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Proteins, Hemoglobin, and Plasma Proteins

Tier 1 · #6 of 33 · highest yield · topic 1.5 — every high-yield fact from the book chapter, exam-ready.

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  1. Front
    Which stereoisomer are all amino acids in human proteins, and what is the single exception?
    Back
    L-stereoisomers ; glycine is the exception ( no stereocenter )
  2. Front
    Approximately what percent double-bond character does the peptide bond have, making it planar and rigid?
    Back
    ~40%
  3. Front
    The six atoms of the peptide unit are locked _____ (in one plane), so free rotation around the peptide bond is forbidden.
    Back
    coplanar
  4. Front
    Free backbone rotation in a polypeptide occurs only around which bonds?
    Back
    The bonds to the alpha-carbon (the phi and psi angles )
  5. Front
    In which direction is a peptide chain conventionally read and written?
    Back
    From the N-terminus (free amino) to the C-terminus (free carboxyl)
  6. Front
    What does Anfinsen's principle state about the relationship between primary sequence and 3D structure?
    Back
    The amino acid sequence alone is sufficient to specify the protein's native 3D structure
  7. Front
    Which enzyme did Anfinsen refold from 8M urea (with disulfides broken) to demonstrate that sequence encodes structure?
    Back
    Ribonuclease A (RNase A)
  8. Front
    Do chaperone proteins carry structural folding information? If not, what do they do?
    Back
    No — they prevent aggregation ; sequence carries the structural information
  9. Front
    What type of bond stabilizes BOTH the alpha-helix and the beta-pleated sheet ?
    Back
    Backbone hydrogen bonds (C=O of one residue to N-H of another)
  10. Front
    How many amino acid residues are there per turn of an alpha-helix ?
    Back
    3.6 residues per turn
  11. Front
    In an alpha-helix , each backbone C=O hydrogen-bonds to the N-H of the residue _____ positions further along the chain.
    Back
    four (n to n+4)
  12. Front
    Are the hydrogen bonds of an alpha-helix parallel or perpendicular to the helical axis?
    Back
    Parallel (along) the helical axis
  13. Front
    Which amino acid is the classic 'helix breaker' and cannot participate in an alpha-helix ?
    Back
    Proline
  14. Front
    Why can proline NOT donate a hydrogen bond within an alpha-helix ?
    Back
    Its side chain is bonded back to its own backbone nitrogen, so there is no N-H to donate
  15. Front
    How many residues make up a beta-turn , and which two amino acids are common in turns?
    Back
    Four residues ; proline and glycine
  16. Front
    In a globular protein's tertiary fold, where do hydrophilic vs hydrophobic residues cluster?
    Back
    Hydrophilic on the surface (exposed to water); hydrophobic packed in the interior core
  17. Front
    Which single interaction is considered the most important contributor to protein folding and stability?
    Back
    Hydrophobic interactions (burial of nonpolar residues away from water)
  18. Front
    Why are disulfide bonds rare in intracellular proteins but common in extracellular ones?
    Back
    The cytoplasm is reducing ; the extracellular space is oxidizing (allows S-S formation)
  19. Front
    What is a 'domain' within tertiary structure, in terms of size?
    Back
    A compact, semi-independently folding globular unit of ~100–200 residues
  20. Front
    Quaternary structure forms when two or more _____ associate into a functional unit.
    Back
    polypeptide chains (subunits)
  21. Front
    Which interactions primarily hold hemoglobin 's four subunits together?
    Back
    Noncovalent interactions (H-bonds, ionic bonds, especially hydrophobic interactions )
  22. Front
    Why is denaturation usually irreversible in practice?
    Back
    Exposed hydrophobic regions aggregate into an insoluble precipitate
  23. Front
    What concentration of urea causes complete unfolding of a protein?
    Back
    8M urea
  24. Front
    A misfolded protein in vivo is either degraded by the _____ or aggregates into insoluble deposits.
    Back
    proteasome
  25. Front
    What secondary-structure content predominates in amyloid fibrils ?
