Kapitel 13 Flashcards Preview

Molecular Biology of the Cell > Kapitel 13 > Flashcards

Flashcards in Kapitel 13 Deck (64)

Hydrolytic enzymes—including proteases - nucleases - glycosidases - lipases - phospholipases - phosphatases - and sulfatases—that work best at acidic pH; these enzymes are found within the lysosome.

acid hydrolases


General term for a protein that functions solely to link two or more different proteins together in an intracellular signaling pathway or protein complex. (Figures 13–9 and 15–10)

adaptor proteins


Monomeric GTPase in the Ras superfamily responsible for regulating both COPI coat assembly and clathrin coat assembly. (Table 15–5 - p. 854)

ARF proteins


Organelle surrounded by a double membrane contains engulfed cytoplasmic cargo in the initial stages of autophagy.



Digestion of cytoplasm and worn-out organelles by the cell’s own lysosomes.



The membrane components and soluble molecules carried by transport vesicles.



Invaginations at the cell surface that bud off internally to form pinocytic vesicles. Thought to form from lipid rafts - regions of membrane rich in certain lipids.

caveola (plural caveolae)


Family of unusual integral membrane proteins that are the major structural proteins in caveolae -



Face on the same or near side.

cis face


Network of fused vesicular tubular clusters that is closely associated with the cis face of the Golgi apparatus and is the compartment at which proteins and lipids enter the Golgi.

cis Golgi network (CGN)


One hypothesis for how the Golgi apparatus achieves and maintains its polarized structure and how molecules move from one cisterna to another. This model views the cisternae as dynamic structures that mature from early to late by acquiring and then losing specific Golgi-resident proteins as they move through the Golgi stack with cargo.

cisternal maturation model


Protein that assembles into a polyhedral cage on the cytosolic side of a membrane so as to form a clathrin-coated pit - which buds off by endocytosis to form an intracellular clathrin-coated vesicle. (Figure 13–6)



Specialized regions typically occupying about 2% of the total plasma membrane area at which the endocytic pathway often begins.

clathrin-coated pits


Coated vesicles that transport material from the plasma membrane and between endosomal and Golgi compartments.

clathrin-coated vesicles


Members of a family of monomeric GTPases that have important roles in vesicle transport - being responsible for coat assembly at the membrane.

coat-recruitment GTPases


Small membrane-enclosed organelle with a cage of proteins (the coat) on its cytosolic surface. Formed by the pinching off of a coated region of membrane (coated pit). Some coats are made of clathrin - others are made from other proteins.

coated vesicle


Broad class of N-linked oligosaccharides - attached to mammalian glycoproteins in the endoplasmic reticulum and modified in the Golgi apparatus - containing N-acetylglucosamine - galactose - sialic acid - and fucose residues.

complex oligosaccharides


Pathway present in all cells by which molecules such as plasma membrane proteins are continually delivered to the plasma membrane from the Golgi apparatus in vesicles that fuse with the plasma membrane. The default route to the plasma membrane if no other sorting signals are present. (Figure 13–63)

constitutive secretory pathway


Coated vesicles that transport material early in the secretory pathway - budding from Golgi compartments.

COPI-coated vesicles


Coated vesicles that transport material early in the secretory pathway - budding from the endoplasmic reticulum.

COPII-coated vesicles


The transport pathway of proteins directly to the cell surface via the nonselective constitutive secretory pathway - entry into which does not require a particular signal.

default pathway


Cytosolic GTPase that binds to the neck of a clathrin-coated vesicle in the process of budding from the membrane - and which is involved in completing vesicle formation.



Common receiving compartment with which most endocytic vesicles fuse and where internalized cargo is sorted either for return to the plasma membrane or for degradation by inclusion in a late endosome.

early endosome


Vesicle formed as material ingested by the cell during endocytosis is progressively enclosed by a small portion of the plasma membrane - which first invaginates and then pinches off to form the vesicle.

endocytic vesicle


Uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membrane-enclosed vesicle. See also pinocytosis and phagocytosis.



Process by which early endosomes mature to late endosomes and endolysosomes; in the conversion process - the endosome membrane protein composition changes - the endosome moves from the cell periphery to close to the nucleus - and the endosome ceases to recycle material to the plasma membrane and irreversibly commits its remaining contents to degradation.

endosome maturation


Four protein complexes (ESCRT-0 - ESCRT-1 - ESCRT-2 - and ESCRT-3) that act sequentially to shepherd mono-ubiquitylated membrane proteins on endosomal membranes into intralumenal vesicles. ESCRT-3 complex catalyzes the pinching-off reaction.

ESCRT protein complexes


Excretion of material from the cell by vesicle fusion with the plasma membrane; can occur constitutive or be regulated.



Complex organelle in eukaryotic cells - centered on a stack of flattened - membrane-enclosed spaces - in which proteins and lipids transferred from the endoplasmic reticulum are modified and sorted. It is the site of synthesis of many cell wall polysaccharides in plants and extracellular matrix glycosaminoglycans in animal cells. (Figure 13–26)

Golgi apparatus (Golgi complex)


Broad class of N-linked oligosaccharides - attached to mammalian glycoproteins in the endoplasmic reticulum - containing two N-acetylglucosamine residues and many mannose residues.

high-mannose oligosaccharides


Compartment formed from a bulbous - vacuolar portion of early endosomes by a process called endosome maturation; late endosomes fuse with one another and with lysosomes to form endolysosomes that degrade their contents.

late endosome


Large complex composed of a single protein molecule and many esterified cholesterol molecules - together with other lipids. The form in which cholesterol is transported in the blood and taken up into cells. (Figure 13–51)

low-density lipoprotein (LDL)


Genetic diseases resulting from defects in or a lack of one or more functional hydrolases in lysosomes of some cells - leading to accumulation of undigested substrates in lysosomes and consequent cell pathology.

lysosomal storage diseases


Membrane-enclosed organelle in eukaryotic cells containing digestive enzymes - which are typically most active at the acid pH found in the lumen of lysosomes. (Figure 13–37)



Transmembrane receptor proteins present in the trans Golgi network that recognize the mannose 6-phosphate (M6P) groups added exclusively to lysosomal enzymes - marking the enzymes for packaging and delivery to early endosomes.

