Download - Endocytosis & Exocytosis
Water and small molecules enter and exit
cells through active transport and diffusion.
Large molecules, however,
(proteins and polysaccharides) as well
as larger particles are transported in and out of
the cell after being packaged in vesicles.
Endo- and exo- cytosis
require energy.Intr
oduc
tion
Exoc
ytos
is:
Cell secretes biological molecules
by the fusion of vesicles with the
plasma membrane. Steps: 1. Transport vesicles that buds off
Golgi body moves along
microtubules of the cytoskeleton to
the plasma membrane.
2. Lipid molecules of from the vesicles
and the plasma membrane
rearrange, forming a fused
membrane. 3. The contents spill outside of the
cell. 4. The vesicle membrane becomes
part of the plasma membrane.
Exoc
ytos
is:
Examples: • Pancreas secretes insulin
into extracellular fluid by
exocytosis. • Neurons release neurotransmitters that
signal other neurons or
muscle cells. • Plant cells ( when making
walls) deliver proteins
and carbs from Golgi vesicles to outside of cell.
Endo
cyto
sis:
Cell takes in biological
molecules by forming new vesicles from
plasma membrane.3 types: • Phagocytosis : (cell eats) • Pinocytosis : (cell drinks) • Receptor-Mediated
Endocytosis (RME)
Endo
cyto
sis:
Steps: 1. Small area of the plasma
membrane sinks inward.
2. The pocket deepens and
pinches into a vesicle containing materials from
the outside of the cell. 3. Becomes a vacuole (for
food or water)
RM
E:
Enables cell to acquire bulk quantities of specific
substances, even though those substances may
not be in high concentration outside the cell.
Steps: 1. The ligands (molecule that binds to a
specific receptor) attach to protein receptors
that are on the outside of the cell.
2. A “fuzzy” layer of coat proteins are on the
opposite side of the receptors on the inside
of the cell. 3. Once the ligands bind to the receptors
pocket forms and pinches into the cell. (The
vesicle is coated by the “fuzzy” coat proteins.
4. Once the ligands are released, the receptor
proteins are recycled back to the plasma
membrane.
RM
E:
Examples : 1. Cholesterols travel in blood
in particles called low density lipoproteins (LDLs)
2. the LDLs act as ligands3. When the LDLs are
defective or missing, cholesterol builds up in
blood vessels and can lead
to arteriosclerosis.
If pieces of the plasma membrane break off
every time exocytosis occurs, how does the cell
remain enclosed?Apparently, endo- and exo-
cytosis offset each other. While
one removes membrane, the
other replenishes.