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78 Cards in this Set
- Front
- Back
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What are all late-onset neurodegenerative disorders caused by?
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Accumulation of protein aggregates or fibers.
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What form do protein aggregates or fibers usually take in late-onset neurodegenerative disorders?
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Amyloid plaques or neurofibrillary tangles (NFTs)
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What pathology is found in Alzheimer's Disease?
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Extracellular amyloid deposits and intracellular NFTs.
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What is the nature of the extracellular amyloid deposits found in Alzheimer's pathology?
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The extracellular amyloid deposits are made of proteolytic fragments of the amyloid precursor protein (APP).
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What is the term for the proteolytic fragments of amyloid precursor protein found in Alzheimer's pathology?
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Amyloid-beta (AB)
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What does the "beta" in amyloid-beta refer to?
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Beta refers to the Beta-strands formed by the 40 aa membrane spanning peptide.
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What are the intracellular NFTs found in Alzheimer's pathology composed of?
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Intracellular NFTs are composed of the microtubule-binding protein tau (t).
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What is the pathological finding in Parkinson's disease?
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Accumulation of neurofibrillary tangles (NTFs) composed of polymers of alpha-synuclein protein.
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Are there plaques found in Parkinson's disease pathology?
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No
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Why do some Parkinson's patients show symptoms of Alzheimer's and vice versa?
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Alpha-synuclein and tau interact.
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What sort of testing is definitive for Huntington's disease?
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Genetic screening is definitive.
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What is Huntington's Disease due to?
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CAG repeats-poly Qs (Glutamine) in huntingtin protein
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What is the pathology found in Huntington's disease?
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Protein deposits originate as nuclear inclusions composed of polyglutamine (polyQ) aggregates and form beta-sheet containing amyloid-like fibrils.
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Where does the polyQ in Huntington's disease appear?
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The polyQ appears on the 3,144 aa huntingtin protein.
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What exon in the huntingtin protein contains a CAG repeat that encodes Gln?
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Exon 1
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How many CAG repeats do most people have for the huntingtin protein?
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<27
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How many CAG repeats are necessary in order to develop Huntington's disease?
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greater than or equal to 40 CAG repeats means that an individual will develop the disease within a normal lifetime
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When, in relation to protein synthesis, do proteins fold?
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Proteins fold during and/or after protein synthesis until it adopts its native conformation.
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What do some proteins require for folding?
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Some proteins require assistance from chaperone machinery (Hsp70, Hsp90, etc.)
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Where is there some freedom of rotation about the bonds in a polypeptide?
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There is some freedom of rotation about the N-Calpha and Calpha-carbonyl C bonds.
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What are the definitions (names) of the angles of the bonds with some degree of freedom of rotation in polypeptides?
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The angle of the N-Calpha and Calpha-carbonyl C bonds are defined as phi and psi, respectively.
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What is Levinthal's paradox?
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If a protein is folded completely @ random, it would take much too long to sample all possible conformations (>10^77yrs for 100a a). Therefore, folding can not occur by completely random processes.
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How is the 3D structure of proteins stabilized?
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The 3D structure of proteins is stabilized by a combination of hydrogen bonding, ionic bonding, van der Waals forces, hydrophobic interactions, and disulfide bonds.
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What is denaturation?
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Denaturation is the unfolding of a protein structure.
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What does increasing temperature do to protein conformation?
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Increasing temperature forces proteins to unfold as they lose both their native structure and disulfide bonds.
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What do chaotropic denaturants do?
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Chaotropic denaturants unfold proteins by extensive disruption of H2O H-bonding to the extent that the hydrophobic portions of the protein can open up and be exposed to the solvent.
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What are two examples of chaotropic denaturants?
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Urea and guanidine HCl
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What do detergents do to proteins?
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Detergents like SDS coat hydrophobic regions of proteins which causes them to unfold.
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What is an example of a detergent used to unfold proteins?
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SDS (sodium dodecyl sulfate)
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What describes the covalent disulfide bonds occurring between 2 Cys?
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Cystines
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Cystines?
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Cystines describe the covalent disulfide bonds occurring between 2 Cys.
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What does formation of the disulfide require?
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Formation of the disulfide requires oxidation (O2 is often the culprit.)
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How are disulfides cleaved?
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Disulfide cleavage requires reduction; common lab reductants include DTT and B-ME.
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What are two common lab reductants used in disulfide cleavage?
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Dithithreitol (DTT) and Beta-mercaptoethanol (B-ME)
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What did Christian Anfinsen find in his experiments with RNase?
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Christian Anfinsen denatured and renatured ribonuclease (RNase) and found that all the information necessary for the protein to adopt its native, active conformation was present in the aa sequence (amino acid sequence dictates 3D structure)
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Describe Anfinsen's 1st experiment.
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1. Unfolded RNase with 8M urea and broke disulfides with B-ME
2. Removed both urea and B-ME slowly (dialysis) and allowed exposure to 21% O2 Result: Recovered ~100% activity; the protein folded back into its native, active conformation. |
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Describe Anfinsen's 2nd experiment.
