Protein conformation Flashcards
What are the structural levels of proteins structure ?
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
What is meant by primary structure of protein ?
It is type , number and sequence of AA in the polypeptide chain and it is genetically determined through the nucleotide sequence of the protein coding region of DNA , it determines secondary , tertiary and quaternary structures.
What stabilizes the primary structure of protein ?
It is stabilized by peptide bonds
What are the shapes of the secondary structure ?
- Alpha helix
- Beta pleated sheets
- Beta turns
What are the characteristics of Alpha helix ?
- It is a rod ( spiral ) structure .
- Side chains of amino acids extend outwards from the axis of the helix.
- A complete turn of the helix contain an average 3.6 aminoacyl residues.
- Twisting of alpha helix is right handed ( clockwise )
What stabilizes the alpha helix ?
Hydrogen bonds
What destabilizes the alpha helix ?
- Two adjacent R groups of the same charge ( Lys and Arg )
- Two adjacent bulky side chains ( Leucine and Isoleucine )
- Pro and Gly ( helix breakers )
What are the examples of the alpha helix ?
- Hemoglobin
- Myoglobin
- Alpha keratin
Describe the structure of the beta pleated sheets .
The polypeptide chains (5-10AA) are arranged in lines side by side forming beta pleated sheets.
Why are Beta pleated sheet called pleated ?
Pleated because the radical groups are arranged alternatively slightly above and below the plane of the main chain of polypeptide to form a zigzag like structure.
How are the beta pleated sheets stabilized ?
They are stabilized by the hydrogen bonds :
- Interchain hydrogen bonds : between separate polypeptide chains.
- Intrachain hydrogen bonds : between segements of the same polypeptide chain.
What is the role of Beta turns ?
Enable the polypeptide chain to reverse its direction and fold back on themselves.
What are the number of amino acids participating in the beta turns ?
4 amino acids , the first amino acid being hydrogen bonded to the fourth and it contains ( glycine , proline and hydrophilic AAs)
What stabilizes Beta turns ?
Hydrogen bonds and ionic bonds
What is meant by tertiary structure of proteins ?
Three-dimensional structure of protein. Every protein has a unique tertiary of folded secondary structure (helices , beta pleated sheets and non-regular regions ) in a specific way.
Why does every protein have unique tertiary structure ?
As the AAs of the primary structure are brought near the AAs of the secondary structure which results in interactions at different points in the secondary coiled structure forming a 3 dimensional structure that suits the function of the protein.
What stabilizes the tertiary structure of proteins ?
- Covalent bonds : Disulphide bonds
2. Non covalent bonds : Hydrogen , Electrostatic bonds , Hydrophobic interactions.
What is the Quaternary structure of proteins ?
It is the arrangement of subunits of proteins consisting of 2 or more polypeptide chains .
What are the type of Quaternary structure ?
- Homogenous proteins : similar subunits
2. Hetrogenous proteins : different subunits
What stabilizes Quaternary structure ?
Non covalent interactions
What are the examples of Quaternary structures ?
- Creatine phosphokinase ( dimmer )
2. Hemoglobin : 4 polypeptide chains ( alpha 2 beta 2 )
