Cellula r Transpo rt Or- How do I get in and out of here?
Dec 27, 2015
Cells need to:
• Move nutrients into the cell• Remove waste products
from the cell• Export products made for
other parts of the organism (hormones, enzymes, neurotransmitters, etc.)
• Control the concentration of materials inside the cell.
The Cell Membrane:
Controls what enters and leaves the cell
Is Semi permeable – allows some molecules to move freely through, but keeps others out
Passive Transport
• The cell does not need to use any energy
• Movement of materials is from an area of
high concentration to an area of low concentration (molecules spread out)
• Molecules move with the concentration gradient
High
Low
Passive Transport - DiffusionMovement :• Occurs until equilibrium is achieved
• Caused by random motion of molecules
Diffusion is Affected by:•Temperature
Faster at higher temperatures•Molecular weight
Lighter molecules move faster•Concentration gradient
Faster when gradient is high
Can diffusion happen through the cell membrane?
YES, as long as the particles are small enough and not charged
Small, non charged molecules and water can move between the phospholipid molecules of the membrane.
This includes: carbon dioxide, oxygen, alcohol, glycerol
Passive Transport: Facilitated
Diffusion• Substances helped
into the cell by channel proteins– Polar molecules such
as glucose – Ionic molecules such
as amino acids
• Still does not use any cellular energy.
Transport Protein
What happens when the particles are too big to cross the membrane and there are no protein channels?
Large Molecules
Large Molecules
Water Moves
osmosis
Passive Transport: Osmosis
• The movement of WATER across a differentially permeable membrane – Solutes can not move across membrane
but water can– Water moves from an area of high water
concentration to low water concentration– Water diffuses towards the higher
concentration of solute.
Three Concentration Situations:
Isotonic: a solution that has an equal solute concentration to a neighboring solution.
Hypertonic: a solution that has a relatively higher solute concentration.
Hypotonic: a solution that has a relative lower solute concentration.
What does this mean to a cell?
The water content of the cell will be affected by the
concentration of solutes around and
in the cell.
HypertonicIsotonic Hypotonic
Plasmolysis occurs – cell shrinks as
water leaves
Water enters the cell. If too much water enters the
cell will burst
No net movement of water in or out of cell
Plants have a cell wall to protect from bursting.
Vegetables are crisp when they hold a lot of water and wilt when they lose it.
Active Transport: Energy Required
Transport protein uses energy (ATP) to
change shape
Transport protein able to move
molecule in or out of cell
Molecule is moved to increase the
concentration gradient
Transports against the concentration gradient (low to high)
Bulk Transport
• Macromolecules are too large to move with membrane proteins and must be transported across membranes in vesicles.
• The transport of macromolecules out of a cell in a vesicle is called exocytosis.
• The transport of macromolecules into a cell in a vesicle is called endocytosis.
Exocytosis – molecules leave the cell when the vesicle fuses with the membrane
Endocytosis – molecules brought into the cell by infolding the membrane and forming a vesicle
Bulk Transport• If the material taken up by
endocytosis is a large particle it is called phagocytosis.
• If the material taken up by endocytosis is a liquid or small particle it is called pinocytosis.
• Receptor-mediated endocytosis is a selective, highly efficient form of endocytosis.
Bulk Transport: Receptor Mediated
Receptor attaches to a specific molecule and moves it into the cell