OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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Get ready for the OCR GCSE Biology exam with our comprehensive quiz, featuring flashcards and multiple choice questions. Understand the exam format, key topics, and effective study strategies to excel.

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Why can't DNA leave the nucleus?

It is too small to exit
It is too big to leave through nuclear pores
It is protected from degradation
It requires specific transport proteins

The correct answer is: It is too big to leave through nuclear pores

DNA cannot leave the nucleus primarily because of its size. The structure of DNA is quite large, particularly when considering the fact that it is tightly coiled and packed as chromatin when in the nucleus. The nuclear envelope contains nuclear pores that regulate transport between the nucleus and the cytoplasm, but these pores are not large enough to allow intact strands of DNA to pass through. Instead, much smaller molecules, such as RNA, can exit easily through these pores. Other options touch on aspects related to DNA and its cellular environment. While DNA is indeed protected from degradation and it does require specific transport mechanisms for certain products like mRNA, these factors do not address the fundamental issue of size that prevents DNA itself from exiting the nucleus.