The Cell Membrane Phospholipids Phosphate head Phosphate attracted

The Cell Membrane

Phospholipids • Phosphate head Phosphate “attracted to water” – hydrophilic • Fatty acid tails – hydrophobic Fatty acid • Arranged as a bilayer “repelled by water” Aaaah, one of those structure–function examples

What passes the bilayer? sugar polar hydrophilic heads nonpolar hydrophobic tails H 2 O salt impermeable to polar molecules polar hydrophilic heads waste lipids

How do polar molecules cross? inside cell NH 3 salt H 2 O aa sugar outside cell

Why are proteins the perfect molecule for transport?

Classes of amino acids What do these amino acids have in common? nonpolar & hydrophobic

Classes of amino acids What do these amino acids have in common? I like the polar ones the best! polar & hydrophilic

Protein domains anchor molecule Polar areas of protein Nonpolar areas of protein

H+ Examples H+ Retinal chromophore NH 2 aquaporin = water channel in bacteria Porin monomer H 2 O β-pleated sheets Bacterial outer membrane Nonpolar (hydrophobic) α-helices in the cell membrane COOH H+ H + Cytoplasm proton pump channel in photosynthetic bacteria H 2 O function through conformational change = protein changes shape

Membrane Proteins

Cholesterol • What is the function of cholesterol? 11

Membrane carbohydrates • Play a key role in cell-cell recognition – ability of a cell to distinguish one cell from another • antigens – important in organ & tissue development – basis for rejection of foreign cells by immune system

Let’s go to the video 13

Any Questions? ?