    Back
    Beta-sheet (highly ordered, insoluble, protease-resistant)
  26. Front
    Which immunoglobulin component, overproduced in plasma cell myeloma , deposits as amyloid in the kidney ?
    Back
    Immunoglobulin light chains
  27. Front
    How does the primary sequence of PrP^sc compare to PrP^c , and what differs?
    Back
    Identical primary sequence ; PrP^sc has an aberrant fold with higher beta-sheet content
  28. Front
    How does PrP^sc propagate without any nucleic acid?
    Back
    It catalyzes the refolding of normal PrP^c into the scrapie ( PrP^sc ) conformation
  29. Front
    Why is an organism lacking PrP entirely immune to prion infection?
    Back
    Without the normal PrP^c substrate, there is nothing for PrP^sc to convert
  30. Front
    Which iron oxidation state must heme be in to bind oxygen?
    Back
    Fe(II) (ferrous)
  31. Front
    Oxidation of heme iron to Fe(III) produces methemoglobin/metmyoglobin — can these bind oxygen?
    Back
    No, they cannot bind oxygen
  32. Front
    How many alpha-helices and heme groups does myoglobin have?
    Back
    Eight alpha-helices (A–H); one heme group
  33. Front
    Which conserved histidine in myoglobin coordinates directly to the heme iron?
    Back
    The proximal histidine (His F8 / His93)
  34. Front
    What is the functional role of the distal histidine in myoglobin ?
    Back
    It sterically/electrostatically lowers the iron's affinity for carbon monoxide (CO)
  35. Front
    How does the distal histidine change CO 's binding advantage over O2 in myoglobin (free heme vs in-protein)?
    Back
    From ~20,000x (free heme) down to ~200x (in protein)
  36. Front
    What shape is myoglobin 's oxygen-binding curve, and what function does that suit?
    Back
    Hyperbolic ; high-affinity O2 STORAGE in muscle
  37. Front
    Why is myoglobin a poor oxygen TRANSPORTER despite high affinity?
    Back
    It is nearly saturated everywhere , so it loads in lungs but won't release O2 in tissues
  38. Front
    What is hemoglobin 's subunit composition (adult HbA)?
    Back
    Two alpha chains and two beta chains (alpha2-beta2)
  39. Front
    What shape is hemoglobin 's O2-binding curve, and what property produces it?
    Back
    Sigmoidal (S-shaped); produced by positive cooperativity
  40. Front
    In positive cooperativity , how does affinity change from the first to subsequent O2 bound?
    Back
    First O2 binds with low affinity ; each subsequent O2 binds with progressively higher affinity
  41. Front
    At the molecular trigger of cooperativity, what happens to the heme iron when O2 binds?
    Back
    The iron drops into the porphyrin plane , pulling the proximal histidine and F helix inward (~0.29 Å)
  42. Front
    Which conformational state of hemoglobin is the deoxy, low-affinity form?
    Back
    The T-state (Tense)
  43. Front
    What is hemoglobin 's approximate P50 at pH 7.4?
    Back
    ~26 mmHg
  44. Front
    Which four allosteric effectors shift the Hb O2 curve to the RIGHT (lower affinity, more O2 release)?
    Back
    H+ , CO2 , and 2,3-BPG ( CO is the effector that shifts it LEFT )
  45. Front
    Which beta-chain histidine is the key molecular player in the Bohr effect , and its approximate pKa?
    Back
    His146 (beta chain), pKa ~6.5
  46. Front
    When protonated, His146 forms a stabilizing ionic bond with which residue, favoring the T-state?
    Back
    Asp94 (of the same beta chain)
  47. Front
    In the Bohr effect , does increased H+ (lower pH) in active tissue shift the curve left or right?
    Back
    Right (lower affinity, promotes O2 release)
  48. Front
    Roughly what fraction of CO2 is transported bound to hemoglobin's N-terminal amino groups as carbaminates ?
    Back
    ~15% (the majority, ~80%, travels as bicarbonate in plasma)
  49. Front
    Which conformational form of hemoglobin does 2,3-BPG bind?
