A1. DNA

Question 1

How is DNA stored? - Eukaryotic cells (5 things)

Answer 1

• Eukaryotic cells contain linear DNA molecules that exist as chromosomes -thread-like structures, each made up of one long molecule of DNA and its associated proteins.
• Chromosomes are found in the nucleus.
• The DNA molecule is really long, so it has to be wound up so it can fit into the nucleus.
• It’s wound around proteins called histones. Histone proteins also help to support the DNA. The DNA (and protein) is then coiled up very tightly to make a compact chromosome.
• The mitochondria and chloroplasts in eukaryotic cells also have their own DNA. This is pretty similar to prokaryotic DNA because it’s circular and shorter than DNA molecules in the nucleus. It’s not associated with histone proteins.

Question 2

How is DNA stored? - Prokaryotic cells

Answer 2

• Prokaryotes also carry DNA as chromosomes - but the DNA molecules are shorter and circular.
• The DNA isn’t wound around histones - it condenses to fit in the cell by supercoiling.