The Endomembrane System

An overview of the relationships in the endo-membrane pathway

Where does protein synthesis begin?

• Protein synthesis always begins on free ribosomes in the cytosol

• free ribosomes are ribosomes that are not associated with any membrane and translate proteins in the cytosol

Where do the proteins made from free ribosomes go?

• They either remain the cytosol or are transported to different organelles

• Destinations

Cytosol

Nucleus

Mitochondria

Chloroplasts

Signal Sequence

• Signal sequences direct proteins to different compartments in the cell

• Signal sequences are short stretches of amino acids attached to a polypeptide

• proteins destined for different locations have different protein signals

Nuclear Localization Signal (NLS)

• directs the protein to the nucleus

Destinations for proteins made in the Rough ER

• Rough ER

• Golgi Apparatus

• Lysosomes

• Cell membrane

• Secreted

Endo-membrane System

An interconnected system of membrane-enclosed compartments

• Nuclear Envelope

• Endoplasmic Reticulum

• Golgi Apparatus

• Lysosomes

• Cell membrane

Vesicles

• small membrane enclosed compartments that can carry molecules between compartments within the endo-membrane system

• Vesicles bud off of one compartment, carrying cargo molecules

Budding

Budding is the process driven by protein coat assembly that causes the vesicle membrane to deform to a pit, then branches off

Cargo Molecules

Substances, often proteins, lipids, or signaling molecules that are transported by vesicles

Lumen

The volume/space enclosed by the vesicle membrane

How do new proteins travel from the ER to the Golgi, and what happens there?

• Vesicles

• They are further modified, packaged, and sorted

Steps of the Secretory Pathway

• Free Ribosomes

• Rough Endoplasmic Reticulum

• Vesicular Transport

• Gogli Apparatus

• Secretory Vesicles

• Exocytosis

Protein containing Vesicles from the Rough ER fuse with what face of the Golgi?

Cis Face

In what order does cargo travel in vesicles regarding the golgi apparatus

Cis - medial - Trans GA

Once cargo leaves the trans - golgi, where may it go?

• lysosomes

• Released (Secreted) from the cell

• Embedded in the Cell membrane

Primary Lysosomes

Originate from the Golgi Apparatus

Secondary Lysosomes

form the fusion of the primary lysosome with a phagosome

Phagosome

a vesicle formed around a particle engulfed via phagocytosis

phagocytosis

process in which a cell uses its cell membrane to enclose and engulf a macromolecule or particle in the extracellular environment

Through what process do food molecules enter the cell?

Phagocytosis