Unit III - Cellular Physiology Flashcards Preview

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Flashcards in Unit III - Cellular Physiology Deck (75)
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Properties & Phenotype of Transformed Cells

Altered morphology
Loss of contact inhibition
Anchorage independence
Reduced requirement for mitogenic growth factors
High saturation density
Increased transport of glucose
Sustained angiogenesis
Clonal in origin


Familial Retinoblastoma

Autosomal dominant cancer susceptibility resulting from inherited heterozygosity in the RB tumor suppressor gene on 13, followed by LOH of RB in a single cell; presents as bilateral retinal tumors


Loss of heterozygosity

Results from duplication of an inherited mutant tumor suppressor gene during S phase, followed by a rare mitotic cross-over event between homologs during M phase; in some cases, one daughter cell will end up with both functional tumor suppressor genes and one daughter cell will end up with NO functional tumor suppressor genes, becoming tumorigenic


Familial Adenomatous Polyposis (FAP) & Wnt Signalling

Results from inheritance of one defective copy of the APC tumor suppressor gene followed by LOH; 90% of affected will develop colon cancer by age 50

Normally, WNT growth factor stimulates the Frizzled receptor, which signals APC to release B-catenin in the cytoplasm; B-catenin then moves to the nucleus and binds TCF which signals transcription of c-myc, a TF that promotes cellular proliferation (oncogene)


Familial Breast Cancer

Caused by inherited heterozygosity in BRCA1 or BRCA2 genes followed by LOH; normally, BRCA1 and BRCA2 function in the ATM/CHK2 DNA-damage check point & repair system



P53 is a tumor suppressor gene that is up-regulated in response to DNA damage; ATM/CHK2 phosphorylate p53 in response to DNA damage, activating p53 to bind DNA and promote transcription of p21, which inactivates S-CDK complexes, thereby inhibiting progression through the cell cycle

Missense mutations in p53 code for a mutant protein that disrupts the normal tetramer structure of p53, "poisoning" it



ErB2 encodes an integral membrane protein kinase that is amplified in 20% of breast cancers; Herceptin is a monoclonal antibody specific for the ErB2 receptor


Von Hippel Lindau Syndrome - Mechanism, Phenotype, & Treatment

Caused by mutation in the VHL gene; normally, VHL binds hypoxia-inducible factor (HIF) subunit alpha and targets it for ubiquitination; in the absence of VHL protein, HIF-a binds HIF-B and translocates into the nucleus to promote transcription of VEGF

Phenotypic tumors: CNS & retina hemangioblastoma, renal cell carcinoma, pheochromocytoma

Target therapies: VEGFR TKIs Sunitinib & Sorafenib


Li-Fraumeni Syndrome

Caused by an inherited mutation in the p53 tumor suppressor gene, which predisposes the affected to many forms of cancer

Diagnostic criteria:

1. Sarcoma diagnosed before 45 years old
2. 1st degree relative with any cancer under 45 years old
3. 1st or 2nd degree relative with any cancer under 45 years old, or sarcoma at any age


SNARE Complex Formation & Disassembly

Formed by association between helical domains of Syntaxin, SNAP-25, and VAMP proteins; hydrophobic surfaces of each helix orient toward each other and form a stable complex; an "ionic bubble" is formed by 1 charged residue on each helix

SNARE complexes are dissassembled by ATPases NSF and alpha-SNAP and N-sec-1 acts as a molecular chaperone to help re-fold SNARE proteins


Viral Fusion (Ex: HIV)

Viral fusion proteins have a transmembrane domain embedded in the viral envelope and a fusion peptide motif - a stretch of hydrophobic AAs that become "activated" to insert into the host cell membrane

Ex: HIV FP gp120 recognizes and binds CD4 expressed on the host cell membrane; this activates FP gp41 to insert into the host cell membrane


3 classes of lipids in a membrane

1. Phospholipids
2. Sphingolipids
3. Cholesterol


Cholesterol Regulation Pathway

SREBP contains a bHLH TF domain that regulates LDLR gene; SREBP is held in the ER and bound by Insig/SCAP when cholesterol is high; when cholesterol is low, Insig releases SCAP and SCAP signalling recruits COPII, which transports the SCAP/SREBP complex into the Golgi where the TF is cleaved from SREBP by S1P and S2P


