Chromosome and nucleoid arrangement

Unit Two Chromosome and Nucleoid Arrangement

A. Bacterial chromosome

most cells have only one main chromosome

1. Structure

DNA is double stranded - 2 strands line up antiparallel to each other & bases are linked together w/ H bonds.

typical E. coli cell has 4.6 x 10⁶ bases: strand of DNA 1 mm long, but E. coli is only 2-3 µm long.

Q. How does it fit?

A. DNA is supercoiled or twisted around itself, stabilized by proteins

But - supercoiled DNA must still be active and functional!

2. Functions

a. Protein production

DNA à RNA à protein

b. Replication

must be precise

ds DNA separates, each strand serves as a template to make a copy or complementary strand - semiconservative replication

because bacterial chromosomal DNA is supercoiled, replication is a little trickier

B. Nucleoid = nuclear region