    Back
    Deoxyhemoglobin (T-state) only
  50. Front
    Where does 2,3-BPG bind within hemoglobin , and why not in the oxy form?
    Back
    The central cavity between the two beta subunits ; the cavity narrows in the R-state so it can't fit
  51. Front
    What happens to hemoglobin 's binding curve in the ABSENCE of 2,3-BPG ?
    Back
    It loses cooperativity and approaches a hyperbola (high affinity, poor tissue delivery — like myoglobin)
  52. Front
    Within 12–24 hours at high altitude, what change in red cells right-shifts the O2 curve?
    Back
    Increased synthesis of 2,3-BPG
  53. Front
    What is the subunit composition of fetal hemoglobin (HbF)?
    Back
    alpha2-gamma2
  54. Front
    Which residue substitution in gamma chains weakens HbF's 2,3-BPG binding?
    Back
    Serine replaces histidine at position 143 (His143→Ser)
  55. Front
    Why does HbF have HIGHER O2 affinity than HbA ?
    Back
    It binds 2,3-BPG weakly (Ser143), so it isn't right-shifted as much — letting it extract O2 from maternal HbA
  56. Front
    Which direction does CO shift the Hb O2 curve, and what is the functional consequence?
    Back
    Left ; O2 loads but cannot be released to tissues ( functional hypoxia )
  57. Front
    Besides competing for heme, how does CO worsen oxygen delivery at the remaining hemes?
    Back
    It stabilizes the R-state , increasing the remaining hemes' affinity for O2 (so O2 won't unload)
  58. Front
    What carboxyhemoglobin (COHb) range do smokers typically have?
    Back
    3–8% (up to ~15%); normal is ~1%
  59. Front
    What amino acid substitution causes sickle cell disease (HbS) in the beta chain?
    Back
    Glu6→Val ( glutamate to valine at position 6)
  60. Front
    Why does the Glu6→Val substitution cause HbS to aggregate?
    Back
    Valine is hydrophobic, creating an exposed hydrophobic surface patch that drives fiber aggregation
  61. Front
    Sickle-cell aggregation of HbS occurs ONLY in which oxygenation state?
    Back
    The deoxy state (deoxy-HbS); oxygenated HbS is relatively normal
  62. Front
    Why does the HbA/HbS heterozygous (sickle trait) state confer a survival advantage in malaria -endemic regions?
    Back
    P. falciparum promotes sickling; macrophages clear sickled cells, killing the parasite before it matures
  63. Front
    Into how many bands does serum protein electrophoresis (SPEP) separate plasma proteins, and name them in migration order?
    Back
    Five : albumin , alpha-1 , alpha-2 , beta , and gamma globulins
  64. Front
    Why does albumin migrate farthest toward the anode on SPEP?
    Back
    It has the most negative charge at pH 7.4 (pI 4.8 → ~20 negative charges per molecule)
  65. Front
    A sharp monoclonal spike in the gamma region of SPEP is the hallmark of which disease?
    Back
    Multiple myeloma (a broad polyclonal rise suggests chronic infection/inflammation )
  66. Front
    Where are most plasma proteins synthesized?
    Back
    The liver
  67. Front
    Almost all plasma proteins are glycoproteins — which major one is the notable exception?
    Back
    Albumin
  68. Front
    What collective physical property do plasma proteins generate to oppose capillary hydrostatic pressure?
    Back
    Oncotic (colloid osmotic) pressure
  69. Front
    A severe fall in plasma protein concentration ( kwashiorkor , nephrotic syndrome , liver disease ) causes what clinical sign?
    Back
    Edema (fluid leaks into the extravascular space)
  70. Front
    What percentage of total plasma oncotic pressure is provided by albumin ?
    Back
    75–80%
  71. Front
    Name three major ligands transported non-specifically by albumin .
    Back
    Fatty acids , bilirubin , and Ca2+/Cu2+/steroid hormones/drugs (e.g., sulfonamides, aspirin)
  72. Front
    In what oxidation state does transferrin carry iron?
    Back
    Fe(III) (ferric)
  73. Front
    How does transferrin release its iron inside the cell?
    Back
    Its iron affinity drops sharply at low pH , releasing iron in the acidic endosome
  74. Front
    What is the primary protective function of haptoglobin ?
    Back
    It binds free hemoglobin from hemolysis, preventing renal damage and iron loss
  75. Front
    What happens to plasma haptoglobin levels in hemolytic anemia , and why?
    Back
    They fall dramatically — Hb-Hp complexes are cleared faster than the liver replaces haptoglobin
  76. Front
    Alpha-1-antitrypsin is the principal plasma inhibitor of which class of enzymes (and name a key target)?
    Back
    Serine proteases (serpin); it inhibits elastase (and trypsin )
  77. Front
    By what mechanism does cigarette smoke inactivate alpha-1-antitrypsin ?
    Back
    It oxidizes a critical methionine residue in A1PI, inactivating it
  78. Front
    Unchecked neutrophil elastase from A1PI deficiency or smoking causes which lung disease?
    Back
    Emphysema (destruction of alveolar walls)
  79. Front
    Which immunoglobulin is the most abundant in the gamma globulin fraction, and its chain composition?
    Back
    IgG ; two heavy chains and two light chains
  80. Front
    Which region of IgG contains the two antigen-binding sites, and which mediates effector functions?
    Back
    Fab regions (tips of the Y) bind antigen; the Fc region (stem) mediates effector functions
  81. Front
    Why does the gamma band appear as a broad smear in health but a sharp spike in myeloma ?
    Back
    Healthy Igs are polyclonal (millions of sequences); myeloma produces one monoclonal antibody
  82. Front
    Which agent does the chapter list FIRST among the classic protein denaturants ?
    Back
    High temperature (typically above 60°C)
  83. Front
    Above roughly what temperature does heat typically denature a protein?
    Back
    ~60°C (varies: lysozyme ~72°C, myoglobin ~79°C)
  84. Front
    Besides heat and 8M urea , name the other two classic denaturing agents listed in the chapter.
    Back
    Extreme pH and organic solvents
  85. Front
    List three clinically important consequences of protein denaturation .
    Back
    Loss of enzyme activity , destruction of toxins , loss of solubility (and improved digestibility — why cooking matters)
  86. Front
    At what carboxyhemoglobin (COHb) level do CO-poisoning symptoms (headache) typically begin?
    Back
    ~15% COHb
  87. Front
    At what COHb range do strong headache and nausea appear in CO poisoning ?
    Back
    20–30% COHb
  88. Front
    Above what COHb level does loss of consciousness occur in CO poisoning ?
    Back
    >50% COHb
  89. Front
    Above what COHb level is CO poisoning typically fatal?
    Back
    >60% COHb
  90. Front
    Write the carbonic anhydrase reaction in tissue that underlies the Bohr effect .
    Back
    CO2 + H2O → H2CO3 → H+ + HCO3-
  91. Front
    Which enzyme catalyzes the hydration of CO2 to carbonic acid that drops tissue pH in the Bohr effect ?
    Back
    Carbonic anhydrase
  92. Front
    Why can drug-drug competition for albumin binding be clinically important?
    Back
    Displacing a drug from albumin raises its free (active) plasma concentration
  93. Front
    With roughly what affinity (Kd) does transferrin bind Fe(III) at pH 7.4?
    Back
    Kd ~10^-22 M (one of the strongest non-covalent interactions in biology)
  94. Front
    In normal plasma, what fraction of transferrin carries two iron atoms (is diferric)?
    Back
    ~12%
  95. Front
    In normal plasma, what fraction of transferrin is monoferric vs iron-free (apo)?
    Back
    ~44% monoferric and ~44% iron-free (apo) — so total iron-binding capacity is far from saturated
  96. Front
    What is the handedness of the alpha-helix ?
    Back
    Right-handed
  97. Front
    What is the pitch (rise per turn) of an alpha-helix ?
    Back
    5.4 angstroms (Å)
  98. Front
    Roughly how much hemoglobin is in 1 liter of adult blood, and how much O2 can it bind?
