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Cell & Tissue Biology > L4: Cell Biology III > Flashcards

L4: Cell Biology III Flashcards

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1
Q

List 3 secretory pathways from the cell

A
  1. ) Exocytosis: bulk secretion
  2. ) Porocytosis: quantal secretion, new model of NT release
  3. ) Exosomes
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2
Q

Exocytosis. What is secreted using this method? Describe where in the cell this occurs? What pathways are used? Energy/substrate requirement?

A
  • Used to secrete proteins/enzymes, hormones and NTs
  • Secretory vesicles are formed by Golgi, fuse with PM. Trafficking within the cell is dictated by COPs (COat ProteinS)
  • Two pathways: a.) constitutive: continuous process as product being secreted is synthesized and directly secreted, ie. not stored. b.) regulated: secreted product is stored in vesicles until signal causes product to be secreted
  • Calcium and ATP
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3
Q

What is released via porocytosis?

A
  • Quantal release of NTs
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4
Q

What are exosomes?

A
  • Secretory products can be released from cells into the EC environment with the products limited by a membrane. Eg. Reticulocytes discard the transferring receptor in this manner
  • Some tumors release exosomes
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5
Q

What structure in the cell is responsible for protein synthesis? Is it basophilic or acidophilic?

A
  • Ribosomes

- Basophilic due to presence of negatively charged phosphate groups

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6
Q

Describe composition of ribosome and where each of the subunits are synthesized

A
  • Composed of protein and rRNA
  • rRNA is synthesized in the nucleolus, proteins are imported into the nucleus and associate with rRNA in nucleolus
  • Subunits are exported to cytoplasm and assembled
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7
Q

In what forms are ribosomes seen?

A
  • Individual granules (ribosomal subunits)

- Polyribosomes with mRNA (free in cytoplasm and bound to ER, forming rER)

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8
Q

Are ribosomes found in erythrocytes?

A
  • Only in immature erythrocytes
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9
Q

What protein is synthesized on free polyribosomes?

A
  • Free polyribosomes synthesize proteins that are generally for use within the cell (ie. not for export or use elsewhere)
  • This includes Hb in immature RBCs, many mitochondrial proteins, proteins in peroxisomes
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10
Q

What are the functions of translocator proteins?

A
  • Move proteins from cytoplasm to peroxisomes and mitochondria
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11
Q

Is the rER basophilic or acidophilic?

A
  • Basophilic
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12
Q

Function of rER?

A
  • Synthesis of proteins for secretion, membrane proteins and lysosomal proteins
  • Synthesis of enzymes associated with sER
  • Modification of proteins (glycosylation and to assist with protein folding)
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13
Q

Describe structure

A
  • Membranous organelle
  • Forms intracellular network of cisternae (fluid-filled tubules)
  • Continuous (in most cases) with outer membrane of nuclear envelope
  • Polyribosomes attached
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14
Q

Describe co-translational translocation of polypeptides

A
  • Polypeptide in ribosome contains signal recognition sequence
  • Signal recognition particle binds to sequence bringing ribosome containing polypeptide to the membrane of the ER. Signal recognition particle binds to receptor
  • Polypeptide is positioned and fed into ER
  • Signal peptidase cleaves signal recognition sequence releasing mature protein into ER lumen
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15
Q

What is ER stress?

A
  • Accumulation of unfolded/misfolded proteins in the ER cisterna
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16
Q

Describe unfolded protein response. Why does this occur?

A
  • Unfolded protein response occurs as a result of ER stress
  • Chaperone synthesis increases in attempt to repair unfolded/misfolded proteins
  • There is decreased synthesis of proteins
  • Misfolded proteins are exported from ER to the cytosol where they are tagged for degradation by proteasomes (ubiquitin)
  • Caspases are activated that can lead to apoptosis if issues aren’t dealt with
17
Q

What is alpha1-antitrypsin deficiency?

A
  • Mutant protein aggregates in ER
18
Q

What are targeting signals and what is their function?

A
  • Targeting signals are sequences of AAs in protein that direct proteins to their target compartments by binding to receptors that are specific for the organelles. Escort factors may deliver protein to the target organelle
19
Q

Is sER acidophilic or basophilic?

A
  • Acidophilic
20
Q

Function of sER

A
  1. ) cholesterol homeostasis via HMG-CoA reductase
  2. ) steroid synthesis
  3. ) synthesis of phospholipids
  4. ) glycogenolysis (G-6-phosphatase is located on intraluminal side of ER membrane
  5. ) detoxification of drugs
  6. ) storage, release and uptake of calcium ions in striated muscle – known as sarcoplasmic reticulum here
21
Q

What is Von Gierke’s disease?

A
  • Defect in Glucose-6-phosphatase or the G-6-phosphate transporter and results in glycogen accumulation in the cytoplasm and nucleus of affected cells
  • Symptoms include: hepatomegaly, hypoglycemia and increased lactate production
22
Q

Why is smooth ER smooth? Location of it?

A
  • Lacks polyribosomes

- Continuous with rER in many cells, not in skeletal muscle

23
Q

What is seen in sER with protracted use of drugs and etoh?

A
  • Volume of sER increases as a result of increased concentration of cytochrome P450 enzymes
24
Q

Discuss synthesis of phospholipids

A
  • Synthesis of phospholipids occurs principally in cytosolic lipid monolayer of sER. Phospholipid translocators, membrane-bound enzymes catalyze flip-flop of phospholipds from one monolayer to another. Without this, new bilayers couldn’t be synthesized. There is a phospholipid exchange mechanism that allows phospholipids synthesized in ER to be transported and added to the membranes of other organelles
25
Q

Deleterious effects of elevated intracellular calcium?

A
  • Membrane damage
  • Nuclear damage
  • Decrease in ATP concentration
26
Q

A 38 yo male was administered a volatile gaseous anesthetic and succinylcholine prior to surgery. During the procedure, the pt went into tachycardia and development muscle rigidity and became febrile (temp = 108degF). Pt was diagnosed with malignant hyperthermia and treated with cooling blankets, rapid saline infusion IV and dantrolene. Explain what was occurring.

A
  • Halothane (anesthetic) promotes excessive leak of calcium across the ryanodine-1 receptor in the sarcoplasmic reticulum.
  • Result = increased muscle rigidity from EC coupling and increased contraction in muscle. Increase in body temp is due to increased activity of SR-Calcium pump which moves calcium back from sarcoplasm into SR

Cell & Tissue Biology (18 decks)

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