What is the difference between DNA and mRNA?

DNA is much longer than mRNA and forms a chromosome, whereas mRNA is much shorter; corresponding to a single gene. DNA is structurally different; it is usually found as a double helix and contains the base thymine and the sugar deoxyribose, whereas mRNA is single stranded and contains the base uracil instead of thymine and ribose instead of deoxyribose. DNA is also more structurally complex, containing introns and extrons and other features that mRNA does not have.