Haemoglobin and Enzymes Flashcards
What are the function and structure of proteins in the body?
Proteins are responsible for:
- Cell shape + inner organisation (structural proteins)
- Carrier and transport of nutrients (haemoglobin)
- Aiding in biochemical reactions (enzymes)
- Signalling and communication
Different levels of structure that are connected to function
What is haemoglobin?
Contained in red blood cells
An iron rich protein and an oxygen carrier
What kind of structures can molecules have?
Primary
Secondary
Tertiary
Quaternary
What is the structure of haemoblobin (Hb)?
Tetrameric = Quaternary structure with 2x alpha polypeptide chains and 2x beta polypeptide chains
Contains globin protein and 4x heme-iron (non-proteins)
Each haemoglobin can bind 4x oxygen molecules, one for each heme
When an oxygen molecule binds to the iron binding site of a heme group, the conformation of haemoglobin protein changes. What are the two conformational states of haemoglobin?
Taut / Tense / T state = deoxyhaemoglobin and having lower oxygen binding affinity
Relaxed / r state = oxyhaemoglobin and favouring oxygen binding
What is the impact of the differet conformational states of haemoglobin?
Binding one oxygen molecule facilitates te binding of another, with every bound oxygen molecule affinity becomes greater
At 75%, Hb has almost 300 times more affinity for binding oxygen than the first
In R state, the centre of the molecule becomes a binding site for 2, 3 - DPG which pushes haemoglobin into a tense state and promotes oxygen unloading
What is the sigmoidal curve?
Function demonstrating the relationship between oxygen partial pressure in lung alveoli and systemic arterial blood (pO2, mmHg) and oxyhaemoglobin saturation percentage in venous blood
After 80mmHg, there is not much change in oxygen saturation (95.8%)
40mmHG = 75% saturation
26.6mmHg = 50% saturation
What is P50 on a sigmoidal curve and what is it’s purpose?
Represents oxygen tension when haemoglobin is 50% saturated
Used to measure the impacts of curve shifts
What changes are exemplified by shifting a sigmoidal curve right and left?
Right curve shift = P50 increases, O2 affinity decreases and Hb unloads more O2
Left curve shift = P50 decreases, O2 affinity increases, Hb takes up more O2
What is the Bohr Effect?
The inversely proportional relationship between Hb oxygen binding affinity and the pH, CO2, and 2,3-BPG levels and right curve shifts
How does the Bohr effect work?
Exercised muscles produce acid, CO2, and 2,3-BPG
2,3-BPG binds and stabilises Hb in the T state, decreasing oxygen affinity
Therefore, in metabolically active cells / organisms:
- Low pH and a high CO2 and 2,3-BPG = less Hb oxygen affinity
- More oxygen availability to other cells as more oxygen is unloaded
How does foetal haemoglobin behave differently?
Oxygen saturation is foetuses is greater than that of an adult (left curve shift)
Allows easier transfer of maternal O2 to the developing foetus as they are required to steal oxygen from the mother’s blood
Uses myoglobin and HbF
What is myoglobin and HbF?
Myoglobin = oxygen binding protein similar to Hb, stores as opposed to transports
HbF = Foetal exclusive haemoglobin made of 2x alpha and 2x gamma chains
What are enzymes?
Macromolecular biological catalysts that aid biochemical reactions of a cell
They are specific to a chemcial reaction ad accelerate its rate
They do not change equilibrium and are not consumed or modified in the reaction
What do enzymes do?
Convert the starting molecule (substrate) into different molecules (product) eg sucrase catalyses hydrolysis of surcose into glucose
How do enzymes work?
Binding of a substrate to an active site causes the substrate to become unstable and react
The resulting products are then released by the active ssite
What are Michaelis-Menten kinetics?
A saturation curve for an enzyme reaction showing the relation between the substrate concentration and reaction rate
What is Vmax?
Maximum rate achieved by the system at maximum (saturating) substrate concentrations
What does Km represent?
The Michealis constant
The concentration of substrate at which the velocity is half of the maximum (Vmax 1/2)
What is the principle rule of Michaelis-Menten kinetics?
If Km is less, affinity is more
If Km is more, affinity is less and therefore needs a higher concentration to reach maximum velocity
