bio214j - Biology 214/414 2009 Packet#9 Suggested problems...

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Biology 214/414 2009 P a c k e t # 9 Suggested problems: Chapter 12: 3, 6, 8, 10, 11, 15, 16 Physical organization/structure of chromosomes I. Structure of bacterial (“prokaryotic ”) chromosomes (the “nucleoid ”) a. The natural form of DNA is in a complex with certain proteins and a small amount of RNA. i. Proteins are macromolecules that are polymers of amino acids; they are the basic machinery of cells (including most enzymes and many structural components). ii. With respect to the bacterial chromosome they have roles in packaging of DNA and in controlling gene expression. b. Most often bacteria have their main DNA in a single, circular chromosome, although its size varies more than 10X in various species. ( Figure 12-3; Table 12.1 ) i. In E. coli it is about 4.5 million base pairs, which makes a circle 1500 microns (1.5 mm) in diameter. This must be folded to fit inside a 1-2 micron cell. 1. To accomplish this it is folded into ~ 50-100 “supercoiled ” loops held with RNA and protein. 2. “Supercoiling ” is found in all natural DNA; it is the coiling of the double helix around itself and can be in either direction. Typically there is about 1 negative supercoil/200 base pairs. ( Figure 12.4 ) 3. “Negative supercoiling ” is probably important in DNA replication and gene expression. II. Chromosome structure of higher organisms (eukaryotes) a. They are usually much larger than bacterial chromosomes (the largest human chromosome, for example, is about 60X as large as the E. coli chromosome). b. Still, each eukaryotic chromosome is a single long double helix (linear, not circular) with a complicated mechanism of organization.
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i. As is the case in prokaryotes, this packaging is important in controlling gene expression and also in packaging the very large chromosomes so that they fit into the nucleus and can be distributed during mitosis and meiosis without getting tangled up. c. The natural form that eukaryotic DNA is found in is called “chromatin ”, and the “chromosomes ” we see during cell division are a special condensed form of chromatin. d. By weight chromatin is ~ 30 % DNA, ~ 60 % protein, and < 10 % RNA. i.
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This note was uploaded on 03/03/2010 for the course BIOL 214 taught by Professor Stark during the Fall '06 term at Illinois Tech.

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bio214j - Biology 214/414 2009 Packet#9 Suggested problems...

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