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A typical eukaryotic chromosome found in humans contains about 100 million bp of DNA. 1 bp of DNA has a linear length of 0.34 nm.

A. What is the linear length of the DNA for a typical human chromosome in micrometers?

B. What is the linear length of a 30-nm fiber of a typical human chromosome?

C. Based on your calculation of part B, would a typical human chromosome fit inside the nucleus (with a diameter of 5 μm) if the 30-nm fiber were stretched out in a linear manner? If not, explain how a typical human chromosome fits inside the nucleus during interphase.

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Sixta Kovacek
Sixta KovacekLv2
28 Sep 2019

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Related questions

I am thinking I need to use the formula V=4/3 3.14 r^3 so r=2.5 cause d=5 so (4/3)(3.14)(15.625)= 65.42 um^3 to convert to L 65.42 x 1x10^-15 = 6.54x10^-14L. for part A

Part B i know to do the same think for volume and divide the two than times it by 100 to get a percent but i am uncertain on how to find the length

Part C dont know where to start.

The nucleus of a typical human cell is roughly spherical with a diameter of about 5 μm. The nucleus contains, among other things, the DNA making up the genome, which for humans consists of 46 chromosomes containing a total of about 3×109 basepairs (bp). The DNA molecules are roughly cylindrical (but flexible) with a diameter of approximately 2 nm and a length of 0.34 nm per base pair.

(a) What is the volume of a typical nucleus? Express your answer in both μm3 and liters.

(b) What is the total length of the DNA making up the human genome? What volume

does the DNA occupy? What fraction of the cell nucleus is occupied by DNA?

(c) An E. coli bacterium is roughly a cylinder 1μm in diameter and 2μm long. Its genome contains approximately 5×106 bp of DNA. What is the volume occupied by the E. coli genome? What fraction of the cell volume does the DNA occupy?

The bacterium E. coli, which is a major model system for the study of genes and DNA, has a singular circular chromosome of about 4x106 bp. In contrast, human diploid cells have __1__ chromosomes, of __2__ different types (don’t forget that the X ¹ Y!). The total amount of DNA found in a haploid cell such as a sperm or egg is called the organism’s “C-value”; the human C-value is __3__.

Also in contrast to the E. coli circular chromosome is the fact that eukaryotic chromosomes are not circular, but instead are __4__. Eukaryotic chromosomes are complexed heavily with protein to form a DNA-protein complex generically called __5__. The proteins found can be considered to fall into two general classes: __6__ and __7__. The first class is made up of 5 major proteins called __8__, __9__, __10__, __11__, and __12__. On a weight to weight basis, these proteins make up about __13__% of the total mass of a chromosome. Since these proteins must associate relatively non-specifically with DNA, they are rich in the basic amino acids __13__ and __14__, which gives the proteins a net __15__ charge.

One goal of packaging the DNA into chromatin is to compact the genome so it will fit into a nucleus. The basic unit of chromatin structure is the __16__, which has __17__ base pairs of DNA wrapped around a “core particle” composed of __18__ copies each of the core histones. Each nucleosome is separated by a stretch of “linker” DNA so that the repeating unit is approximately 200 bp. Lets do a little arithmetic: If we consider that the nucleosome is approximately __19__ nm in diameter, that there is about 200 bp in this structure, and that 200 bp of DNA would normally occupy __20__ nm if stretched out straight (recall that each base is spaced about 0.34 nm from the next), we can see that the nucleosome alone allows for a __21__-fold compaction ratio.

The nucleosome structure is further compacted by histone __22__, which is not a part of the core particle. Instead, this histone __23__ (does what?) to cause the nucleosomal 10 nm fiber to condense into a higher-order structure referred to as the __24__ nm fiber. In the nucleus, chromosomes do not just float around freely: they are tethered to a proteinaceous structure called the __25__ at specific DNA regions called “SARs”, which stands for __26__. SARs are rich in topoisomerases, to allow the winding and unwinding of the DNA that accompanies replication and transcription to occur, despite this constraint.

The 30 nm fiber discussed above is the form in which transcriptionally active DNA is believed to exist in the nucleus; however, further condensation leads to a highly condensed inactive form called __27__; in this terminology, the active form is referred to as __28__. The inactive condensed form can be divided into two types: one type is essentially invariant between cell types, and since it is “on all t time”, it is referred to as __29__. The other type comes and goes, depending on the expression of the genes present in that region of the chromosome; it is referred to as __30__.

Eukaryotic chromosomes carry the genes, of course, but also have other functional regions. One such region is the place where the spindle apparatus attaches during mitosis and meiosis; this region of the chromosome is called the __31__. Another important part of the linear eukaryotic chromosome is the ends; these are called __32__. In humans, the end of each chromosome is composed of many repeats of the short sequence __33__. One more type of functional region on each chromosome is the place where DNA replication starts; in humans, each chromosome has several of these __34__. Thus, eukaryotic chromosomes carry several different types of functional sequences, which together allow for their __35__ during S phase, __36__ during mitosis and meiosis, and the __37__ of their genes

The human diploid genome contains 6.4x109 bp. For B-form DNA, assume an average distance of 0.34nm per base pair along the DNA molecule and an average diameter of a DNA molecule to be 2.4nm. Does the genome, in B-form, fit inside a nucleus (approximate a sphere of 6µm diameter)? If so, what fraction of the nucleus is taken up by DNA? If not, how many nuclei do you need to contain one diploid human genome?

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