Ch. 2 Cell Cytoplasm Flashcards
Specific functions are identified with specific {…} components and domains within the cell.
Structural
What are the two major compartments in which a cell is divided?
1) Cytoplasm
2) Nucleus
The organelles, cytoskeleton, and inclusions contained within the cytoplasm come together to form this aqueous gel compartment.
What is the cytoplasmic matrix?
The cytoplasmic matrix contains a variety of {…}, including inorganic ions and organic molecules.
Solutes
How does a cell influence the rate of metabolic activity within the cytoplasmic compartment/matrix?
The cell controls solute concentration within the matrix
What are the two categories of organelles?
1) Membranous
2) Nonmembranous
What is the key difference between membranous and nonmembranous organelles?
Membranous organelles are surrounded by plasma membranes, while nonmembranous organelles are not
The spaces enclosed by the organelles’ membranes constitute these compartments where substrates, products, and other substances are segregated or concentrated.
What are intracellular microcompartments?
Non-organelle structures found within the cytoplasm that are usually not surrounded by a plasma membrane.
What are inclusions?
Lipid bilayer that forms the cell boundary as well as the boundaries of many organelles within the cell.
What is a plasma (cell) membrane?
A region of the endoplasmic reticulum (ER) associated with ribosomes and the site of protein synthesis and modification of newly synthesized proteins.
What is the rough ER (rER)?
A region of the endoplasmic reticulum (ER) involved in detoxifying xenobiotics (foreign drugs or chemicals) and synthesis of lipids and steroids but not associated with ribosomes.
What is the smooth ER (sER)?
A membranous organelle composed of multiple flattened cisternae responsible for modifying, sorting, and packaging proteins and lipids for intracellular or extracellular transport.
What is the Golgi apparatus?
Membrane-bounded compartments interposed within endocytic pathways that have the major function of sorting proteins delivered to them via endocytic vesicles and redirecting them and redirecting them to different cellular compartments for their final destination.
What are endosomes?
Endosome-derived, membrane-bound vesicles released via exocytosis that act as mediators for near- and long-distance communication between cells.
What are exosomes?
Where do exosomes originate from?
The lumen of multivesicular bodies
Small organelles containing digestive enzymes that are formed from endosomes by targeted delivery of unique lysosomal membrane proteins and enzymes.
What are lysosomes?
Vesicles that are involved in both endo- and exocytosis and vary in shape and the material that they transport.
What are transport vesicles?
List 3 examples of transport vesicles mentioned in the text.
1) Pinocytic
2) Endocytic
3) Coated
Organelles that provide most of the cell by producing adenosine triphosphate (ATP) in the process of oxidative phosphorylation.
What are mitochondria?
Small organelles involved in an oxidative type of metabolism. They are involved in the degradation of fatty acids and production and degradation of reactive oxygen intermediates.
What are peroxisomes?
Microtubes, which together work with {…} and {…} filaments, form elements of the cytoskeleton and continuously elongate and shorten.
1) Actin
2) Intermediate
How do microtubules elongate and shorten?
By adding or removing tubulin dimers
What is the continuous elongation and shortening of microtubules referred to as?
Dynamic instability
What are the 2 classifications of cytoskeletal filaments?
1) Actin filaments
2) Intermediate filaments
This type of cytoskeletal filament is a flexible chain of actin molecules.
What is an actin filament?
This type of cytoskeletal filament consists of rope-like fibers formed from a variety of proteins.
What is an intermediate filament?
What is the purpose of intermediate filaments?
To provide tensile strength to withstand tension and confer resistance to shearing forces
Short, paired cylindrical structures found in the center of the microtubule-organizing center.
What are centrioles?
What is another name for the microtubule-organizing center?
The centrosome
Derivatives of the centrioles give rise to the…
Basal bodies of cilia
Structures essential for protein synthesis and composed of ribosomal RNA (rRNA) and ribosomal proteins.
What are ribosomes?
Protein complexes that enzymatically degrade damaged and unnecessary proteins into small polypeptides and amino acids.
What are proteasomes?
What is the name for the current interpretation of the molecular organization of the plasma membrane?
The modified fluid-mosaic model
What 3 molecules primarily comprise the plasma membrane?
1) Phospholipid
2) Cholesterol
3) Protein
The plasma membrane is described as “amphipathic.” What does this mean?
The phospholipids comprising the membrane contain polar (hydrophilic) heads and nonpolar (hydrophobic) tails
How much of the plasma membrane’s mass do protein molecules make up?
