DNA Structure, Replication, and Protein Synthesis Explained

1. DNA: The Molecule of Inheritance

• In eukaryotic cells, genetic material is condensed into chromosomes, which consist of two chromatin strands made of DNA and proteins.
• The double helix model of the DNA molecule was proposed by Watson and Crick in 1953.

Basic Components of DNA

A molecule of DNA is formed from thousands of nucleotides. Each nucleotide is made up of:

• Deoxyribose
• Nitrogenous base
• Phosphate

There are 4 types of nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). When nucleotides join together, they form a chain where deoxyribose alternates with phosphate. The nitrogenous bases are attached to the deoxyribose.

Structure of DNA

• DNA is made up of two chains (strands) of nucleotides twisted around each other in the shape of a double helix.
• The two strands are connected because the complementary nitrogenous bases are linked by hydrogen bonds.

Genetic information is the same in every cell of an organism, but during the cell division cycle, the amount of DNA in a cell varies.

2. Replication of Genetic Information

DNA inside the cell needs to copy itself before mitosis begins. DNA duplicates itself in a process called replication:

1. The double helix of DNA opens up and the two strands separate.
2. Free-floating nucleotides attach to the DNA strands, and each nucleotide links with a complementary nitrogenous base.
3. New strands are formed.
4. At the end of the replication process, there are two identical copies of DNA. This is called semiconservative replication.

3. The Expression of Genetic Information

A gene is a piece of DNA that contains the information necessary to synthesize a protein. Proteins are formed from amino acids.

3.1 Protein Synthesis

Ribosomes carry out protein synthesis. Since DNA cannot leave the nucleus, it copies its genetic message into RNA, which takes the information to the cytoplasm.

RNA is made of the following nitrogenous bases: Adenine, Uracil, Guanine, and Cytosine. There are 3 types of RNA:

• Messenger RNA (mRNA): A copy of the genetic message from the DNA needed to synthesize a protein.
• Ribosomal RNA (rRNA): Where amino acids are joined together to make protein chains.
• Transfer RNA (tRNA): Transports the amino acids from the cytoplasm to the ribosomes.