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41 Cards in this Set
- Front
- Back
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Describe the alpha-helical structure of peptides and proteins.
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The alpha-helical structure of peptides and proteins represent a tightly coiled helix with 3.6 aa/turn.
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What stabilizes the alpha-helical structure of peptides and proteins?
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Alpha-helical structures are stabilized by H-bonding between carbonyl oxygen and amide hydrogen (n+4) within a single helix.
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How are the side groups of amino acids in an alpha helix oriented?
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Side groups of amino acids in the alpha helix stick out away from the long axis of the helix.
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Beta pleated sheet peptides are spread out how far?
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3.5 A/aa
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How are strands of Beta pleated sheets stabilized?
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Beta pleated sheets are stabilized by H-bonding between two or more strands; carbonyl oxygen with amide hydrogen.
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What often connects anti-parallel Beta strands?
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Anti parallel beta strands are often connected by beta turns which allow a polypeptide chain to turn 180' in ~3 amino acids.
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How are beta turns stabilized?
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Beta turns are stabilized by H-bonding (n+3)
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What two amino acids are often found in beta turns?
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Proline and glycine. Proline forces bends and glycine is the most flexible.
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Why is proline rarely found in alpha helices and beta sheets?
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Steric hindrance; Pro is a structure breaker.
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What is the heme prosthetic group in myoglobin and hemoglobin?
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Protoporphyrin IX ring with Fe2+
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What does the proximal His bind to?
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The proximal His binds directly to Fe2+.
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What does the distal His do?
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The distal His H-bonds with O2 (and CO) and forces bent geometry between Fe2+ and the gas.
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Why is bent geometry important in myoglobin/hemoglobin?
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The bent geometry weakens the CO binding to the point where its affinity is only 200x greater than O2.
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# of deaths annually in the US due to CO poisoning?
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>2500
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Why are the 3D structures of any Hb subunit and Mb virtually superimposable even though the amino acid identity is often low?
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Key amino acids such as the proximal and distal His are conserved.
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Why is Hb considered an allosteric protein?
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Hb is an allosteric protein because the binding of small molecules at one site affect binding of a 2nd molecule at a distant site.
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In Hb, binding of the first O2 favors which state?
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The binding of the first O2 favors the relaxed state (R) which increases affinity for the 2nd O2 to bind and so on.
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What is the Bohr effect?
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In active tissues, lower pH weakens O2 affinity (favors the T state). Also, higher pCO2 weakens O2 affinity (favors the T state).
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JBS Haldane:
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In the alveoli, high pO2 favors the R state, promoting release of H+ and CO2.
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Which state does 2,3-BPG favor?
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2,3-BPG favors the T state which weakens affinity for O2.
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Within hours of moving to high altitude, what happens in the blood?
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Within hours of moving to high altitude, [2,3-BPG] rises in the blood which reduces O2 affinity in the lungs and tissues. The reduction of O2 affinity, however, is greater in the tissues. Thus, a greater amount of O2 can be released in the tissues.
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What is the effect of increasing [2,3-BPG] in the blood?
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Increasing [2,3-BPG] in the blood reduces O2 affinity in the lungs and tissues (especially in the tissues).
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Where is the reduction in O2 affinity the greatest in the presence of 2,3-BPG?
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Tissues
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Why does fetal hemoglobin (Hb F) have a higher affinity for O2 than the mother's hemoglobin (Hb A)?
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Mother Hb A (alpha2 beta2) binds 2,3-BPG, while fetal Hb F (alpha 2 gamma 2) does not.
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How is adult Hb A1c (alpha2beta2-glucose) glucosylated?
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Adult Hb A1c is a non-enzymatic glucosylation of the beta subunit.
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How can [Hb A1c] be used diagnostically?
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Since red blood cells last ~120 days, Hb A1c analysis provides a 3 month window on avg serum [glucose].
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What group of individuals typically have high [Hb A1c]?
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Diabetics which often have high blood [glucose] usually have high levels of Hb A1c.
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What are two types of hemoglobinopathies?
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1. Qualitative
2. Quantitative |
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What is a qualitative hemoglobinopathy?
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Structurally abnormal Hb with reduced function
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What is a quantitative hemoglobinopathy?
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Decreased production of Hb. Most of the more than 800 mutant alleles of Hb in humans are benign and rare.
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What is the primary structure of a protein?
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sequence of amino acids
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What is the secondary structure of a protein?
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regular arrangement of amino acids located near to each other in primary structure
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What is the tertiary structure of a protein?
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The three-dimensional shape of the folded chain
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What is the quaternary structure of a protein?
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The arrangement of multiple polypeptide subunits in the protein.
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The native conformation of a protein can be either....
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Fibrous or globular
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The native conformation of proteins may be assisted by...
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chaperones
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What determines the biologic function of a protein?
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its native conformation, which is dependent on its 1,2,3, and 4 structure.
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The secondary structures of a protein consist of... (5)
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1. alpha-helix
2. beta-sheet 3. beta-bends/turns 4. non-repetitive structures 5. supersecondary structures |
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The tertiary structure of a protein is stabilized by... (4)
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1. Hydrophobic interactions
2. Hydrogen bonds 3. Electrostatic interactions 4. Disulfide bonds |
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The quaternary structure of a protein is stabilized by... (3)
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1. Hydrophobic interactions
2. Hydrogen bonds 3. Electrostatic interactions |
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Essential amino acids:
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