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TLS Online TPP Program

#Id: 4050

The interphase nuclei of some tissues of the larvae of dipteran flies contain chromosomes that are greatly enlarged relative to their usual condition. They possess both increased diameter and greater length. shows an example of a chromosome set from the salivary gland of D. melanogaster. The members of this set are called polytene chromosomes.

#Unit 2. Cellular Organization #Structure of chromatin and chromosomes #Part B Pointers
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TLS Online TPP Program

#Id: 7713

#Unit 1. Structure and Function of Biomolecules

                                                        𝝅-Turn

Consists of 6 amino acids, generally termed as i, i + 1 , i + 2 i + 3 i + 4 and i + 5

H-bond is seen between i and i + 5 (First and sixth residue)
TLS Online TPP Program

#Id: 8443

#Unit 1. Structure and Function of Biomolecules

The 310 helix has 3 residues per tum and contains 10 atoms between the hydrogen bond donor and acceptor, hence its name.
TLS Online TPP Program

#Id: 8444

#Unit 1. Structure and Function of Biomolecules

Both the pi helix and the 310 helix occur rarely and usually only at the ends of a helices or as single-tum helices. They are not energetically favorable, since the backbone atoms are too tightly packed in the 310 helix and so loosely packed in the n helix that there is a hole through the middle. 
Only in the a helix are the backbone atoms properly packed to provide a stable structure.
TLS Online TPP Program

#Id: 8445

#Unit 1. Structure and Function of Biomolecules

Right-handed helical conformation has 3.6 residues per turn and 1.5A/aa.
TLS Online TPP Program

#Id: 8446

#Unit 1. Structure and Function of Biomolecules

In the α helix, the backbone hydrogen bonds are arranged such that the peptide CO bond of the nth residue points along the helix axis toward the peptide NH group of the (n + 4)th residue. 
TLS Online TPP Program

#Id: 8447

#Unit 1. Structure and Function of Biomolecules

This results in a strong hydrogen bond that has the nearly optimum N…O distance of 2.8 A.