Vesicular transport

Name 2 ways small molecules travel across the membrane

Passive transport

Active transport

How do large molecules travel across the membrane

Using vesicles

Name 2 types vesicular transport

Exocytosis

Endocytosis

Exocytosis?

secretions of macromolecules through fusion of vesicles with the plasma membrane.

Endocytosis?

cell takes in macromolecules by forming new vesicles from the plasma membrane.

Describe process of budding and fusion

Budding from donor

Fusion with target

Membrane is transferred

Proteins retain original configuration

Soluble components transferred

pathways

Describe composition and function of vesicles

Form part of the endomembrane system

Small membrane-bound sacs

Transport or store substances

Membrane is made of two layers = lipid bilayer

Vesicles can fuse with organelles to release their contents within the cell

Vesicles can also fuse with the cell/plasma membrane and release their contents outside of the cell

Name 6 types of vesicles

Vacuoles

Lysosomes

Peroxisomes

Endosomes

Transport vesicles

Secretory vesicles

Exocytosis process, name 2 types

Constitutive exocytosis

Regulated exocytosis

Constitutive exocytosis?

Steady stream of transport vesicles from trans Golgi to plasma membrane.

New lipids and proteins are continuously supplied to the plasma membrane for membrane growth, rejuvenation and remodelling

Regulated exocytosis?

Functions only in cells specialised for secretion.

Lots of secretory vesicles found in specialised secretory cells hormones, mucous, digestive enzymes

Extracellular signal will stimulate their fusion with the plasma membrane and release into the extracellular fluid

Endocytosis?

New vesicles are formed by the plasma membrane. • It is the reverse process of exocytosis, using different proteins. • Plasma membrane pinches in to form a vesicle containing extracellular material. • Three types of endocytosis.

Name 3 types of  endocytosis and describe

PHAGOCYTOSIS is engulfment of a particle, usually food or microorganisms, by wrapping cell membrane around it to form a vacuole.

2. PINOCYTOSIS is the same process except that fluids are taken into small vesicles.

3. RECEPTOR-MEDIATED ENDOCYTOSIS is where receptors in a receptor-coated pit interact with a specific protein, initiating formation of a vesicle

Phagocytosis?>

• A cell engulfs a particle, wrapping pseudopodia around it and packaging it into a membrane enclosed sac large enough to be classified as a vacuole. • The particle is digested after the vacuole fuses with a lysosome containing hydrolytic enzymes

Pinocytosis?

The cell ‘gulps’ droplets vesicles. of extracellular fluid in tiny • Example: Droplets of extracellular fluid enters the cells via small vesicles. • Pinocytic vesicles are returned to the cell surface after ingestion.

Receptor mediated endocytosis

Selective uptake of specific macromolecules from extracellular fluid occurs via receptor proteins in the membrane. Ligands bind to these receptors, which are clustered in ‘coated pits’—areas lined on the cytoplasmic side with special proteins.
Example: Cholesterol, carried in the blood as low-density lipoproteins (LDLs), binds to LDL receptors on the membrane.

Name 3 types of coated vesicles

CLATHRIN

COP I

COP II

Clathrin?

comprised of 3 light chains and 3 heavy chains. • Clathrin coated vesicles traffic between the golgi network and the lysosomes; and between the plasma membrane and the endosomes. • Triskelions form a framework of hexagons and pentagons to form coated pits on the membrane surface.

Formation of a clathrin coated vesicle process?

Molecules bind to surface receptors of the plasma membrane proteins located in areas of clathrin-coated pits. 2. Pits bud to form clathrin-coated vesicles. 3. Fusion with endosomes or lysosomes

Endosomes?

Endosomes appear as a complex membrane tubes and larger vesicles. • Two populations of endosomes: set of connected • Early endosomes Late endosomes (near nucleus) Endosome – main sorting station in the endocytic pathway