The DNA is about 1.74 meters if stretched to its full length. To get DNA into the nucleus, it must have a compact form. The structural flexibility of the DNA allows it to form a compacted structure. Eukaryotes contain about 1000 times more amount of DNA than prokaryotes; therefore the method of organizing and packaging is more complex. The typical human cell contains 46 chromosomes whose total DNA length is about 2 meters.
Different levels of organization of eukaryotic DNA
Nucleosomes are the primary structure of chromatin. Eukaryotic DNA interacts with the equal weight histones. Histones contains large amount of basic amino acid, arginine and lysine. There are five types of histones:
Two molecules of each H2A, H2B, H3 are associated with one another to form a structural core called histone octamer. Around this octamer, a segment of double helix of DNA is wound and forms the nucleosome core particles.
The DNA wrapped around the nucleosome core is continuous and joins one nucleosome to the another and forms a chromatin fiber. Individual nucleosome of a chromatin fiber are separated by a spacer DNA which is stabilized by H1 histone. One nucleosome and one bound H1 histone are together known as chromatosomes. The entire complex of cell DNA and associated protein is called chromatin fiber.
After the formation of chromatin fiber, additional shortening packaging of DNA is done by an orderly helical arrangement of six nucleosome per turn and is known as solenoid. The solenoids are further folded into super-coiled loops of 250-400 nm long. These are then attached to the nuclear lamina to form chromosomes
A schematic diagram of different levels of organization of DNA in the chromosome is shown below.
This picture is taken only for educational purpose from qph.fs.quoracdn.net
Multiple Choice Questions (MCQs)
1. What is the length of DNA if stretched to its full length?
A. 1. 4 m
2. Which histone stabilizes the complex?
D. all of the above
3. How much DNA is present in eukaryotes?
A. 1000 times less than prokaryotes
B. 500 times less than prokaryotes
C. 500 times more than prokaryotes
D. 1000 times more than prokaryotes
4. Fill the blank- nucleosome is the primary structure of ——?
5. Arginine is which type of amino acid?
D. None of the above
6. The histones form a structural core known as?
A. Histone hexamer
B. Histone pentamer
C. Chromatin thread
D. None of the above
7. How many types of histones are there?
8. What separates one nucleosome core from another?
B. Spacer DNA
9. How long are the solenoids after folded into super-coiled loops?
10. How many molecules of each histone is associated with other to form structural core?
11. Which of the following statement is NOT true?
A. Human genomic DNA contain 2.8*109 base pairs
B. There are 4 types of histones
C. DNA is organized in 3 different forms
D. Chromatin contains the entire DNA of cell
12. To get nucleus into the DNA, what should be the structure of DNA?
D. Any of the following will work
13. What is chromatin fiber?
A. Nucleosome + H1 histone
B. DNA complex + associated protein
C. Wrapping of DNA in double helix
D. Both A and C
14. Which of the following comes under level of organization of DNA?
B. Chromatin fiber
D. All of the above
3. 1000 times more than prokaryotes
6. None of the above
8. Spacer DNA
11. There are 4 types of histones
13. DNA complex + associated protein
14. All of the above
REFERENCE:- 1. Pankaja Naik- Biochemistry; 4th edition; page no:- 136-138