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1. Unfolded RNase with 8M urea and broke disulfides with B-ME
2. Removed B-ME first and exposed to 21% O2 3. Removed urea Result: ~1-2% activity; the disulfides reformed randomly in the presence of the urea |
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Describe Anfinsen's 3rd experiment.
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1. Using the scrambled protein from experiment 3, add B-ME
Result: After 10 hours, he recovered ~100% activity. Amino acid sequence specifies conformation. |
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What are the transmissible spongiform encephalopathies caused by?
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TSEs are caused by misfolded forms of the prion protein, PrP.
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What is a TSE?
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TSE = Transmissible Spongiform Encephalopathy --> prion disease
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What is the misfolded form of the protein, PrPsc, expecially resistant to?
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PrPsc is especially resistant to protease treatment (& heat treatment) which allows the protein to persist in the neuronal tissue.
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What is Prpsc capable of doing to normal proteins?
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PrPsc is capable of converting the normal, benign form of the prion protein, PrPc, into more of the PrPsc, which accounts for the accumulation of the protein.
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What do the accumulations of PrPsc eventually do?
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Accumulations of PrPsc form amyloid-type plaques which ultimately perforate cells causing a spongiform destruction of the brain.
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Why are there different disease manifestations for various prion diseases?
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Different forms of the disease causing PrPsc preferentially affect different regions of the brain.
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What are a few examples of PrPsc associated diseases?
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1. Fatal Familial Insomnia
2. vCJD 3. CJD 4. Kuru |
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With regard to TSEs, why does the sequence of the PrP protein matter?
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There are certain sequences that favor one or more forms of TSE. They have strong biases for different codons.
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The mad cow form of the disease, vCJD, has a strong bias for what amino acid at which codon?
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vCJD has a strong bias for Met @ codon 129.
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What is the misfolded form of the protein, PrPsc, expecially resistant to?
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PrPsc is especially resistant to protease treatment (& heat treatment) which allows the protein to persist in the neuronal tissue.
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What is Prpsc capable of doing to normal proteins?
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PrPsc is capable of converting the normal, benign form of the prion protein, PrPc, into more of the PrPsc, which accounts for the accumulation of the protein.
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What do the accumulations of PrPsc eventually do?
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Accumulations of PrPsc form amyloid-type plaques which ultimately perforate cells causing a spongiform destruction of the brain.
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Why are there different disease manifestations for various prion diseases?
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Different forms of the disease causing PrPsc preferentially affect different regions of the brain.
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What are a few examples of PrPsc associated diseases?
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1. Fatal Familial Insomnia
2. vCJD 3. CJD 4. Kuru |
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What do oxidoreducatases do?
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Catalyze oxidation-reduction reactions (ex. dehydrogenation)
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What do transferases do?
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Catalyze transfer of C-, N-, or P- containing groups.
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What do hydrolases do?
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Catalyze cleavage of bonds by addition of water.
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What do lyases do?
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Catalyze cleavage of C-C, C-S, and certain C-N bonds.
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What do isomerases do?
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Catalyze racemization of optical or geometric isomers.
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What do ligases do?
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Catalyze formation of bonds between carbon and O, S, N coupled to hydrolysis of high-energy phosphates.
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Where does a substrate bind an enzyme?
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At the active site
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Holoenzyme
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Active enzyme with it nonprotein component
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Apoenzyme
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Inactive enzyme without its nonprotein component
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Cofactor
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Non-protein moiety that is a metal ion (e.g. Zn2+ or Fe2+)
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Coenzyme
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Small organic molecule
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Vmax
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Maximal velocity attainable by an enzyme
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What is the shape of the curve for allosteric enzymes?
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Sigmoidal
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What is the shape of the curve for most enzymes?
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Hyperbolic
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Vo
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initial reaction velocity
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Km
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Michaelis constant-affinity of the enzyme for its substrate-the substrate concentration at which the rxn velocity is = to 1/2Vmax
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At low concentrations of substrate ([S]<<Km), the velocity of the reaction is what order?
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First order-proportional to substrate concentration
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At high concentrations of substrate ([S]>>Km), the velocity of the reaction is what order?
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Zero order-It's constant and independent of substrate concentration.
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Why is the Lineweaver-Burk plot useful?
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It can be used to calculate Km and Vmax and can be used to determine the MOA of enzyme inhibitors.
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Competitive Inhibitor-effect on Vmax?
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Competitive inhibitors have no effect on Vmax
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Competitive inhibitor-effect on Km?
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Competitive inhibitors increase Km (more substrate need to reach 1/2 Vmax)
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What is an example of a class of drugs that are competitive inhibitors?
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Statins
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Noncompetitive inhibitors-effect on Vmax?
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Noncompetitive inhibitors decrease Vmax
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Noncompetitive inhibitors-effect on Km?
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Noncompetitive inhibitors don't affect Km.
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What is an example of a noncompetitive inhibitor?
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Lead-noncompetitively inhibits ferrochelatase
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Negative/Positive effectors on allosteric enzymes-are Km or Vmax altered?
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BOTH Km and Vmax are altered.
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