quizz pt 1

• Secondary structure in proteins mainly stabilized by hydrogen bonds between atoms of the polypeptide backbone
• Disulfide bonds between the side chains of cysteine residues in some proteins covalently link regions of proteins, thus restricting the protein's flexibility and increasing the stability of their tertiary structures
• Epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells or T cells.
• Cytoplasmic proteins degradation by proteasomes can account for up to 90 percent of the protein degradation in mammalian cells.
• Once bound to Ca2+, calmodulin acts as part of a calcium signal transduction pathway by modifying its interactions with various targets proteins such as kinases or phosphatases.
• Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen
• immunofluorescence microscopy makes use of antibodies to localized specific components in fixed and permeabilized cells
• cell fractionation is used to isolate (fractionates) cell components based on size and density
• Small Interfering (si) RNAs can knock down expression of specific proteins
• Most transmembrane proteins have membrane-spanning alpha-helices
• Multiple Beta strands in porins form membrane-spanning "barrels"
• Peripheral membrane proteins do not directly contact the hydrophobic core of the phospholipid bilayer
• Many transmembrane proteins contain carbohydrate chains covalently linked to serin, threonine or asparagine side chains of the polypeptide
• Flippases move phospholipids from one membrane leaflet to the opposite leaflet
• Membrane potential is the voltage difference across a membrane.
• Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
• The protist Paramecium which is hypertonic to its pond water environment has a contractive vacuole that acts as a pump
• human erythrocytes consume up to 50% percent of their available ATP fir this purpose for ion transport. Most of this ATP is used to power the Na+/K+ pump.
• Cystic fibrosis transmembrane regulator is a chloride channel.
• Lectins are carbohydrate-binding proteins, macromolecules that are highly specific for sugar moieties
• In the presence of Tunicamycin, which inhibits the synthesis of all N-linked oligosaccharides, the flu virus hemagglutinin precursor polypeptide (HA0) is synthesized, but the protein remains, misfolded, in the rough ER
• A key participant in this unfolded-protein response is Ire1, an ER membrane protein that exists as both a monomer and a dimer. The dimeric form, but not the monomeric

  form, promotes formation of Hac1, a transcription factor in yeast that activates expression of the genes induced in the unfolded-protein response
• Ire1, a transmembrane protein in the ER membrane, has a binding site for BiP on its luminal domain; the cytosolic domain contains a specific RNA endonuclease.
• Unassembled or misfolded proteins in the ER are often transported to the cytosol for degradation
• Amphipathic N -terminal signal sequences direct proteins to the mitochondrial matrix.
• Mitochondrial protein import requires outer-membrane receptors and translocon in both membranes
• Two arginine residues at the N -terminus of the thylakoid-targeting sequence and a pH gradient across the inner membrane are required for transport of the folded protein into the thylakoid lumen
• Most peroxisomal matrix proteins contain a C -terminal PTS1 uptake-targeting sequence (red) that binds to the cytosolic receptor Pex5.
• In the nucleoplasm, Ran GTP binds to the importin, causing a conformational change that decreases its affinity for the NLS and releasing the cargo