“the edge of life” chapter 7 plasma membrane · chapter 7 plasma membrane “the edge of life...
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Chapter 7Plasma membrane
“the edge of life”
Fig. 6.2a (TEArt)
Fatty acidPhosphorylated
alcohol
Fatty acidGLYCEROL
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membranes = lipids, proteins & carbohydrates
• MOSTLY phospholipids
HYDROPHILIC - polar! Usually(Ionic – polar – usually)
HYDROPHOBIC
Polar(hydrophilic) region
Nonpolar (hydrophobic) region
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Lipid monolayer Ben Franklin
Cells – amphiphileamphipathic
H2O inside and outside lipid bilayer
6-8 nm thick – keep out water soluble
SELF ASSEMBLE
•relatively weakhydrophobicinteractions
WHAT IS HAPPENING WITH THE WATER MOLECULES HERE?
WHAT IS HAPPENING WITH THE WATER MOLECULES HERE?
Fig. 3.22(TE Art)
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Saturated fat
Unsaturated fat
OC
HCH
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HCH
HCH CH
HCH
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kinks prevent tight packingunsaturated hydrocarbon tails-fluid when cold
Is solid bad?Lose permeability Enzymes inactivated
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steroid cholesterol -wedged between phospholipidswhen cold -prevents tight packing of phosoholipids.
•Cholesterol influenced by temperaturephospholipids alone are usually closely packed in cold
How could you make plantsthat will grow in cold
temperatures?
membranes are fluid
•lateral movements •rapid
•2 microns per second
kinks in tail preventtight packing
Singer & Nicholson - 1972
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• drift–directed (motor proteins)
• anchored
1 hour
What happened to the “presidential” stem cell lines?
Micron = micrometer = 1 millionth of a meterNanometer = 1 billionth of a meter
• 100,000 nanometers (nm) = 1 hair
• 100 microns (um)= 1 hair
• Membrane = 6-8 nanometers
• Bacteria, mitochondria, chloroplasts = ½ -1 X 5 um
Freeze-fracture and freeze-etch
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bumps are proteins
Sidedness of the plasma membrane
Membrane models have evolved
SINGER AND NICOLSONFluid mosaic model (1972)A membrane is a fluid structure with proteins embedded or attached to a double layer of phospholipids.
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• Cell membrane components– phospholipid bilayer– transmembrane proteins– interior protein network– cell surface markers
transmembrane protein
Proteins:
•integral
•transmembrane
•peripheral
•Also amphipathic
• Anchoring proteins in the bilayer• Transmembrane proteins
• single-pass anchors• multiple-pass channels and carriers• pores
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Carbohydrates – oligosaccharides
some attached to lipids – glycolipid (glyco=carbohydrate)
cell-cell recognition
recognition
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Glycoproteins— combination of proteinsand carbohydrates often used as cell-surface receptors
(some hormones)
– NOTE: Lipoproteins—proteins and lipids transport fat throughaqueous bloodbstream.
• High-Density Lipoproteins (HDL)—greater proportion of dense protein;also known as “good cholesterol.”
• Low-Density Lipoproteins (LDL)—“bad cholesterol” because they carrycholesterol to outlying tissues (arteries) where they accumulate inblockages called plaques.
• VIRUS host range:• “lock-and-key” fit –membrane proteins
• rabies virus - several species• most- single species
(except pigs!)
• Most specific tissues– Human cold viruses - upper respiratory tract– AIDS virus - certain white blood cells
Membrane Proteins• transporters• enzymes• cell surface identity markers• cell adhesion proteins• attachments to cytoskeleton
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Some functions of membrane proteins
proteins have to change shape – membranes must be fluid
Passive Transport• Diffusion
– Random motion causes a net movement ofsubstances from regions of high concentrationto regions of low concentration.
The diffusion of solutes across membranes
passive transportbased on thermal motion (heat) – intrinsic kinetic energy
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Facilitated Diffusion• Carriers transport ions and other solutes across
the plasma membrane.– Facilitate movement by physically binding molecules
on one side of the membrane, and releasing them onthe other.
• essential characteristics– specific– passive
–saturates
Osmosis –passive diffusion of water
Rate = change time
Rate = ΔV ΔT
HIGH SOLUTESLOW WATER
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Osmosis
• Osmotic concentration - concentration of allsolutes in solution– Hyperosmotic - solution with the higher solute
concentration– Hypoosmotic - solution with the lower solute
concentration– Isosmotic - solute concentrations are equal
• Hypertonic – higher osmotic pressure• Higher solute concentration
• Hypotonic – lower osmotic pressure• Low solutes
• aquaporins
Maintaining Osmotic Balance
lyse
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The water balance of living cells
hypo and hyper – SOLUTE CONCENTRATION in solution
Fig. 6.15c (TEArt)
Cell body shrinksfrom cell wall
Flaccid cell Normal turgid cell
Plant cells
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The contractile vacuole of Paramecium: an evolutionary adaptation forosmoregulation WATER BALANCE
•Solutions to beinghypoosmotic to theenvironment
–extrusion
–isosmotic solutions
–turgor
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Bulk Transport• Endocytosis - enveloping food
– phagocytosis - material taken in is in particulateform
– pinocytosis - material taken in is in liquid form– receptor-mediated - transport of specific
molecules
• Exocytosis - discharge of material fromvesicles at the cell surface
The three types of endocytosis in animal cells
•phagocytosis
•pinocytosis
•receptor-mediated
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Secretoryvesicle
Plasmamembrane
Cytoplasm
Secretoryproduct
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• no membranes-
– dead!
• Disequilibrium –membranes defining feature of life