cell bio

• Three Things Needed to Generate a Microscopic Image


  • Magnification
  • Resolution
  • Contrast
• Magnification


  How much larger an object appears
• Resolution


  Ability to see septate objects as separate
• Contrast


  Differences in light intensity, contrast shows images
• How Resolution Can be Increased in Microscopy

  1. Increase NA

  2. Decrease wavelength of light
• Different Ways that Contrast Can be Generated in Microscopy

  • Can be stained to create contrast
  • Fluorescent Probes
  • Phase contrast
  • Phase Contrast Microscopy
  • Dark Field Microscope
  • Bright Field Microscope
• Types of Microscope (Advantages and Disadvantages)

  • Confocal Fluorescence
  • Transmission Electron
  • Scanning Electron
  • Light Microscopy
• Confocal Fluorescence


  • Provide better resolution (eliminates out of focus light)
  • Optical sectioning
  • Three dimensional reconstruction (Multiple optical sections can be digitally combined to create a three-dimensional reconstruction of the cell)
• Transmission Electron


  • High resolution imaging
  • Can view internal structures
  • Visualize molecular structure
• Scanning Electron


  • Surface coated with heavy metal allows for better visualization
  • Measures quantity
  • Good for visualizing external features
  • Uses scattered electrons to produce 3D images
• Bright Field


  • Uses unmanipulated transmitted light
  • Generates dark image over a light background
• Dark Field


  • Enables microbes to be visualized as halos
• Phase Contrast


  • Visualize living cells
• Fluorescent


  • Can be used to view marine bacteria and gut bacteria
• Processing of Tissue Samples/Staining

  1. Fixation

  2. Embedding

  3. Tissue thinly sliced with a microtome for observation under a light microscope
• Fixation


  Covalent cross-linking locks proteins into place
• Embedding


  Wax permeates and the solidifies to harden and stabilize tissue
• Fluorescence


  • Fluorescent probes work by absorbing light of a specific wavelength, exciting their electrons to higher energy states
  • When these electrons return to their ground state, they emit light at a longer wavelength, a process known as fluorescence
  • In fluorescence microscopy, the specimen absorbs light at the excitation wavelength, causing fluorescent molecules within it to fluoresce, emitting light at a lower energy, longer wavelength
  • This emitted fluorescent light is then focused and detected, allowing for visualization of fluorescent molecules within the sample
• The Wealth of Nations was written in 1776
• Rational


  (in classical economic theory) economic agents are able to consider the outcome of their choices and recognise the net benefits of each one
• Producers act rationally by


  Selling goods/services in a way that maximises their profits
• Workers act rationally by


  Balancing welfare at work with consideration of both pay and benefits
• Governments act rationally by


  Placing the interests of the people they serve first in order to maximise their welfare
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• Demand curve shifting right

  Increases the equilibrium price and quantity
• Marginal utility


  The additional utility (satisfaction) gained from the consumption of an additional product
• If you add up marginal utility for each unit you get total utility
• When analysing markets, a range of assumptions are made about the rationality of economic agents involved in the transactions
• Phospholipid Structure


  • Hydrophilic head
  • Hydrophobic tail
  • Amphilippic
  • Two major types: Phosphoglycerides and sphingolipids
• Membrane Properties


  • Selective permeability
  • Membrane transport
  • Membrane potential
• Properties of Molecules that Diffuse Across Membrane

  • Size
  • Charge
  • Polarity
  • Lipid Solubility
  • Concentration Gradient
  • Temperature
  • Presence of Transport Proteins
• Ion Gradients Across Plasma Membrane and Creation


  Sodium (Na+): Higher concentration outside, Sodium-Potassium Pump, Sodium Leak Channels

  Potassium (K+): Higher concentration inside, Sodium-Potassium Pump, Potassium Leak Channels

  Calcium (Ca2+): Higher concentration outside, Calcium ATPase Pumps, Calcium Leak Channels, Calcium Ion Channels

  Chloride (Cl-): Higher concentration outside, Chloride Leak Channels, Chloride-Bicarbonate Exchanger
• Simple Diffusion


  Passive movement of molecules across a membrane down their concentration gradient, without the need for energy input or specific transport proteins

  Rate depends on concentration gradient, membrane permeability, and molecular properties

  Non-specific, can occur for any molecule that can cross the lipid bilayer

  Not regulated by the cell, occurs spontaneously
• Channel Transport


  Passive movement of ions or small polar molecules across a membrane through protein channels

  Rate influenced by number and activity of channels, electrochemical gradient, and ion concentration

  Highly specific, different channels allow passage of specific ions or molecules

  Activity can be regulated by membrane potential, ligand/cofactor binding, and post-translational modifications
• Transporter-Mediated Transport


  Facilitated movement of molecules across a membrane via specific transport proteins (carriers or pumps)

  Rate depends on concentration gradient, transporter turnover rate, and substrate affinity

  Highly specific, transporters exhibit substrate specificity

  Activity can be regulated by allosteric regulation, substrate binding, phosphorylation, and changes in membrane potential or intracellular signaling pathways
• Transcellular Glucose Transport


  Asymmetric Distribution of Transporters in Epithelial Cells: Gut epithelial cells have glucose transporters (e.g., SGLT) predominantly on the apical membrane facing the lumen

  Transcellular Transport of Glucose: Glucose is transported across gut epithelial cells through a transcellular pathway, Apical transporters facilitate uptake into the cell, Basolateral transporters (e.g., GLUT1, GLUT4) mediate exit into the extracellular space

  Role of Asymmetric Distribution: Ensures efficient and selective transport of glucose from the lumen to the extracellular space, Allows for regulation of glucose absorption and maintenance of blood glucose levels
• Glucose transport across gut epithelial cells

  1. Glucose molecules transported through transcellular pathway

  2. Apical glucose transporters (e.g., SGLTs) facilitate uptake from lumen into cytoplasm

  3. Glucose transported across cytoplasm towards basolateral membrane

  4. Basolateral glucose transporters (e.g., GLUT1 and GLUT4) mediate exit into extracellular space
• Asymmetric distribution of glucose transporters

  • Ensures efficient and selective transport of glucose from lumen to extracellular space
  • Glucose transporters on apical membrane facilitate uptake from lumen
  • Glucose transporters on basolateral membrane mediate release into extracellular space
  • Allows regulation of glucose absorption and maintenance of blood glucose levels
• Aquaporins


  • Highly permeable to water, facilitating movement of approximately 10 billion water molecules per second
  • Impermeable to ions due to specific structural features
• Structure of aquaporins


  • Narrow pore lined with carbonyl groups from peptide backbone, forming hydrogen bonds with water molecules
  • Peptide chain backbone and carbonyl oxygens contribute to selective permeability of water while excluding ions