The Endomembrane System

The Endomembrane system

A network of interconnected membranes within cells

Nuclear envelope → ER → Cis golgi → rest of Golgi → trans Golgi

There are many vesicles that mediate between.

Purpose of Organelles

Organelles compartmentalize functions that are not compatible with each other (for example, lysosomes can degrade cells due to acidic pH)

Organelles provide more lipid surface area to carry out functions that need a membrane

Organelles allow concentrations needed for processes to occur more efficiently

Cytosol

Contains many metabolic pathways, protein synthesis, the cytoskeleton

Nucleus

Contains genome, DNA and RNA synthesis

ER

Smooth: where most lipid synthesis happens

Rough: where proteins destined for the plasma membrane/other organelles are distributed

Golgi Apparatus

Stack of membranes close to ER/nucleus. Modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle

Lyosomes

Intracellular degradation

Endosomes

Sorting of endocytosed material

Mitochondria

ATP synthesis by oxidative phosphorylation

Chloroplasts

ATP synthesis and carbon fixation by photosynthesis

Peroxisomes

Oxidative breakdown of toxic molecules

Exocytosis

Secretion of things to the extracellular space

Endocytosis

Import of molecules from outside the cell

Origin of organelles

Organelles in the Endomembrane system arise from invagination of the plasma membrane. Selective pressure favored organelles with organelles.

Protein Sorting

Proteins have different sequences that direct them.

Made in cytosol → mitochondria, nuclear, chloroplast, peroxisomes. Directly imported

Made on ER → ER, Golgi, vesicle, cell membrane, or outside the cell

Relocated signal sequence

How we figured out signal sequences. Attaching signal sequence from one protein to another can indicate where the “barcode” directs cells to go

Retention Signal

Indicates that a protein will stay inside the ER.