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USC / Biology / BIOL 543 / What makes the cell membranes dynamic systems?

What makes the cell membranes dynamic systems?

What makes the cell membranes dynamic systems?


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LECTURE 3If you want to learn more check out What is the formula to compute the predetermined factory overhead rate?

  • Phospholipids: polar head carries charge, non-polar tails
  • Saturated fatty tails are straight
  • Unsaturated fats have double bonds, creates kinks in tails
  • The polarity of the phospholipids helps the cell membrane self-assemble
  • Cell membranes are dynamic systems, constant ebb and flow
  • Components move relative to each other
  • Ex: butter is solid because it is saturated, able to pack closer together.

  • Figure 2.3: Phospholipids in cell membranes of fish
  • Species in colder water, more phospholipids present are unsaturated, kinks make them not pack as tightly, allowing for more membrane fluidity in cold water.
  • Epithelial cells can create a membrane of sorts for an entire organism

  • Proteins: how they regulate chemical reactions as enzymes.
  • Synthesis: coded by DNA, transcribed to RNA that acts as the messenger, every three letters acts as a codon, read by the ribosome, to produce amino acids
  • Primary and secondary structures (alpha-helix and beta-sheets) are formed by covalent and hydrogen bonds
  • Proteins, like cell membranes, are dynamic structures
  • Keratin: a protein that makes hair, nails, animal horns
  • Composed of alpha-helices, able to pack really densely

  • Enzymes: how they regulate chemical interactions
  1. Speed up chemical reactions
  2. Regulate chemical reactions
  • Enzymes accelerate reactions
  • Any reaction can happen spontaneously
  • Enzymes make these interactions more likely to occur
  • Enzymes lower En
  • Reaction velocity tells you how fast substrate in converted to product

  • Reaction Velocity (V1) Formula
  • V1 = { Vmax [s] } / { Km + [s] }
  • Km = ½ Vmax → describes the slope velocity curve
  • Figure 2.11 - 2.14
  • Three separate enzymes with the same Vmax
  • But accelerations are different because enzymes have different affinity to bind to a substrate

  • Bioluminescent Animals
  • Some organisms can produce their own light
  • Luciferin → Oxyluciferin + Light
  • The enzyme luciferase is added to speed up the reaction, therefore, producing more light
  • Enzymes Regulating Reactions
  • Cells achieve speedier regulation by modulating the catalytic activity of their existing enzyme molecules
  • Enzymes are well positioned to exert control over metabolism
  • Rate- limiting reaction (linear)
  • Branch- point reaction
  • Permit two or more final products to be made from a single initial reactant.

Don't forget about the age old question of Are there any new screening methods that could help in detecting cancer earlier?


  • Membrane Proteins (page 39 in textbook):
  • Proteins are the 2nd major constituent of cell membranes
  • Channel Proteins: permit diffusion of solutes or osmosis of water through a membrane. Move with change and concentration gradient.
  • Permits simple diffusion of solutes in an aqueous solution
  • Transporter (Carrier) Proteins: bind reversibly with certain molecules and move them across membranes intact

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  • Aquaporins: water channels in cell membranes
  • Only a single H2O molecule can pass through at a time.
  • H2O molecule is shaped in a way that the molecule has to turn so it can pass through
  • The permeability of a cell to H2O depends on the presence or absence of these proteins (page 126 in textbook)
  • If you change a couple of proteins’ amino acids, it would not work anymore. Some particular amino acids are essential to the function of the protein.

  • Gated Ion Channels (pg. 108)
  • Charges in membrane potentials open and close the channels
  • They are able to “open” and “close” because the proteins which they are composed of are able to undergo conformational changes.
  • Phosphorylation-Gated Channels: addition of a phosphate group can open or close the channel
  • Voltage-Gated Channels: change in response to voltage difference across membrane.
  • Stretch-gated Channels: change in response to physical tension
  • Ligand-gated Channels: act as both receptors of extracellular signals and as ion channels. Open when their receptor sites bind to a specific ligand.

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