Protein Structure Flashcards
1
Q
Describe primary protein structure.
A
- Linear sequence of amino acid residues
- Joined by peptide bonds
- Synthesis begins at N-terminus and ends at C-terminus
- Forms hydrogen bonds - water soluble
2
Q
Describe secondary protein structure.
A
- Forms alpha-helices and beta sheets
- Alpha-helices held by hydrogen bonds between C=O and N-H
- Beta sheets - repeated hydrogen bonds between adjacent polypeptide strands. Can be parallel/antiparallel.
3
Q
Describe tertiary protein structure.
A
- Folding into domains
- Determined by side chain interactions - ionic, hydrogen, disuplhide bonds etc.
- Globular protein folding - hydroophobic core - polar amino acids present as hydrophilic shell
4
Q
Define quaternary protein structure.
A
- Interactions between multiple polypeptide subunits
- Held by noncovalent interactiolns e.g ionic/hydrogen bonding
- Increases protein stability/aids in protein function/ difficult to unfold
5
Q
Describe sickle cell anaemia
A
- Substitution of glutamic acid in position 6 of beta chain to valine
- Long fibres form in Hb - distort biconcave RBCs and form sickle shape to clog arteries
- Leads to hypoxia/tissue damage
6
Q
Describe globular proteins
A
- Folding of polypeptide chains into spherical shape
- Water soluble
- Have catalytic/regulatory functions
7
Q
Describe fibrous proteins
A
- Arrangement of polypeptides in long strands
- Water insoluble
- Structural proteins
8
Q
Describe secondary and tertiary structures of haemoglobin
A
- SECONDARY - forms alpha helices
- TERTIARY - alpha-helical chains connected by segments and stabilised by H-bonds
- TERTIARY - folds into globin chain containing haem group. Hydrophobic core protects haem group.
9
Q
Describe quaternary structure of Haemoglobin.
A
- Tetramer of globin subunits
- Two alpha2 and two beta2 subunits
- Binds 4 O2 molecules
10
Q
What is collagen?
A
- Found in connective tissues
- Packed together in long fibrils
11
Q
How are collagen fibres formed?
A
- Repeating glycine and proline amino acids form helix
- Three helical strands combine to form triple helix
- Triple helices bundled into collagen fibrils
12
Q
What are chaperonins?
A
- Bind to and stabilise exposed hydrophobic regions in nascent polypeptides
- Prevents premature folding
13
Q
What is protein denaturation and what causes it?
A
- Irreversible unfolding of secondary and tertiary structures
- No hydrolysis of peptide bonds/disrupts hydrogen and ionic bonds
- Caused by changes in pH and heat
13
Q
What is the effect of increasing salt concentration?
A
- Increases solubility
- Reduce electrostatic interactions with neighbouring proteins
14
Q
What happens when the following occur:
- pH=pI
- pH<pI
- pH>pI
A
- Protein has both +/- charges - form salt bonds - bond protein molecules into aggregates
- POSITIVE charge
- NEGATIVE charge
15
Q
How can proteins be separated?
A
- Charge (electrophoresis)
- Molecular weight (dialysis)
16
Q
How can protein misfolding cause disease?
A
- Misfolded proteins aggregate to form amyloids
- Amyloids insoluble in water and harms tissues/damage organs where it deposits and accumulates in extracellular space
- If they form in brain, neurodegenerative disease
17
Q
Describe Alzheimer’s Disease. PART 1
A
- Amyloid beta formed by proteolytic cleavage of APP
- Beta- and gamma-secretase cleaves polypeptide, causing intra/extracellular amyloid beta
18
Q
Describe Alzheimer’s Disease. PART 2
A
- Extracellular peptides form into parallel beta sheets, aggregate into amyloid fibres, form plaques
- Amyloid plaques deposit in brains destroying nerve cells
