BB3 Tertiary Quaternary Structure Flashcards
Examples of proteins w/ single polypeptide chain
- myoglobin
* concanavalin A
Tertiary Structure of a protein
the spatial arrangement of amino acids usually far apart from each other in the linear sequence
Native Structure of a Protein
a 3-D structure of a protein when in a physiological environment
RNase A
- 124 amino acids
- 4 disulfide bonds
- hydrolyzes RNA
- digestive enzyme
Hydrolysis
cleavage of chemical bonds by addition of water
Orthologs
- identical structures across different species
* similar secondary structure
Paralogs
- similar structural appearance, but carries out different function
- same species
Proteins lose their structure (denature) in
- Urea 8M
* Guanidine Hydrochloride 6M
Unfolded protein
random coil
Urea and guanidine hydrochloride disrupt…
noncovalent bonds
Reducing agent which breaks disulfide bonds
beta-mercapto ethanol
donates electrons
Conclusion of Anfinsen’s Experiment #1
- the amino acid sequence of RNase A provides the info needed to specify its native structure
- the primary structure of a protein dictates its tertiary structure
Conclusion of Anfinsen’s Experiment #2
- the thermodynamically most stable structures of RNase A is its native structure
- true for all proteins
Quaternary Structure of a protein
the spatial arrangement in a protein made up from more than one polypeptide chain
Each chain of a protein is a …
subunit
Hemoglobin’s quaternary structure
• 4 separate polypeptide chains – 2 alpha subunits, 2 beta subunits
Reasons for quaternary structure
smaller quantities of genetic material to create larger proteins and structures
Quaternary structure is excellent for
regulating protein function (allosteric effect)
Allosteric effect
change in one subunit induces a change in another
Protein conformation
The 3D arrangement of a proteins atoms in its structure
•independent of number of chains in the protein
•not always in native conformation
Principal factor governing folding
- burying of hydrophobic side chains
* forms protein core
Levinthal’s Paradox
- proteins don’t fold via a random pathway
- fold to native structures via formation of a stable partially correct secondary structure features as intermediate stages in folding
Anfinsen - Experiment 1
• dissolve RNase A in betamercaptoethanol and 8M Urea (denature) = loses enzyme activity
• remove BOTH betamercaptoethanol and 8M Urea by dialysis
• oxidize cysteine = reform disulfide bond
== regains all activity
Anfinsen - Experiment 2
- denature RNase A
- remove ONLY betamercaptoethanol
- retain 8M urea
- regains 1% activity bc only 1 correct arrangement of disulfides in 105
- add trace amounts of betamercaptoethanol = disulfide bonds rearrange = regains enzymatic activity
- thermodynamics drives protein to its native structure
