Endomembrane System

Functions of endomembrane system

storage + trafficking, metabolism, detoxification

organelles of endomembrane system

Plasma membrane, nuclear envelope, endoplasmic reticulum, golgi apparatus, lysosomes, vacuoles

Gated transport

protein trafficking vis protein channels or pores in the nuclear envelope

transmembrane transport

protein trafficking via protein translocation channels in the ER

Vesicular transport

protein trafficking via membrane bound intermediates traveling between the ER and golgi apparatus

Smooth ER functions

synthesis of steroid hormones, sequestering of Ca2+ ions, detoxification in liver, synthesis of membrane lipids (only cytostolic side)

Rough ER functions

protein synthesis by bound ribosomes, protein translocation, protein modification, folding, quality control, and export

signal recognition particle

interacts with the signal peptide of proteins made for the endomembrane system and directs it to the correct place to be implanted into the membrane

transitional ER

site of exit from the ER and entry to the secretory pathway, in mutual feedback with golgi apparatus

Golgi apparatus

receiving & shipping center consisting of flattened membranous sacs called cisterna, has cis and trans faces that differ in structure and function

Golgi Apparatus functions

receives newly synthesized proteins from the ER and modifies them (proteolysis, hydroxylation, modifying carbohydrate chains); sorts and ships materials into transport vesicles

Coat proteins

different ones of these tag different steps in the secretory and endocytic pathways of vesicular transport

lysosomes

digestive compartments made of membranous sacs of hydrolytic enzymes

lysosome functions

fuses with food vacuoles and digests its contents, recycle the cell’s organelles and macromolecules by autophagy

acid hydrolases

enzymes found in lysosomes, only have optimal activity at an acidic pH to prevent them from hydrolysing anything outside of lysosomes

autophagy

degrades unwanted proteins and organelles and recycles their components, regulated by nutrient availability

mitophagy

selective autophagy that is mediated by receptors on the autophagosome membrane

Vacuoles

diverse maintenance compartments made of large vesicles derived from the ER or golgi apparatus

contractile vacuoles

found in freshwater protists to pump excess water out of cells

central vacuoles

found in plant cells and contain sap, a repository of inorganic ions

digestive vacuoles

plant’s version of lysosomes

storage vacuoles

found in plants for reserves

Peroxisomes

oxidative organelles which are specialized metabolic compartments bounded by a single membrane; breaks down various substances to form hydrogen peroxide

Catalase

enzyme found in peroxisomes that decomposes hydrogen peroxide to water