MGD S2 - Haemoglobin, Myoglobin and Enzymes Flashcards Preview

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Flashcards in MGD S2 - Haemoglobin, Myoglobin and Enzymes Deck (25):

Describe structure and function of myoglobin

Single subunit
One haem group
Hyperbolic binding
No cooperativity


Describe structure and function of hemoglobin

Four haem groups
Sigmoidal binding
Cooperative binding (hence Sigmoidal)


What are the two states of haemoglobin and their relative oxygen affinities?

Low affinity t state
High affinity r state


What prompts 2,3-BPG release in the body?

High altitudes
Released in metabolism


What effect does CO inhalation have on the body?

Binds to Hb 250x more readily than O2 and at >50% Hb bound to CO this effect is fatal.
CO binding to Hb increases other subunits affinity for oxygen.


What effect do the genetic defects of sickle cell anaemia have on a patients physiology?

Hint: What is the effect on Haemoglobin and what are the knock on effects?

Substitution for valine creates a sticky hydrophobic pocket that allows deoxygenated Hb to polymerise.
This leads to the distortion of RBCs leading to the sickle shape.
Sickle shape causes blockages in microvasculature.


What is the symptomatic difference between alpha and beta thalassaemia?

Alpha thalassaemia symptoms appear before birth
Beta thalassaemia symptoms appear after birth


Describe alpha thalassaemia

Decreased or absent alpha chains

Multiple levels of severity due to multiple copies of alpha chain genes (some correct alpha chains produced by correct copies)

Rarer than beta

Can form unstable Hb tetramers (tetrameric beta) with increased O2 affinity

Symptoms appear before birth


Describe beta thalassaemia

Decreased or absent beta chains

Cannot form stable tetramers

Symptoms appear after birth


Define Km

Michaelis Menten constant
This is the substrate conc that gives 1/2 Vmax


What effect do competitive inhibitors have on enzyme kinetics?

Will not prevent Vmax being reached
Adding more substrate will overcome the effect of the inhibition


What is the significance of myoglobin's very high oxygen affinity?

Will only release O2 when pO2 very low


Why does Hb have a Sigmoidal O2 affinity curve

As the Hb binds to oxygen it increases in affinity (transitions from t to r state)


What effect does 2,3-BPG have on the body?

Decreases haemoglobin oxygen affinity prompting oxygen release in all tissues


What effect does metabolic rate have on 2,3-BPG release and why is this beneficial?

Higher metabolic rate prompts more BPG release and hence haemoglobin releases oxygen in proportion with level of metabolism.


Explain fully the Bohr effect.

Increased concentration of CO2 and H+ in tissues (eg exercising muscle) prompts Hb to lower its oxygen affinity and hence release more oxygen to the tissue.


What type of disorder is sickle cell anemia?

Autosomal recessive blood disorder


What is the direct genetic cause of sickle cell anaemia and where does it occur?

Substitution of glutamate for valine on the B-globulin subunit of haemoglobin.


What is thalassaemia?

A group of genetic disorders that leads to imbalance between Alpha and Beta Hb subunits.


What is the function of enzymes and how do they perform this function?

They catalyse reactions (increasing rate) by binding the substrate the active site of the enzyme increasing local concentration of the substrate and stabilising the formation of the high energy transition state.


How do enzyme and substrate concentration affect rate of reaction?

Increase in conc of enzyme or substrate leads to hyperbolic increase of rate of reaction up to Vmax (saturation).


Define Vo

Rate of reaction


What is the michaelis menten equation?

Describes how Vo varies with substrate conc.

Vo = (Vmax x [S]) / (Km + [S])


What effect does non-competitive inhibition have on enzyme kinetics?

Prevents Vmax from being reached, has no effect on Km


Describe the changes of globin chains throughout development from -9 months to 6 months

Alpha-like globins:
- Initially xi then to alpha at - 7 months

Beta-like chains:
- Initially epsilon, then to gamma at - 7 months
- Then gamma to beta at 1-2 months after birth