Endocytosis - Vesicle Movement in Cells

Endocytosis

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis

• Vesicle is a small sac of membrane with flied inside, they are normally present in eukaryotic cells
• Dynamic feature of cells
• Constructed, moved around and then deconstructed
• Can be happen because of the fluidity of membranes, which allows structures surrounded by a membrane to change shape and move

• The vesicle is formed on the inside of the plasma membrane, which contains material that was outside of the cell
• Method taking materials into the cell
• Contain water and solutes from outside the cell but also often contain larger molecules needed by the cell that cannot pass the plasma membrane
• e.g. Placenta including antibodies are absorbed into the fetus by endocytosis
• e.g. Some types of white blood cells take in pathogens by endocytosis and then kill them, as body’s response to infection

Vesicle movement in cells

Vesicle move materials within cells

• Can be used to move materials around inside ells
•  e.g. in secretory cells, protein is synthesized by ribosomes on rER and accumulates inside of it
• Vesicles containing proteins bud off the eEr and carry them to the Golgi apparatus
• The vesicles fuse with Golgi, which make protein into its final form, bud off the Golgi and move to the plasma membrane, where protein is secreted
• In a growing cell, the area of the plasma membrane needs to increase
• Phospholipids ae synthesized and become inserted into the rER membrane
• This method can also used to increase the size of organelles

Exocytosis

The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis

• vesicles fuses with the plasma membrane, the contents are then outside of the membrane and therefore outside of the cell
• polypeptides in the enzymes are synthesized by eER, processed in Golgi then carried to the membrane in vesicles for exocytosis
• Also be used to expel waste products
• e.g. removal of excess water from unicellular organisms
• Water is loaded into a vesicle, sometimes called a contractile vacuole, then moved to the plasma membrane for expulsion by exocytosis
• Can be easily seen in paramecium, by using microscope

Simple diffusion

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

• spreading particles
• Particles move from higher concentration to an area of lower concentration
• No need energy it is a passive process
• Involves particles passing between the phospholipids in the membrane
• Can only happen if the phospholipid bilayer is permeable to the particles
• Non-polar oxygen diffuse easily

• The center of membrane is hydrophobic, ions with positive or negative charges cannot easily pass through
• Polar molecules over their surface can diffuse at low rates between the phospholipids of the membrane
• Small polar particles (e.g. ethanol gas/urea) pass through more easily

Facilitated diffusion

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active  transport.