Chromosomes are typically huge structures - at least length-wise (and relative to a cell's proportions). A single chromosome "fiber or thread" can be close to 4+ mm long while a cell may only be approximately 10 micrometers in diameter! DNA is therefore very tightly wrapped up inside of the nucleus - somewhat analogous to a spool of thread. What are the structural "units" of coiled chromosome DNA packing called?
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To give you some idea of how incredibly small condensed chromosomes are, our text points out that if human chromosome 1 were expanded to be as thick as a strand of (cooked) spaghetti, it would stretch for 25 miles (p. 87). Imagine that you've invented a way to make single cells so much larger that a DNA duplex has a diameter of 0.1 mm — about the thickness of a human hair. a. (5 points) If you were to do that, how long a ‘hair’ would there be in a typical human fibroblast (assuming the DNA is not compacted)? Note that I want you to take into account all of the DNA in a typical human nucleus. [Show your calculations here, and be sure to include any information you use about the dimensions of DNA molecules.] b. (5 points) How big would a single cell be? [Be sure to tell me what you think the actual dimensions of a fibroblast are, so that I can properly evaluate your answers here!] c. (5 points) How big would that cell's nucleus be? [Again, be sure to tell me what you think the actual dimensions of the nucleus are, so that I can properly evaluate your answers here!]
Sri K.
The size of a eukaryotic cell nucleus is approximately 10 µm in diameter, and a human chromosome is approximately folded in a way that it can fit into the nucleus 10 times, 1,000,000 times, 10,000 times, and 320 times. The chromosome is approximately 0.1 mm long. Given this information, we need to fold the chromosome.
Marlyn J.
The length of a DNA molecule in a typical mammalian cell is calculated to be approximately 2.2 meters. How is the packaging of this long molecule done to accommodate it within the nucleus, which has a size of approximately 6 micrometers?
Kerissa B.
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