L6: Cell Biology V

Question 1

Describe methods of protein transportation between compartments within cell

Answer 1

1. ) Coated vesicle transport
   a. ) Clathrin
   b. ) COPII = anterograde transport from ER to cis Golgi
   c. ) COPI = retrograde transport from cis Golgi back to ER.
2. ) SNARE proteins
   - These proteins associate with vesicles (v-SNAREs), t-SNAREs associate with targets
   - Examples = synaptotagmin and synaptophysin
   - SNARE proteins allow vesicle to recognize its target domain
   - Example of NT movement
   - SNAP25/syntaxin associates with secretory vesicle containing neurotransmitter
   - Vesicle bound to SNAP25, associates with VAMP/synaptobrevin at cell membrane and bulk release of NT occurs

Question 2

Clinical relevance of SNARE proteins

Answer 2

• neurotoxins of tetanus and botilism enter nerve terminals and proteolyse SNARE proteins
• this prevents vesicles containing NTs from docking with pre-synaptic membrane of nerve cell

Question 3

Is the mitochondria acidophilic or basophilic?

Answer 3

• Acidophilic

Question 4

Lifespan of mitochondria? How do they reproduce?

Answer 4

• Short life span of ~ 10 days

- Reproduce by fission, can also fuse with one another

Question 5

Describe physical characteristics of mitochondria

Answer 5

• Comprised of mainly protein, some lipids, small quantities of RNA and mtDNA
• Outer membrane: permeable d/t large porins, contains translocator protein
• Inner membrane: selectively permeable d/t high conc of cardiolipin, contains enzymes for ETS with translocator proteins
• Intermembrane space b/w membranes
• Inner membrane invaginates to for cristae (shelf-like in hepatocytes, cardiac and sk muscle cells; tubular in steroid-secreting cells where mitochondria participate in synthesis of steroid hormones)
• Matrix contains enzymes for Krebs, beta-oxidation and also matrix granules (phospholipoprotein, calcium, mag)

Question 6

Discuss production of proteins for mitochondria

Answer 6

• Small proportion of mitochondrial proteins and oxphos enzymes are produced within the mitochondria
• Most are synthesized by free polyribosomes of cytoplasm and are actively imported into mitochondria by translocator proteins

Question 7

What exogenous molecules block the electron transport system?

Answer 7

• CO and CN

Question 8

How does mitochondria regulate apoptosis?

Answer 8

• Release of cytochrome c from mitochondrial activates the apoptotic cascade

Question 9

Clinical relevance of mitochondria

Answer 9

• Mutations in mitochondrial DNA implicated in DM, deafness, heart dz, Alzheimers Parkinsons and LHON
• MERRF: myoclonic epilepsy with ragged red fibers histologically recognized by red appearing mitochondria imparted by using modified trichrome stain. Mitochondria harbor parking lot inclusions and assume peculiar shapes and have cristal disruption. Symptoms of this disorder: myoclonus, seizures and ataxia

Question 10

Functions of peroxisomes

Answer 10

• Beta-oxidation of FFAs
• Plasmalogen synthesis (phospholipid found in myelin)
• Regulate hydrogen peroxide concentration – catalase break down, amino acid oxidase and hydroxyacid oxidase form hydrogen peroxide
• Kill pathogens
• Oxidize etoh

Question 11

What is Zellweger syndrome?

Answer 11

• Defect in import of peroxisomal enzymes to peroxisome

- Due to defective import protein on unit membrane of peroxisome

Question 12

Effect of antilipidemics (eg. Lipitor) on peroxisomes

Answer 12

• Lipitor leads to increased uptake of TGLs and cholesterol by hepatic cells
• Increased uptake ramps up beta oxidation of FAs by mitochondria and peroxisomes
• Peroxisomes increase in number during chronic administration of antilipidemics

Question 13

Components of cytoskeleton

Answer 13

• Microtubules
• Microfilaments
• Thick filaments
• Intermediate filaments

Question 14

Describe structure of microtubules

Answer 14

• How tubules that are comprised of 13 longitudinally arranged protofilaments, each with subunits known as tubulin dimers
• Microtubules polymerize and form ring of gamma-tubulin within a micro-tubule organizing center possessing capping proteins. This polymerization process requires GTP and mag ions

Question 15

Drugs that inhibit polymerization of microtubules

Answer 15

• Colchicine, vinblastine, vincristine

- Taxol inhibits depolymerization

Question 16

Functions of microtubules

Answer 16

• Supports cytoplasm and gives cell shape
• Organelle support
• Cell division
• Motility of cilia and flagella
• Does long range transport of vesicles by microtubule motor proteins, which are ATPases

Question 17

Name and describe long-range transport proteins of vesicles using microtubules

Answer 17

1. ) Kinesin. Moves vesicles toward periphery

2. ) Dynein. Moves vesicles toward nucleus

Question 18

Clinical relevance of defect in kinesin

Answer 18

• Defect in kinesin motor has been shown to decrease transport of serotonin receptors. Implicated in development of anxiety disorders

Question 19

A 38 yo female presents to a cosmetic surgeon complaining of excessive facial wrinkles. The physician explains that she is an excellent candidate for botox injections as a means to diminish wrinkles by weakening facial muscle contractions. How does botulinum toxin mediate its effect?
A. Proteolysis of coating proteins
B. Stabilization of microtubules
C. Proteolysis of SNARE proteins
D. Disrupts endocytosis of released neurotransmitter

Answer 19

• C

Question 20

A five month old male presents with a constellation of craniofacial congenital malformations. These include a high forehead, large anterior fontanelle, deformed earlobes, micrognathia, and widened nasal bridge. Other findings are hypotonia, depressed deep tendon reflexes, seizures, cataracts and retinal degeneration. Lab results show an elevation of VLCFAs and pipecolic acids in the plasma and a decrease in erythrocyte plasmalogens. What is the most likely diagnosis?

Answer 20

• Zellwegers syndrome