Cell Biology II Flashcards
Proteins
Peripheral, integral proteins
Peripheral protein
can be removed from the plasma membrane with salt solutions
Integral proteins
Some are partially embedded in the plasma membrane and others extend across the entire thickness of the membrane
a. Transmembrane–extend through entire thickness of membrane
- —-Clinical relevance-Beta-amyloid precursor protein in Alzheimer’s disease. The protein aggregate that forms is resistant to proteolysis. Beta-amyloid precursor protein is important in neuronal migration during development, synaptic formation and repair, cell signaling, long-term potentiation of memory, and cell adhesion.
Creutzfeldt-Jacob disease
Prion diseasea
Cell-surface glycosylated, glycophosphatidylinositol-anchored protein (within lipid rafts), of neurons is converted to its abnormal variant. The variant forms cross-linked filaments that are resistant to proteolysis. The variant also accelerates conversion of normal PrP to the same form. In this context, the variant is infectious. Normal prion proteins may be neuroprotective against ischemia, control circadian rhythms, and may serve serve to organize the myelin sheath.
Functions of proteins
Receptors,transport of chemical across cell membrane, enzymatic control, linker proteins for structural support, cellular identification tags (antigens), anchor cell to extracellular matrix, intercellular junctional complexes
Transport of chemicals across cell membrane
Transport proteins (carriers and pumps) and Pores (channels)
Pores (channels)
- Aquaporins–proteins channels for H2O and 12 isoforms.–Aquaporin-2 is expressed by renal collecting tubule cells for water reabsorption. Vasopressin, vis-à-vis its receptor, causes translocation of aquaporin receptors to the plasma membrane of the collecting tubule cell. This increases the reabsorption of water across the apical domain of the tubule cells
- Chloride conductacne & cystic fibrosis
Transport proteins (carriers and pump)
Carriers may transport one or more chemicals in one direction or transport two chemical in opposite directions without the direct expenditure of energy. Transport proteins requiring the direct expenditure of energy are referred to as pumps. require the expenditure of energy (active transport). The Na/K pump is an example of a protein transporter that expends ATP.
Multidrug resistant transporters
Subfamily of primary transporter proteins that are ATPases
-MDR-1, MDR-2, MDR-3
MDR-1
Expressed in the kidney, intestine, liver, and blood-brain barrier.
1. Transports drugs. Overexpression of multidrug-resistance (MDR-1) protein causes some cancer cells to become resistant to cytotoxic drugs. Resistance is conferred by an overexpression of MDR-1 transport proteins which pump (ATP-dependent) the cytotoxic agents out of the cell. Targeted intervention with RNA interference and pharmacologic inhibitors.
MDR-2
Transports conjugated(direct) bilirubin. This protein is defective in Dubin-Johnson syndrome.
MDR-3
Expressed in the liver.
1. Functions as a flippase of phosphatidylcholine; flips it to the outer canalicular membrane of hepatocytes so that it may be excreted in bile
Carbohydrates
Attached to lipids and proteins forming glycolipids and glycoproteins
i. Glycolipids are found exclusively in the noncytosolic lipid monolayer. These molecules are also found in some intracellular membranes.
ii. Have negative charges which repel other negatively charged substances (keep erythrocytes apart)
iii. React with regulatory molecules
iv. Play a role in cell-to-cell and cell-to-matrix recognition and adhesion
v. Protection
Translation to clinical relevance for carbs
Ganglioside GM1, a glycolipid, serves as a cell receptor (on intestinal epithelial cells for example) for the cholera toxin. The toxin subsequently enters the cell by binding to ganglioside GM1. The toxin then ramps up synthesis of cyclic adenosine monophosphate which ultimately causes a substantial efflux of sodium ions and water into the intestine. The net result is diarrhea.
