Signal sequences

contain one or more positively charged amino acids adjacent to a continuous stretch of 6–12 hydrophobic residues (known as the hydrophobic core)

TLS Online TPP Program

#Id: 3969

#Unit 2. Cellular Organization

An unrestrained supercoil in the DNA path creates tension, but no tension is transmitted along DNA when a supercoil is restrained by protein binding.

TLS Online TPP Program

#Id: 3970

#Unit 2. Cellular Organization

Chromosomal packaging is maintained by supercoiling of DNA in case of bacteria

TLS Online TPP Program

#Id: 3971

#Unit 2. Cellular Organization

Because supercoiled DNA molecules are more compact than relaxed molecules, they migrate more rapidly during gel electrophoresis

TLS Online TPP Program

#Id: 3972

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 3974

#Unit 2. Cellular Organization

E. coli has at least four individual topoisomerases (I through IV). Those of type I (topoisomerases I and III) generally, relax DNA by removing negative supercoils (increasing Lk).

TLS Online TPP Program

#Id: 3976

#Unit 2. Cellular Organization

A bacterial type II enzyme, called either topoisomerase II or DNA gyrase, can introduce negative supercoils (decrease Lk). It uses the energy of ATP to accomplish this.

To alter DNA linking number, type II topoisomerases cleave both strands of a DNA molecule and pass another duplex through the break.