Chp 5: Protein Function Flashcards
Characteristics of myoglobin
Classical globular protein
Contains a heme (prosthetic) group
Chemical nature, properties, and role of the heme group
A heme group is a prosthetic group found in myoglobin and hemoglobin.
Without the hem group, myoglobin would not be able to attach to oxygen. The Hem group is permanently attached to the myoglobin.
In nature, it is non-polar.
Write the equation describing binding of O2 to myoglobin and meaning of Kd
Dissociation constant = Kd and it is the reciprocal of the binding or equilibrium constant
Kd = reactants/products
When Kd is small, the product is greater and equilibrium is shifting to the right
The smaller the Kd the stronger the affinity
K
Interpretation of oxygen binding curve of myoglobin and meaning of p50
Binding of O2 to myoglobin shows a hyperbolic curve. p50 is the saturation or proportion of myoglobin that has bound to O2 (2.88torr)
How 1, 2 and 3 structure of myoglobin and alpha and beta subunits of hemoglobin differ
Myoglobin is monometic (no cooperative effect) and Hemoglobin (alpha2beta2) is tetrametic (cooperative effect). Secondary and Tertiary structures of myoglobin and hemoglobin are very similar but primary AA sequence is different. Their AA sequences are only 18% identical.
Interpretation of oxygen binding curve of hemoglobin and meaning of p50
Oxygen binds cooperatively to Hgb creating a sigmoid curve. 50p is where O2 is at 26 torr and first subunit of Hgb is attacked
Use of binding curves to explain why hemoglobin is suitable for oxygen transport
Sigmoid curve, in the beginning, few hemoglobin are binding but then once one oxygen binds to one of the four Hgb subunits then the Hgb has more of an affinity to the oxygen.
Hbg has a very low affinity for oxygen which is an advantage for transporting oxygen.
Effect of O2 binding to the Fe atom of heme group and on the alpha-helix that has the proximal histidine, and on the overall quaternary structure of hemoglobin
Hemoglobin undergoes conformational changes upon binding to O2
The two quaternary structures of hemoglobin
Deoxy (w/out O2, tense T state) and Oxy (w/ O2 relaxed R state)
Meaning of an allosteric protein
Hemoglobin is an allosteric protein
- Multiple subunits/binding sites
- Cooperative binding
Meaning of the cooperative effect
acceptance or release of a molecule to change conformation
Chemical nature of bisphosphoglycerate, binding site in hemoglobin and role in hemoglobin function
Binds through electrostatic interactions since it is very negative.
Decreases Hgb’s O2 affinity. BPG prevents oxygen binding to hemoglobin in vivo.
BPG only binds to the tense (deoxy) conformation of Hgb between the 4 subunits
What is the Bohr effect
Lower pH decreases Hemoglobin’s oxygen binding affinity.
Biochemical bases for sickle-cell anemia
Glu-6 is replaced by Val in sickle-cell hemoglobin (Hb S)
Composition of microfilaments, role of ATP in their formation
Cytoskeletal fibers are composed of structural proteins including actin filaments, intermediate filaments, and microtubules.
Actin filaments (microfilaments) are the most abundant and actin polymerization is driven by hydrolysis of ATP
Overall process of assembly of actin filaments
General amino acid sequence of collagen
Every 3rd AA residue is Gly. 1/3 of residues is Pro or Hyp (hydroxylated proline)
Collagen is the most abundant structural protein in multicellular animals.
Structure of collagen
Most common AA sequences of collagen are Gly-Pro-X and Gly-X-Hyp where X is any AA residue
The amino groups of Pro and Hyp constrain the geometry of the peptide group
Individual polypeptides are left handed helices; but 3 polypeptides wrap around each other to form an overall right handed triple helix
Why is glycine so abundant in collagen
The assembly of the triple helix puts this reside at the interior axis of the helix where there is no space for a larger side group than glycines single hydrogen atom. For the same reason, rings of Pro and Hyp point outward
B. It’s planar but mostly hydrophilic
(MOSTLY HYDROPHOBIC)
C. Myoglobin’s affinity for oxygen is low
A. Their primary structures are similar
C. Hemoglobin’s affinity for O2 is very high
B. Bohr effect
C. Increases hemoglobin’s oxygen affinity
B. Glu-6 is replaced by Val
D. None; All are correct
A. Three polypeptides wind around each other to form a right handed triple helix
