Genetics Chapter 12 Homework
Terms in this set (24)
Viral chromosomes exist in a variety of structures and can be made up of the following:
DNA or RNA
In E. coli, the genetic material is composed of
Circular, double-stranded DNA
Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. These two regions are:
Heterochromatin and euchromatin
In human chromosomes, satellite DNA sequences of about 170 base pairs in length are present in tandem arrays of up to 1 million base pairs. Found mainly in centromere regions, they are called
In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences exist. What is it called and what types of elements are involved?
Moderately repetitive DNA, SINEs, LINEs, and VNTR
Chromatin of eukaryotes is organized into repeating interactions with protein octamers called nucleosomes. Nucleosomes are composed of which class of molecules?
Supercoiling relies on the enzyme
Telomerase is an enzyme involved in the replication of the ends of eukaryotic chromosomes.
In contrast to euchromatin, heterochromatin contains more genes and is earlier replicating.
Viral genomes are always either double-stranded DNA or single-stranded RNA.
Polytene chromosomes are unique because they are composed of a large number of identical DNA strands.
Presence of heterochromatin is characteristic of prokaryotic chromosomes.
Oocytes and spermatocyes
Lysine and arginine
How does super-coiling arise? What is the difference between positive and negative super coiling?
Supercoiling arises from overwinding (positive supercoiling) or underwinding (negative supercoiling) the DNA double helix when the DNA molecule does not have free ends, as in circular DNA or when the ends of the linear DNA molecule are bound to proteins that prevent them from rotating around each other.
Describe the structure and composition of nucleosome (core particle) and chromatosome.
Nucleosome core particle: contains two molecules each of histone H2A, H2B, H2, and H4, which form a protein core with around 147 base pairs of DNA wound around the core.
Chromatosome: Nucleosome core + one molecule of histone H1
Describe the different types of DNA sequences that exist in eukaryotes.
1) Unique-sequence DNA: constitute most of the protein-coding sequences as well as a large number of sequences without any known function. One or a few copies are present per haploid genome.
2) Moderately repetitive sequences: ranging from a few hundred to few thousand base pairs in length. Some consist of function genes that code for rRNAs and tRNAs, but most is made up of transposable elements. Present in several thousand copies per haploid gamete.
3) Highly repetitive DNA: consists of clusters of tandem repeats of short sequences, often less than 10 base pairs in length, present in hundreds of thousands to millions of copies per haploid gamete.
What are the three different packaging steps involved to package a fully extended DNA to a highly condensed mitotic chromosome?
The first level of packing happens when DNA strands wrap titghtly around the histone octomer (11 nm diameter fiber)
Numerous nucleosomes coil closely together (six-fold increase in compactness), creating the second level of packing (30 nm diameter fiber).
The third level of packing occurs just before mitosis. The 30 nm fiber further condenses into 300 nm chromatin fiber. Next, the 300 nm fiber condenses into 700 nm chromatids of metaphase (value varies among organisms).
What is the difference between heterochromatin and euchromatin?
Euchromatin undergoes the normal process of condensation and decondensation in the cell cycle. It contains the majority of chromosomal material and most of the transcription takes place here.
Heterochromatin remains in a highly condensed state throughout the cell cycle. It is found at the centromeres and telomeres of all chromosomes, along the entire length of the inactivated X chromosome in females and at other specific places. Most heterochromatin remains inactive during transcription.