Week 5: Cell Membrane & Transport
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Questions and Answers

What is the primary function of exocytosis?

  • To fuse with lysosomes
  • To form vesicles
  • To take in nutrients
  • To export products from the cell (correct)

    • Phagocytosis is known as 'cellular drinking.'

    False

    What is required for bulk transport processes, such as exocytosis and endocytosis?

    Energy

    In receptor-mediated endocytosis, the binding of _____ to receptors triggers vesicle formation.

    <p>ligands</p> Signup and view all the answers

    Match the type of transport with its description:

    <p>Phagocytosis = Cellular eating Pinocytosis = Cellular drinking Receptor-mediated endocytosis = Ligand-triggered vesicle formation Exocytosis = Release of substances from the cell</p> Signup and view all the answers

    What is the primary composition of the cell membrane?

    <p>Phospholipids and proteins</p> Signup and view all the answers

    The plasma membrane is 8 nm thick.

    <p>True</p> Signup and view all the answers

    What characteristic describes the arrangement of phospholipids in the cell membrane?

    <p>Amphipathic</p> Signup and view all the answers

    The fluid mosaic model describes the membrane as being a _________ structure.

    <p>fluid</p> Signup and view all the answers

    Match the following features of the cell membrane with their descriptions:

    <p>Selective Permeability = Allows some substances to cross more easily than others Hydrophobic Interactions = Weaker than covalent bonds, hold the membrane together Fluidity = Allows lateral movement of lipids and proteins Phospholipid Bilayer = Two layers of phospholipids with hydrophilic heads and hydrophobic tails</p> Signup and view all the answers

    Which part of the membrane proteins is oriented towards the cytosol?

    <p>Hydrophilic regions</p> Signup and view all the answers

    It is common for molecules to easily flip-flop between the layers of the phospholipid bilayer.

    <p>False</p> Signup and view all the answers

    What model explains the structure of the plasma membrane?

    <p>Fluid mosaic model</p> Signup and view all the answers

    What type of molecules can pass through the cell membrane rapidly?

    <p>Nonpolar molecules</p> Signup and view all the answers

    Polar molecules can cross the plasma membrane easily.

    <p>False</p> Signup and view all the answers

    What is the role of transport proteins in the cell membrane?

    <p>To facilitate the passage of hydrophilic substances across the membrane.</p> Signup and view all the answers

    A __________ protein has a hydrophilic channel that allows certain molecules or ions to pass through the membrane.

    <p>channel</p> Signup and view all the answers

    Which of the following describes passive transport?

    <p>Involves the diffusion of substances down their concentration gradient</p> Signup and view all the answers

    Dynamic equilibrium occurs when molecules no longer cross the membrane.

    <p>False</p> Signup and view all the answers

    What term describes the movement of molecules from an area of high concentration to an area of low concentration?

    <p>Diffusion</p> Signup and view all the answers

    Substances diffuse down their __________ gradient.

    <p>concentration</p> Signup and view all the answers

    Match the following types of transport proteins with their descriptions:

    <p>Channel proteins = Facilitate passage of ions or water Carrier proteins = Bind and change shape to transport molecules Aquaporins = Specialized for water transport Transport proteins = Facilitate transport across the membrane</p> Signup and view all the answers

    Carrier proteins transport substances without changing shape.

    <p>False</p> Signup and view all the answers

    What is the process of osmosis?

    <p>Diffusion of water from lower solute concentration to higher</p> Signup and view all the answers

    Isotonic solutions cause cells to gain or lose water?

    <p>False</p> Signup and view all the answers

    Define tonicity in the context of cellular environments.

    <p>The ability of a solution to cause a cell to gain or lose water.</p> Signup and view all the answers

    A solution with a lower solute concentration compared to the cell is termed a ______ solution.

    <p>hypotonic</p> Signup and view all the answers

    Match the following types of solutions with their effects on red blood cells:

    <p>Isotonic = Normal Hypertonic = Shriveled Hypotonic = Lysed</p> Signup and view all the answers

    What role do transport proteins play in facilitated diffusion?

    <p>They speed up the passive movement of molecules.</p> Signup and view all the answers

    Water moves from an area of high solute concentration to low solute concentration during osmosis.

    <p>False</p> Signup and view all the answers

    What is the primary role of glycoproteins in cell membranes?

    <p>Serve as identification tags for cell-cell recognition</p> Signup and view all the answers

    Intercellular joining is typically short-lived compared to cell-cell recognition.

    <p>False</p> Signup and view all the answers

    What happens to a cell in a hypertonic solution?

    <p>The cell loses water and shrivels.</p> Signup and view all the answers

    What is the function of integrins in a cell membrane?

    <p>Attachment to the cytoskeleton and extracellular matrix (ECM)</p> Signup and view all the answers

    In facilitated diffusion, molecules move across the plasma membrane with the help of ______ proteins.

    <p>transport</p> Signup and view all the answers

    Cells recognize each other by binding to surface molecules, often ________ on the plasma membrane.

