Movement across the Cell Membrane 2006-2007

Diffusion 

Diffusion



movement from HIGH



LOW concentration



Down the concentration gradient What did it take to make the concentration gradient?

2006-2007 The concentration gradient stores potential energy

It takes energy to generate the gradient The process is still considered passive

3

Facilitated Diffusion

• Diffusion through protein channels – highly specific – passive process

HIGH

what sort of molecules will use this process?

LOW “The Bouncer”

Active Transport • Cells may need to move molecules

against

gradient concentration – conformational shape change transports solute from one side of membrane to other – protein “pump” – “costs” energy = ATP

LOW Once completed, where has the energy for the active transport gone? ATP HIGH “The Doorman”

Active transport • Many models & mechanisms

ATP ATP antiport symport

Getting through cell membrane • Passive Transport – Simple diffusion • nonpolar, hydrophobic molecules –HIGH  LOW concentration gradient – Facilitated transport • polar, hydrophilic molecules • through a protein channel –HIGH  LOW concentration gradient • Active transport – against concentration gradient • LOW  HIGH – uses a protein pump (requires ATP)

ATP

Transport summary

simple diffusion facilitated diffusion active transport ATP

What about large molecules?

• Moving large molecules into & out of cell – through vesicles & vacuoles – endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” – exocytosis

exocytosis

Endocytosis

phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

What about Osmosis?

• Diffusion of water from HIGH concentration of water to LOW concentration of water – across a semi-permeable membrane

Why does osmosis need a 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

water hypotonic net hypertonic movement of water

Hypotonic , Hypertonic, Isotonic How does sugar concentration lead to water movement? 13

Let’s watch the video Which way would water move if oil was added to the left side of the tube?

Managing water balance • Hypotonic • Animal cell/protist cell problem?

• Solutions?

• Plant cells....

• turgid = full • cell wall protects from bursting

KABOOM! No problem, here freshwater

Managing water balance • Hypertonic • Animal cells: • How can they adjust:

I’m shrinking, I’m shrinking!

• Take up water or pump out solutes.

– plant cells • plasmolysis = wilt Why do people make beef jerky, and add syrup to preserve canned fruit?

I will survive! saltwater

Managing water balance • Isotonic – Animal cell problems: – none – solutes are equally concentrated on both sides of membranes

perfect!

– Plant cell problems – flaccid cells lose structure.

I could be better… balanced

Aquaporins • Water moves rapidly into & out of cells – evidence that there were water channels • protein channels allowing flow of water across cell membrane

Peter Agre John Hopkins Roderick MacKinnon Rockefeller

Which way will water move?

.05 M .03 M

Hey...watch this