Cell Transport Notes
I.
Cell Membranes
A.
Fluid mosaic model held together by hydrophobic
interactions
B.
Selectively permeable phospholipid bi-layer that regulates
what enters and exits cell
C.
Made up of:
1. lipids with a hydrophobic (tail) and hydrophilic (head) region;
cholesterol (steroid) stabilizes
2. proteins types:
a. transport – acts as channels or pumps
b. receptor - enzymes bind with substrates for a chemical
reaction
c. recognition/glycoproteins - act as “ID” cards depending
on their oligosaccharides chains
d. adhesion – allows similar cells to locate and stick to one
another
D. Cross-section:
Extracellular space (outside the cell)
Carbohydrate chain on a
receptor protein
Hydrophobic tail
Phospholipid bilayer
Hydrophilic head
Channel protein
Recognition protein
Transport protein
Cholesterol
Intracellular space (inside)
II. Cell Transport
A. Thermal motion: molecules constantly move and collide, spreading
out across the plasma membrane
B. Passive transport - DOES NOT require energy
1. Diffusion:
a. molecules move from high concentration to low,
down the concentration gradient
b. even after equilibrium is reached, molecules still
move across the membrane in both directions
c. O2, CO2, small nonpolar molecules diffuse
2. Osmosis: diffusion of water
a. because a cell is filled with molecules such as salts,
sugars, and proteins, it is usually hypertonic to fresh
water = net movement of water into a cell
b. osmotic pressure – osmosis exerts pressure on the
hypertonic side of the membrane since water moves
from the hypotonic (more dilute) side to the
hypertonic side cell lyses
3. Carrier - Facilitated Diffusion – transport proteins in membrane
help ions and larger, polar molecules (sugars, salts) move
across membrane since they are hydrophilic
C. Transport that DOES require energy
1. Active transport - molecules move when transport proteins bind
to them and pump them across the membrane against the
concentration gradient (from areas of low concentration to high
concentration); uses ATP
2. Endocytosis – cells take in macromolecules or particulate
matter by forming cell membrane derived vesicles
a. Pinocytosis – engulfing of extracellular fluid
b. Phagocytosis – engulfing macromolecules forming a
vacuole
3. Exocytosis – cells secrete molecules by the fusion of secretory
vesicles (from the ER or Golgi) to the plasma membrane; ex.
insulin made in pancreas is secreted into blood stream