2006-2007 Movement across the Cell Membrane
Jan 14, 2016
2006-2007
Movement across the Cell Membrane
Diffusion
DiffusionDiffusionmovement from HIGH → LOW concentrationDown the concentration gradient
DiffusionDiffusionmovement from HIGH → LOW concentrationDown the concentration gradient
Is this a passive or
active process?
Is this a passive or
active process?
What did it take to What did it take to make the make the
concentration concentration gradient?gradient?
32006-2007
The concentration gradient stores potential energy
It takes energy to generate the gradient
The process is still considered passive
Facilitated Diffusion• Diffusion through
protein channels– highly specific– passive process
“The Bouncer”
HIGHHIGH
LOWLOW
what sort of what sort of molecules molecules
will use this will use this process?process?
Active Transport
“The Doorman”
• 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
LOWLOW
HIGHHIGH
Once completed, Once completed, where has the where has the energy for the energy for the
active transport active transport gone? gone?
symportsymportantiportantiport
Active transport• Many models & mechanisms
ATP ATP
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
simplesimplediffusiondiffusion
facilitatedfacilitateddiffusiondiffusion
activeactivetransporttransport
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-specificprocess
triggered bymolecular signal
What about Osmosis?
• Diffusion of water from HIGH concentration of water to LOW concentration of water– across a
semi-permeable membrane
Why does Why does osmosis need osmosis need a membrane?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
hypotonic hypertonic
water
net movement of water
13
Hypotonic , Hypertonic, Isotonic
How does sugar How does sugar concentration lead to concentration lead to water movement? water movement?
1414
Which way would Which way would water move if oil was water move if oil was added to the left side added to the left side
of the tube?of the tube?
Let’s watch the video
Managing water balance
• Hypotonic• Animal cell/protist
cell problem?
• Solutions?
• Plant cells....
• turgid = full• cell wall protects
from bursting
freshwater
No problem,here
KABOOM!
Managing water balance• Hypertonic
• Animal cells:• How can they adjust:• Take up water or pump
out solutes.– plant cells
• plasmolysis = wilt
saltwater
I willsurvive!
I’m shrinking,I’m shrinking!
Why do people make Why do people make beef jerky, and add beef jerky, and add syrup to preserve syrup to preserve
canned fruit?canned fruit?
Managing water balance• Isotonic
–Animal cell problems:–none–solutes are equally
concentrated on both sides of membranes
–Plant cell problems–flaccid cells lose structure.
balanced
I couldbe better…
That’sperfect!
Aquaporins• Water moves rapidly into & out of cells
– evidence that there were water channels• protein channels allowing flow of water across
cell membrane
Peter AgreJohn Hopkins
Roderick MacKinnonRockefeller
.05 M.05 M .03 M.03 M
Which way will water Which way will water
move?move?