Approximately half of the total membrane mass
This type of membrane protein is either embedded in the lipid bilayer or passes through it completely.
What is an integral membrane protein?
This type of membrane protein isn’t embedded in the lipid bilayer, but it holds strong ionic interactions with integral proteins along the extra- and intracellular surfaces of the plasma membrane.
What is a peripheral membrane protein?
On the extracellular surface of the membrane, carbohydrates may attach to proteins, forming {…}, and they can even attach to the lipids of the bilayer, forming {…}.
1) Glycoproteins
2) Glycolipids
Glycoproteins and glycolipids constitute a layer at the surface of the cell, colloquially referred to as this structure.
What is the cell coat?
What is the scientific term for the cell coat?
Glycocalyx
List 4 functions of the glycocalyx.
1) Metabolism
2) Cell recognition
3) Cell association
4) Receptor sites for hormone
Localized regions (i.e., MICRODOMAINS) of the cell membrane containing high concentrations of CHOLESTEROL and GLYCOSPHINGOLIPIDS.
What are lipid rafts?
What is the function of lipid rafts?
To control the movement and distribution of proteins within the lipid bilayer
What are the 2 types of lipid rafts?
1) Planar lipid rafts
2) Caveolar rafts (caveolae)
This type of lipid raft is the larger of the 2 types that contains proteins known as FLOTILLINS (47-kDa).
What are planar lipid rafts?
What are the 4 functions of flotillins?
1) Serve as molecular markers
2) Serve as scaffolding proteins
3) Recruiting specific membrane proteins into rafts
4) Serve as active partners in various signaling pathways
This type of lipid raft is the smaller of the two and represents small, flask-shaped invaginations containing integral membrane proteins called caveolins (18- to 24-kDa).
What are caveolar rifts?
How do caveolins create invaginations in the cell membrane?
The oligomerization of caveolins creates a caveolin scaffold
What types of cells are caveolae most prominent in?
Smooth muscle cells
What 3 structures will you find along the caveolae in smooth muscle cells?
NOTE: Lots of ions, particularly calcium
1) Calcium ion channels
2) Sodium/calcium ion exchangers
3) G protein-coupled receptors
What is the function of the G-couple protein receptors contained within caveolae?
Ligand-mediated regulation of intracellular calcium levels
What does the term SIGNALING PLATFORMS refer to when talking about lipid rafts?
The variety of integral and peripheral membrane proteins within the lipid raft that are involved in cell signaling
What is the role of lipid rafts in bacterial and viral infections?
The lipid raft serves as the initial point of contact for the microbe, from where they utilize the rafts in some way to gain entry into the cell
This tissue preparation technique was used to visualize the existence of the plasma membrane’s integral proteins.
What is freeze fracture?
What does the freeze-fracture tissue prep entail?
Cleaving the membrane along the hydrophobic plane to expose the inner membrane faces, referred to as the E- and P-faces
What is the difference between E-face and P-face?
(E)-face - backed by (E)xtracellular space
(P)-face - backed by cytoplasm/(P)rotoplasm
Where will you typically find more proteins? Along the E-face or P-face?
P-face
What are the 6 broad categories of membrane proteins?
1) Pumps
2) Channels
3) Receptors
4) Linkers
5) Enzymes
6) Structural proteins
This type of membrane protein actively transports specific ions and metabolic precursors of macromolecules across membranes.
What is a pump?
This type of membrane protein allows the passage of small ions, molecules, and water across the plasma membrane in either direction (i.e., passive diffusion).
What is a channel?
This type of membrane protein allows recognition and localized binding of ligands in processes such as hormonal stimulation, coated vesicle endocytosis, and antibody reactions.
What is a receptor protein?
This type of membrane protein anchors the intracellular cytoskeleton to the extracellular matrix (e.g., fibronectin).
What is a linker protein?
This type of membrane protein has various roles as biological catalysts (e.g., ATPases, disaccharidases, dipeptidases, etc.).
What is an enzyme?
This type of membrane protein is visualized by the FREEZE-FRACTURE method, especially where they form junctions with neighboring cells.
What is a structural protein?
What is meant when the 6 categories of membrane proteins are referred to as NOT MUTUALLY EXCLUSIVE?
Each category is capable of functioning as any of the other proteins
What contributes to the fluidity of the plasma membrane?
The various types of phospholipids in local concentrations
Given that the FLUID MOSAIC MODEL describes the plasma membrane’s behavior, can it be said that particles are capable of moving along the cell surface?
