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34 Cards in this Set
- Front
- Back
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Name some important post-translational modifications.
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Attachment of oligosaccharides to form glycoproteins and phosphorylation of proteins.
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What amino acids typically get oligosaccharides attached to them?
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Serine, threonine, and asparagine. The oligosaccharide is added to the side chain portion of the AA. The resulting molecule is called a glycoprotein.
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What is a glycoprotein?
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A protein with oligosaccharides attached to it.
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What is the only isoform of amino acids found in eukaryotes?
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The L-amino acids.
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What does cancer typically do to phosphorylation of proteins?
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It disregulates it.
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By convention, an AA sequence is written with its __ terminus on the left and its __ terminus on the right.
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Amino; Carboxyl.
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Why do polypeptides assume such unique and permanent 3D configurations?
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Peptide bonds. They behave like partial double bonds, and do not freely rotate.
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The immediate cause of a protein's secondary stucture is:
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H-bonding between nearby amino acids.
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What is an alpha helix?
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A right-handed helix, in which every backbone N-H group donates a H+ to the backbone C=O group of the AA 4 residues earlier. H bonds are parallel to the helix.
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What is a beta sheet?
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Backbone N-H groups in one strand donate a H+ to backbone C=O groups of the AAs in an adjacent strand. The H bonds run perpendicular to the AA chain. There are parallel and anti-parallel beta sheets.
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What causes a protein's tertiary structure?
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Interactions between non-adjacent AAs resulting in the folding of domains and the arrangement of domains. Can be stabilized by disulfide bonds.
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What causes a protein's quaternary structure? Give an example.
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Interactions between polypeptides. The drug version of insulin forms hexamers around two Zn ions. The native form of insulin is a monomer.
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What is protein denaturation? What are its effects?
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The unfolding and disorganization of a protein. Can reverse solubility. Sometimes it's reversible, sometimes it's not.
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What can denature proteins?
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Heat, organic solvents like ethanol and acetone, strong acids or bases, detergents, and heavy metals.
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When are proteins folded?
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During synthesis and immediately after (seconds to minutes).
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How do proteins fold correctly?
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Most of the information to ensure proper folding is in a protein's primary structure. However, chaperone proteins also promote proper folding.
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What's another name for chaperone proteins and why?
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Heat shock proteins. They were discovered when cells were exposed to high temperature (they were keeping proteins folded). They prevent the non-specific aggregation of proteins.
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What is the resultant disease of a primary gene mutation that alters the primary structure of a protein such that it misfolds? What's a famous example?
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Amyloidoses. Alzheimer's disease is one. Creutzfeldt-Jacob disease is another example of a protein-misfolding disease.
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What is craniopharyngioma and what can it lead to?
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It's a benign brain tumor that can lead to panhypopituitarism.
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What structural characteristics of proteins enable them to carry out their functions in a regulated manner?
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1) The interactions between amino acid side groups.
2) Post-translational modifications. |
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What are the functions of proteins?
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Catalysis (enzymes), transport (carrier/pump), mechanical support (collagen/keratin), motion (microfilaments), recognition (antibodies, receptors, antigens), sensation, regulation of gene activity (DNA binding proteins), and osmotic force (albumin).
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Where/when does regulation of protein function occur?
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Rate of gene transcription, RNA splicing, RNA degradation, rate of translation, rate of protein degradation, transport of protein to its final location, and post-translational mods of the protein.
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What are some conditions that affect protein function?
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Mutations in DNA, changes in RNA stability (myc overexpression in breast cancer), rates of protein translation and degradation are altered in many diseases, often as a result of undernutrition; virtually all diseases involve changes in the post-translational modification of proteins. Many times, this is due to altered cell signaling.
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What AAs are non-polar?
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Alanine, Glycine, Isoleucine, Leucine, Methionine, Phenylalanine, Tyrosine, Tryptophan, and Valine.
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What AAs are uncharged polar?
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Asparagine, glutamine, serine, and threonine.
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What AAs are acidic?
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Aspartic acid and glutamic acid.
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What AAs are basic?
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Arginine, histidine, and lysine.
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Which basic AA is uncharged at physiological pH?
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Histidine.
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What determines the charge of a protein?
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The side chains, because the amino and carboxyl portions of AAs are involved in peptide bonds.
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What's so special about proline?
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Non-polar side chain that includes an alpha-imino group and forms a ring structure. Contributes to the structure of collagen. Proline often interrupts the alpha helices found in globular proteins.
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What's so special about cysteine?
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It can form disulfide bonds. A cysteine dimer formed through disulfide linkage is called cystine. Insulin uses this linkage.
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What's so special about serine, threonine, and tyrosine?
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The polar hydroxyl groups on their side chains can accept phosphate groups. Therefore, these three AAs get phosphorylated all the time and everywhere. Of them, it's usually serine and threonine. Kinases phosphorylate. Phosphatases dephosphorylate.
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What AAs can have oligosaccharides attached to them?
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Serine, threonine, and asparagine. This process makes them glycoproteins.
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What's the AA isoform found in all eukaryotes?
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L form.
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