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Chapter 12: Problem 6

Describe the structure of lampbrush chromosomes. Where are they located?

Short Answer

Expert verified
Answer: The primary function of lampbrush chromosomes during the meiotic prophase of oocyte nuclei is to synthesize large amounts of RNA required for the early development of the embryo after fertilization.

Step by step solution

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1. Definition of Lampbrush Chromosomes

Lampbrush chromosomes are a specific type of chromosome found during the meiotic prophase of oocyte nuclei in animals. They are named "lampbrush chromosomes" due to their appearance, which is similar to a test tube brush or a lamp cleaner.
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2. Structure of Lampbrush Chromosomes

Lampbrush chromosomes consist of chromatin fibers that are organized into loops called chromomeres. These chromomeres extend out from the chromosome axis, forming a brush-like structure. Each chromomere loop consists of DNA, RNA, and proteins. In each loop, transcription takes place, meaning that the DNA in the loop is used as a template to synthesize RNA. This process produces numerous RNA transcripts along the loop, which leads to the formation of structures called RNP-matrix. The RNP-matrix consists of RNA and proteins and is responsible for the lampbrush appearance.
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3. Loops and Chromomeres

Loops of lampbrush chromosomes can be categorized as either simple or complex loops. Simple loops consist of a single chromomere, while complex loops are composed of two or more chromomeres. The size and shape of the loops can vary, with some being short and thick, and others being long and thin.
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4. Functions of Lampbrush Chromosomes

Lampbrush chromosomes play a significant role in the synthesis of RNA during the meiotic prophase of oocyte nuclei. They enable the oocyte to produce vast amounts of RNA that will be required for the early development of the embryo after fertilization. This high level of transcriptional activity is unique to lampbrush chromosomes compared to other types of chromosomes.
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5. Location of Lampbrush Chromosomes

Lampbrush chromosomes are located within the oocyte nucleus during the meiotic prophase I in the germinal vesicle of animals, including amphibians, birds, and some mammals. They are not present in somatic cells, and their appearance is mostly limited to oocytes that are in the process of development.

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Most popular questions from this chapter

A number of recent studies have determined that disease pathogenesis, whether it be related to viruses, cancer, aging, or a host of other causes, is often associated with specific changes in DNA methylation. If such patterns are to be considered as biomarkers for disease diagnosis what requisite criteria would you consider essential to their use?

The human genome contains approximately \(10^{6}\) copies of an Alu sequence, one of the best-studied classes of short interspersed elements (SINEs), per haploid genome. Individual Alu units share a 282 -nucleotide consensus sequence followed by a \(3^{\prime}\)-adenine-rich tail region (Schmid, 1998 ). Given that there are approximately \(3 \times 10^{9}\) base pairs per human haploid genome, about how many base pairs are spaced between each Alu sequence?

A particular variant of the lambda bacteriophage has a DNA double-stranded genome of 51,365 base pairs. How long would this DNA be?

While much remains to be learned about the role of nucleosomes and chromatin structure and function, recent research indicates that in vivo chemical modification of histones is associated with changes in gene activity. One study determined that acetylation of \(\mathrm{H} 3\) and \(\mathrm{H} 4\) is associated with 21.1 percent and 13.8 percent increases in yeast gene activity, respectively, and that yeast heterochromatin is hypomethylated relative to the genome average (Bernstein et al, 2000 ). Speculate on the significance of these findings in terms of nucleosome-DNA interactions and gene activity.

In this chapter, we focused on how DNA is organized at the chromosomal level. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions: (a) How do we know that viral and bacterial chromosomes most often consist of circular DNA molecules devoid of protein? (b) What is the experimental basis for concluding that puffs in polytene chromosomes and loops in lampbrush chromosomes are areas of intense transcription of RNA? (c) How did we learn that eukaryotic chromatin exists in the form of repeating nucleosomes, each consisting of about 200 base pairs and an octamer of histones? (d) How do we know that satellite DNA consists of repetitive sequences and has been derived from regions of the centromere?
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