Transcript Membranes

Membranes
• Everything in life is variable
– Chaotic
• Membranes organize the chaos of
cellular metabolism
– E.g. houses & stores with doors &
gates
– E.g. streets organize traffic
• Selectively permeable
– Allows some things in & blocks some
things
• Plasma membrane (cell)
– Takes up what cell needs & takes out
the trash
• Thin, requires EM at 200,000x
• 3 zones
– Construction of Phospolipids
Phospholipid
• Polar, hydrophilic
head
– Phosphate group
– React and interact with
the environment
• Non-polar,
hydrophobic tail
– Two-tailed fatty acid
• Relation w/ water = Phospholipid Bi-layer
– Non-polar, hydrophobic molecules move more freely
through the membrane (soluble in lipids)
• E.g. vessicles and vacuoles transporting packages
throughout membrane system
• E.g. soap to clean (breakdown) grease
– Polar molecules & ions not soluble
• Membrane = Fluid mosaic of
phospholipids and proteins
• Mosaic
– Made up of
many small
pieces
• Mosaic = diverse proteins embedded in
phospholipids
• Fluid = proteins can drift laterally within bi-layer
• Cholesterol – helps stabilize at body temperature &
maintains fluidity at lowered temperatures
• Glycolipids & glycoprotiens
– Carbohydrate ID tags
• E.g. immune system recognizes good cells from bacterial cells
• E.g. embryonic development – cells differentiate (tissues & organs)
• Proteins – do most of the work
Membrane Proteins
• Very diverse
– E.g. >50 different proteins
in plasma membrane of
human blood cells
• Enzymes – catalyze
molecule assembly (e.g.
modify by increasing rate)
• Receptors – messengers
from other cells (e.g.
hormones)
• Transport – allows large
molecules to pass
Passive Transport = diffusion
• Diffusion = natural tendency of particles to
spread evenly (from high concentration to low
concentration) to reach balance
• No energy required
• Many smaller molecules simultaneously
• E.g. O2 and CO2 move in & out of rbc’s
Facilitated Diffusion
• Size or polarity
prevents diffusion?
• Protein creates a
channel or pore for
passage
– E.g. sugars, amino
acids, ions, & water
• Down concentration
gradient (high conc.
to low conc.)
• Passive transport
– No energy required
Active Transport
• Spends energy to push solutes against conc. gradient
• Passive transport down a gradient is “as easy as falling
in a hole”
• But, how do you climb back up/out?
• Use the notches/cracks/crevices, but takes energy - ATP
Transport of LARGE molecules
• Exocytosis – transport out of cell
– Vesicle (membrane package) fuses with
plasma membrane, opens, releases outside
– E.g. salty tears from tear glands
• Endocytosis – reverse of exocytosis
– bringing in macromolecules from outside of
plasma membrane
– Pinching of membrane to form vesicle
• Phagocytosis – cellular eating
– Engulfs food molecules forming a vacuole, fuses with lysosomes
for digestion
• E.g. Amoeba
• Pinocytosis – cellular drinking
– Vesicles of non-specific liquid
• Receptor mediated endocytosis
– Pit forms in plasma membrane that is lined with specific
receptors, pinches closed, releases molecules inside cytoplasm