M6P receptor proteins


Phagocytic cell derived from blood monocytes - resident in most tissues but able to roam. It has both scavenger and antigen-presenting functions in immune responses.



Clathrin-independent - dedicated degradative endocytic pathway induced in most cell types by cell-surface receptor activation by specific cargoes.



Intermediates in the endosome maturation process; early endosomes that are on their way to becoming late endosomes.

multivesicular bodies


White blood cell that is specialized for the uptake of particulate material by phagocytosis. Enters tissues that become infected or inflamed. (Figure 24–5)



Hexameric ATPase that disassembles a complex of a v-SNARE and a t-SNARE. (Figure 13–20)



Addition of one or more sugars to a hydroxyl group on a protein.

O-linked glycosylation


Process by which unwanted cells - debris - and other bulky particulate material is endocytosed (“eaten”) by a cell. Prominent in carnivorous cells - such as Amoeba proteus - and in vertebrate macrophages and neutrophils. From Greek phagein - to eat.



Large intracellular membrane-enclosed vesicle that is formed as a result of phagocytosis. Contains ingested extracellular material. (Figure 13–61)



A lipid containing a phosphorylated inositol derivative. Minor component of the plasma membrane - but important in demarking different membranes and for intracellular signal transduction in eukaryotic cells. (Figure 13–10)

phosphoinositides (PIPs; phosphatidylinositol phosphates)


Literally - “cell drinking.” Type of endocytosis in which soluble materials are continually taken up from the environment in small vesicles and moved into endosomes along with the membrane-bound molecules. Compare phagocytosis. (Figure 13–48)



An ordered recruitment of sequentially acting Rab proteins into Rab domains on membranes - which changes the identity of an organelle and reassigns membrane dynamics.

Rab cascade


Molecules that bind activated - membrane-bound Rab proteins and act as downstream mediators of vesicle transport - membrane tethering - and fusion.

Rab effectors


Monomeric GTPase in the Ras superfamily present in plasma and organelle membranes in its GTP-bound state - and as a soluble cytosolic protein in its GDP-bound state. Involved in conferring specificity on vesicle docking. (Table 15–5 - p. 854)

Rab proteins


Internalization of receptor–ligand complexes from the plasma membrane by endocytosis. (Figure 13–52)

receptor-mediated endocytosis


Organelle that provides an intermediate stage on the passage of recycled receptors back to the cell membrane. Regulates plasma membrane insertion of some proteins. (Figure 13–58)

recycling endosome


A second secretory pathway found mainly in cells specialized for secreting products rapidly on demand—such as hormones - neurotransmitters - or digestive enzymes—in which soluble proteins and other substances are initially stored in secretory vesicles for later release. (Figure 13–62)

regulated secretory pathway


Monomeric GTPase responsible for regulating COPII coat assembly at the endoplasmic reticulum membrane.

Sar1 protein


Membrane-enclosed organelle in which molecules destined for secretion are stored prior to release. Sometimes called secretory granule because darkly staining contents make the organelle visible as a small solid object. (Figures 13–65)

secretory vesicle


Members of a large family of transmembrane proteins present in organelle membranes and the vesicles derived from them. SNAREs catalyze the many membrane fusion events in cells. They exist in pairs—a v-SNARE in the vesicle membrane that binds specifically to a complementary t-SNARE in the target membrane.

SNARE proteins (SNAREs)


Small neurotransmitter-filled secretory vesicle found at the axon terminals of nerve cells. Its contents are released into the synaptic cleft by exocytosis when an action potential reaches the axon terminal.

synaptic vesicle


Transmembrane SNARE protein - usually composed of three proteins and found on target membranes where it interacts with v-SNAREs on vesicle membranes.



Face on the other (far) side.

trans face


Network of interconnected tubular and cisternal structures closely associated with the trans face of the Golgi apparatus and the compartment from which proteins and lipids exit the Golgi - bound for the cell surface or another compartment.

trans Golgi network (TGN)


Uptake of material at one face of a cell by endocytosis - its transfer across a cell in vesicles - and discharge from another face by exocytosis. (Figure 13–58)



Cell-surface receptor for transferrin (a soluble protein that carries iron) that delivers iron to the cell interior via receptor-mediated endocytosis and recycling of the receptor–transferrin complex.

transferrin receptor


Membrane-enclosed transport containers that bud from specialized coated regions of donor membrane and pass from one cell compartment to another as part of the cell’s membrane transport processes; vesicles can be spherical - tubular - or irregularly shaped.

transport vesicle


Transmembrane SNARE protein - comprising a single polypeptide chain - usually found in vesicle membranes where it interacts with t-SNAREs in target membranes.



Large fluid-filled compartment found in most plant and fungal cells - typically occupying more than a third of the cell volume. (Figure 13–41)



One hypothesis for how the Golgi apparatus achieves and maintains its polarized structure and how molecules move from one cisterna to another. This model holds that Golgi cisternae are long-lived structures that retain their characteristic set of Golgi-resident proteins firmly in place - and cargo proteins are transported from one cisterna to the next by transport vesicles.

vesicle transport model