Session 2 Flashcards
Define Primary structure
The amino acid sequence of a protein.
Define Secondary structure
Stretches of the polypeptide chain that form Alpha-helices and Beta-sheets. Bonds on either side of the peptide bond can rotate freely
Define Tertiary structure
The full 3D structure of the protein. Involves the folding up of the secondary structures and some have molecular chaperones (to aid)
What is Amyloidosis?
Where the tertiary structure of a protein is not folded correctly
Define Quaternary structure
Interaction between and arrangement of different polypeptide chains (subunits) within the same protein
Define Homomeric
Polypeptide chains in the Quaternary structure are identical
Define Heteromeric
Polypeptide chains in the Quaternary structure are different
Define Globular protein
Several types of secondary structure. eg Enzymes and regulatory proteins
Define Fibrous protein
One repeating primary structure. eg Structure, support, protection
What are the key features of an alpha helix?
Right handed
3.6 AA per turn
0.54 nm pitch
Pro/Gly act as helix breakers
What are the key features of a beta sheet?
Can be parallel or anti parallel
Multiple H bonds
What is Myoglobin?
A single subunit protein that contains one Haem group for the binding and transport of oxygen
What type of binding does Myoglobin exhibit?
Hyperbolic O2 binding – no cooperativity.
What is Haemoglobin?
A tetrameric protein (2xalpha, 2xbeta subunits) containing four Haem groups.
What type of binding does Haemoglobin exhibit?
Sigmoidal O2 binding. (Cooperative binding)
What is Haemoglobin’s oxygen affinity in the T state?
Low
What is Haemoglobin’s oxygen affinity in the R state?
High
What state is deoxyhaemoglobin in?
Can exist in a low affinity T-state (tense) or a high affinity R-state (relaxed). The binding of O2 promotes the stabilisation of the R-state
How does 2,3-bisphosphoglycerate (BPG) effect the binding of O2?
Decreases the affinity of Hb for O2. Curve shifts right. BPG concentration increases at high altitudes and made during metabolism
How does CO2 and H+ effect the binding of O2?
Decrease the affinity of Hb for O2. Sites of low pH and increased CO2, eg muscle in exercise
How does CO interact with Haemoglobin?
Binds to Hb 250x more readily than oxygen.
Fatal when COHb is > 50%.
Binding of CO also acts to increase the affinity of unaffected subunits for oxygen.
Explain Sickle cell Anaemia
Autosomal recessive. Single nucleotide polymorphism resulting in substitution of hydrophilic amino acid to hydrophobic in the Beta-subunit of Hb
Distortion of RBC’s into the sickle cell shape, cell lysis
What are Thalassaemias?
group of genetic disorders where there is an imbalance between Alpha and Beta subunits.
What are the 2 types of Thalassaemias?
Beta-Thalassaemias – Decreased or absent Beta-chains. Alpha chains unable to form stable tetramers. Symptoms appear after birth.
Alpha-Thalassaemias – Decreased or absent Alpha- chains. Beta-Chains can form stable tetramers with increased affinity for oxygen. Onset before birth
