Plasma Membrane and Movement in and out of cell membrane

Prokaryotic Cell No nucleus No nuclear membrane One circular chromosome ribosomes No membrane bound organelles

Eukaryotic Cell nucleus Nuclear membrane Chromosomes are linear Membrane bound organelles

History: Discovery of membrane Structure 1895: Overton: lipids and lipid soluble materials enter the cell more rapidly than non-soluble lipid substances

History: Discovery of membrane Structure 1925 Gorter and Grerndel reasoned the membrane was a phospholipid bilayer.

History: Discovery of membrane Structure 1935: Davson and Danielli membrane model was a sandwich: a phospholipid bilayer between 2 layers of globular proteins

History: Discovery of membrane Structure Problems with Davson and Danielli Model 1.Not all membranes of all cells are the same 2.Problems with placement of the proteins

History: Discovery of membrane Structure 1972: Singer & Nicolson developed Fluid Mosaic Model Proteins are embedded in the phospholipid bi- layer due to the amphipathic nature of some protein molecules. hydrophilichydrophilic (water-loving) and lipophilic (fat-loving) propertieslipophilic

History: Discovery of membrane Structure Singer & Nicolson cont. Membrane is about as fluid as salad dressing. Composed of various lipids, proteins, and carbohydrates The arrangement due to the bonding properties of the molecules that make up the membrane.

History: Discovery of membrane Structure

Plasma Membrane Video

3 Types of Membrane Proteins Transmembrane Proteins- – Straddle bilayer with protruding parts on both faces – Most bear oligosaccharide side chains that function as receptors – Allow cell to cell recognition

3 Types of Membrane Proteins Integral Proteins – Imbedded to different degrees in the bilayer – Some span into the membrane – Can form channels/pores through the entire membrane – Allow H2O/dissolved materials to move in and out – Swerve as selective channels for certain materials (ions, amino acids, glucose)

3 Types of Membrane Proteins Peripheral Proteins Not embedded, but attached to membrane surfaces Function as enzymes

Ligands Ligand: means “to bind”, like a key into a lock They combine with specific receptors of transmembrane proteins

Ligands continues Ligands include substrates, activators, inhibitors, hormones, drugs and neurotransmitters.

Cell Membranes Cell or plasma membranes can be described as selectively permeable and in a dynamic state.

Functions of Plasma Membrane 1. shape and mechanical strength to cell, serves as an anchor to cytoskeletal fibers.

Functions of Plasma Membrane 2. Inactivate foreign substances (pathogens and poisons often need to pass through to cause harm) Illustration of HIV virus “tricking” an Integral Protein to let it in

Functions of Plasma Membrane 3. Catalyzes membrane/cellular reactions

Functions of Plasma Membrane Regulates every interaction between cell and environment. – Movement of materials through membrane – Conveys messages EX: hormones – Links cells together – Maintains electric potential difference across membrane

Transport across Cell Membrane Diffusion – net movement from areas from high to low concentration…unhampered movement!

Transport across Cell Membrane Facilitated transport: Diffusion helped by a transport protein Usually work by shape transformation, not catalyzed by enzymes

Transport across Cell Membrane Permeation – diffusion hampered by a permeability barrier Ex: water through a lipid bilayer

Transport across Cell Membrane Active Transport: movement of materials across a concentration gradient.

Transport across Cell Membrane Osmosis: diffusion of water through a selectively permeable barrier.

Transport across Cell Membrane Endocytosis/Exocytosis: physiological process of moving macromolecules through the plasma membrane. 1.Phagocytosis – engulfing of solid particles using a pseudopod 2.Pinocytosis – engulfing of liquid droplets

Transport across Cell Membrane Receptor-Mediated Endocytosis: Importing specific macromolecules by way of vesicles in response to the binding of specific ligands to receptors on cell surfaces.

Transport across Cell Membrane Vesicular transport: Movement of substances in vesicles (vacuoles)

Transport across Cell Membrane Gating: movement of substances through selective channels in transport proteins…type of facilitated transport