Cell Org II

Question 1

5 components of cell nucleus

Answer 1

1. Nuclear envelope (NE)
2. Nuclear lamina (NL)
3. Nuclear Pore Complexes (NPCs)
4. Nucleolus
5. Nucleoplasm

Question 2

Describe the NE

Answer 2

1. Inner nuclear membrane
   
   1. Faces the nucleoplasm
   2. In contact with the nuclear lamina
      
      1. functions as a scaffold stabilizing the nuclear envelope
2. Outher nuclear membrane
   
   1. Faces the cytoplasm
   2. Continuous with ER
   3. Cytoplasmic surface contains ribosomes (rER)

Question 3

Describe the nuclear lamina

Answer 3

1. Nuclear lamina
   
   1. Thin, sheet like meshwork beneath the inner nuclear membrane
   2. Scaffold for nuclear envelope, chromatin and nuclear pores

Question 4

Describe the nuclear pore complex (NPC)

Answer 4

1. Spans the inner and outer nuclear membranes (80-100nm in diameter)
2. 2000-3000 NPCs in a typical nuclear envelope
3. Allows transport of molecules between the nucleus and cytoplasm
   
   1. 9nm is the threshold between free/active transport

Question 5

describe the Nucleolus (the 3 zones)

Answer 5

1. Site of ribosome production
   
   1. Fibrillary center
      
      1. DNA loops of 5 chromosomes
      2. Contains rRNA genes
   2. Fibrillar material
      
      1. Transcription of rRNA genes
   3. Granular material
      
      1. Initial ribosomal assembly

Question 6

describe chromatin (2 types)

Answer 6

1. Chromosomes in various degrees of uncoiling
2. Packaged into nucleosomes
   
   1. Complex of DNA and proteins called histones
3. 2 Types
   
   1. Euchromatin (EC)
      
      1. Lightly staining
      2. Less condensed chromatin, which makes it more transcriptionally active
   2. Heterochromatin (HC)
      
      1. Densely staining
      2. Highly condensed (HC) chromatin, which makes it less transcriptionally active

Question 7

describe the nucleosome

Answer 7

1. It is the fundamental structural unit of chromatin
2. Macromolecular complex, like beads on a string
3. Found in both EC and HC

Question 8

describe where ribosomes are made and what they are

Answer 8

1. They are made in the nucleolus and leave the nucleus and enter the cytoplasm
2. Consists of 2 ribosomal RNA subunits and associated proteins
3. Sites of protein synthesis (translation)

Question 9

describe the 2 types of ribosomes

Answer 9

1. Membrane-bound
   
   1. Attached to cytoplasmic surface of the ER
   2. Synthesize proteins that are being translocated into the ER lumen
   3. Produce
      
      1. Lysosomal proteins
      2. Secereted proteins
      3. PM proteins
2. Free ribosomes
   
   1. Unattached to any membrane
   2. synthesize all other proteins
      
      1. nuclear proteins
      2. mitochondrial proteins
      3. cytosolic proteins
      4. peroxisomal proteins

Question 10

describe the structure of the ER

Answer 10

1. Interconnected network of branching tubules and flattened sacs distributed throughout the cytoplasm
2. At certain sites, the ER membrane is continuous with the other NE membrane

Question 11

describe the smooth ER

Answer 11

1. Smooth ER: functions in the synthesis of lipids and detox
   
   1. Region of the ER that lacks bound ribosomes
   2. Abundant in cells specialized in lipid metabolism
      
      1. This makes it well developed in cells that synthesize and secrete steroids
   3. Plays a major role in detox
   4. Also functions to sequester calcium in muscle cells/sarcoplasmic reticulum

Question 12

describe the rough ER

Answer 12

1. Rough ER functions in the synthesis of proteins destined for PM, lysosomes or secretion
2. Only mRNA molecules with an ER signal sequence bind to rER membranes
3. Abundant in cells specialized in protein synthesis
   
   1. Secretory cells producing proteins for extracellular export

Question 13

describe structure and location of GA

Answer 13

1. Complex of flattened, membrane-enclosed cisternae
2. Usually located next to the nucleus and centrosome
   
   1. Location is microtubule dependent

Question 14

describe the 2 faces of the GA

Answer 14

1. Cis face
   
   1. Entry
   2. Cis Golgi Network (CGN)
2. Trans face
   
   1. Exit
   2. Trans Golgi Network (TGN)

Question 15

which cells would the GA be most developed?

