Cell Membrane
Endosymbiosis Theory
• Origin of eukaryotes
• Mitochondria from aerobic bacteria living
within host cell
• Chloroplast evolved from cyanobacteria
• Why?
Insane in the Membrane
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Barrier around cytosol of the cell
Composed of lipids, proteins, steroids
Protection
Transport
Fluid Mosaic Model
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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 bilayer
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
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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
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Transport larger molecules
Require energy
Exocytosis: export of molecules
Endocytosis: import of molecules
– Pinocytosis
– Receptor-mediated
– Phagocytosis
Exocytosis
Pinocytosis
Receptor-mediated
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Homework
• Page 86 # 1-13
• Page 97 # 3-9