DNA and RNA Structure and Function Chapter 12

DNA DEOXYRIBONUCLEIC ACID Section 12-1

DNA STRUCTURE The chemical components of DNA are: –sugar (deoxyribose) –phosphate groups –Four different nitrogen containing bases

THE FOUR BASES ARE: 1. Adenine 2. Guanine 3. Thymine 4. Cytosine

Nucleotide - made up of a sugar, a base, and a phosphate group. DNA is like a twisted ladder and is called a double helix.

The uprights of the ladder are made of the sugar and phosphate of the nucleotides. The rungs are two nitrogen bases held together by hydrogen bonds.

THE DNA LADDER Uprights = sugars and phosphates Each rung = 2 bases connected by H bonds

COMPLIMENTARY BASES Adenine binds with Thymine. Guanine binds with Cytosine.

Figure 16.5 The double helix

Chromosomes and DNA Replication Section 12-2

GENE Genetic code - the order of the bases Different order = different genes Different order = different people and even different species.

Gene = a specific sequence of nucleotides along a DNA molecule. A gene gives instructions for a specific protein to be made.

Chromosome – made up of a long strand of DNA One chromosome (one strand of DNA) has thousands of genes and millions of base pairs (See p. 295). Humans have 46 chromosomes and have thousands of genes on those chromosomes

REPLICATION OF DNA Replication begins with DNA Polymerase (an enzyme) binding to a part of DNA.

DNA polymerase breaks Hydrogen bonds between base pairs (unzips the DNA). The enzyme then adds complementary nucleotides to each new strand. Unzipping can occur at several places.

Each new DNA molecule consists of one original chain and one new chain. Proof-reader enzymes - proof-read the new chains and check for mistakes (these include DNA polymerase).