Download presentation
Presentation is loading. Please wait.
1
The Phospholipid Bilayer aka The Cell Membrane
2
Phospholipids Phosphate head Fatty acid tails Arranged as a bilayer
“attracted to water” Phosphate head hydrophilic Fatty acid tails hydrophobic Arranged as a bilayer Fatty acid “repelled by water”
3
The Cell Membrane is arranged as a Phospholipid Bilayer
Serves as a barrier or border sugar H2O salt polar hydrophilic heads nonpolar hydrophobic tails impermeable to polar molecules polar hydrophilic heads waste lipids
4
Permeability to Polar Molecules?
Membrane becomes semi-permeable via protein channels specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3
5
The Cell Membrane is more than lipids…
Transmembrane proteins embedded in phospholipid bilayer create semi-permeable channels lipid bilayer membrane Transmembrane protein channels in lipid bilayer membrane
6
Other proteins anchor Transmembrane Protein
Within membrane nonpolar amino acids hydrophobic anchors protein into membrane On outer surfaces of membrane polar amino acids hydrophilic extend into extracellular fluid & into cytoplasm (cytosol) Polar areas of protein Nonpolar areas of protein
7
H+ NH2 H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic) a-helices in the cell membrane Examples Aquaporin Porin monomer b-pleated sheets Bacterial outer membrane H2O H+ Ion channel Proteins function through conformational change… meaning proteins shape determines their function H2O
8
Examples of conformational differences in Transmembrane Proteins
Outside Cell Membrane Inside Transporter Enzyme binding site Cell surface receptor aka “Antigens” Signal transduction - transmitting a signal from outside the cell to the cell nucleus, like receiving a hormone which triggers a receptor on the inside of the cell that then signals to the nucleus that a protein must be made. Cell surface identity marker Cell adhesion Attachment to the Cytoskeleton
9
Types of Membrane Proteins
Proteins determine membrane’s specific functions The cell membrane & organelle membranes each have a unique collection of proteins Classes of membrane proteins: Embedded (or Peripheral) Proteins loosely bound to surface of membrane ex: cell surface identity marker (antigens) Transmembrane (or Integral) proteins Span across the Cell Membrane ex: transport proteins Channels or pumps (permeases)
10
Filaments of cytoskeleton
The Cell Membrane is a mosaic of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein Extracellular fluid Glycolipid Transmembrane proteins The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins. Phospholipids Filaments of cytoskeleton Cholesterol Peripheral protein Cytoplasm 1972, S.J. Singer & G. Nicolson proposed “Fluid Mosaic Model”
11
Membrane carbohydrates (antigens)
Play a key role in cell to cell recognition the ability of a cell to distinguish one cell from another important in organ & tissue development basis for rejection of foreign cells by the immune system Ex. A, B, AB, O blood groups The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells.
Similar presentations