Yes
Why is the lateral migration of proteins across the membrane limited by physical connections between membrane proteins and intracellular or extracellular structures? List 2 reasons.
1) These connections localize/restrict proteins to specialized regions of the plasma membrane
2) These connections act as transmembrane linkers between intra- and extracellular filaments
What are the 2 types of membrane remodeling?
1) Remodeling that excludes cytoplasm (from the lumen of forming vesicles/tubules)
2) Remodeling that includes cytoplasm (within the newly formed structures)
Remodeling that EXCLUDES CYTOPLASM from the lumen of forming vesicles, such as during the formation of {…} vesicles.
Endocytic
In plasma membrane remodeling that EXCLUDES CYTOPLASM, proteins residing on the {…} (cytoplasmic) membrane change the shape of the plasma membrane into vesicle-like {…}.
1) Inner
2) Invaginations
The {…} family of membrane scission proteins is essential to mediate the liberation of the vesicles from the plasma membrane during the formation of endocytic vessels.
Dynamin
Similar invaginations, as seen during the formation of endocytic vessels, can be found in muscle cells, where {…} are connected to the external cell environment.
T tubules
In smooth muscle cells, {…} and endocytic vessels help regulate calcium homeostasis.
Caveolae
In remodeling that INCLUDES CYTOPLASM within newly formed structures, cytoplasmic-embedded {…} particles bud from the cell membrane.
Viral
This protein complex participates in the formation of multivesicular bodies (MVBs), exosomes, microvesicles, apoptotic bodies, the resealing of the post-mitotic nuclear envelope, and the closure of autophagosomes. Additionally, it controls the remodeling of the membrane and the liberation of vesicles or the scission of tubules filled with cytoplasm.
What is the endosomal sorting complex required for transport (ESCRT complex)?
This term refers to the cytoplasmic separation into two daughter cells during cell division.
What is cytokinetic abscission?
Cell injury often manifests as morphologic changes in the cell’s plasma membrane that result in the formation of these detachments of the plasma membrane from underlying actin filaments of the cell cytoskeleton.
What are plasma membrane blebs?
These toxins act on actin filaments to cause extensive membrane blebbing.
What are cytoskeletal toxins?
List 3 viral infections in which the ESCRT complex is hijacked during virus budding at the surface of infected host cells.
1) HIV
2) Ebola
3) T-lymphotropic virus
The process by which extracellular stimuli are received, processed, and conveyed by the cell to regulate its own physiologic responses.
What is cell signaling?
Mechanisms by which cells respond to the external environment.
What are signal transduction pathways?
Signal transduction pathways are initiated by {…} molecules, which are also referred to as {…} messengers or {…}.
1) Signaling
2) Primary
3) Ligands
Signals from receptors are conveyed to target molecules inside the cell via this system.
What is the second messenger system?
What are the 3 classifications of receptors?
1) Channel proteins
2) Intracellular receptors
3) Cell surface receptors
An intercellular communication pathway in which functional proteins, metabolites, and nucleic acids are delivered to recipient cells using exosomes as transfer vehicles.
What is exosomal signaling?
The very small, membrane-bound cargo vesicles that are secreted into extracellular space by virtually every prokaryotic and eukaryotic cell.
What are exosomes?
These modifications of intracellular proteins contribute to the amplification of a signal that a cell receives.
What are posttranslational modifications?
This posttranslational modification involves the addition of phosphate groups.
What is phosphorylation?
This posttranslational modification involves the addition of a diverse selection of sugar moieties (i.e., functional groups).
What is glycosylation?
This posttranslational modification involves adding acetyl functional groups.
What is acetylation?
This posttranslational modification involves the reaction of nitric oxide [NO] with protein-free cysteine residues.
What is nitrosylation?
This posttranslational modification involves attaching ubiquitin protein.
What is ubiquitination?
This posttranslational modification involves the addition of small ubiquitin-related modifier [SUMO] protein.
What is SUMOylation?
This family of enzymes mediates the phosphorylation of cellular proteins.
What is protein kinase?
This family of enzymes mediates the dephosphorylation of cellular proteins.
What is protein phosphatase?
This class of protein kinases includes enzymes such as cyclic adenosine monophosphate (cAMP)-dependent protein kinase.
What are second messenger-dependent protein kinases?
This class of protein kinases includes enzymes such as mitogen-activated protein kinase (MAPK), cyclin-dependent kinase (Cdk), and protein tyrosine kinase.
What are second messenger-independent protein kinases?
