Download Active Transport

Cell Transport: moving things in and out of the cell
Plasma membrane:
Material that surrounds
all cells and certain
organelles within the cell
- location of plasma
membrane gives it more
specialized name like
cell membrane, nuclear
membrane etc.
Cell Transport
Phospholipid – primary molecule in the cell
membrane consisting of two parts
Phosphate Group (POLAR)
Fatty Acid Tails (NON POLAR)
Remember the Triglycerides?
What’s the difference between them and a
phospholipid?
Phospholipids and Polarity
• Fatty acid tails are
non-polar.
– Hydrophobic
(water-haters)
• Phosphate heads
are polar
– Hydrophilic
(water-lovers)
Phospholipids Bi-layer
Plasma Membrane Structure
• 1. Phospholipid Bi-layer – makes up most of
membrane structure
• 2. Proteins – many different roles
• 3. Carbohydrate Chains – cell identification
Role of Proteins
Membrane Model
• Membrane as a whole is often described
as a fluid mosaic
– two-dimensional fluid of freely diffusing lipids,
dotted or embedded with proteins
– Think of the lipid bi-layer as a body of water
with various proteins and associated
carbohydrate chains moving around.
- Proteins can change location by moving
through the phospolipids.
Figure 8.5 Evidence for the drifting of membrane proteins
Movement of substances
through the membrane
May be
• PASSIVE– requires no energy
expenditure by cell.
– Diffusion and Osmosis
– Facilitated diffusion
• ACTIVE– does require energy
expenditure
– Why?
– Ex. Transport Proteins, Bulk Transport
Diffusion
- Molecules will move from areas of high
concentration to areas of lesser concentration
(concentration gradient)
- Due to random collisions of molecules
– If occurs across a membrane, the membrane
must be permeable to the substance.
• Size is a major factor
• Electrical charges
• Polar vs non-polar
Factors that affect permeability:
Diffusion (cont.)
• Movement of particles (solute) from
high to low concentration will continue
until there is an even distribution of
particles.
• This is called equilibrium.
• Particles move across the membrane
randomly at equilibrium. (In other
words, movement still happens, just no
NET MOVEMENT!)
Special Type of Diffusion - Osmosis
• Diffusion of water across a selectively permeable
membrane
• Water moves from a high concentration of water
(less salt or sugar dissolved in it) to a low
concentration of water (more salt or sugar
dissolved in it)
Figure 8.11 Osmosis
Tonicity
• When comparing the concentrations of
2 solutions:
• Isotonic – same concentration of solute
• Hypertonic – higher concentration of
solute
• Hypotonic – lower concentration of
solute
Osmotic Pressure Effects on Cells
• Inside of cells are usually hypertonic to fresh water
(hypotonic)
• Animals cells tend to be surrounded by isotonic
solutions (blood, saliva, etc)
• Plant cells have tough cellulose cell walls that
protect them from over-expanding
Facilitated Diffusion
• Charged particles and some molecules
can move passively through protein
channels. Glucose is a great example
of a molecule that enters cells via
facilitated diffusion
• Important to note that this is still
happening through the process of
diffusion using the concentration
gradient to move molecules in/out of
cell.
– Energy Not Needed!
Facilitated Diffusion
• Those molecules which cannot move freely
through the membrane have to diffuse through
special integral membrane proteins
ACTIVE TRANSPORT Small molecules and ions can be
“pumped” in/out of cell using energy (ATP). We will look at a
couple really important examples of these when we look at cell
respiration and photosynthesis. Also key in neuron function!
Active Transport
• Two main categories
– Small Stuff – Transport Proteins
• Molecules can move in/out of cell using transport
proteins.
– Big Stuff – Vesicle Transport
• Large materials (ie. chunks or food, complex molecules,
liquid and even cells) that cannot pass through a protein
channel need to be brought in through complex
movement of membrane vesicles
– Exocytosis
– Endocytosis
The three types of endocytosis in animal cells
SUMMARY OF WAYS TO MOVE STUFF IN AND OUT:
Passive Transport:
Requires no energy
- simple diffusion
- facilitated diffusion (via proteins)
Active Transport:
Requires energy in the form of ATP (energy molecule)
- transport proteins
- endo/exocytosis