4.6.1.4 - DNA and the Genome

DNA in chromosomes

The genetic material in the nucleus of a cell is a chemical called DNA. DNA is a polymer, which means it is a long molecule made from repeating smaller units. At this point in the course, you only need the boundary-safe structure statement: DNA is made up of two strands forming a double helix.

In cells with a nucleus, DNA is contained in structures called chromosomes. A chromosome is not separate from DNA; it is a structure that contains DNA. This is why exam answers should say that chromosomes contain DNA, not that DNA contains chromosomes.

Genes are sections of DNA

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids. The amino acids are joined to make a specific protein.

The phrase codes for is important. In this lesson, it means the gene carries the information for the amino-acid sequence of a protein. The detailed DNA chemistry and the detailed mechanism for making proteins belong to the next DNA-structure lesson, so do not add them here unless a question gives that information.

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What genome means

The genome of an organism is the entire genetic material of that organism. A genome is bigger than a single gene because it includes all the DNA, including all the genes.

Use the words in the correct order:

1. DNA is the chemical genetic material.
2. DNA is contained in chromosomes.
3. A gene is a small section of DNA on a chromosome.
4. A genome is the entire genetic material of an organism.

This order stops two common mistakes: calling a genome one gene, and saying that a gene contains a chromosome. A gene is a section; a genome is the whole set.

The human genome and medicine

The whole human genome has now been studied. For GCSE Biology, the importance of this is limited to three areas. The first two are about medicine: searching for genes linked to different types of disease, and improving the understanding and treatment of inherited disorders.