary for cell division and function
  • The cell cycle involves multiple stages like G1, S, and M phases and checkpoints or control processes
  • Important for accurate DNA segregation

Cellular Communication

  • Cells communicate with one another through signaling molecules interacting with cell surface receptors or intracellular receptors.
  • Different signaling pathways activate different intracellular response
  • Signaling can affect gene expression.

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