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17 Cards in this Set

  • Front
  • Back

Regulators of cell cycle checkpoints

cyclins, cyclin-dependent kinases (CDKs) & tumor suppressors


constitutive & inactive


regulatory proteins that control cell cycle events; phase specific; activate CDKs

Cyclin-CDK complexes

must be both activated & inactivated for cell cycle to progress

Tumor suppressors

p53 & hypophosphorylated Rb normally inhibit G1 to S (synthesis) progression;

-mutations result in unrestrained cell division (e.g. Li-Fraumeni syndrome)

Permanent cell types

remain in G0, regenerate from stem cells

(neurons, skeletal & cardiac muscle, RBCs)

Stable (quiescent) cell types

enter G1 from Go when stimulated

(hepatocytes, lymphocytes)

Labile cell types

never go to G0, divide rapidly with a short G1

*most affected by chemotherapy

(BM, gut epithelium, skin, hair follicles, germ cells)

Rough endoplasmic reticulum

site of synthesis of secretory (exported) proteins & of N-linked oligosaccharide addition to many proteins

-Nissel bodies (RER in neurons) synthesize peptide NTs for secretions

-Free ribosomes: unattached to any membrane (site of synthesis of cytosolic & organellar proteins)

Smooth endoplasmic reticulum

site of steroid synthesis & detox of drugs/poisons

-lacks surface ribosomes

Golgi trafficking

golgi is the distribution center for proteins & lipids from ER to vesicles & plasma membrane

-modifies N-oligosaccharides on asparagine

-adds O-oligosaccharides on serine & threonine

-adds mannose-6-phosphate to proteins


sorting centers

I-cell disease (inclusion cell disease)

inherited lysosomal storage disorder

-defect in phosphotransferase > failure of golgi to phosphorylate mannose residues (e.g. decrease mannose-6-phosphate) on glycoproteins > proteins are secreted extracellularly rather than delivered to lysosomes

*Sx: coarse facial features, clouded corneas, restricted joint movement, & high plasma levels of lysosomal enzymes (often fatal in childhood)

Signal recognition particle (SRP)

abundant, cytosolic ribonucleoprotein that traffics proteins from the ribosome to the RER.

-absent or dysfunctional SRP > proteins accumulate in cytosol

Vesicular trafficking proteins

COPI: golgi > golgi (retrograde); Golgi > ER

COPII: Golgi > golgi (anterograde); ER > golgi

Clathrin: trans-Golgi > lysosomes; plasma membrane > endosomes (receptor-mediated endocytosis [e.g. LDL receptor activity])


membrane-enclosed organelle involved in catabolism of very-long-chain fatty acids, branched-chain fatty acids & amino acids


barrel-shaped protein complex that degrades damaged or ubiquitin-tagged proteins. Defects in the ubiquitin-proteasome system have been implicated in some cases of Parkinson disease.