Cell Membrane Function (Movement Across the Cell Membrane)
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Cell Membrane Function (Movement Across the Cell Membrane) Bi 1a Cell Membrane Structure and Function
description
Bi 1a Cell Membrane Structure and Function. Cell Membrane Function (Movement Across the Cell Membrane). Cell (plasma) membrane. Cells need an inside & an outside… separate cell from its environment cell membrane is the boundary. IN food - sugars - proteins - fats salts O 2 H 2 O. - PowerPoint PPT Presentation
Transcript of Cell Membrane Function (Movement Across the Cell Membrane)
Cell Membrane Function(Movement Across the Cell Membrane)
Bi 1a Cell Membrane Structure and Function
Cell (plasma) membrane Cells need an inside & an outside…
separate cell from its environment cell membrane is the boundary
INfood- sugars- proteins- fats
saltsO2H2O
OUTwaste-
ammonia- salts- CO2- H2O
products- proteinscell needs materials in & products or waste out
Building a membrane How do you build a barrier that
keeps the watery contents of the cell separate from the watery environment?
What substance do you know that doesn’t mix with water?
FATS LIPIDS Remember: oil & water don’t mix!!
Lipids of cell membrane Membrane is made of special kind of lipid
phospholipids “split personality”
Membrane is a double layer phospholipid bilayer
inside cell
outside cell
lipid
“repelled by water”
“attracted to water”
phosphate
Semi-permeable membrane
Cell membrane controls what gets in or out
Need to allow some materials — but not all — to pass through the membrane semi-permeable▪ only some material can get in or out
aa H2Osugar lipids salt waste
So what needs to get across the membrane?
O2
Crossing the cell membrane
What molecules can get through the cell membrane directly? fats and oils can pass directly through inside cell
outside cell
lipid
salt
aa H2Osugar
waste
but…what about other stuff?
Cell membrane channels Need to make “doors” through
membrane protein channels allow substances in & out▪ specific channels allow specific material in & out▪ H2O channel, salt channel, sugar channel, etc.
inside cell
outside cell
sugaraaH2O
saltwaste
How do you build a semi-permeable cell membrane?
Channels are made of proteins proteins both “like” water & “like” lipidsbi-lipidmembrane
protein channelsin bi-lipid membrane
Protein channels Proteins act as doors in the
membrane channels to move specific molecules
through cell membraneHIGH
LOW
Movement through the channel Why do molecules move through
membrane if you give them a channel??
?
HIGH
LOW
Molecules move from high to low
Diffusion move from HIGH to LOW concentration
Diffusion Move from HIGH to LOW
concentration passive transport no energy needed
diffusion
Diffusion 2nd Law of Thermodynamics
governs biological systems universe tends towards disorder
(entropy)
Diffusion movement from HIGH LOW
concentration
Simple Diffusion Move from HIGH to LOW
inside cell
outside cell
Which way will fat move?fat
fat
fat
fat
fat
fat fat
fatfat
fat
fat
fat
fat
fat
LOW
HIGH
Facilitated Diffusion Move from HIGH to LOW through a
channel inside cell
outside cell
sugar
sugar
sugar
sugar
sugarsugar
sugar sugar
sugarsugarsugar
Which way will sugar move?
sugarsugar
LOW
HIGH
Diffusion Move from HIGH to LOW
concentration directly through membrane▪ simple diffusion▪ no energy needed
help through a protein channel▪ facilitated diffusion (with help)▪ no energy needed
HIGH
LOW
Simple vs. facilitated diffusion
inside cell
outside cell
lipidinside cell
outside cell
H2O
simple diffusion
facilitated diffusion
H2O
protein channel
Diffusion
Random motion drives diffusion
Movement is based on kinetic energy (speed), charge, and mass of molecules
Equilibrium is reached when there is an even distribution of solute molecules
2
3
14
(water)
Active transportCells may need molecules to
move against concentration “hill” need to pump “uphill”▪ from LOW to HIGH using energy
protein pump requires energy▪ ATP
ATP
Active Transport
“The Doorman”
conformational change
Cells may need to move molecules against concentration gradient conformational shape change transports solute
from one side of membrane to other protein “pump” “costs” energy = ATP
ATP
LOW
HIGH
symportantiport
Active transportMany models & mechanisms
ATP ATP
Transport summarysimplediffusion
facilitateddiffusion
activetransport
ATP
How about large molecules?
Moving large molecules into & out of cell through vesicles & vacuoles REQUIRES ENERGY endocytosis▪ phagocytosis = “cellular eating”▪ pinocytosis = “cellular drinking”
exocytosis
exocytosis
Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered bymolecular signal
2006-2007
OsmosisMovement of Water Across Cell Membrane
Osmosis Water is very important, so we talk
about water separately Osmosis
diffusion of water from HIGH concentration of water to LOW concentration of water▪ across a semi-permeable membrane
Concentration of water Direction of osmosis is determined by
comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water
hypotonic hypertonic
water
net movement of water
Osmosis Diffusion of water through a
semi-permeable membrane Semi-permeable:
permeable to solvents (WATER), but not to large molecules
High [water] to low [water]
Dissolved molecules (i.e. glucose, starch) are called solutes
REMEMBER:Water = solventGlucose, Starch = solutes
freshwater balanced saltwater
Managing water balance Cell survival depends on balancing
water uptake & loss
Managing water balance Hypotonic
a cell in fresh water high concentration of water around cell
▪ problem: cell gains water, swells & can burst
▪ example: Paramecium ▪ ex: water continually enters Paramecium cell
▪ solution: contractile vacuole ▪ pumps water out of cell▪ ATP
plant cells▪ turgid = full▪ cell wall protects from bursting
freshwater
ATP
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No problem,here
KABOOM!
Keeping right amount of water in cell Saltwater ( lots of salt) HYPERTONIC
a cell in salt water low concentration of water
around cell▪ cell loses water
example: shellfish problem: cell loses water▪ in plants: plasmolysis▪ in animals: shrinking cell
solution: take up water
saltwater
I willsurvive!
I’m shrinking,I’m shrinking!
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Keeping right amount of water in cell Balanced conditions (ISOTONIC )
no difference in concentration of water between cell & environment▪ cell in equilibrium▪ example: blood▪ problem: none▪ water flows across membrane equally, in both directions▪ volume of cell doesn’t change
balanced
I couldbe better…
That’sbetter!
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Effect of Water on Cells Hypertonic Environment
High [solute], low [water]
Hypotonic Environment High [water], low [solute]
Isotonic Environment [water] = [solute]
Isotonic
HypotonicHypertonic
Part 3 pg. 85
Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic
Sheep red blood cells
0.9% saline
10% NaCl
Distilled water
•
Predictions?
Crenation
Effect of Water on red blood cell
Osmosis in Plant Cells
• Elodea leaves
10% NaCl
Distilled water
Hypertonic
Hypotonic
Predictions?
Plasmolysis
THOUGHT QUESTIONS
WHY ARE PASSIVE TRANSPORT ( diffusion, facilitated diffusion, osmosis) and ACTIVE TRANSPORT IMPORTANT TO THE CELL?
HOW DOES THE CELL MAINTAIN ITS HOMEOSTASIS?
