Cell Signalling and Communication
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Questions and Answers

What type of receptors are responsible for transmitting signals through a second messenger?

  • Nuclear receptors
  • G-protein linked receptors (correct)
  • Serine/threonine kinase receptors
  • Tyrosine kinase receptors
  • Which type of receptors are typically found in the cytoplasm and bind to ligands such as steroids or retinoids?

  • Serine/threonine kinase receptors
  • Tyrosine kinase receptors
  • Nuclear receptors (correct)
  • G-protein linked receptors
  • What is the role of Hsp chaperones in the activation of nuclear receptors?

  • To bind to the receptor in its inactive form (correct)
  • To hydrolyze GTP to GDP
  • To release the receptor from the nucleus
  • To phosphorylate the receptor
  • What is the response of a G-protein linked receptor upon ligand binding?

    <p>It releases GDP and takes up GTP</p> Signup and view all the answers

    What is the role of Smads in signal transduction through Serine/threonine kinase receptors?

    <p>They act as transcription factors in the nucleus</p> Signup and view all the answers

    What type of receptors bind to the TGFb family of signals?

    <p>Serine/threonine kinase receptors</p> Signup and view all the answers

    What is the role of Ga in G-protein linked receptors?

    <p>It dissociates from Gbg</p> Signup and view all the answers

    What is the ultimate effect of signal transduction through nuclear receptors?

    <p>Activation of transcription of target genes</p> Signup and view all the answers

    What is the primary function of cell signalling?

    <p>To facilitate communication between cells</p> Signup and view all the answers

    Which type of signal acts on a local set of cells?

    <p>Paracrine signal</p> Signup and view all the answers

    What is the result of cell-cell signalling on gene expression?

    <p>Change in the repertoire of transcription factors</p> Signup and view all the answers

    What determines cell fate in some signalling pathways?

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

    What is the function of nuclear receptors in cell signalling?

    <p>To allow signals to pass through the plasma membrane</p> Signup and view all the answers

    What is the term for the process by which a signal is translated into changes in cell physiology or gene expression?

    <p>Signal transduction</p> Signup and view all the answers

    What is the characteristic of autocrine signals?

    <p>They act on the secreting cell</p> Signup and view all the answers

    What is the purpose of signal gradients in cell signalling?

    <p>To determine cell fate</p> Signup and view all the answers

    What is the main difference between simple diffusion and facilitated diffusion?

    <p>The size of the molecules being transported</p> Signup and view all the answers

    In which type of solution will a cell swell, potentially causing lysis?

    <p>Hypotonic solution</p> Signup and view all the answers

    What is the primary function of channel proteins?

    <p>To form a hydrophilic passage through the membrane</p> Signup and view all the answers

    What is the direction of movement in active transport?

    <p>Against a concentration gradient</p> Signup and view all the answers

    What type of proteins are involved in facilitated diffusion?

    <p>Channel proteins and carrier proteins</p> Signup and view all the answers

    What is the energy source for direct active transport?

    <p>ATP hydrolysis</p> Signup and view all the answers

    What is the term for the diffusion of water molecules through a selectively permeable membrane?

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

    What is the state of a solution that has the same concentration of solutes as the cell interior?

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

    What is the primary mechanism by which cells maintain an ionic gradient across the membrane?

    <p>Direct ATP-powered pumps</p> Signup and view all the answers

    What is the approximate electrical potential maintained across the membrane due to differences in ion concentrations?

    <p>70mV</p> Signup and view all the answers

    How do cells synthesize new membranes?

    <p>By the expansion of existing membranes</p> Signup and view all the answers

    What is the characteristic of the cytosolic K+ concentration compared to the extracellular concentration?

    <p>Higher in the cytosolic space</p> Signup and view all the answers

    What is the purpose of regulating hydrogen ion concentration in the cytosol?

    <p>To regulate pH levels</p> Signup and view all the answers

    What is the mechanism by which some membranes grow and receive new lipids?

    <p>Vesicle-independent mechanism</p> Signup and view all the answers

    What determines the fluidity of the membrane?

    <p>The ratio of saturated to unsaturated fatty acids and the length of the fatty acid tails</p> Signup and view all the answers

    What is the role of cholesterol in the membrane?

    <p>To buffer the fluidity of the membrane</p> Signup and view all the answers

    What is the term for the movement of lipids from one leaflet to another in the lipid bilayer?

