Protein Function and Enzymes Flashcards
What type of curve does oxygen binding to myoglobin show?
Hyperbolic
Which two complexes transport oxygen in the body?
Haemoglobin and myoglobin
Describe the features of haemoglobin structure
2 polypeptide chains - 2 alpha and 2 beta
Each chain contains a haem prosthetic group
What type of curve does haemoglobin show on binding to oxygen?
A sigmoidal curve
What gives haemoglobin its shape of binding curve?
It can move between the T state and the R state
What does the binding of oxygen in haemoglobin promote?
The R state
What is meant by ‘cooperative binding’ of haemoglobin?
The binding of one oxygen molecule promotes the binding of subsequent oxygen molecules
What effect does 2,3-BPG have on the affinity of haemoglobin for oxygen?
2,3-BPG decreases its affinity by stabilising the T state
How do H+ and carbon dioxide affect haemoglobin’s affinity for oxygen?
Decrease its affinity - the Bohr effect
How does foetal haemoglobin differ to the mother’s haemoglobin (affinity)
It has a higher affinity
What is the mutation in sickle cell anaemia?
Glutamate (negative hydrophilic) to valine (neutral hydrophobic)
What happens to BPG concentrations at high altitudes and what effect does this have?
Increases. This promotes oxygen release at tissues from haemoglobin
What type of inheritance is sickle cell anaemia?
Autosomal recessive
In sickle cell anaemia, what is the result of the mutation?
A sticky hydrophobic pocket forms allowin deoxygenated haemoglobin to polymerise.
Why are sickle cells bad?
More prone to lysis and leading to anaemia
More rigid so block microvasculature
What are thalassaemias?
A group of genetic disorders where there is an imbalance in the alpha and beta sub-units in haemoglobin.
What is beta-thalassaemia?
Decreased/absent beta chain production so alpha chains are unstable to form tetramers
When do symptoms occur in beta-thalassaemia?
After birth
When do symptoms occur in alpha-thalassaemia?
Before birth
What is alpha-thalassaemia?
Decreased/absent alpha-chain production.
What is the activation enthalpy?
The minimum energy a substrate must have for the reaction to occur
What is the transition state?
The high energy intermediate between substrate and product
How does increasing the temperature increase the rate of an enzyme reaction?
Increases the number of molecules with the activation enthalpy.
How does increasing the concentration increase the rate of an enzyme reaction?
Increases the chance of molecular collisions
What is an enzyme?
A biological catalyst that increases the rate of a reaction by lowering the activation enthalpy
What does Vmax mean?
Maximal rate when all active sites are saturated with substrate
What is Km?
The substrate concentration that gives half of the maximal velocity
Does a low Km mean an enzyme has a high or low affinity for its substrate?
High affinity
In a Lineweaver-Burk plot, what does the intercept at the x-axis mean?
-1/Km
In a Lineweaver-Burk plot, what does the gradient of a line mean?
Km/Vmax
In a Lineweaver-Burk plot, what does the intercept at the y axis mean?
1/Vmax
What is an enzyme inhibitor?
Molecules that slow down or prevent an enzyme reaction
What type of bonds do irreversible inhibitors form?
Covalent bonds
Do competitive inhibitors affect Vmax or Km?
Km
Do non-competitive inhibitors affect Vmax or Km?
Vmax
What is product inhibition?
The build of a product inhibits an enzyme reaction
What is an allosteric enzyme?
A multi-subunit enzyme with more than one active site for the substrate
What do allosteric activators do?
Increase the proportion of enzymes in the R state
Which way do allosteric inhibitors shift the sigmoid curve for the rate of an enzyme reaction?
To the right
Name two allosteric activators
AMP
Fructose-2,6-bis phosphate
Name two allosteric inhibitors
ATP, citrate, H+
What type of enzyme is phosphorylation catalysed by?
A kinase
What is phosphorylation?
The addition of a phosphate group to an -OH group on an amino acid
What is a zymogen?
The inactive precursor of a proteolytic enzyme
Give examples of enzymes which have zymogens
Digestive enzymes eg pepsin, chymotrypsin, trypsin
Some protein hormones eg insulin
What activates the intrinsic pathway for the clotting cascade?
Membrane damage
What is a zymogen?
An inactive precursor of an enzyme
What initiates the intrinsic pathway of the clotting cascade?
Damage to endothelial lining of blood cells. This releases factor 12.
What initiates the extrinsic pathway
Trauma to tissue. This releases factor 3.
Give an example of an enzyme which is controlled allosterically and name it’s inhibitors and activators.
Phosphofructokinase
Activators: AMP, fructose 2,6-bisphosphate
Inhibitors: ATP, citrate, H+
Give an example of an enzyme inhibited by substrate/product concentration
Hexokinase in glycolysis.
Inhibited when glucose 6-P concentration increases.
Give two examples of zymogens and their active enzymes
Trypsinogen ➡️ trypsin
Pepsinogen ➡️ pepsin
Prothrombin ➡️ thrombin
Fibrinogen ➡️ fibrin