Voltage-gated channel structure

4 membrane-spanning domains, each containing 6 alpha helices (S1-S6). S4 helices have positively charged residues (Lys or Arg) which form the voltage sensor. S5 and S6 helices are connected by the P loop and assemble to form the ion-conducting pathway

Kv = 4 separate polypeptides
Nav = 1 polypeptide


NaV Mechanism

Activation: Depolarization causes repulsive electrostatic interactions with the positive charge on S4, causing the activation gate to swing open

Inactivation: The inactivation gate is formed by the cytoplasmic loop which connects repeats III and IV; it swings up into a binding site on the inner portion of the channel causing current to decay to 0

Removal of inactivation: The inactivation gate leaves it's binding site, allowing deactivation to occur in which the activation gate swings shut and the channel is re-set


2 Mechanisms of Glucose Transport

1. Glucose is pumped across the apical membrane via secondary active transport driven by the Na gradient

2. Facilitated diffusion into muscle cells followed by immediate phosphorylation to G-6-P; these GLUT receptors are exocytosed to the membrane in response to insulin signalling from pancreatic beta cells


Uses of Na powered secondary active transport

1. Na/Ca exchanger uses the inward leak of Na+ to pump Ca2+ out of the cell

2. Na/H exchanger uses the inward leak of Na+ to pump H+ out of the cell


Microtubule structure

The basic subunit of a microtubule is a heterodimer of alpha and beta tubulin, which bind GTP and align in tandem to form a protofilament with a free beta subunit at the (+) end and a free alpha subunit at the (-) end; 13 protofilaments assemble to form a microtubule ~25 nm in diameter



AKA microtubule organizing center (MTOC); most cells contain a single MTOC with a pair of centrioles located near the nucleus; microtubules grow from the pericentriolar material with their (-) ends anchored in the complex and their (+) ends growing into the cell


Kinesin Structure & Function

Exists as a homodimer; each subunit consists of a head group which binds microtubules, a coil motif, and a tail group which binds an adapter molecule for a specific cargo

Kinesin is an ATPase that moves cargo along microtubules toward the (+) end



Dynein transports cargo toward the (-) end of microtubules; ex: it is responsible for retrograde transport of materials from axonal terminals to neuronal cell bodies


Role of centrosome during mitosis

During mitosis, the centrosome is duplicated and one moves to each pole of the dividing cell; astral microtubules radiate out from the centrosomes; (+) ends of kinetochore microtubules attach to centromeres of chromosomes; (+) ends of overlap microtubules slide against each other, creating a force that pushes the poles apart while (-) directed motors separate daughter chromosomes and move them toward the centrosomes


Intermediate filament structure & function

Basic subunit is composed of two globular protein domains linked by an alpha helical region; the subunit forms tetramers and 8 tetramers twist into a rope-like filament 10 nm in diameter


Actin microfilament structure

In the presence of ATP, globular actin (G-actin) monomers assemble to form two-stranded, helical filaments (F-actin) 7 nm in diameter with (+) and (-) ends

FH2/Formin nucleates linear networks of actin filaments; Arp2/3 nucleates branched networks


4 main roles of actin in cell function

Epithelial cell polarity - anchors TJ/AJ proteins
Contraction - via interactions with Myosin
Motility - via polymerization in the filopodia and lamellipodia
Division - via actomyosin ring formation


Nernst Equation

E = (60/Z) x log (Co/Ci)


Osmolarity vs. Tonicity

Osmolarity describes the total concentration of solutes in a solution, whereas tonicity describes the effect of a solution on a cell (hypertonic or hypotonic)


Ionic driving force

Vm - Eion


Donnan Rule

[K]o[Cl]o = [K]i[Cl]i


Na/K Pump - Mechanism

While ATP-bound, the pump binds 3 intracellular Na+ ions; ATP hydrolysis phosphorylates the pump and triggers the closing of the inner gate and the opening of the outer gate; 3Na+ molecules are released extracellularly and 2K+ molecule are bound from the ECF; dephosphorylation of the pump triggers closing of the outer gate and opening of the inner gate; 2K+ are released intracellularly, and ATP binds again.