Chapter 16: The Molecular Basis of Inheritance (3)

The main component of the genome in most bacteria is one __that is associated with a small amount of __.

Difference between bacteria. and eukaryote?

Within a bacterium, certain proteins cause the __ to coil and “supercoil,” densely packing it so that it fills only part of the cell. Unlike the nucleus of a eukaryotic cell, this dense region of DNA in a bacterium, called the __, is not bounded by membrane.
Eukaryotic chromosomes each contain a single linear __ that averages about 1.5 x 10­­8 nucleotide pairs.

In the cell, eukaryotic DNA is precisely combined with a large amount of __.
Together, this complex of DNA and protein, called __, fits into the __through an elaborate, multilevel system of DNA packing.

__undergoes striking changes in its degree of packing during the course of the __.
· In __cells stained for light microscopy, the __ usually appears as a diffuse mass within the nucleus, suggesting that the __is highly extended. As a cell prepares for __, its __coils and folds up (condenses), eventually forming a characteristic number of short, thick __that are distinguishable from each other with the LM

Though __ is generally much less condensed than the chromatin of mitotic chromosomes, it shows several of the same levels of higher-order packing.
Some chromatin comprising a chromosome seems to be present as a 10 nm fiber, but much is compacted into a 30 nm fiber, which in some regions is further folded into __.

Although an __lacks an obvious __its __appear to be attached to the __, on the inside of the nuclear envelope, and perhaps also to fibers of the __· These attachments may help organize regions of chromatin where genes are active. The chromatin of each chromosome occupies a specific restricted area within the __nucleus and the chromatin fibers of different chromosomes do not become entangled.

Even during interphase, the __ and __ of chromosomes exist in a highly condensed state similar to that seen in a metaphase chromosome.
· This type of interphase chromatin, visible as irregular clumps with a light microscope, is called __, to distinguish it from the less compacted, more dispersed __(“true chromatin”)

Because of its compaction, __ is largely inaccessible to the machinery in the cell responsible for expressing (making use of) the genetic information coded in the DNA.

In contrast, the looser packing of __makes its DNA accessible to this machinery, so the genes present in euchromatin can be expressed.

The chromosome is a dynamic structure that is condensed, loosened, modified, and remodeled as necessary for various cell processes, including __, __ and __.

It has become clear that __ are not simply inert spools around which the DNA is wrapped.
· Instead, they can undergo chemical modifications that result in changes in chromatin organization.

Terry Orr- Weaver showed that __of a specific __on a __ tail plays a crucial role in chromosome behavior during __of meiosis.

__and other chemical modifications of __also have multiple effects on gene activity.