Ch 7 Text 1

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  1. ·         __ times as much energy is extracted from glucose in the presence of __ than in its absence
    o   For single-celled and other small organisms, oxygen can be absorbed into __ directly from the __
    • Fifteen
    • oxygen
    • actively metabolizing cells
    • air or surrounding water
  2. o   Vertebrates have two methods for supplying oxygen:
    What are they?
    • §  Circulatory system
    • §  Oxygen-transport and oxygen-storage proteins, hemoglobin and myoglobin
    • · Hemoglobin transports oxygen from lungs to tissues and contributes to the transport of carbon dioxide and hydrogen ions back to the lungs
    • · Myoglobin provides a reserve supply of oxygen for when needed
  3. Comparison of hemoglobin and myoglobin

    - Structure
    • o   Nearly identical structures for oxygen binding, but hemoglobin is more efficient, able to use 90% of its potential oxygen-carrying capacity effectively
    • §  Myoglobin uses 7% because it’s a single polypeptide;

    - hemoglobin has four chains, each of which binds oxygen cooperatively (one change in shape favorably changes other chains)
  4. §  The oxygen-binding properties of hemoglobin are modulated by __ 
    the binding of hydrogen ions and carbon dioxide in a manner that enhances oxygen-carrying capacity
  5. Comparison of hemoglobin and myoglobin

    - Cooperativity
    • §   
    • · Both cooperativity and the response to modulators are made possible by variations in the quaternary structure of hemoglobin when different combinations of molecules are bound
  6. Comparison of hemoglobin and myoglobin

    o   Both were first for which 3D structures were determined by X-ray crystallography.
  7. ·         __ revealed that myoglobin has __linked to one another by __ to make a globular structure
    ·         Myoglobin can exist in an __ called __ or in an __ called __
    • X-ray crystallography
    • alpha helices 
    • turns

    oxygen-free form called deoxymyoglobin

    oxygen bound form called oxymyoglobin
  8. o   The presence of a heme does what?
    enables hemoglobin and myoglobin to bind oxygen

    § It also gives muscle and blood the red color due to central iron
  9. · The organic component, called __, is made up of __ linked by __ to form a __. __, __, and __ are attached
    · Iron atom lies in center of __, bonded to the __ atoms
    o   Only the__ can bind oxygen
    • protoporphyrin
    • four pyrrole rings
    • methane bridges
    • tetrapyrrole ring
    • Four methyl groups, two vinyl groups and two propionate side chains
    • protoporphyrin
    • four pyrrole nitrogen
    •  Fe2+ state
  10. · The iron atom can form __ bonds on each side; these are the __ and __ 
    o   In myoglobin, the __ is occupied by __, which is the __
    • two more
    • fifth and sixth coordination sites
    • fifth coordination site
    • imidazole ring of histidine
    • proximal histidine
  11. o   __ occurs at the __ except in __
    §  Why?

    • Oxygen binding
    • sixth coordination site
    • deoxymyoglobin

    The iron ion is too big and lies outside porphyrin plane

  12. o   Binding of oxygen at the sixth coordination site does what?
    rearranges the electrons within the iron so that the ion becomes effectively smaller, allowing it to move within the plane of the porphyrin
  13. ·     ·         The structure of myoglobin prevents the __

    o   Oxygen binding to iron in heme is accompanied by the __--> a complex between __ and __

    release of reactive oxygen species

    partial transfer of an electron from the ferrous ion to oxygen

    ferric ion and superoxide anion
  14. §  It is crucial that oxygen, when released, leaves as dioxygen rather than superoxide, for two important reasons. What are they?
    • · Superoxide and other species generated from it are reactive oxygen species that can be damaging to many biological materials
    • · Release of superoxide would leave the iron ion in the ferric state
    • o   This species, called metmyoglobin, does not bind oxygen; and potential oxygen-storage capacity is lost
  15. o   Features of myoglobin stabilize the oxygen complex such that __. In particular, the __ of myoglobin includes an __ that __. The __ character of the bound oxygen species does what?

    Thus, the protein component of myoglobin does what?
    • superoxide is less likely to be released
    • binding pocket
    • additional histidine residue (distal histidine)
    • donates a hydrogen bond to the bound oxygen molecule
    • superoxide
    • strengthens this interaction

    controls the intrinsic reactivity of heme, making it more suitable for reversible oxygen binding
  16. Structure of hemoglobin
    ·         four polypeptide chains, two identical alpha chains and two identical beta chains, each of which has a set of alpha helices in the same arrangement as the alpha helices in myoglobinà globin fold
  17. o   The hemoglobin tetramer, __, is described as pair of __ that __ to form __
    §  In deoxyhemoglobin, these __ are __.
    §  The heme groups are well separated in the tetramer by __ ranging from __
    • hemoglobin A
    • identical alpha-beta dimers
    • associate
    • form the tetramer

    alpha-beta dimers are linked by an extensive interface, which includes the carboxyl terminus of each chain

    iron-iron distances ranging from 24 to 40 angstroms
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Ch 7 Text 1
Test Two
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