Regents Biology 2006-2007

Chapter 7-Cell Membrane

Regents Biology

A. Cell (plasma) membrane Cells need an inside & an outside…

separate cell from its environment INfood- sugars- proteins- fats

saltsO2

H2O

OUTwaste- ammonia- salts- CO2

- H2O Products - proteins

• cell needs materials in & products or waste out

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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!!

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B. Cell membrane structure Is made of special kind of lipid

phospholipids (‘the lollipop’) Is a double layer

the ‘bilayer’

inside cell

outside cell

hydrophobic‘tail’

“repelled by water”

“attracted to water”

hydrophilic‘head’

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C. Cell membrane function Controls what gets in or out Allows some materials to pass easier than

others is ‘selectively permeable’

only some material can get in or out

a.a. H2Osugar lipids salt waste

So what needs to get across the membrane?

O2

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D. Crossing the cell membrane Which molecules move through directly?

fats and oils can pass directly through

inside cell

outside cell

lipid

salt

aa H2Osugar

waste

but…what about other stuff?

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E. Cell membrane channels Need to make “doors” through membrane

protein channels allow other substances and ions in & out H2O channel, salt channel, etc.

inside cell

outside cell

sugaraaH2O

saltwaste

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F. Building a ‘semi-permeable’ cell membrane Protein channels that are within the bilayer

proteins both “like” water & “like” lipids

bi-lipidmembrane

protein channelsin bi-lipid membrane

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Other proteins can signal with other moleculesCalled peripheral proteins

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G. Fluid Mosaic Model Describe it (p.205)

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Chapter 7.3

Transport & Homeostasis

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Molecules move from high to low Diffusion

move from HIGH to LOW concentration

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Diffusion Move from HIGH to LOW concentration

passive transport no energy needed

diffusion osmosis

diffusion of water

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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

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Facilitated Diffusion Move from HIGH to LOW through a protein carrier

inside cell

outside cell

sugar

sugar

sugar

sugar

sugarsugar

sugar sugar

sugarsugarsugar

Which way will sugar move?

sugarsugar

LOW

HIGH

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Diffusion Move from HIGH to LOW concentration

directly through membrane simple diffusion no energy needed

help through a protein carrier facilitated diffusion (with help) no energy needed HIGH

LOW

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Simple vs. facilitated diffusion

inside cell

outside cell

lipidinside cell

outside cell

H2O

simple diffusion facilitated diffusion

H2O

protein carrier

Regents Biology 2006-2007

OsmosisMovement of Water Across Cell Membrane

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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

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Keeping water balance Cell survival depends on balancing

water uptake & water lossFreshwater (hypotonic)

Balanced(isotonic)

Saltwater(hypertonic)

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Keeping right amount of water in cell Freshwater

a cell in fresh water high concentration of water

around cell cell gains water

example: Paramecium problem: cells gain water,

swell & can burst water continually enters Paramecium cell

solution: contractile vacuole pumps water out of cell

freshwater

No problem,here

KABOOM!

1

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Controlling water Contractile vacuole in Paramecium

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Keeping right amount of water in cell Saltwater

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!

2

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Keeping right amount of water in cell Balanced conditions

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!

3

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Active transport Cells may need molecules to move against concentration “hill” need to pump “uphill”

from LOW to HIGH using energy protein pump requires energy

ATP

ATP

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Transport summary

simplediffusion

facilitateddiffusion

activetransport

ATP