Endocytosis &

Exocytosis Pooja Patel

Elizabeth Pemberton

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.  

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