Answer 15

• Secretory cells
  
  • Plasma cells, which secrete antibodies
  • Pancreatic acinar cells, which secrete digestive enzymes

Question 16

describe the differences between COP I and COP II

Answer 16

• COP-I coated vesicles
  
  • Retrograde transport
  • CGN back to rER
• COP-II coated vesicles
  
  • Anterograde transport
  • Carry newly synthesized proteins from rER to CGN

Question 17

describe the 3 functions of the GA

Answer 17

1. Post-translational modification
   
   1. Glycolysation
   2. Sulfation
   3. Phosphorylation
   4. Proteolysis
2. Sorting
3. Packaging

Question 18

describe the different types of vesicular trafficking in the GA

Answer 18

1. Constitutive
   
   1. Constantly prouducing vesicles for secretion
      
      1. Fibroblasts secreting ECM components
2. Regulated secretory pathway
   
   1. Vesicles are stored and secreted with stimulus
      
      1. Neurons, beta cells (endocrine) and acinar cells (exocrine) of pancreas
3. Lysosomal pathway
   
   1. Precursor lysosomal hydrolases are covalently modified by the addition of M6P in the GA
   2. the TGN recognizes this for transport to lysosomes

Question 19

describe the structure and function of lysosomes

Answer 19

1. Digestive organelles
   
   1. Function in the controlled intracellular digestion of macromolecules
2. Membrane-enclosed compartments filled with ~40 types of hydrolytic enzymes
   
   1. Require an acidic environment, around pH 4.7

Question 20

How many lysosomal storage diseases are there and what are the results?

Answer 20

• 1:7000 live births
• Results
  
  • Accumulation of undigested products
  • Disruption of normal cell function
  • Cell death

Question 21

describe Tay-Sachs (gene location, results)

Answer 21

1. First LSD
2. Deficiency of HEXA
3. Gene location: chromosome 15q24.1
4. Results in the accumulation of GM2 ganglioside
5. Death of neurson in the brain and spinal cord

Question 22

what are the pathways that lead to digestion by lysosomes?

Answer 22

1. Phagocytosis
2. Endocytosis
3. Autohphagy (self-eating): major cellular pathway to degrade proteins and organelles
   
   1. intracellular membrane surrounds the organelle and cytoplasm
   2. autophagosome formed (double membraned vacuole)
   3. fusion of autophagosome with lysosome
   4. contents are degraded, recycled and reused

Question 23

describe proteasomes and how they function

Answer 23

• Proteasomes are large protein complexes involved in protein degradation
• ATP-dependent
• Destroys proteins without involving lysosomes

Question 24

how do proteasomes destroy proteins and which do they target?

Answer 24

• Polyubiquitination
  
  • Proteins targeted for destruction are covalently tagged with the ubiquitin protein
• Destruction of abnormal proteins and normal short-lived regulatory proteins
  
  • Ex: cyclins, transcription factors, tumor suppresors
• Proteasome inhibitors used as anti-cancer agents
  
  • proteasome inhibition may prevent degradation of pro-apoptotic factors such as the p53 protein

Question 25

what are inclusions and name the 3 pigments

Answer 25

• Inclusions are cytoplasmic or nuclear structures formed from metabolic products of the cell
• Pigments: membrane bound
  
