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Membrane Structure (Chapter 5) - Coggle Diagram
Membrane Structure (Chapter 5)
Proteins
Integral / Intrinsic Membrane
Transmembrane
- hydrophobic region
Transport Proteins
Channels
- open passageway; mostly gated
Transporters
- aka carriers; activated by conformational change
Uniporter - one molecules
Symporter - same direction
Antiporter - opposite directions
Lipid-anchored
- amino acid attached to lipid
Peripheral / Extrinsic Membrane
- noncovalently bounded to integral membrane proteins or polar heads
Composition
Phospholipid Bilayer
hydrophobic (inside)
hydrophilic (outside)
proteins, lipids, carbohydrates
asymmetrical leaflets
Fluid-mosaic model
semi-fluid
factors
length of fatty acyl tails
double bonds
cholesterol levels
high temp - stiff membrane
low temp - fluid
lipid & proteins move
lipids
spontaneous: lateral & rotational
non-spontaneous: flip-flop via flippase
lipid rafts
composition
high cholesterol levels
unique membrane proteins
role in endocytosis & cell signaling
synthesis
in cytosol & smooth ER
fatty acids - building blocks
made via enzymes
transfer to other membranes
lateral diffusion
transport via vesicles
to Golgi, lysosomes, vacuoles, plasma membrane
lipid exchange proteins
(integral membrane)
proteins
10-70% are restricted
maybe cytoskeleton-bounded
maybe extracellular matrix-bounded
synthesis of transmembrane proteins
mostly directed to ER
transferred to other membranes via vesicles
some to semiautonomous organelles
selectively permeable
Transmission Electron Microscopy (
TEM
)
sample: thin & stained
dye binds to polar heads
visible membrane bilayer
Glycosylation
- covalent attachment of carbohydrates to protein or lipids
function
recognition signals for other proteins
cell surface recognition
damage protection of proteins
two types
N-linked
- Carbohydrate to Nitrogen of asparagine; in ER and membrane proteins
O-linked
- Sugars to Oxygen of Serine/Threonine; only in Golgi
Membrane Transport
Two Types
Active
requires energy
against gradient flow
low to high conc.
small transport
primary
secondary
large transport
exocytosis
endocytosis
receptior-mediated
pinocytosis
phagocytosis
Passive
two types
passive diffusion
- without transport protein
osmosis
facilitated diffusion
- with transport protein
with gradient flow
high to low conc.
no input of energy
Gradients
transmembrane - conc. of solute
ion electrochemical - electrical & chemical
Tonicity
Isotonic - equal solute conc.
Hypertonic - higher solute conc.
crenation (animal cells)
plasmolysis (plant cells)
Hypotonic - lower solute conc.
osmotic lysis (animal cells)
high turgor pressure (plant cells) - help of cell wall or vacuoles