Type of natural selection

1. Stabilized natural selection

2. Directional Natural selection

3. Disruptive Natural selection

4. Balance natural selection

#Id: 7691

#Unit 1. Molecules and their Interaction Relevant to Biology

                                             bab Motif

These motifs are generally found in right handed helix above the plane of the beta sheet

Almost all the proteins containing parallel beta sheets have this motif. 

The helix is generally not seen below the plane of beta sheets                                           

#Id: 7692

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                  bab Motif

#Id: 7693

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                           aa motif / Coiled-coils

Two helices are wound around each other

Alpha-helices are packed together through the hydrophobic interactions

These two helices are found to be stable in solution

They are generally found in transcription factors and intermediate filaments

They have heptad (7 amino acid) repeated sequences


#Id: 7694

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                        aa motif / Coiled-coils

3.6 a.a / turn in helix 

abcdefg 'a' &'d’ are hydrophobic residues 'e' and 'g' are found to be charged amino 

7.2 a.a / 2 turns acids 

 —7 amino acids per 2 turns in the helix 

For every turn there could be one hydrophobic residue coming same side of the helix 

Ex: GCN4

#Id: 7695

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                        aa motif / Coiled-coils



#Id: 7697

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                 Greek Key Motif

Made-up of beta-sheets

Four adjacent antiparallel strands linked by loops

Three anti-parallel beta sheets are connected 3 loops

The pattern is similar to ornamental pattern used I ancient Greece, therefore called as Greek Key motif