DNA Organization Mastering

viral or bacterial genomes

- a short, circular DNA molecule - relatively little amount of DNA-associated proteins - consists mostly of coding DNA sequences - consist of mostly unique DNA sequences

eukaryotic genomes

- contain a mixture of both unique and repetitive DNA sequences - contain large amounts of DNA - consist mostly of noncoding DNA sequences

heterochromatin

- few expressed genes - condensed chromatin - deeply strained - few genes present (or repressed genes) - replicated late in S phase - associated with telomeres and centromeres

euchromatin

- many expressed genes - less chromatin condensation - weakly strained - many genes present (or expressed genes) - replicated early in S phase

How many base pairs of DNA wrap around a single nucleosome "bead"? Enter your answer as a whole number.

146

Referring to the image, there appears to be a span of 13 "beads" present. Ignoring the DNA before the first bead and after the 13th bead, how much DNA is present in the photo?

2546 base pairs

The human genome contains approximately 106106 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'-adenine-rich tail region (Schmid, 1998). Given that there are approximately 3×1093×109 base pairs per human haploid genome, about how many base pairs are spaced between each Alu sequence?

3000 base pairs

How many histone proteins make up the nucleosome core (the "bead" that the DNA is wrapped around)? Enter your answer as a whole number.

8

How many total polypeptide chains would be present in a single nucleosome core particle?

8

What is the first order of chromatin packing?

Coiling around nucleosomes

Viral chromosomes exist in a variety of conformations and can be made up of ________.

DNA or RNA

Which histone helps stabilize the solenoid structure?

H1

Histone acetyltransferases (HATs) are capable of remodeling chromatin by adding acetyl groups to various lysine residues in histones that comprise the nucleosome. Following this modification, the lysine residue no longer has a positive charge. Which statement is true?

Histones in general have a net positive charge that allow them to bind to DNA. Acetylation of histones, decreases their positive charge and weakens the histone-DNA interaction.

At the end of the short arm of human chromosome 16 (16p), several genes associated with disease are present, including thalassemia and polycystic kidney disease. When that region of chromosome 16 was sequenced, gene-coding regions were found to be very close to the telomere-associated sequences. Could there be a possible link between the location of these genes and the presence of the telomere-associated sequences?

It is possible that erosion of the end of chromosome 16 is related to each disease.

Which of the following is true of negatively supercoiled DNA?

It is underwound.

Why are LINELINEs referred to as retrotransposons?

Long interspersed elements (LINELINEs) are repetitive Long interspersed elements (L I N Es) are repetitive transposable D N A sequences in humans. The most prominent family, designated L1, is about 6 kb each and is represented about 100,000 times. L I N Es are often referred to as retrotransposons because their mechanism of transposition resembles that used by retroviruses.

Viral genomes and eukaryotic genomes are similar in which of the following ways?

They have the ability to pack a genome into a small volume

What makes up the protein component of a nucleosome core?

Two tetramers of histone proteins

Chromatin structure is dynamic. In regions of highly condensed chromatin, such as the centromere, the boundary between heterochromatin and euchromatin is variable. Genes that are near this boundary region can be influenced by either type of chromatin in what is referred to as position effects.Recall the early Drosophila melanogaster experiments by Hermann Muller where the repositioning of the w + allele (normal activity of the w + allele produces red eye pigment) by translocation or inversion near this boundary of chromatin produced intermittent w + activity. In the heterozygous state (w +/w), a variegated eye is produced, with white and red patches. Which statements are true in relation to this experiment? Select all that apply.

When heterochromatin spreading encompasses the new location of w +allele, the gene is not transcribed, producing white eye patches. Even though eye color phenotypic variegation exists within the eye, all cells have the same genotype. When heterochromatin spreading does not reach the new location of the w +allele, the gene will be transcribed, producing red eye patches.

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, these DNA sequences are called ________.

alphoid families

Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. These two regions are ________.

called heterochromatin and euchromatin

Which of the following are examples of heterochromatin?

centromeric DNA, telomeric DNA, Barr body, repetitive DNA

In E. coli, the genetic material is composed of ________.

circular, double-stranded DNA

Each human contains an identical set of VNTRs.

false

In contrast with euchromatin, heterochromatin contains more genes and is earlier replicating.

false

The second order of chromatin packing occurs when nucleosomes coil together to form a fiber that is 300 nm in diameter.

false

Viral genomes are always linear, double-stranded DNA.

false

Chromatin of eukaryotes is organized into repeating interactions with protein octomers called nucleosomes. Nucleosomes are composed of which class of molecules?

histones

Rank the following levels of chromatin compaction in eukaryotes from the least compact to the most compact.

least compact naked DNA nucleosome solenoid loop domains chromatid metaphase chromosome most compact

In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences exists. What is it called, and what types of elements are involved in it?

moderately repetitive DNA; SINEs, LINEs, and VNTRs

All of the following are examples of repetitive DNA EXCEPT __________.

telomerase DNA

Assume that the DNA associated with a nucleosome core particle plus the DNA in the linker adds up to 200 bp. Approximately how many base pairs are found in the linker region?

~54