MGD Session 2 Flashcards
What is Myoglobin?
A single subunit protein with one haem group for binding and transport of one molecule of oxygen.
What is the name of the shape that a myoglobin binding graph would exhibit?
Hyperbolic (no cooperativity)
What is haemoglobin?
A tetrameric protein with 2 alpha subunits and 2 beta subunits and four Haem groups. It can bind four molecules of oxygen.
What is the name of the shape that a myoglobin binding graph would exhibit?
Sigmoidal (cooperative binding)
Where in the body will you find myoglobin and why?
In the muscle as a temporary store of O2 in muscle.
Where will you find haemoglobin?
In the blood for oxygen transport
Haemagolobin can exist in two states, what are these state?
Low affinity T state (tense)
High affinity R state (relaxed)
How does cooperativity work in O2 binding in haemoglobin?
As more O2 binds, the affinity of the haemoglobin for oxygen increases. Oxygen binding promotes stabilisation of the R state.
How does 2,3-bisphosphate (BPG) affec the affinity of Haemoglobin for O2?
It decreases the affinity shifting the curve to the right. BPG increases at high altitudes and is produced during metabolism so O2 needs to be released at the tissues.
How do CO2 and H+ affect the affinity of haemoglobin for o2?
They decrease the affinity, shifting the graph to the right. This is because at sites of high H+ and high CO2 in the body, respiration is obviously going on so oxygen is released. This is the Bohr effect.
How does CO affect oxygen binding to haemoglobin?
CO binds 250x more readily to haemoglobin than oxygen so it increases the affinity of unaffected subunits for oxygen.
When oxygen binds to the haem group, how does the Fe group positioning change?
Fe is positioned slightly below the plane of the ring but when oxygen binds, Fe moves into the plane of the ring. This causes movement of the proximal histidine residue and so protein conformation changes slightly.
Why does HbF have a higher o2 binding affinity compared to HbA?
So oxygen transfer from the maternal blood supply to the foetal blood supply can take place easily.
What is the mutation that causes sickle cell anaemia?
Glutamate to Valine mutation forming a sticky hydrophobic pocket.
By what mode of inheritance is the sickle cell anaemia gene transferred? e.g. Austosomal Dominant
Autosomal Recessive.
Why does the distortion of Red Blood Cells into the sickle shape cause a problem?
It causes stress to the cell membrane and causes premature cell lysis. The lifespan of a sickled blood cell is only 30 days compared to normal RBC lifespan. The sickled cells can also block small blood vessels.
What is a thalassaemia?
Thalassaemias are genetic disorders where there is an imbalance between alpha and beta subunits in haemoglobin.
What is a beta-thalassaemia? When does onset occur?
In beta thalassaemias, there is a decrease (or absence) in beta globin chain production so alpha chains cannot form stable tetramers. Symptoms appear after birth.
What is an alpha thalassaemia? When does onset occur?
Decrease in alpha-globin chain production. Several different levels of severity due to multiple copies of the alpha genes being present. Beta chains can form stable tetramers with increased o2 affinity. Onset is before birth.
Enzymes can be grouped into six classes. Name them.
Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases
What are the three main ways to increase a rate of reaction?
Increase temperature
Increase concentration
Add an enzyme
What are the 5 important properties of enzymes?
They are specific They remain unchanged after the reaction They increase the rate of the reaction They do not affect the equilibrium They are proteins.
What is the difference between a cofactor and a coenzyme?
A cofactor is an inorganic ion such as Fe2+, Mn2+ etc. whereas coenzymes are organic compounds that act as temporary carriers of groups in the reaction e.g. CoA, NAD
How do enzymes work?
By lowering the activation energy.
What is the active site?
Where the reaction occurs - a cleft or crevice made up of a few amino acids from different parts of the primary sequence. It is highly specific.
What is the Lock and Key hypothesis?
That only molecules that have a complementary shape to the active site will be able to bind.
What is the Induced Fit model?
That binding of a substrate changes the shape of the enzyme to enhance binding.
What is the Michaelis-Menten Model equation?
Vo = (Vmax [S]) / (Km + [S]) Vo is initial reaction velocity [S] is substrate concentration Vmax is maximal velocity Km is the Michaelis Constant
