Cell Membrane

Endosymbiosis Theory Origin of eukaryotes Mitochondria from aerobic bacteria living within host cell Chloroplast evolved from cyanobacteria Why?

Insane in the Membrane Barrier around cytosol of the cell Composed of lipids, proteins, steroids Protection Transport

Fluid Mosaic Model Asymmetrical Membranes are not rigid Lipids with freely moving proteins Lipids make up bilayer Proteins “embedded” within bilayer – Transport – Structure – Enzymes Glycoprotein and glycolipid – Interactions

Phospholipids Hydrophobic tail Hydrophilic head Polar extracellular fluid – Forms bilayerbilayer

When I Move, You Move Lipid bilayer is very motile/fluid – Not rigid Fluidity dependent on 2 factors – Density of lipids – Temperature Membrane also contain sterols – Steroid with an OH group and a non-polar hydrocarbon – Ex. cholesterol

Membrane Proteins “Embedded” into membrane – Integral membrane proteins – Peripheral membrane proteins Transport – Protein channel Enzymatic activity Triggering signals – Initiate process Attachment and recognition – Structural – Cell-cell recognition

We Like to Move It Move It Take in nutrients, expel waste, communicate with environment/cells, transport molecules Selective permeable cell membrane – Passive membrane transport – Active membrane transport Exchange occurs across all membranes

Passive Membrane Transport Movement without chemical energy needed Diffusion – Simple diffusion – Facilitated diffusion Dynamic equilibrium

Simple Diffusion Unassisted diffusion Small non-polar molecules Non-polar steroid hormones/drugs Small uncharged polar molecules

Facilitated Diffusion Assisted diffusion via protein complexes Transport proteins – Channel proteins – Carrier proteins Still driven by concentration gradient Transport specific molecules

Channel vs. Carrier Protein What limits rate of diffusion?

Osmosis Passive diffusion of water Low solute concentration to high solute concentration Hypotonic vs. isotonic vs. hypertonic

Active Membrane Transport Against concentration gradient Energy dependent process – ATP Primary active transport Secondary active transport

Primary Active Transport Directly require ATP Move positively charged ions Create electrochemical gradient

Secondary Active Transport Does not directly require ATP – Works with primary pumps Cotransport – Requires two molecules Symport vs. antiport

Exocytosis & Endocytosis Transport larger molecules Require energy Exocytosis: export of molecules Endocytosis: import of molecules – Pinocytosis – Receptor-mediated – Phagocytosis

Exocytosis

Pinocytosis

Receptor-mediated Click me!

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