Cell biology III Flashcards
What are the three secretory pathways?
1) Exocytosis (bulk secretion)2) Porocytosis (quantal secretion)3) Exosomes and exosome-like vesicles
Exocytosis secretes what types of products?
1) Proteins and enzymes2) Hormones3) Neurotransmitters
In exocytosis, where are the secretory vesicles formed?
Golgi complex
In exocytosis, what do the secretory vesicles fuse with?
Plasma membrane
In exocytosis, what molecules are responsible for the intracellular trafficking of vesicles?
COPs (COat Proteins)
What are the two pathways specific to exocytosis?
1) Constitutive - continuous secretory process - no storage involved2) Regulated - secretory product is stored in secretory vesicles until a signal causes secretion
What is the definition of constitutive exocytosis?
Continuous secretion - no storage involved
What is the definition of regulated exocytosis?
Secretory product is stored in secretory vesicles until a signal causes secretion
What molecules are required for exocytosis?
Calcium and ATP
Calcium and ATP are required for what secretory pathway?
Exocytosis
What is porocytosis?
Quantal release of neurotransmitters
Quantal release of neurotransmitters is characteristic of what secretory pathway?
Porocytosis
What three characteristics define exosomes and exosome-like vesicles?
1) Secretory products are membrane-bound when released into the ECM 2) Discard of unneeded membrane proteins (e.g. TfR)3) May represent biomarker (e.g. for tumor cells)
Where are ribosomes synthesized?
Nucleolus
Where are the proteins in ribosomes synthesized?
Cytoplasm
What are two ways ribosomes are present in the cytoplasm?
1) Individual granules (subunits)2) Polyribosomes (mRNA + ribosomes)
What are two characteristics of polyribosomes?
1) Free in the cytoplasm2) Bound to the ER to form rER
Are ribosomes found in mature erythrocytes?
No
Are polyribosomes found in immature erythrocytes?
Yes
What role do polyribosomes have in immature erythrocytes?
Hemoglobin synthesis
Where are mitochondrial and peroxisomal proteins synthesized?
Cytoplasm
Is the rER basophilic or eosinophilic?
Basophilic
The rER is continuous with what other organelle?
Nuclear envelope
What can you expect to see in protein-secreting cells?
A lot of rER
rER will be a prominent feature of what type of cells?
Protein-secreting cells (e.g. pancreatic acinar cells)
What is the definition of ER stress?
Accumulation of unfolded / misfolded proteins in the ER cisterna
What are the four steps in the Unfolded Protein Response?
1) Chaperone synthesis2) Decreased synthesis of protein3) Export from ER to cytoplasm for proteasomal degradation4) Activation of caspases - apoptosis
In alpha-1-antitrypsin deficiency, what happens in the ER?
Mutant protein aggregates in ER
What disease is characterized by an aggregation of mutant protein in the ER?
Alpha-1-antitrypsin deficiency
Does the sER appear acidophilic or basophilic?
Acidophilic
Why does the sER appear acidophilic?
Lacks basophilic polyribosomes
What are the functions of the sER?
1) Cholesterol synthesis via HMG-CoA reductase2) Steroid synthesis3) Synthesis of phospholipids4) Glycogenolysis
Von Gierke disease is due to a defect in what enzyme?
Glucose-6-phosphatase (or glucose-6-phosphate transporter)
A defect in glucose-6-phosphatase (or glucose-6-phosphate transporter) is the cause of what disease?
Von Gierke disease
What is the presentation in von Gierke disease?
Glycogen accumulation in the cytoplasm and nucleus of affected cells
What are the symptoms of von Gierke disease?
1) Liver enlargement2) Hypoglycemia3) Increased lactate
What happens to the volume of the sER in protracted use of certain drugs and alcohol?
Increase
An increase in sER volume can be seen in what conditions?
Protracted use of certain drugs and alcohol
Where does phospholipid synthesis occur?
Principally in cytosolic lipid monolayer
What molecule is synthesized primarily in the cytosolic lipid monolayer?
Phospholipids
What happens if phospholipid translocators are defective?
Cannot catalyze the flip-flop of phospholipids from one monolayer to another - new bilayer could not be synthesized
What is an important function of the sER in striated muscle cells?
Storage, release, and uptake of calcium
What organelle is implicated in the development of malignant hyperthermia?
sER
The sER is implicated in the development of what condition?
Malignant hyperthermia
What receptor is mutated in malignant hyperthermia?
Ryanodine-1 receptors
Ryanodine-1 receptors are mutated in what condition?
Malignant hyperthermia
In malignant hyperthermia, what does a mutation in ryanodine-1 receptors lead to in the cell?
Excessive movement of Ca 2+ from the sarcoplasmic reticulum into the cytoplasm in response to anesthetic (halothane and succinyl choline)
What is the cause of hyperthermia in anesthetic-induced malignant hyperthermia?
The SR-Ca 2+ pump consumes large quantities of ATP to increase uptake of Ca 2+ (mutated ryanodine-1 receptor pushes Ca 2+ out of SR and into cytoplasm)
What agent is administered to counteract malignant hyperthermia?
Dantrolene
How does Dantrolene interact with ryanodine-1 receptors?
Inhibits SR release of Ca 2+ into cytoplasm
