Biological termHard0.5 marks
4(b)
Give appropriate biological or technical terms for the following:
The complex consisting of a DNA strand and a core of histones.
Topic: Nucleosome
Previous-year question practice database
Answer
Exam answer
NUCLEOSOME.
Explanation
A nucleosome is the basic packing unit of a chromosome: a length of DNA wound around a core of HISTONE proteins, like thread round a spool.
WHY PACKING IS NECESSARY: the DNA in a single human cell would measure about two metres if stretched out, and it must fit inside a nucleus a few micrometres across. Winding it round histones, and coiling those again, achieves that compression.
The hierarchy: DNA → NUCLEOSOME → CHROMATIN FIBRE → CHROMOSOME.
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