Assignment 2 ABIO 212Y
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.
The nucleosome "bead" is an octomer of histone proteins. Indicate which specific histone proteins are part of each tetramer within the octomer, and which histone protein fastens the DNA to the "bead."
Tetramer: dimer H2A, H2A dimer H2B, H2B tetramer H3, H3 dimer H4, H4 dimer Histone "fastener": H1
All of the following chromosomes can be discerned by light microscopy EXCEPT __________.
interphase chromosomes
Rank the following levels of chromatin compaction in eukaryotes from the least compact to the most compact.
naked DNA nucleosome solenoid loop domains chromatid metaphase chromosome
Chromosomal regions that represent evolutionary vestiges of duplicated copies of genes that have underdone sufficient mutations to render them untranscribable are called ________.
pseudogenes
What is a "puff" in a polytene chromosome?
site of gene transcription
What genetic process is occurring in a puff of a polytene chromosome?
transcription
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
Which characteristics of heterochromatin are supported by the experimental data? Select the two statements that are true.
-Heterochromatic genes are less active than euchromatic genes. -Heterochromatin is more tightly packed than euchromatin.
The nucleosome "bead" is an octomer of histone proteins. Indicate which specific histone proteins are part of each tetramer within the octomer, and which histone protein fastens the DNA to the "bead."
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
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
Compare the characteristics of heterochromatin and euchromatin.
Heterochromatin: -deeply stained -more condensed -few genes present (or repressed genes) -replicated late in S phase -associated with telomeres and centromeres Euchromatin: -many genes present (or expressed genes) -less condensed -weakly stained -replicated early in S phase
Which of the following are examples of heterochromatin?
Barr body telomeric DNA centromeric DNA repetitive DNA
Contrast the major differences between the organization of DNA in viruses and bacteria versus eukaryotes.
Eukaryotic: -consists mostly of noncoding DNA sequences. -Contain a mixture of both unique and repetitive DNA sequences -contain large amounts of DNA Viral or Bacterial" -consist mostly of coding DNA sequences -a short, circular DNA molecule -relatively little amount of DNA- associated proteins -consist of mostly unique DNA sequences
What is the first order of chromatin packing?
Coiling around nucleosomes
Which histone helps stabilize the solenoid structure?
HI
Sort each characteristic into the appropriate bin.
Euchromatin: less chromatin condensation many expressed genes Heterochromatin: condensed chromatin few expressed genes
The second order of chromatin packing occurs when nucleosomes coil together to form a fiber that is 300 nm in diameter.
False
Based on the finding that acetylation of H3 and H4 histones increases gene activity, what is the mechanism behind this effect?
It alters the association of DNA and nucleosomes so that genes become more accessible to factors that promote transcription.
Based on the finding that heterochromatin is hypomethylated, what effect does methylation of histone proteins have on transcription?
It increases gene expression
The E. coli chromosome is circular and double-stranded DNA.
True
What makes up the protein component of a nucleosome?
Two tetramers of histone proteins
In situ hybridization allows one to "visualize" the location of labeled RNA or DNA in a tissue or cell.
True
How do we know this experimentally?
by autoradiography (incorporation of radioactive ribonucleotides)
Eukaryotic chromosomes contain two general domains that relate to the degree of condensation. These two regions are ________.
called heterochromatin and euchromatin