    <p>Flip-flop</p> Signup and view all the answers

    What is the term for the fluid mosaic model of membrane structure?

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

    What type of membrane proteins are anchored to the cytoskeleton or extracellular matrix?

    <p>Integral membrane proteins</p> Signup and view all the answers

    What is the term for the layers of the lipid bilayer?

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

    What is the mechanism by which van der Waals forces stabilize the packing of phospholipids?

    <p>Van der Waals forces</p> Signup and view all the answers

    What is the result of having longer fatty acid tails in the lipid bilayer?

    <p>Decreased fluidity</p> Signup and view all the answers

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

    <p>To support the cell and prevent it from bursting in a hypertonic solution</p> Signup and view all the answers

    What is the composition of the cell wall in plant cells?

    <p>Cellulose microfibrils embedded in pectin and hemicellulose</p> Signup and view all the answers

    What is the relationship between the plasma membrane and the cell wall in plant cells?

    <p>The plasma membrane is sandwiched between the cell wall and the cytoskeleton</p> Signup and view all the answers

    What is the structure that provides support to the cell and is located beneath the plasma membrane?

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

    What is the environment within a membrane often different from?

    <p>The environment outside the membrane</p> Signup and view all the answers

    What is the function of the cytoskeleton in relation to the plasma membrane?

    <p>To provide support to the plasma membrane</p> Signup and view all the answers

    What is the primary function of membranes in the cell?

    <p>To regulate the transport of solutes</p> Signup and view all the answers

    What is the characteristic of lipids found in cell membranes?

    <p>They are amphipathic and have a polar head</p> Signup and view all the answers

    What is the result of the hydrophobic and hydrophilic interactions between lipids in a membrane?

    <p>The formation of a lipid bilayer with a hydrophobic core</p> Signup and view all the answers

    Which type of lipid is a steroid and found in membranes?

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

    What is the function of membranes in cell signaling?

    <p>To detect and transmit both electrical and chemical signals</p> Signup and view all the answers

    What is the role of lipid bilayers in membranes?

    <p>To create a barrier between the cell and its environment</p> Signup and view all the answers

    Why do different membranes have different lipid compositions?

    <p>Because they have different functions in the cell</p> Signup and view all the answers

    What is the characteristic of the Rough Endoplasmic Reticulum?

    <p>It is a type of membrane that provides a surface for reactions</p> Signup and view all the answers

    Study Notes

    Cell Signalling

    • Cell signalling is the communication between cells, involving a chemical messenger (signal/ligand) released by the signalling cell.
    • The signal is detected by the responding cell (receptor), triggering intracellular reactions that influence the behaviour of the responding cell.

    Tasks of Cell Communication

    • Signal release: synthesis and excretion of the signalling molecule by the signalling cell.
    • Signal detection: interaction of signal and receptor.
    • Signal transduction: translation of detection to changes in cell physiology or gene expression.

    Types of Signals

    • Paracrine signals: act on a local set of cells.
    • Autocrine signals: act on the secreting cell itself.
    • Endocrine signals: long-range signals moving through the bloodstream.

    Signalling and Control of Gene Expression

    • Cell-cell signalling can change the repertoire of transcription factors in the responding cell, resulting in different gene expression.
    • Some signals can form gradients, and cell fate depends on signal concentration.

    Signal Entry into the Cell

    • Two strategies for signal entry:
      • The signal can pass through the plasma membrane (e.g., nuclear receptors).
      • The signal can activate a membrane receptor (e.g., G protein linked receptors, Serine/threonine kinase receptors).

    Nuclear Receptors

    • Signals are steroids or retinoids.
    • These signals can pass through the plasma membrane and encounter nuclear receptors in the cytoplasm.
    • The receptor-ligand complex then enters the nucleus to activate genes.

    Signalling through Nuclear Receptors

    • Nuclear receptors like the glucocorticoid receptor are cytoplasmic proteins.
    • In their inactive form, they are bound to Hsp chaperones.
    • Ligand binding releases the Hsp, and the receptor-ligand complex moves to the nucleus to activate the transcription of target genes.

    G-Protein Linked Receptors

    • Transmembrane receptors are linked to a G-protein.
    • Upon ligand binding, the G protein releases GDP and takes up GTP.
    • Ga dissociates from Gbg and activates downstream 'second messengers' (e.g., cAMP).
    • GTP is hydrolyzed to GDP, and Ga reassociates with Gbg.

