Cell Transport and Membrane Dynamics

Protein Targeting and Cellular Transport

Signal Sequences and Sub-Chaperones

  • Sub-chaperones recognize amino acid sequences, such as those that direct proteins to the mitochondria.
  • These sequences function like "ZIP codes" embedded within the amino acid structure, guiding proteins to their correct cellular locations.

Types of Cellular Transport

  • Cells engage in both:
    • Bulk transport (taking up large amounts of material).
    • Single-molecule transport (moving one molecule at a time).

Solubility of Secreted Proteins

  • Soluble hormones are secreted into the bloodstream.
  • Soluble proteins can theoretically associate with the polar regions of a membrane.

Membrane Structure and Protein Interactions

  • The phospholipid bilayer's structure.
  • How proteins interact with this bilayer due to its mosaic nature.

Membrane Fluidity and Temperature Regulation

  • Animals adjust the fluidity of their membranes to cope with temperature changes throughout the year.
  • The plasma membrane's primary function is to allow the transport of molecules.

The Butter Effect

  • The core of a membrane is composed of fat, which can solidify.
  • Solidification can prevent the transport of molecules across the membrane.
  • Animals adjust their phospholipids to prevent solidification or what I call the "butter effect" in freezing temperatures.

Adjusting Membrane Fluidity

  • Membrane fluidity decreases in cold temperatures.
  • To counteract this, organisms adjust the double bonds in the phospholipid tails.
    • Adding double bonds increases fluidity in cold temperatures.
    • Removing double bonds decreases fluidity in high temperatures, pulling phospholipids together.

Facilitated Diffusion

  • Facilitated diffusion requires energy input, such as heating a solution to extract a dye.
  • A carrier protein binds to a specific molecule, like a sugar or amino acid.
  • The carrier protein changes shape to move the molecule down its concentration gradient, through the membrane, and into the cell.
  • Facilitated diffusion is similar to simple diffusion because both transport molecules down their concentration gradients.