    <p>carbohydrates</p> Signup and view all the answers

    Match the following solutions with their concentration relationships:

    <p>Isotonic = Same concentration inside and outside Hypertonic = Higher concentration outside Hypotonic = Lower concentration outside</p> Signup and view all the answers

    What type of junctions do membrane proteins of adjacent cells form for intercellular joining?

    <p>Gap junctions and tight junctions</p> Signup and view all the answers

    Membrane carbohydrates are always covalently bonded to proteins.

    <p>False</p> Signup and view all the answers

    Name one major function of membrane proteins.

    <p>Signal transduction, cell-cell recognition, intercellular joining, or attachment to the cytoskeleton and ECM</p> Signup and view all the answers

    The external messenger interacting with a protein typically leads to a change in ________ of the protein.

    <p>shape</p> Signup and view all the answers

    Match the following membrane protein functions with their descriptions:

    <p>Cell-cell recognition = Binding to surface carbohydrates Intercellular joining = Formation of tight junctions Signal transduction = Relaying messages inside the cell Attachment to ECM = Stabilizing membrane protein locations</p> Signup and view all the answers

    Which of the following describes a function of membrane carbohydrates?

    <p>Facilitating cell recognition</p> Signup and view all the answers

    Study Notes

    Cell Membrane Structure & Function

    • The plasma membrane is the outer boundary of a cell, separating it from its surroundings.
    • It's selectively permeable, allowing certain substances to cross more easily than others.
    • Lipids and proteins are the primary components of membranes, with carbohydrates also playing a role.
    • Phospholipids, the most abundant lipids, have a hydrophilic head and a hydrophobic tail, forming a bilayer.
    • Membrane proteins are embedded in the phospholipid bilayer, with their hydrophilic regions exposed to the aqueous environment.
    • The fluid mosaic model describes the membrane as a fluid structure with embedded protein molecules.

    Membrane Fluidity

    • Membranes aren't rigid structures; they're held together by weak hydrophobic interactions.
    • Lipids and some proteins can move laterally within the membrane.
    • Transverse movement (flip-flopping) across the bilayer is less common.

    Functions of Membrane Proteins

    • Cell-cell recognition: Glycoproteins act as identification tags for cell-cell interactions.
    • Intercellular joining: Membrane proteins from adjacent cells form junctions like gap junctions and tight junctions.
    • Attachment to cytoskeleton and extracellular matrix (ECM): Proteins connect to cytoskeleton and ECM, contributing to cell shape and stability.
    • Transport: Carrier and channel proteins facilitate the movement of molecules across the membrane.
    • Enzymatic activity: Proteins can act as enzymes, catalyzing reactions within the membrane.
    • Signal transduction: Membrane proteins can receive signals from the environment and relay them to the cell's interior.

    Membrane Carbohydrates in Cell-Cell Recognition

    • Carbohydrates are often covalently bonded to lipids (glycolipids) or proteins (glycoproteins) on the cell surface.
    • These sugar variations on the external membrane contribute to cell-cell recognition, explaining differences between species, individuals, and cell types.

    Permeability of the Lipid Bilayer

    • Hydrophobic (nonpolar) molecules can easily cross the lipid bilayer, while polar molecules struggle.
    • Transport proteins provide passage for hydrophilic substances.

    Transport Proteins

    • Channel proteins: Create hydrophilic channels for specific molecules or ions to pass through. Aquaporins are a type of channel protein for water.
    • Carrier proteins: Bind to molecules, change shape, and shuttle them across the membrane.

    Passive Transport

    • Diffusion: The tendency for molecules to move from areas of high concentration to areas of low concentration, driven by a concentration gradient.
    • Osmosis: The diffusion of water across a selectively permeable membrane, moving from regions of lower solute concentration to regions of higher solute concentration.

    Tonicity

    • Isotonic solution: Solute concentration is equal inside and outside the cell, resulting in no net water movement.
    • Hypertonic solution: Higher solute concentration outside the cell, causing water to leave the cell.
    • Hypotonic solution: Lower solute concentration outside the cell, causing water to enter the cell.

    Facilitated Diffusion

    • Type of passive transport where proteins help move molecules across the membrane down the concentration gradient.

    Bulk Transport

    • Requires energy to move large molecules or particles across the membrane.

    Exocytosis

    • The cell releases contents from vesicles by fusing them with the plasma membrane.
    • Many secretory cells use this to export products.

    Endocytosis

    • The cell takes in macromolecules by forming vesicles from the plasma membrane.
    • Three types:
      • Phagocytosis: “Cellular eating,” engulfing large particles.
      • Pinocytosis: “Cellular drinking,” engulfing extracellular fluid.
      • Receptor-mediated endocytosis: Specific ligands bind to receptors, triggering vesicle formation.

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    Cell Membrane & Transport PDF

    Description

    Test your knowledge on the structure and function of cell membranes. This quiz covers topics like the fluid mosaic model, membrane fluidity, and the roles of lipids and proteins. Perfect for biology students studying cell biology concepts.

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