4 - Protein Structure Flashcards
What are some of the roles of proteins?
- Ligands
- Receptors
- Membrane transport
- Catalysts
- Muscle contraction
- Structural support
- Immune protection
What are the 1,2,3,4 structures of proteins?
1 - Covalently bound linear amino acid sequence coded for by a gene
2 - Local arrangement of polypeptide backbone. Hydrogen bonds so alpha helix or beta pleated sheets
3 - 3D spatial arrangement of amino acids, electrostatic attractions, disulphide bonds, VDW
4 - Association of different polypeptides to form a multisubunit protein, all of the above forces
What is the structure of an amino acid?
What deermines the properties of an amino acid?
The R group
What is an amino acid residue?
What can amino acids be classified as?
What is pK?
- Measure of acid strength worked out from Ka
- Smaller pK means greater acid strength
What will happen if:
- pH < pK?
- pH > pK?
- Amino acid will be protonated
- Amino acid will be deprotonated
What is a conjugate protein?
Polypeptide containing a covalent attachment of a non-polypeptide e.g lipoprotein
How is a peptide bond formed and draw a peptide bond?
What are the characterisitcs of a peptide bond?
- Rigid (N-C has partial double bond characteristics)
- Planar (Ca-CO-NH-Ca all in same plane)
- Trans (Ca‘S on opposite sides)
Why are peptide bonds not cis?
Would be steric clashes between R groups as they are too close
What is pI?
The isoelectric point of a protein, where there is no overall net charge on the protein
What is the pI of a basic and acidic amino acid?
Basic- pI > 7
Acidic - pI < 7
pH > pI deprotonated
pH < pI protonated
What are the differences in structure between alpha helix and beta pleated sheet?
What structure of beta pleated sheets isn’t as stable?
- Parallel
What are the differences between fibrous and globular proteins?
Globular have motifs and domains
What is a motif and a domain?
- In globular proteins
Motif: Folding patterned containing multiple secondary structures
Domain: Part of a polpeptide that folds into a distinct shap for a function
How do water soluble proteins and membrane proteins fold? fold?
Water soluble: Hydrophilic outside, hydrophobic inside
Membrane protein: Reverse
What is the main difference between a secretory protein and an intrinsic protein?
Secretory protein has disulphide bonds
What are all the types of bonds in each protein structure
How do proteins fold?
- In a semi-ordered process according to the primary sequence
- Driven by localised folding to find the most stable conformation
What are amyloid fibres?
Misfolded beta pleated sheet proteins so proteins that were normally soluble are now insoluble
e.g CJD, BSE, dementia
How do you work out the ratio of protonated to deprotonated forms of amino acid at a certain pH?
Henderson-Hasselbalch