The transfer of substances across the plasma membrane down their concentration gradient without the expenditure of metabolic energy and without the help of transport proteins.
What is simple/passive diffusion?
All other molecules that cannot simply cross the plasma membrane without aid must employ the use of these proteins
What are membrane transport proteins?
Generally speaking, what are the 2 classes of transport proteins?
Carrier & channel proteins
How are carrier & channel proteins similar?
They both transfer small, water-soluble molecules across the membrane
How are carrier & channel proteins different?
Carrier proteins can engage in both active AND passive transport, while channel proteins only engage in passive transport
Some carrier proteins, such as ion pumps, require energy for {…} transport of molecules against their concentration or electrochemical gradient. Others, such as glucose carriers, do not require energy and participate in {…} transport.
1) Active
2) Passive
Channel proteins usually contain this domain, which partially penetrates the membrane bilayer and serves as an ion-selectivity filter.
What is a pore domain?
What are 3 ways to regulate channel protein transport?
1) Membrane potentials
2) Neurotransmitters
3) Mechanical stress
Give an example of a channel protein that utilizes membrane potential.
Voltage-gated ion channels found in neurons
Give an example of a channel protein that utilizes a neurotransmitter.
Ligand-gated ion channels, such as acetylcholine receptors in muscle cells
Give an example of a channel protein that utilizes mechanical stress.
Mechanically gated ion channels in the inner ear
A process that involves configurational changes in the plasma membrane at localized sites and subsequent formation of vesicles from the membrane or fusion of vesicles with the membrane, allowing substances to enter and leave cells.
What is vesicular transport?
The major mechanism by which large molecules enter, leave, and move within the cell.
What is vesicle budding?
What is the key difference between endo- and exocytosis?
Endocytosis - uses vesicular transport to bring substances into the cell
Exocytosis - uses vesicular transport to move substances out of the cell
Recent experimental studies have revealed that neurotoxins from these two bacteria can block exo- and endocytosis.
What are tetanus and botulinum?
These are proteins that mediate exocytosis and vesicular membrane fusion, as well as have a role in initiating endocytosis.
What are SNARE proteins?
Do SNARE proteins play a role in initiating endocytosis or exocytosis?
Endocytosis
The best-known protein that interacts with the plasma membrane in vesicle formation.
What is clathrin?
What is the difference between clathrin-dependent and clathrin-independent endocytosis?
Dependent - utilizes clathrin protein for vesicle formation
Independent - utilizes other proteins (i.e., caveolins & flotillins) for vesicle formation
List the 3 major mechanisms for endocytosis.
1) Pinocytosis
2) Phagocytosis
3) Receptor-mediated endocytosis
One of two different pinocytotic pathways involving the nonspecific ingestion of fluid and small protein molecules via vesicles.
What is micropinocytosis?
Why is micropinocytosis considered constitutive?
NOTE: Think about what this means for vesicle formation
It involves a continuous dynamic formation of vesicles at the cell surface
What 2 proteins associated with lipid rafts will you see within micropinocytosis?
Caveolin and flotillin
Why is MICROPINOCYTOSIS considered both a CLATHRIN-INDEPENDENT & ACTIN-INDEPENDENT endocytosis?
1) It utilizes caveolins & flotillins
2) It doesn’t require remodeling of the actin cytoskeleton
One of two different pinocytotic pathways involving a nonspecific uptake mechanism for extracellular fluids, solutes, nutrients, and antigens.
What is macropinocytosis?
What causes the SURFACE MEMBRANE RUFFLES present during MACROPINOCYTOSIS?
Rearrangement of the actin cytoskeleton at the plasma membrane
NOTE: This also makes MACROPINOCYTOSIS a form of ACTIN-DEPENDENT endocytosis
The large endocytic vacuoles that occur due to the SURFACE MEMBRANE RUFFLES caused by MACROPINOCYTOSIS.
What are macropinosomes?
This form of endocytosis involves the ingestion of large particles such as cell debris, bacteria, and other foreign materials.
What is phagocytosis?
Large vesicles (i.e., pseudopodia) sent out by the plasma membrane to engulf phagocytized particles.
What are phagosomes?
Small molecular structures commonly expressed on pathogen surfaces by toll-like receptors that trigger phagocytosis.
What are pathogen-associated molecular patterns (PAMPs)?
Why is PHAGOCYTOSIS considered CLATHRIN-INDEPENDENT but ACTIN-DEPENDENT endocytosis?
