week 5 part 1 lectures

Week 5 Lecture 1, Membranes:

The Plasma Membrane-Barrier between interior and exterior of cell. -Selectively permeable.

-Some molecules can get in. -Some molecules can get out. -Some molecules can’t pass at all.

-Phospholipid bilayer

Selective Permeability-Phospholipids block almost all molecules-Proteins make the membrane permeable to specific molecules (they are selective).

Membranes are a Mosaic

Integral Membrane Proteins-Integrated into the membrane-Most are transmembrane (TM) proteins-Composed of hydrophobic and hydrophilic amino acids

General TM Protein Structure

(d) Cell-cell recognition

(e) Intercellular joining

ex. desmosomes

(f) attachment to the cytoskeleton and extracellular matrix (ECM)

Side of Proteins-The side of the protein facing the ER lumen will face the Golgi lumen and will face the outside of the cell.

Membranes are a Fluid Mosaic-Phospholipids can move laterally-Only rarely do they switch leaflets

Membranes are a Fluid Mosaic-Unsaturated fatty acids increase fluidity. -Saturated fatty acids decrease fluidity. -Cholesterol “buffers” fluidity.

-Keeps it fluid in the cold. -Keeps it viscous in the heat.

Proteins move laterally too

Diffusion-Molecules want to reach an equal distribution (dynamic equilibrium)

Diffusion across a biological membrane-If a membrane is permeable to a molecule that molecule will diffuse down its concentration gradient in an attempt to reach equilibrium.

Osmosis-Water has a concentration too!-Only include “free” water in concentration. -Osmosis is diffusion of free water.

Tonicity-Total concentration of solutes (whether or not the membrane is permeable to it)-In biology, it is in relation to the cytoplasm. -Isotonic-solution has same concentration as cytoplasm. -Hypotonic-solution has lower concentration than cytoplasm. -Hypertonic-solution has higher concentration than cytoplasm.

Week 5 Lecture 2, Organelles:

Lysosome-A digestive organelle-Contains a variety of hydrolytic enzymes that are activated by acid

Mitochondria-The space in between the two lipid bilayers is acid-Acid=high concentration of protons (H+¿¿)-Concentration gradient