Globular Proteins Flashcards
What is the structure of the heme group
Iron in the middle, 6 bonds with it, 4 bonds is with nitrogen, 2 bonds to the planar porphyria ring. In myoglobin and hemoglobin, one of these attach to histidine side chain and O2
What is the structure of myoglobin
8 stretches of alpha helix, labelled A - H, they terminate when they are with proline as it cannot be fit into the alpha helix or B bends
What is the difference between hemoglobin and myoglobin
Hemoglobin is more complex, has 4 tetramers, can transport protons and CO2 and 4 oxygen molecules, it can also regulate interaction with allosteric effectors
When is the oxygen dissociation curve for hemoglobin steepest
Steepest at the pO2 in the tissue, this allows for oxygen delivery to respond in small changes of pO2
What is the oxygen half saturation for hemoglobin and myoglobin
Oxygen affinity for myoglobin is high at all levels of pO2, half saturation for myoglobin is 1mmHg, while 26mmHg is needed to reach half saturation with hemoglobin
What allosteric effectors affect the ability of hemoglobin to bind oxygen
pO2 of oxygen, pO2 of CO2, pH and 2,3 BPG
What represents the shift of the oxygen dissociation curve to the left or right
Left side means that there is a higher affinity for oxygen to reach half saturation so less pO2 is needed, Right side means that there is a lower affinity for oxygen to reach half saturation so more pO2 is needed
Why is sigmoid curve for hemoglobin important
Sigmoidal curve is important as it allows for oxygen to have high and low affinity in different areas, so that oxygen can be released in tissues and absorbed in lungs. Myoglobin has hyperbolic curve so it has high affinity for hemoglobin in all tissues, so it cannot release it in tissues
Why does Bohr effect occur
Bohr effect occurs because deoxy form of hemoglobin has higher affinity to H+ than oxyhemoglobin, due to it having a higher pKa. Increase in H+ causes protanation of histidine groups with the higher pKa stabilizing salt bridges that form deoxy state
How does 2,3 BPG bind in hemoglobin
2,3 BPG binds to the B chains of the deoxy tetramer, which is lined by positive amino acids that attract the negatively charged phosphates in 2,3 BPG
What happens when hemoglobin binds to CO
Binding of CO binds tightly but reversibly, this causes R form to be favoured and forms carboxyhemoglobin. This has high affinity for oxygen and shifts the curve to the left while making it hyperbolic so that the oxygen cannot be used by the tissues
What are the 4 different minor hemoglobins
HbA: 2 alpha and 2 beta
HbA2: 2 alpha 2 delta
HbF: 2 alpha and 2 gamma
Hb1Ac - 2 alpha and 2 beta with glucose
Where does the Hb1Ac attach the glucose
2 alpha and 2 beta chains, the beta chains have the N-terminal valines that are glycosylated
What are the characteristics of the alpha gene family and beta gene family
Alpha gene family - chromosome 16, two genes for a chain and zeta gene
Beta gene - chromosome 11, 1 gene for a chain
What causes alpha and beta thalssemia
Beta because of point mutations, alpha because of deletions
