Biochemistry Lecture 8 - O2 Transport Flashcards
(18 cards)
What does H+ bind to in Hb?
The histidine on the alpha subunit.
What does CO2 bind to in Hb?
The alpha subunit.
What does BPG bind to in both Myoglobin and Hb?
The beta chain.
Does CO bind to heme in myoglobin more or less readily than O2? Why?
CO binds less readily to heme in myoglobin because the distal histidine sterically hinders molecules that are bound to Fe in heme to adopt a 120 degree bond angle. O2 naturally bonds at this angle, while CO would naturally bond at a 180 degree angle.
What does a positive slope of a Hill coefficient indicate?
It indicates cooperativity.
What subunits make up HbA? HbF?
Two alpha and two beta subunits for HbA. Two alpha and two gamma for HbF.
How many hemes does HbA contain?
4
What are the two states of Hb? Which form has greater affinity for O2?
Taut and relaxed. Relaxed binds O2 more readily.
Which conformation of Hb contains more H-bonds between the two alpha-beta dimers?
The T form is has more H-bonds and is more stable.
The Bohr effect shifts the Hb O2 binding curve in which direction? What does this mean in regards to O2 affinity?
To the right. It decreases Hb’s affinity for O2.
What are the three allosteric effectors of O2?
H+, CO2, BPG. They are NEGATIVE allosteric effectors.
Do gamma chains bind BPG more or less readily than adult beta chains? Why?
Gamma chains bind BPG less readily because the gamma chains have fewer positively charged residues, and BGP is negatively charged.
Upon low O2 conditions, what is the effect of BPG levels? Why?
BPG levels increase so that more O2 is released to tissues per cycle.
What does deoxy HbS do in low O2 conditions?
It can form a polymer.
How do you treat sickle-cell anemia (4 ways)?
- Antibiotics to secondary infection prophylaxis.
- Hydroxyurea somehow stimulates HbF production which will break up HbS polymers.
- Bone-marrow transplant.
- Gene therapy in clinical trials now.
What is methemoglobinemia and how is it caused?
It is when Fe is in the oxidized form in hemoglobin (Fe 3+). This form does not carry O2. It is caused by ingestion of oxidizing agents such as nitrates (such as nitrogen runoff in rural farming areas into the water).
How do you treat methemoglobinemia?
Administer reducing compounds such as vitamin c and methylene blue.
What are the thalassemias?
Hb diseases where there is an imbalance in the synthesis of the two chains of HbA. Due to splicing mutations of the mRNA.
