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study notes for lecture one: membrane transport

7 Pages
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Department
Physiology
Course Code
PSL201Y1
Professor
Doug Mac Kay

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1
LECTURE ONE: MEMBRANE TRANSPORT
SPOTLIGHT ON:CELL MEMBRANE
Composition
Transport Mechanism/
Permeability
Fluidity
- phospholipid bilayer
- fluid mosaic model
- glycocalyx
- proteins for structural
support/anchors for cytoskeleton
{the framework inside the cell}
- transmembrane protein channels
- protein transporters/carriers
- receptors
- enzymes/ion pumps
- cholesterol
if a substance can cross the membrane by any means = the membrane is
permeable to that substance
gases and lipid-soluble molecules diffuse through readily across the
membrane
impermeable to organic anions (like proteins)
polar molecules and ions need the help of proteins ± channels or carriers
± to cross
water diffuse via aquaporin channels
TM channels for diffusion of selected molecules/ions
selective transporters/carriers for transport across membrane for
molecules
receptors for signalling molecules
enzymes/ion pumps for active transport
o determined by lipid
composition
o fluidity is essential for
efficient carrier and channel
protein function
o cholesterol is inserted
among FA chains to
stabilize the membrane and
prevent diffusion of polar
molecules across it
o reduced by aging and poor
diet
MEMBRANE PROTEINS
TYPE
Structure & Composition
Function
Other Considerations
phospholipid
- polar head group (phosphate group
and head group)
- glycerol backbone
- hydrophobic tails
- polar end = glycerol + phosphate
(hydrophilic) + serine/choline/etc
{head group}
- non-polar end = 2 long FA chains
(hydrophobic)
determines fluidity of membrane
saturated tails are straight-chain alkanes
and pack very tightly resulting in rigid
structures
unsaturated tails contain alkenes/double
bonds which create kinks, allowing
fluidity, disrupt tight packing
tails associate with proteins
unsaturation of hydrophobic tails regulates
melting temperature by lowering it as it
takes less energy to break the bonds that
are not packed tightly
o head group may be neutral or
negatively charged
o phosphate group always carries a
negative charge
o hydrophobic tails can be
saturated (all single bonds) or
unsaturated (double bonds)
o normally one FA is saturated and
the other is polyunsaturated
o amphi-philic/phatic molecules =
have both highly polar and
highly non-polar regions
o
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2
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TYPE
Structure & Composition
Function
Other Considerations
glycocalyx
- extracellular polymeric material
(glycoprotein)
- ³VXJDUFRDW´ QHWZRUNRI
polysaccharides that project form
cellular surfaces
- matrix of long carbohydrate
filaments
- major components = hyaluronic
acid, chondroitin sulfate
- consists of acidic
mucopolysaccharides and
glycoproteins that project from the
apical plasma membrane of
epithelial absorptive cells
- has enzymes secreted by the
adsorptive cells essential for the
finals teps of digestion of proteins
and sugars
- contains acidic residues = net
negative charge
acts like a coat on the outside of the cell
membrane
fills extracellular space
slows diffusion
cell identification
triggers immune responses = enables
immune system to recognize and selective
attack foreign organisms
changes in the glycocalyx of cancerous
cells enable the immune system to
recognize and destroy them
forms the basis for compatibility of blood
transfusions, tissue grafts and organ
transplants
cell adhesion (binds cells together so that
tissue do not fall apart)
cell growth and development
creates a meshwork 0.3 micrometers thick
provides additional surface for adsoption
has net negative charge that sequesters
Ca2+ (cations) via electrostatic attraction
cushions plasma membrane protecting it
from chemical injury
enables sperm to recognize and bind egges
during embryonic development, guides
embryonic cells to their destinations in the
body
glycocalyx coating on endothelial walls in
blood vessels prevents leukocytes from
rolling/binding in healthy states
o carbohydrate filaments attach on
the outside of the membrane
o inside the cell are cytoskeletal
attachments
o glycoproteins and glycolipids
attach to a protein anchor
o produced by bacteria, epithelia
and other cells
o polysaccharide matrix excreted
by epithelial cells forming a
coating on the surface of
epithelial tissues
o found on the apical protion of
microvilli within the digestive
tract (especially within the small
intestine)
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Description
LECTURE ONE: MEMBRANE TRANSPORT SPOTLIGHT ON:CELL MEMBRANE Composition Transport Mechanism Fluidity Permeability - phospholipid bilayer if a substance can cross the membrane by any means = the membrane is o determined by lipid - fluid mosaic model permeable to that substance composition - glycocalyx gases and lipid-soluble molecules diffuse through readily across the o fluidity is essential for - proteins for structural membrane efficient carrier and channel supportanchors for cytoskeleton impermeable to organic anions (like proteins) protein function {the framework inside the cell} polar molecules and ions need the help of proteins channels or carriers o cholesterol is inserted - transmembrane protein channels to cross among FA chains to - protein transporterscarriers water diffuse via aquaporin channels stabilize the membrane and - receptors TM channels for diffusion of selected moleculesions prevent diffusion of polar - enzymesion pumps selective transporterscarriers for transport across membrane for molecules across it - cholesterol molecules o reduced by aging and poor receptors for signalling molecules diet enzymesion pumps for active transport MEMBRANE PROTEINS TYPE Structure & Composition Function Other Considerations phospholipid - polar head group (phosphate group determines fluidity of membrane o head group may be neutral or and head group) saturated tails are straight-chain alkanes negatively charged - glycerol backbone and pack very tightly resulting in rigid o phosphate group always carries a - hydrophobic tails structures negative charge - polar end = glycerol + phosphate unsaturated tails contain alkenesdouble o hydrophobic tails can be (hydrophilic) + serinecholineetc bonds which create kinks, allowing saturated (all single bonds) or {head group} fluidity, disrupt tight packing unsaturated (double bonds) - non-polar end = 2 long FA chains tails associate with proteins o normally one FA is saturated and (hydrophobic) unsaturation of hydrophobic tails regulates the other is polyunsaturated melting temperature by lowering it as it o amphi-philicphatic molecules = takes less energy to break the bonds that have both highly polar and are not packed tightly highly non-polar regions o 1 www.notesolution.com
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