1) Phagosome formation doesn’t require clathrin
2) The actin cytoskeleton must be rearranged in a process that requires depolymerization and repolymerization of the actin filaments
This form of endocytosis allows the entry of specific molecules into the cell via CARGO RECEPTORS, which accumulate in well-defined regions of the cell membrane, which are represented by the lipid rafts and eventually become COATED PITS.
What is receptor-mediated endocytosis?
During receptor-mediated endocytosis, clathrin interacts with the cargo receptor via these proteins, which are instrumental in selecting appropriate cargo molecules for transport into the cells.
What are clathrin adaptor proteins (adaptin, AP180)?
Which 2 forms of endocytosis utilize the dynamic GRPase family of membrane scission proteins?
1) Micropinocytosis
2) Receptor-mediated endocytosis
In this exocytosis pathway, substances designated for export are continuously delivered in transport vesicles to
the plasma membrane. Proteins that leave the cell by this process are SECRETED IMMEDIATELY after their synthesis and exit from the Golgi apparatus, as seen in the secretion of immunoglobulins by plasma cells and procollagen by fibroblasts. THIS PATHWAY IS PRESENT TO SOME DEGREE IN ALL CELLS.
What is the constitutive pathway?
In this exocytosis pathway, SPECIALIZED CELLS, such as endocrine and exocrine cells and neurons, concentrate secretory proteins and transiently store them in secretory vesicles within the cytoplasm. In this case, A REGULATORY RESPONSE (hormonal or neural stimulus) MUST BE ACTIVATED FOR SECRETION to occur, as in the release of secretory vesicles by chief cells of the gastric mucosa and by acinar cells of the pancreas.
What is the regulated secretory pathway?
The precise targeting of vesicles to the appropriate cellular compartment is initially controlled by {…} proteins, and specificity is ensured by interactions between {…} proteins.
1) Docking
2) SNARE
A {…} mechanism can be likened to a taxi driver in a large city who successfully delivers a passenger to the proper street address.
Targeting
In the cell, the street address is recognized by {…} bound to the membrane of the traveling vesicle.
Rab-GTPase
Rab-GTPase interacts with {…} proteins located on the target membrane. This initial interaction provides recognition of the vesicle and recruits the necessary number of tethering proteins to dock the incoming vesicle.
Tethering
The {…} complex between Rab-GTPase and its receptor immobilizes the vesicle near the target membrane
Docking
The {…} family of small transmembrane proteins (name derived from “Soluble NSF Attachment REceptor”) is expressed on both the vesicles and target membranes to mediate accurate vesicle trafficking and subsequent membrane fusion.
SNARE
The {…} SNARE (i.e., v-SNARE) interacts with the target plasma membrane that contains {…} (i.e., t-SNARE).
NOTE: Both blanks are hyphenated terms
1) Vesicle-specific
2) Target-specific
When a vesicle reaches its destination membrane, both groups of SNARE proteins located on separate membranes must recognize each other and assemble into a tight α-helical configuration called the {…} complex.
Trans-SNARE
What 2 things does the successful assembly of the trans-SNARE complex guarantee?
1) Specificity of interaction between particular vesicle and its particular membrane
2) The fusion of the vesicle and plasma membrane (i.e., membrane fusion)
After the membrane fuses, proteins of the trans-SNARE complexes are located in this single fused membrane and are now referred as {…} complexes.
cis-SNARE
New cis-SNARE complexes are dismantled with the help of the {…} protein complex and recycled for use in another round of vesicle fusion.
NSF/𝛂-SNAP
In nerve terminals, the smaller integral membrane protein (18-kDa) found in the vesicle (v-SNARE).
What is synaptobrevin?
In nerve terminals, the larger integral membrane protein (33-kDa) found in the presynaptic membrane (t-SNARE).
What is syntaxin?
In nerve terminals, the peripheral membrane protein covalently attached to the intracellular surface of the presynaptic plasma membrane via modified lipid (palmitic acid) in the process called palmitoylation. In addition, it is essential for neurotransmitter release from synaptic terminals, and it is considered a t-SNARE protein.
What is SNAP-25?
The interactions of synaptobrevin, syntaxin, and SNAP-25 are required for 2 key functions. What are these functions?
1) Formation of trans-SNARE complexes
2) Neurotransmitter release
This neurotoxin, produced by the anaerobic bacterium Clostridium botulinum, blocks neuromuscular transmission.
What is botulinum neurotoxin?
