0.1 Basic principles of genetics  (Page 2/19)

A gene, a unit of hereditary information, is a stretch of DNA sequence, encoding information in a four-letter language in which each letter represents one of the nucleotide bases. Much of the information stored in stretches of DNA sequence is subsequently expressed as another class of biopolymers, the proteins. 

Work on cytology in the late 1800s had shown that each living thing has a characteristic set of chromosomes in the nucleus of each cell. During the same period, biochemical studies indicated that the nuclear materials that make up the chromosomes are composed of DNA and proteins. In the first four decades of the 20th century, many scientists believed that protein carried the genetic code, and DNA was merely a supporting "scaffold." Just the opposite proved to be true. Work by Avery and Hershey, in the 1940s and 1950s, proved that DNA is the genetic molecule.

Lecture 3. genes are made of dna or rna

Structure of dna

Base pairs bond the double helix together. The "beginning" of a strand of a DNA molecule is definedas 5'. The "end" of the strand of A DNA molecule is defined as 3'. The 5' and 3' terms refer to the position of the nucleotide base, relative to the sugar molecule in the DNA backbone, which is make up by the phosphodiester bonds linking between the 3' carbon atom and the 5' carbon of the sugar deoxyribose (in DNA) or ribose (in RNA).

Each chromosome is composed of a single DNA molecule.  Our DNA contains greater than 3 billion base pairs--an enormous amount by any measure.  All of this information must be organized in such a manner that it can be packaged inside the nucleus of the cell.  To accomplish this, DNA is complexed with histones to form chromatin.  Histones are special proteins that the DNA molecule coils around to become more condensed.  The chromatin then becomes coiled upon itself, which ultimately forms chromosomes.