bi 1a cell membrane structure and function cells need an inside & an outside… separate cell...

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

saltsO2

H2O

OUTwaste-

ammonia- salts- CO2

- H2O products- proteins

cell 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

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

sugarsugar

sugarsugar

sugar

Which way will sugar move?

sugar

sugar

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”“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 summary

simplediffusion

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

1

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!

2

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!

3

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?