    Back
    ~150 g Hb per liter , binding ~200 mL O2
  99. Front
    How much more oxygen does hemoglobin let a liter of blood carry compared to plasma alone?
    Back
    ~90 times more O2 per liter than plasma alone
  100. Front
    Do adjacent strands in a beta-sheet run only one direction?
    Back
    No — they can run the same direction ( parallel ) or opposite directions ( antiparallel )
  101. Front
    In a beta-pleated sheet , where do the side chains project relative to the plane of the sheet?
    Back
    They alternate above and below the plane of the sheet
  102. Front
    How many strands does a beta-sheet in a globular protein typically contain?
    Back
    2 to 12 strands (up to ~15 residues each)
  103. Front
    How many total positive charges does 2,3-BPG interact with in the deoxyhemoglobin central cavity, and from which residues?
    Back
    8 positive charges : 2 lysines, 4 histidines, and the 2 beta-chain N-terminal amino groups
  104. Front
    From what metabolic pathway is 2,3-BPG produced in red blood cells?
    Back
    Glycolysis (it is a side product)
  105. Front
    Why is the sickle-cell vaso-occlusive crisis a self-amplifying (positive-feedback) event?
    Back
    Low tissue pO2 favors deoxy-HbS , which aggregates and occludes flow, further lowering local pO2 and driving more sickling
  106. Front
    Why do sickle cell patients develop hemolytic anemia ?
    Back
    Sickled red cells are recognized and destroyed by the spleen
  107. Front
    What is the normal plasma concentration of albumin ?
    Back
    ~4.5 g/dL
  108. Front
    What is the molecular weight of albumin ?
    Back
    ~69,000 Da (69 kDa)
  109. Front
    How is total body albumin distributed between plasma and the extravascular space?
    Back
    40% intravascular (plasma); 60% extravascular extracellular space
  110. Front
    Roughly how much albumin does the liver synthesize per day?
    Back
    ~12 g per day
  111. Front
    Which amyloid protein deposits in the brain in Alzheimer's disease ?
    Back
    Amyloid-beta (Aβ)
  112. Front
    How many amino acids build human proteins, and what rare residue is sometimes counted as the 21st?
    Back
    20 standard amino acids ; selenocysteine is the rare 21st
  113. Front
    Where are D-amino acids found, given they are never in human proteins?
    Back
    Bacterial cell walls and some peptide antibiotics
  114. Front
    The drive of a polypeptide to fold into its native structure reflects a search for the conformation of lowest _____.
    Back
    free energy
  115. Front
    Give the equation for myoglobin 's hyperbolic O2-saturation curve.
    Back
    Y = pO2 / (P50 + pO2) , where Y = fractional saturation
  116. Front
    Below roughly what tissue pO2 is myoglobin still nearly fully saturated, fitting its storage role in resting muscle?
    Back
    Below ~30 mmHg
  117. Front
    Roughly what fraction of its bound O2 does hemoglobin unload in resting tissue (pO2 ~40 mmHg)?
    Back
    About 25%
  118. Front
    During cooperativity, which subunit pair slides relative to the other to destabilize the T-state?
    Back
    The alpha1-beta2 interface slides relative to the other alpha-beta dimer
  119. Front
    Roughly what fraction of CO2 is carried in the plasma as bicarbonate ?
    Back
    ~80%
  120. Front
    Besides 2,3-BPG , what acid-base change at high altitude initially accompanies the right-shift (and is dominated by the BPG effect within a day)?
    Back
    Respiratory alkalosis from hyperventilation
  121. Front
    Over days to weeks at high altitude, which hormone drives increased hemoglobin synthesis and hematocrit?
    Back
    Erythropoietin (EPO)
  122. Front
    About how many distinct proteins have been identified in human blood plasma?
    Back
    More than 150
  123. Front
    In heme , to how many porphyrin-ring nitrogen atoms is the central iron coordinated?
    Back
    Four (the four pyrrole nitrogens of the porphyrin ring)
  124. Front
    Oxygen binds heme iron as the _____ ligand, on which face of the heme?
    Back
    The sixth ligand , on the distal face (the proximal histidine occupies the fifth coordination position)

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