    Serine/Threonine Kinase Receptors

    • Transmembrane receptors that bind the TGFb family of signals.
    • Ligand brings together type I and type II receptors.
    • Type II phosphorylates type I.
    • Smads become phosphorylated and move into the nucleus to act as transcription factors.

    Membrane Selective Permeability

    • Membranes define a barrier between the inside and outside of a cell, and the inside must interact with the outside.
    • Examples of selective permeability include:
      • Bulk transfer by endo and exocytosis
      • Secreting and importing proteins
      • Solute molecules, such as ions (e.g. Na+, K+, Cl-) and metabolites (e.g. sugars, amino acids)

    Transport Across the Membrane

    • Simple diffusion:
      • Occurs down a concentration gradient towards equilibrium
      • Small, uncharged polar molecules can diffuse across the membrane best
    • Osmosis:
      • A special case of simple diffusion where water is diffused
      • The plasma membrane is highly permeable to water
    • Facilitated diffusion:
      • Larger and/or polar molecules are helped across the membrane
      • Two types of integral membrane proteins involved: carrier proteins and channel proteins
    • Active transport:
      • Moves molecules against a concentration gradient
      • Divided into direct active transport (uses ATP hydrolysis) and indirect transport (uses co-transport of a solute favorably down its gradient)

    Bulk Transfer

    • Endo and exocytosis are forms of bulk transfer

    Ion Concentrations

    • The cytosolic pH is maintained at around 7.2 by regulating hydrogen ion concentration
    • K+ is generally higher intracellular than extracellular
    • Na+ is generally lower intracellular than extracellular
    • Direct ATP-powered pumps maintain an ionic gradient across the membrane

    Synthesis of the Membrane

    • Cells synthesise new membranes by expanding existing membranes
    • Lipid precursors are synthesised in the cytosol and ER
    • Membrane lipids are distributed to target membranes by vesicles and vesicle-independent mechanisms

    Membrane Structure and Composition

    • Varying lipid composition alters membrane physical properties
    • Fluidity depends on the ratio of saturated to unsaturated fatty acids and fatty acid tail length
    • Cholesterol affects fluidity by preventing it from becoming too fluid or too crystalline

    Lipid Bilayer

    • The lipid bilayer is fluid, with lipids able to move laterally but not flip into the opposing layer
    • Long-chain fatty acids pack against each other, stabilized by van der Waals forces
    • The longer the chain, the less fluidity the lipid has in the membrane

    Leaflets and Flippases

    • The two layers of the lipid bilayer are referred to as leaflets, which often have different lipid compositions
    • Moving from one leaflet to another is a slower process than lateral movement within a leaflet, facilitated by integral membrane proteins called flippases

    Proteins in the Lipid Bilayer

    • Proteins float in the lipid bilayer, representing the mosaic part of the fluid mosaic model of membrane structure
    • There are three main groups of proteins associated with the lipid bilayer: lipid-anchored, peripheral, and integral membrane proteins

    Asymmetry of the Lipid Bilayer

    • The layers of the lipid bilayer can be asymmetric in lipid and protein composition
    • Some proteins are mobile in their layer, while others are anchored to the cytoskeleton or extracellular matrix

    Cell Wall and Cytoskeleton

    • The cell wall is a rigid structure surrounding plant and some fungal cells, composed of cellulose microfibrils embedded in pectin and hemicellulose
    • The plasma membrane is associated with the cell wall
    • The cytoskeleton is an array of filaments beneath the plasma membrane, providing support to the cell

    Membrane Functions

    • Membranes define cells and organelles within cells
    • Membranes regulate the transport of solutes, detect and transmit electrical and chemical signals, and provide surfaces for reactions

    Biomembranes

    • Biomembranes are composed of lipid bilayers
    • Lipids found in cell membranes are amphipathic, with a polar head and non-polar tail
    • Amphipathic lipids spontaneously form lipid bilayers with hydrophilic heads facing the aqueous solution and hydrophobic tails stacking upon themselves

    Lipid Classes

    • Examples of amphipathic membrane lipids include phosphoglycerides, sphingolipids, and cholesterol
    • Lipids are important for membranes, energy storage, and cell signaling
    • Phospholipids, glycolipids, and cholesterol are the main classes of membrane lipids

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    Description

    Learn about the process of cell signalling, including the role of chemical messengers, signal detection, and how it influences cell behaviour.

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