Cell Structure: Endomembrane System

Endomembrane

System is a network of organelles used for trafficking or macromolecules

Endomembrane System (Function)(and relationship organelle)

Endoplasmic reticulum and Golgi complex are sites for synthesis, processing, and sorting of specific proteins.

• Proteins destined for organelles

• Membrane proteins

• Secreted proteins

Vesicles

Small membrane bound organelles, often used for subcellular transportation, which can bud from or fuse with other membranes.

Proteins are carried in these

• Is generic term for any small membrane bound organelle.

Endosomes

Carry and sort material brought into the cell (what is developed from endocytic vesicles)

Lysosomes

Digest ingested material and unneeded cellular components.

Endoplasmic Reticulum (ER) (Composed)

Cistermae - Tubular membranes and flattened sacs

• Internal space is called the lumen

Endoplasmic Reticulum (ER) (types)

• Rough ER

• Smooth ER

Rough ER (Composed of Ribosomes)

• Has ribosomes (Site of synthesis of membrane proteins) that are built in and transported by vesicles while other proteins are released into the ER lumen

Hydrophobic patches of proteins (What is it)

When translation nascent hydrophobic domains are inserted into the membrane, one at a time.

If they are not proteins are mis-folded.

ER-associated degradation

Form a quality control

Smooth Endoplasmic Reticulum

Site of synthesis of lipids and steroids and site for inactivation and detoxifying potentially harmful substance

Smooth ER (Components)

Lipids

Rough ER (components)

Membrane Proteins

Golgi Apparatus (function)

Molecules synthesized in the ER for processing and packaging for transport.

Glycosylation

Begins in ER and ends in the golgi

Transition vesicles

Molecules made in ER that are shipped to the golgi by these vesicles

Shuttle vesicles

Used for transport within the golgi

Secretory vesicles (or transport vesicles)

Molecules more to other locations in the cell through transport vesicles or secretory vesicles that bud from the golgi and are packaged to leave the cell.

Structure of Golgi Apparatus

• CGN: cis golgi network (near the ER)

• Medial cisternae (between CGN and TGN)

• TGN (trans golgi network, far from ER)

• Cis/trans indicates location and direction of movement

Secretory Vesicles (Movements)

Moves to the plasma membrane and fuses with it, releasing its contents outside the cell (exocytosis)

Forming Vesicles

1) Small segment of the plasma membrane folds inward

2) Then pitches off to form an endocytic vesicle containing ingested substances or particles (steps 2-4)

Flow of molecules to and from the membrane

• Exocytosis adds lipids and proteins to plasma membrane

• Endocytosis removes lipids and proteins from plasma membrane

It is important that steady-state composition results in balance between the two

Endosomes (form vesicles)

Happens early and acquired digestive enzymes from TGN

Phagocytosis (basic function)

Cellular ‘eating’:

• Ingestion of solid particles

how some organisms acquire food

Lysosomes (pH-dependent hydrolytic enzymes)

• Acid hydrolases (like in the stomach)

• Lysosomes are acidified to pH of 4-5

• They degrade and recycle macromolecules

The motivation molecule (exocytosis)

Dopamine is a neurotransmitter

• Released by exocytosis into the synaptic space between two neurons

Binds dopamine receptors to activate target neurons

• Ex: mice that cannot convert tyrosine to L-DOPA are ‘dopamine-deficient’.