There are seven distinct serotypes (A to G) of botulinum toxins, each cleaving the SNARE proteins at different sites. This prevents the release of the neurotransmitter acetylcholine from the neuromuscular terminal and the depolarization of muscle cells. Serotypes B, D, F, and G cleave {…}; serotypes A, C, and E cleave {…}; and serotype C cleaves {…}.
1) Synaptobrevin
2) SNAP-25
3) Syntaxin
In humans, the botulinum neurotoxin A, B, and E serotypes are responsible for {…}, a life-threatening disease characterized by progressive muscle weakness.
Botulism
The botulin toxin serotypes A and B are used therapeutically to treat patients with nerve and muscle disorders. Injection of a small amount of botulin toxin into specific muscles is used in ophthalmology for treating {…} (excessive blinking) or {…} (not aligned eyes).
1) Blepharospasm
2) Strabismus
Another anaerobic bacterium, Clostridium tetani, produces {…} toxin, which causes {…}.
1) Tetanospasmin
2) Tetanus
Tetanospasmin cleaves {…} (v-SNARE protein) and prevents the release of inhibitory neurotransmitters (mainly glycine and γ-aminobutyric acid [GABA]) from synaptic vesicles at the {…} motor nerve endings in the central nervous system.
1) Synaptobrevin
2) Inhibitory
TEM of the cell cytoplasm reveals membrane-enclosed compartments associated with all endocytic pathways. These compartments are restricted to a portion of the cytoplasm near the cell membrane.
What are early (sorting) endosomes?
The contents of vesicles incorporated into early endosomal compartments remain in this compartment. As the early endosome matures, it becomes more acidic and sinks into deeper regions of the cytoplasm to become this type of endosome.
What is a late-sorting endosome?
The ESCRT cytoplasmic protein complex controls membrane remodeling (pages 35-36), which is the basis of the sorting and maturation of early endosomes into late endosomes. The sorting function continues in late endosomes. The endosomal membrane of some late endosomes undergoes inward invagination to generate INTRALUMINAL VESICLES known as these intracellular structures.
What are multivesicular bodies (MVBs)?
Some mature into {…} (where their contents will be degraded), and others fuse with the plasma membrane to release intraluminal vesicles by exocytosis. These extracellular vesicles originating from MVBs are called {…}.
1) Lysosomes
2) Exosomes
This endosomal compartment model describes early and late endosomes as stable cellular organelles that maintain their connection to the external environment of the cell and Golgi apparatus by vesicular transport. Coated vesicles formed at the plasma membrane fuse only with early endosomes because they express specific surface receptors; these receptors remain part of the early endosomal membrane.
What is the stable compartment model?
This endosomal compartment model suggests that early endosomes are formed de novo from endocytic vesicles originating from the plasma membrane. Therefore, the composition of the early endosomal membrane changes progressively as some components are recycled between the cell surface and the Golgi apparatus. This maturation process leads to the formation of late endosomes and, subsequently, lysosomes. As this compartment matures, specific receptors present on early sorting endosomes (e.g., for coated vesicles) are removed by recycling, degradation, or inactivation.
What is the maturation model?
What is the major function of early endosomes?
To sort and recycle proteins internalized by endocytic pathways
The fate of the internalized ligand–receptor complex depends on the sorting and recycling ability of the early endosome. List the 4 scenarios in which ligand-receptor complexes are processed.
1) Receptor recycled, ligand degraded (NOTE: low-density lipoprotein [LPL] receptor complex, insulin-glucose transporter [GLUT] receptor complex, and peptide hormones)
2) Receptor & ligand recycled (NOTE: transferrin & major histocompatibility complex [MHC] I/II)
3) Receptor & ligand degraded (NOTE: epidermal growth factor [EGF])
4) Receptor & ligand transported through the cell (NOTE: secretion of immunoglobulins [secretory IgA] into saliva and human milk)
{…} endosomes can be found in the more peripheral cytoplasm, where the pH is more {…}. On the other hand, {…} endosomes are often positioned near the Golgi apparatus and the nucleus, where the pH is more {…}.
1) Early
2) Basic
3) Late
4) Acidic
Late endosomes destined to become lysosomes receive newly synthesized lysosomal enzymes that are targeted via the {…} (M-6-P) receptor.
Mannose-6-phosphate
Some endosomes also communicate with the vesicular transport system of the rER. This pathway provides constant delivery of newly synthesized lysosomal enzymes, also called these.
What are hydrolases?
A hydrolase is synthesized in the rER as an enzymatically inactive precursor.
What is a prohydrolase?
