Structure and Function of DNA

Structure of DNA(deoxyribonucleic acid)

• Discovered by Watson & Crick in 1953

• DNA is a nucleic acid

• DNA is made up of small subunits called nucleotides

The nucleotides are made up of:

•deoxyribose(sugar)

•phosphate group

• nitrogen bases-4 types1. Adenine- A2. Guanine-G3. Cytosine- C4. Thymine-T

DNA is actually 2 long chains of nucleotides that are joined together in the form of a ladder. The ladder is twisted in the form of a double helix or spiral

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

 Structure of DNA

The sides of the ladder are composed if alternating deoxyribose(sugar) and phosphate. The rungs of the ladder are composed of pairs of nitrogen bases.

The nitrogen bases always pair up in a specific pattern.

•Adenine(A) pairs up with Thymine(T)

•Guanine(G) pairs up with Cytosine(C)

Example

A G C T A C G C A one side T C G A T G C G T other side

All organisms have the same type of nucleotides. The nucleotide arrangement provides for all the different types

Ex- A mouse and a rosebush have the same nucleotides. However, they are different because their nucleotides are in different orders.

*This sequence of nucleotides forms the genetic information(code) of an organism.

Replication of DNA

During meiosis and mitosis a copy of DNA must be made so that when the new cells are formed, they each get an exact copy of the genetic information.

This DNA copy is made through a process known as replication.

Steps of Replication

During replication, each strand serves as a pattern to make new DNA molecule.

• First step: DNA (H bonds are broken) unzips into 2 strands

• Second step: free nucleotides join onto “unzipped” strands to form 2 new strands of DNA

• 2 complete strands will result, these will be exactly alike

Figure 12–11 DNA ReplicationSection 12-2

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand