Genetics Ch 12
During retrotransposition, the enzyme that makes a DNA copy of the transposable element for insertion at a new site is called
reverse transcriptase.
The enzyme that produces a double-stranded DNA molecule from an RNA transcript of a retrotransposon is
reverse transcriptase.
The centromere plays a role in the
segregation of eukaryotic chromosomes.
Hybrid dysgenesis is a(n)
set of harmful outcomes including mutation and sterility that occurs with high levels of P element insertion into Drosophila genes.
DNA gap repair synthesis produces
short direct repeats at both ends of transposable elements
In the diagram there are two models of the 30 nm fiber level of chromosome compaction. The model on the left is known as the
solenoid model
The chromosomal structures that prevent both chromosomal shortening and chromosomal rearrangements are called
teleomeres
Exon shuffling is
the insertion of exons from one gene into another gene to produce a different gene sequence
Transposase is an enzyme that catalyzes
the removal of a transposable element from its original location and the insertion of the element at a new location
A typical eukaryotic gene ranges in size from several thousand to tens of
thousand
What are the characteristics of the nuclear matrix?
A fine network of filamentous proteins Attached to the nuclear lamina Fills the interior of the nucleus
Which type of DNA sequence would be found in a simple transposon but not seen in an insertion element?
Antibiotic-resistance gene
Where on the chromosome are telomeres located?
At both ends of the chromosome
In a nucleosome, what is the nature of the chemical attraction between the histone proteins and the DNA?
The positively charged histone proteins are attracted to the phosphate groups along the DNA backbone
What is heterochromatin?
The tightly compacted regions of chromosomes
What is a chromosome territory?
A discrete region in the nucleus where a chromosome is located
What kind of cell would contain linear chromosomes found in sets and located in a nucleus?
A eukaryotic cell
What length of DNA is associated with a nucleosome?
146 or 147 base pairs
Which types of DNA sequences are typically found in an insertion element?
Direct repeats at both ends Coding region for a transposase enzyme Inverted repeats at both ends
In the diagram of the nucleosome, to what do the black and red arrows point?
Black arrows: core histones; Red arrow: DNA
What is the function of the nuclear matrix?
Compacting DNA into radial loop domains
Which process gives rise to the small direct repeats flanking all transposable elements?
DNA gap repair synthesis
Chromatin is the complex of ____ and ____ found within eukaryotic chromosomes
DNA; protein
True or false: Heterochromatin is transcriptionally active.
False; It is euchromatin that is transcriptionally active.
What is the function of matrix attachment regions (MARs) of the nuclear matrix?
Formation of chromosomal loops
What are the defining features of eukaryotic chromosomes?
Found in nucleus, linear, present in one or more sets
What kinds of filaments are used to construct the nuclear lamina?
Intermediate filaments
What is true of histone H1?
It binds DNA. It is called the linker histone. It binds between nucleosomes.
In Markus Noll's experiment that tested the "beads on a string" nucleosome theory, what did Noll assume about DNase I?
It would cut mainly in the linker regions.
A transposable element with long terminal repeats at both ends that also includes coding regions for genes required for transposition is called a(n)
LTR retrotransposon.
Which statement accurately shows the difference between LTR and non-LTR retrotransposons?
LTR retrotransposons have sequences that resemble retroviruses while non-LTR retrotransposons do not
What are the key features of eukaryotic chromosomes?
Linear Tens of millions to hundreds of millions of base pairs long Multiple origins of replication Occur in sets (e.g. diploid) Possess centromeres Possess telomeres
Where is the nuclear lamina located?
Lining the inner nuclear membrane
Which types of DNA sequences are characteristic of LTR retrotransposons?
Long terminal repeats at both ends Coding regions for retroviral-related proteins needed for transposition
Which type of transposable element has a coding region for an enzyme that acts as both a reverse transcriptase and an endonuclease and could contain sequences derived from normal eukaryotic genes
Non-LTR retrotransposon
Match the name of the nuclear structure on the left to the description of the structure on the right.
Nuclear matrix: Filamentous protein structure involved in radial loop domain formation Nuclear lamina: Intermediate filaments lining inner nuclear membrane Inner nuclear membrane: A membrane facing the inside of the nucleus Outer nuclear membrane: A membrane facing the cytoplasm
Which lines of evidence accurately reflect the status of the P element in the Drosophila melanogaster species?
Only laboratory strains that were collected prior to the 1950s lack the P element. Wild populations of Drosophila melanogaster worldwide carry the P element.
Looking at the results of the Noll nucleosome digestion experiment below, what would you predict if DNase I were used at 1200 units/ml?
Only the smear at 200 bp would remain.
What are the functions of telomeres?
Prevention of chromosomal shortening Prevention of chromosomal rearrangements
Transposable elements can cause harmful changes including chromosomal
Rearrangements Breakage
What is euchromatin?
Regions of chromosomes that are less condensed
Which types of DNA sequences could be found in non-LTR retrotransposons?
Sequences derived from normal eukaryotic genes Coding region for an enzyme with both reverse transcriptase and endonuclease activities
Approximately how large is a typical eukaryotic gene?
Several thousands to tens of thousands of base pairs
A transposon is a transposable element that moves via
Simple transposition
Which statement identifies an accurate difference between insertion elements and simple transposons?
Simple transposons have genes that are not required for transposition while insertion elements only have DNA sequences required for transposition.
Which structure(s) are NOT present in a typical bacterial cell?
Telomeres and nucleus
What was the conclusion from the Noll experiment that found DNase I cut the DNA into multiples of about 200bp?
The DNA had exposed linker regions every 200 bp.
For Markus Noll's nucleosome digestion experiment, what might you predict if it was repeated with 150 units/ml of DNase I but with a much longer incubation at 37oC?
The bands would look more like those on the right.
