the endomembrane system

what is the endoplasmic reticulum

a network of membrane tubules

functions of smooth endoplasmic reticulum

involved in lipid biosynthesis

calcium storage for signalling

functions of rough endoplasmic reticulum

protein production, modification, folding, packaging

what happens during packaging of proteins

protein wound in a membrane-bound vesicle

what is the Golgi apparatus

a series of flattened membrane discs (cisternae)

structure of Golgi apparatus

3 sides - cis, medial, trans

cis is receiving end → faces ER

trans is dispatching end → faces PM

function of Golgi apparatus

modifies proteins and lipids, preparing them for transport

how does Golgi modification work

receives protein-containing vesicles which fuse with cis cisternae, vesicles move through the ordered discs, and specific reactions take place (adding oligosaccharides)

where can proteins be synthesised

cytosolic ribosomes or the RER

depends on their eventual location

examples of proteins synthesised on free ribosomes

cytosolic enzymes, cytoskeleton proteins, cytosolic regulators

what do secretory proteins carry

a signal peptide

structure of a signal peptide

N terminal 16-30 amino acids

signal peptide function

directs the secretory protein to the ER and is cleaved upon entry

what happens to newly synthesises proteins upon entering ER

undergo processing

examples of protein processing

cleavage of signal peptides and glycosylation (addition of carbohydrate)

when can proteins leave the ER

when fully folded and assembled

what do chaperone proteins do

use energy to fold proteins into their proper shape

what happens after proteins move through the Golgi

packaged into secretory vesicles, which bud off and fuse with the plasma membrane (exocytosis)

which proteins help the vesicle fuse with the plasma membrane

v-SNARES and t-SNARES

what are lysosomes

membrane-bound organelles containing digestive enzymes

how are lysosomes and their enzymes produced

lysosomes produced by Golgi, enzymes by RER

what is the name of the digestive enzymes contained by lysosomes

acid hydrolases

how do lysosomes maintain their acidic pH 5

through proton pumps which actively pump H+ ions from the cytosol

what is autophagy

controlled digestion of cytosolic materials, degrading unwanted proteins or organelles

what are peroxisomes

main sites of oxygen utilisation

function of peroxisomes

contains oxidative enzymes to perform oxidation reactions without energy production

examples of oxidative enzymes

catalase, urea oxidase

pathways to lysosomes

from autophagosome/phagosomes

endocytotic vesicle → late endosome

Golgi → late endosome