BCH 261 Lecture Notes - Lecture 10: Leucine, Capillary, Hydrogen Bond

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Ryerson University – Winter 2018

BCH 261-011&071 Biochemistry -March 28th, 2018

Lecture - Chapter 7 Protein Function (Binding Proteins)

Myoglobin and hemoglobin binding to oxygen

Globins in oxygen transport

● Myoglobin

○ Monomeric heme protein that binds to oxygen in tissues

● Hemoglobin

○ Tetrameric heme protein that transports oxygen from lungs to peripheral tissues

and returns carbon dioxide to lungs

Oxygen is not very soluble hence the need for a carrier and there are no amino acids that have

a good affinity for oxygen

Myoglobin and hemoglobin are built on a common protein folding motif

Function of Fe in myoglobin

● Fe2+ can form free radicals

● In order to prevent hat Fe2+ is coupled to the organic group HEME

● Fe2+ (can bind to oxygen) in free heme can be oxidized to Fe3+(cannot bind to oxygen)

Heme

● Heme is an iron porphyrin specifically a protoporphyrin

● Has 4 pyrrole rings

● Fe2+ has 6 coordinate bonds

● 4 of those bonds are coordinated with 4 nitrogen atoms

from pyrrole

● What binds to the other sites? Answer: Oxygen

● What are the spectral properties of porphyrin?

Answer: Very coloured due to conjugation of double

bonds which makes hemoglobin red

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Ryerson University – Winter 2018

BCH 261-011&071 Biochemistry -March 28th, 2018

Heme bond to Myoglobin

● The 5th bond is oxygen and the 6th bond to proximal histidine residue of gloving protein

which hold oxygen in place

● Distal histidine stabilizes the oxygen bond via hydrogen bonding

Carbon monoxide kills because it bind HEME better than oxygen

● Carbon monoxide has similar size and shape to oxygen

● CO bonds to free HEME 20,000 times better than O2

● Myoglobin protein pocket decreases affinity for CO but it still binds 250 times better

than O2

● CO blocks the function of myoglobin, hemoglobin

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Ryerson University – Winter 2018

BCH 261-011&071 Biochemistry -March 28th, 2018

Oxygen binding curve for myoglobin

● PO2 - partial pressure of oxygen

● YO2 - fraction of sites occupied

● Dissociation reaction: Mb02 ⇌ Mb + 02

● Kd = [Mb][02]/[Mb02]

● YO2 = PO2/ P50+ PO2 where P50 is PO2 at half saturation

● YO2 = sites occupied / sites available

Myoglobin vs Hemoglobin

● Myoglobin

○ Monomer

○ Binds to oxygen in muscle

○ Has to bind to oxygen even when concentration is low

○ Only releases when oxygen concentrations are low on tissue

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Document Summary

Lecture - chapter 7 protein function (binding proteins) Monomeric heme protein that binds to oxygen in tissues. Tetrameric heme protein that transports oxygen from lungs to peripheral tissues and returns carbon dioxide to lungs. Oxygen is not very soluble hence the need for a carrier and there are no amino acids that have a good affinity for oxygen. Myoglobin and hemoglobin are built on a common protein folding motif. In order to prevent hat fe2+ is coupled to the organic group heme. Fe2+ (can bind to oxygen) in free heme can be oxidized to fe3+(cannot bind to oxygen) Heme is an iron porphyrin specifically a protoporphyrin. 4 of those bonds are coordinated with 4 nitrogen atoms from pyrrole. Answer: very coloured due to conjugation of double bonds which makes hemoglobin red. The 5th bond is oxygen and the 6th bond to proximal histidine residue of gloving protein which hold oxygen in place.

Related Questions

what i got is wrong

1. The dominant motif found in hemoglobin and myoglobin is: a) twisted beta sheet b) beta barrel c) helix-loop-helix d) 7-TM 2. Myoglobin has how many polypeptide chains? A) 1 b) 2 c) 3 d) 4 3. Structurally and functionally, hemoglobin closely resembles a(n) a) transmembrane protein b) mucopolysaccharide c) bile salt d) allosteric enzyme 4. The oxygen binding site in hemoglobin and myoglobin is called: a) BPG b) heme c) proximal-His d) N-terminal carbamate 5. The proximal His residue in hemoglobin and myoglobin binds to which atom or molecule? A) CO2 b) O2 c) Fe d) BPG 6. The distal His residue in hemoglobin and myoglobin binds to which atom or molecule? A) CO2 b) O2 c) Fe d) BPG 7. BPG binds to: a) N-terminal carbamate b) proximal His c) heme group d) central cavity 8. Indirect activity of CO2 is a result of increased concentration of which chemical species? A) BPG b) H+ c) heme iron d) distal His 9. Direct activity of CO2 is a result of binding to which molecular feature? A) the heme group b) the N-terminal ends of the 4 polypeptide chains c) the central cavity d) the proximal His 10. The sigmoidal, cooperative binding curve commonly observed for hemoglobin is a result of: a) competition between CO2 and O2 for heme binding. B) competition between heme and distal His for O2 binding c) competition between BPG and CO2 for binding at the central cavity site d) T to R transition 11. Hemoglobin has a tendency to release its oxygen to the tissues because: a) in this region pH is high and O2 concentrations are low b) in this region both pH and O2 concentrations are low c) in this region both pH and O2 concentrations are high d) there is much BPG in this region 12. Which statement about fetal hemoglobin is not true? A) fetal hemoglobin has gamma chains instead of beta chains b) fetal hemoglobin binds BPG less strongly than maternal hemoglobin c) fetal hemoglobin binds oxygen less strongly than maternal hemoglobin d) fetal hemoglobin binds oxygen more strongly than maternal hemoglobin 13. Which process is most responsible for the sickling of cells seen in sickle cell disease? A) aggregation of the oxygenated R form of hemoglobin-S to form insoluble fibers b) aggregation of the deoxygenated T form of hemoglobin-S to form insoluble fibers c) Hemoglobin-S does not contain heme d) Hemoglobin-S contains a mutant form of heme which will not bind oxygen 14. A person with sickle-cell trait is very unlikely to catch which disease? A) malaria b) colon cancer c) avian flu d) whooping cough 15. A person with a genetic defect which results in the synthesis of an insufficient amount of the alpha chain of hemoglobin is said to have which disease? A) alpha thalassemia b) beta thalassemia c) pernicious anemia d) Crohnâs disease

BCH 261 Lecture Notes - Lecture 10: Leucine, Capillary, Hydrogen Bond

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