13, 14. Intracellular membrane systems, trafficking Flashcards
detoxification, ribosome
detoxification
A process which is typical for liver cells. Lipid-soluble /hydrophobic compounds, drugs and
dangerous substances arising in the body are transformed to water-soluble /hydrophilic
compounds by an enzyme system present in the smooth endoplasmic reticulum of liver cells
(the most important component is cytochrome P450). The hydrophilic molecules can be
released from the body. Mutagenic and/or carcinogenic substances are commonly produced
during detoxification.
ribosome
A two-subunit cellular constituent built up from proteins and RNA (ribosomal RNA, rRNA). It
is found in both prokaryotic and eukaryotic cells. It catalyses the synthesis of proteins
(polypeptides).
macroautophagia, glycosilation
(macro-)autophagy
A process by which a cell decomposes its own components in its lysosomes. An organelle or
cellular constituent separated from the rest of the cell by a membrane is an autophagosome
which is converted to an autolysosome by fusion with a lysosome. It has an important role in
regulating the amount of cell organelles or in elimination of senescent cell components. It
occurs in most cells.
glycosylation
A post-translational modification of proteins by which oligo/monosaccharide residues are
attached to certain amino acid residues of proteins in the rough endoplasmic reticulum and the
Golgi complex. The two most frequent types are N-glycosylation and O-glycosylation. During
N-glycosylation an oligosaccharide residue is linked to an Asn amino acid residue of proteins,
whereas during O-glycosylation a single monosaccharide is attached or several
monosaccharides are attached one after the other to a OH-group found in Ser, Thr or OH-Lys.
ER singnal sequence, ER quality control
ER signal sequence
A sequence composed of ~15-30, mainly hydrophobic, amino acids on the N-terminal of certain
polypeptides. The ER signal sequence binds to the SRP (signal recognition particle) in the
cytoplasm and directs the ribosome to the docking site (signal recognition particle receptor) on
the surface of the ER. Ihe signal sequence is removed by the signal peptidase located in the ER
lumen.
quality control in the ER
The quality control system located in the ER lumen ensures that only correctly folded proteins,
whose appropriate 3D structure has formed spontaneously or with the help of chaperon proteins
(e.g. Bip), can leave the ER. If the faulty conformation of a proteins cannot be corrected, it will
get degraded by proteasomes.
protein sorting *in the golgi(
protein sorting (in the Golgi)
Classification of proteins reaching the Golgi complex takes place in the trans-Golgi network,
whose sorting activity directs proteins into different pathways while trans-Golgi resident
proteins having a Golgi retention signal stay in the trans Golgi network (e.g. sialyltransferase).
The transport pathways from the trans-Golgi network lead to the lysosomes or to the plasma
membrane and beyond (i.e. the extracellular space). The latter, so-called secretory pathways
have two major types: constitutive secretion transporting e.g. extracellular matrix proteins and
regulating secretion transporting e.g. hormones and digestive enzymes.
Snare proteins, endocitosis
SNARE proteins
A compartment-specific molecule pair whose members recognize each other during vesicular
transport. This recognition process ensures the specificity of docking and fusion of vesicles.
The molecule in the donor vesicle membrane and the target organelle membrane is called vSNARE and t-SNARE, respectively. Moreover, they can bind SNAP, a protein necessary for
membrane fusion. Hence their name SNARE, which is the abbreviation for SNAP Receptor.
endocytosis
A process by which cells take up materials in a membrane-enclosed vesicles formed by the
invagination of the plasma membrane. According to the size and solubility of the endocytosed
material it can be classified to pinocytosis (uptake of soluble materials) and phagocytosis
(uptake of particulate matter).
receptro mediado endocytosis, trnasitosis
receptor-mediated endocytosis
Selective uptake of materials by cells. In its most important form a clathrin coat is generated at
the cytoplasmic face of the plasma membrane. These clathrin-coated pits recruit the
transmembrane proteins and their cargo to be endocytosed. Clathrin is bound to the
transmembrane proteins through adaptin. Molecules selectively enriched by transmembrane
receptors in budding clathrin-coated pits are transported to the cell.
transcytosis
Transcellular vesicular transport in which materials taken up by endocytosis at the apical
membrane domain of cells are released without any modification by exocytosis at the
basolateral membrane domain. The process can take place in the opposite direction as well. It
plays a role in transepithelial transports of proteins (e.g. immunoglobulins)
exocitosis , phagocytosisv
exocytosis
A vesicular transport process in which the membrane of a transport vesicle fuses with the
plasma membrane thereby releasing its content to the extracellular space. The membrane of
vesicles causes the rearrangement of the lipid and protein composition of the cell membrane.
phagocytosis
A special type of endocytosis in which larger particles are engulfed by single cell organisms or
cells of multicellular organisms (e.g.by macrophages and neutrophil granulocytes that are
subtypes of white blood cells). In humans, phagocytosis plays a role in preventing different
infections and in the elimination of senescent or apoptotic cells.
clatrhins
clathrin
A coat-forming protein. A clathrin monomer composed of three heavy and three light chains is
arranged in special three-legged, so-called triskelion units, which can oligomerize to form fivesided or six-sided rings (pentagons and hexagons) whose interactions lead to the creation of the
lattice on the cytoplasmic face of clathrin-coated pits or vesicles important in clathrin-mediated
endocytosis.
