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54 terms

Chapter 5: Membrane Structure, Synthesis and Transport

Vocab from Ch5
STUDY
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Phospholipids
composed of hydrophobic fatty acid tails and hydrophilic phosphate heads
Proteins and carbohydrates
carbohydrates vary in number; most membranes are 50% protein by mass
leaflet
half of a phospholipid bilayer; strikingly asymmetrical
Integral membrane protein
protein that cannot be released without dissolving the membrane
Transmembrane protein
most common integral membrane protein; has at least one region physically inserted into the hydrophobic region of the bilayer
Transmembrane segments
Stretches of nonpolar amino acids that span or traverse the membrane from one leaflet to the other
Lipid-anchored protein
Integral membrane protein that has amino acid side chain covalently attached to a lipid molecule
Peripheral membrane proteins
AKA extrinsic proteins; do not interact with hydrophobic interior rather noncovalently bound to protruding integral proteins or polar phosphate heads
Lipid raft
group of lipids that float together in a unit within a larger sea of lipids; high amount of cholesterol
Factors that affect membrane fluidity
1) Shorter tails= less likely to interact --> more fluidity
2) Double bonds present in acyl tails --> unsaturated --> more fluidity
3) presence of cholesterol --> less fluid at high temps, more fluid at low temps
Cholesterol
Short and rigid planar molecule produced by animal cells that stabilizes the membrane (plants have similar phytosterols)
Larry Frye and Michael Edidin Experiment
In 1970, Larry Frye and Michael Edidin fused human and mouse cells, cooled some, and incubated then cooled others then exposed them to labeled mouse antibodies revealing lateral movement in incubated cells
glycosylation
process of covalently attaching a carbohydrate to a lipid or protein resulting in a glycolipid or glycoprotein
role of carbohydrates
1) sometimes serve as recognition signals for other cellular proteins
2) play a role in blood type
Cell coat AKA glycocalyx
carbohydrate-rich zone on the surface of certain animal cells which sheilds them from mechanical and physical damage
FFEM Freeze Fracture electron microscopy
used to analyze the interiors of phospholipid bilayers; invented by Russel Steere in 1957; the sample is frozen in liquid Nitrogen and split with a knife
Ways new lipids can be transfered to diff membranes
1) diffuse laterally to the nuclear envelope
2) transported via vesicle to the golgi, lysosomes, vacuoles, or plasma membrane
3) lipid exchange proteins
Lipid exchange proteins
extract a lipid from one membrane, diffuse through the cell, and insert into another membrane
Lipid Synthesis
Occurs at the cytosolic leaflet of the ER
Transmembrane segment composition
If a polypeptide has a stretch of 20 hydrophobic amino acids that forms an alpha helix, it will be a transmembrane segment
N-Linked glycosylation
Involves attachment of a carbohydrate to the amino acid the Nitrogen of asparagine in a polypeptide chain; also occurs in archaea
O-Linked glycosylation
Involves addition of a string of sugars to the Oxygen atom of serine or threonine side chains in polypeptides; occurs only in the Golgi apparatus; important for production of proteoglycans
Proteoglycans
help organize the extracellular matrix; make up mucus
Highly permeable to phospholipid bilayer
1) Gases (CO2, N2, O2)
2) very small, uncharged molecules (ETHANOL)
Moderately permeable to phospholipid bilayer
1) Water
2) Urea (H2NCONH2)
Low permeability to phospholipid bilayer
1) Polar organic molecules
2) Sugars
Not permeable to phospholipid bilayer
1) Ions (Na+, K+, Mg+, Ca2+, Cl-)
2) Polar charged molecules and macromolecules (amino acids, ATP, proteins, polysaccharides, nucleic acids)
electrochemical gradient
Dual gradient that has both electrical and chemical components; occurs with solutes that have a net positive or negative charge
Crenation
shriveling as a result of being placed n a hypertonic solution
plasmolysis
in PLANT cells, when in hypertonic solution, the inner membrane shrinks away from the cell wall
Turger
when cell membran= is pressed up against the cell wall
Channels
Open passageway for facilitated diffusion; most are gated
Ligand-gated channels
controlled by noncovalent binding of small molecules (ligands)
Transporters (AKA carriers)
bind to solutes in a hydrophilic pocket and undergo a conformational change; slower than channels; principal method for organic molecules, hormones and neurotransmitters; key role in export
Uniporters
transporters that bind a single ion or molecule
Symporters (AKA cotransporters)
transporters that bind two or more ions or molecules and transport them in the same direction
Antiporters
Transporters that bind two or more ions or molecules and transport them in the opposite direction
Primary active transport
use of a pump
pump
a type of transporter that directly uses energy to transport a solute against a gradient
secondary active transport
use of pre-existing gradient to drive active transport of another solute
Na+/K+ ATPase
Proposed by Jens Skou; Antiporter that transports 3 Na+ out of the cell and 2 K+ into the cell using energy from ATP
electrogenic pump
pump that generates an electrical gradient
exocytosis
vesicle is loaded with cargo, released from the golgi, and fuses with the plasma membrane. Protein coat wraps around as vesicle is formed and is shed before the vesicle fuses with the plasma membrane
endocytosis
1) cargo binds to receptor and the receptors aggregate, the receptors cause coat proteins to bind the surrounding membrane. The plasma membrane invaginates as coat proteins cause a vesicle to form
2) The vesicle is released into the cell
3) The protein coat is shed
4) The vesicle fuses with an internal organelle such as a lysosome
5) cargo is released into the cytosol
pintocytosis
formation of membrane vesicles to internalize the extracellular fluid
phagocytosis
giant endocytosis (like engulfing a bacterium)
myelin
a fatty substance that helps insulate neurons and speeds the transmission of nerve impulses; has 3% carbohydrate
lamella
a thin membrane that is one of the calcified layers that form bones; has no carbohydrates
hydrophobic exclusion
The tendency of nonpolar molecules to aggregate together when placed in water. Exclusion refers to the action of water in forcing these molecules together; relevant to imbedded proteins
Which transmembrane protein processes drugs?
G-protein coupled receptors and channels ABC transporters and solute carriers are also targets for drug therapy
Cotranslational imports
sorting signals (first thing to think of)
proteoglycans
a glycoprotein consisting of a small core protein with many carbohydrate chains attached, found in the extracellular matrix of animal cells.
Hyperosmotic
solution with the higher SOLUTE concentration
Hypo-osmotic
solution with the lower SOLUTE concentration