McMurry (Kap 19,8) - protein structures Flashcards
What are the two classifications of protein?
Globular or fibrous.
What are the difference between globular or fibrous proteins?
Difference in 3D shape.
Fibrous (collagen, myosin in muscle tissue) = consist of polypeptide chains arranged side by side in long filaments (tough and insoluble in water - used for structural materials by nature).
Globular (enzymes) are coiled into compact roughly spherical shapes (soluble in water and mobile within cells).
Proteins are so large, that the word structure for them takes on a larger meaning.
What are the four different structures when speaking of proteins?
1) Primary structure
(Shows the amino acid sequence of the protein)
2) Secondary structure
(Shows how the segment of the peptide backbone orient into a regular pattern) - a helic and B pleated.
3) Tertiary structure.
(Shows how the entire protein molecule coils into an overall 3D shape).
4) Quaternary structure
(Shows how different protein molecules comes together to yield a large structure).
How is the secondary, tertiary and quarternary strucutre determined in praksis?
By either NMR or X-ray crystallography.
What is the difference between the seconddary structures a helic and B pleated?
a helix is a right handed coil of the proteins backbone - like the coil of a spiral staircase (each turn contains 3,6 amino acid residues).
In the B pleated sheet the peptide chain is fully extended rather then coiled and the hydrogen bonds occur between residues in adjacent chains (see page 702). - the antiparralle arrangement is more common and somewhat energetically more favorable.
How is the structure of the a helix stabilized?
By the hydrogen bonds (between amide NH groups and C=O groups 4 residues away).
how is the strucutre of the B pleated stabilized?
Hydrogen bonds form between the carbonyl oxygen (C=O) of one amino acid and the amide hydrogen (N−H) of another amino acid in a different segment of the polypeptide chain.
Antiparallel: Strands run in opposite directions (𝑁→𝐶) alignment in one strand and (C→N) in the other.
What about the tertiary structure, why does the protein adapt the shape it does?
The shape is determined by the maximum stability.
Important are the hydrophilic (water loving) interactions of the polar side chains on acidic or basic amino acids and the hydrophobic (water fearing) interactions of non polar side chains.
those acidic or basic amino acids with charged side chains tend to be on the exterior of the protein . where they can be solvated by water.
The neutral amino acids (with nonpolar side chains) - tend to be on the interior of a protein molecule away from the aqueous medium.
What is important for stabilizing the proteins tertiar structure?
Also important for stabilizing the proteins tertiar structure are the formation of disulfide bridges between the cystein residues.
The formation of hydrogen bonds between nearby amino acid residues.
Presence of ionic attractions called salt bridges between positive and negative charged sites of various amino acid side chains in the protein.
what is denaturation of a tertiary structure?
The tertiary structure of a globular protein is delicately held together by the weak intermolecula forces - a modest change in temparature or pH is enoght to distrupt the strucure - denaturation
Denaturation = the primary structure remains intact, but the tertiary structure unfolds from a specifik globular shape to something random.
Solubility is decreased - when denaturated. And most enzymes lose their ability to catalyze.