  • Lipofuscin
    
    • 1. Brownish-gold pigment
    • Generally seen in non-dividing cells
    • Conglomerate of lipids, metals, organic molecules
  • Hemosiderrin
    
    • 1. Brown pigment
    • 2. Iron-storage complex found in the cytoplasm
    • Likely formed by indigestible residues of hemoglobin
      
      • Easily seen in spleen
  • Melanin
    
    • Brown pigment

Question 26

name 2 storage forms of inclusions

Answer 26

1. Glycogen
   
   1. Non-membrane bound, TEM dense bodies
   2. Storage form of glucose
      
      1. catabolism releases glucose for energy
2. Lipid
   
   1. Non-membrane bound, TEM dense
   2. Fat droplets
   3. Energy store and source of short carbon chains for membrane synthesis
   4. Lipid stroage disease (lipidoses)
      
      1. Lipid droplets accumulate in abnormal amounts or locations

Question 27

describe the 2 membranes of the mitochondria

Answer 27

1. Outer
   
   1. Contains porins
      
      1. Large channel-forming proteins, which allow free passage of small molecules <5000 daltons
2. Inner
   
   1. Thinner and thrown into folds
      
      1. Cristae
   2. 3 major functions
      
      1. Oxidation reactions
         
         1. Respiratory ETC
      2. Synthesize ATP
         
         1. ATP synthase
      3. Regulate metabolite transport into and out of the matrix

Question 28

describe the 2 compartments of the mitochondria

Answer 28

1. Intermembrane space
   
   1. Space between the inner and outer membranes
   2. Oxidative phosphorylation takes place here
   3. Contains specific enzymes that use ATP generated by the inner membrane
      
      1. Creatine kinase
      2. Adenylate kinase
      3. Cytochrome C
         
         1. Important factor in intrinsic apoptosis pathway
2. Matrix
   
   1. Mixture of hundreds of enzymes
      
      1. Oxidation of pyruvate and fatty acids
      2. Krebs Cycle
   2. Matrix granules
      
      1. Storage site for Ca2+ and other divalent cations
   3. Mitochondrial DNA, ribosomes and tRNAs

Question 29

what is the primary function of the mitochondria

Answer 29

1. generate ATP
   
   1. Krebs Cycle
   2. OP
   3. Beta oxidation of fatty acids
2. Abundant in cells that generate and expend large amount of energy

Question 30

describe mitochondrial diseases and the 2 types described

Answer 30

• Results in defects in MT enzymes required for ATP production
  
  • Dysfunctional mitochondrial respiratory chain
• Affects tissues that require large amounts of ATP
  
  • Neurons and muscle cells
• Myoclonic elilepsy with ragged red fibers (MERRF)
  
  • Mutation in the tRNA gene
  • MT-TK
• Leber hereditary optic neuropathy
  
  • Mutations in the MT-ND1, MT-ND4, MT-ND4L or MT-ND6

Question 31

what role do peroxisomes have and what synthesizes them

Answer 31

• Important role in fat metabolism
  
  • Very long chain fatty acid (VLCFA) beta-oxidation
  • Catalyze initial reactions in formation of plasmalogens
    
    • Abundant class of phospholipids in myelin
    • Deficiencies cause profound abnormalities in myelination of nerve cells
• Peroxisomal proteins are synthesized by free (cytoplasmic) ribosomes
  
  • Proteins must have a peroxisomal targeting signal

Question 32

how do peroxidases function and which cell are they particularly important in

Answer 32

• Specialized to compartmentalize and degrade toxic reactive oxygen moleculesContains catalase and other peroxidases
  
  • Converts H2O2 to O2 and H2O
• Particularly in hepatocytes
  
  • Detox of ingested alcohol

Question 33

describe peroxisomal diseases

Answer 33

• Dysfunctional peroxisomes
• Zellweger Syndrome
  
  • Mutations in genes required for peroxisome function
  • Defective import of peroxisomal proteins