The structures in the nucleus made of large molecules of DNA are called chromosomes. Chromosomes are composed of DNA and associated proteins; they represent the condensed form of chromatin, which is the complex of DNA wrapped around histone proteins. Chromatin itself is organized into nucleosomes, which are DNA-histone complexes, and during cell division, chromatin condenses to form visible chromosomes.

To summarize:

• DNA in the nucleus is organized as chromatin.
• Chromatin is DNA wrapped around histone proteins forming nucleosomes.
• During cell division, chromatin condenses into chromosomes, which are the recognizable DNA structures.

Therefore, the name given to these DNA-containing structures in the nucleus is chromosomes.