Which aspects of gene expression can be affected by transposition?
The control of a gene can be changed by the insertion of a transposable element into regulatory regions near the gene. A gene can be inactivated by the insertion of a transposable element. A gene can be mutated by incorrect excision of a transposable element. Insertion of a transposable element can increase the number of exons in the coding region of the gene.
What is the name of the structure that assembles on the centromere and connects the centromere to the mitotic spindle to ensure the proper segregation of chromosomes?
The kinetochore
What are possible advantages to having transposable elements within a cell?
Through exon shuffling, new gene combinations can be produced. Transposable elements may promote recombination, leading to increased genetic diversity. Transposable elements carrying antibiotic-resistance genes assist with bacterial cell survival
A small segment of DNA that can integrate into a chromosome at many possible locations is called a(n)
Transposable element
How could the presence of transposable elements within a cell increase genetic diversity?
Transposable elements may cause the insertion of exons from one gene into another gene. Transposable elements may promote recombination.
In the process of transposition, which step would occur first?
Transposase monomers bind to inverted repeat sequences at the end of the transposable element
Put the steps of transposition in order from earliest to latest
Transposase monomers bind to inverted.. The transposase monomers form a dimer The transposable element is excised Transposase carries the transposable The transposable element is inserted
True or false: Histone H1 binds to the DNA between nucleosomes
True. Histone H1 is called the linker histone because it binds in the linker region between nucleosomes, to bring them closer together.
Select all of these that form the octamer of core histone proteins in a nucleosome.
Two H4 Two H2B Two H2A Two H3
In the diagram there are two models of the 30 nm fiber level of chromosome compaction. The model on the right is known as the
Zigzag model
A transposable element is
a small segment of DNA that can integrate at many possible locations on a chromosome.
In simple transposition
a transposable element is removed from its original site and inserted at another location.
In retrotransposition
a transposable element is transcribed into RNA and this RNA is used as a template to produce DNA that is inserted into a new site
A retrotransposon is a transposable element that moves via
an RNA intermediate
Direct repeats, also called target-site duplications,
are found at both ends of all transposable elements
A transposable element that contains all of the sequences necessary for transposition or retrotransposition is called a(n)
autonomous element
The number of copies of specific LTR retrotransposon can increase rapidly within a genome because a single retrotransposon can be
copied into many RNA transcripts.
Transposable elements can
cause chromosome breakage and chromosomal rearrangements.
The sequence of DNA involved in the segregation of chromosomes, upon which the kinetochore assembles, is called the
centromere
What is the name of the complex of DNA and protein found within eukaryotic chromosomes?
chromatin
Producing a new gene sequence by introducing exons from one gene into another gene is called
exon shuffling
If a simple transposon located in a DNA region that has been replicated relocates to position where the DNA has not yet been replicated, the number of copies of that transposon in the genome will
increase
The primary function of the genome is the storage of genetic
information
The nuclear lamina lines the ___ ___ membrane
inner nuclear
All of the following outcomes of transposition could decrease gene activity except for
insertion of a transposable element into a non-coding sequence that does not serve as a regulatory region for a gene.
The enzyme that recognizes the long terminal repeats at the ends of a DNA copy of an LTR-retrotransposon and catalyzes the insertion of the element into its new location is
integrase
The nuclear lamina is made from one of the types of structure that make up the cytoskeleton; specifically, it is composed of ____ filament proteins
intermediate
The fine network of filaments found connected to the nuclear lamina inside the nucleus is called the ___ ___ matrix
internal nuclear
The group of proteins that assembles on the centromere to attach the chromosome to the spindle apparatus is called the
kinetochore
In retrotransposons, a region of a few hundred DNA base pairs where a large number of repeated sequences are arranged in tandem is called a
long terminal repeat.
During retrotransposition, reverse transcriptase
makes a DNA copy from the RNA intermediate representing the transposable element
Like the microdomains in bacterial chromosomes, eukaryotic chromosomes can be compacted into radial loop domains. In eukaryotic cells, this compaction is one of the functions of the nuclear ___ and nuclear lamina
matrix
The formation of chromosomal loops in eukaryotic chromosomes by the nuclear matrix is specifically regulated by _____-attachment regions
matrix
During transposition, small segments of DNA
move themselves to new locations within chromosomal DNA.
In some instances, simple transposons will increase in number within a genome. This results from
movement of a transposon from a region of the chromosome that has been replicated to another region that will be replicated later.
Retrotransposons can integrate at (a) ______ site(s) within the genome and rapidly _____ in number as a result of the transposition process
multiple; increase
In a nucleosome, the DNA can associate with the histone proteins because the DNA has a ___ charge and the histone proteins have a ___ charge
negative; positive
Transposable elements that use reverse transcriptase in the transposition process but do not otherwise resemble retroviruses in their DNA sequences are called
non-LTR retrotransposons.
The Ds element in corn is unable to transpose unless an Ac element is found in the same genome. The Ac element encodes a functional transposase enzyme while the Ds element does not. The Ds element would be described as
non-autonomous
Suppose Retrotransposon A lacked a functional copy of reverse transcriptase but was able to move to a new location because Retrotransposon B in the same genome could supply the reverse transcriptase activity. Retrotransposon A would be considered to be a(n)
non-autonomous element.
The DNA in a ____ wraps around the core octamer of histone proteins and it takes 146 or 147 base pairs of DNA to form this structure.
nucleosome
In eukaryotic cells, chromosomes reside within the bounded compartment known as the
nucleus
The ______ of interphase eukaryotic chromatin are approximately 25,000 to 200,000 base pairs long.
radial loop domains
A transposition process that makes use of an RNA intermediate is called
retrotransposition.
The selfish DNA hypothesis suggests that
transposable elements use a cell's resources to multiply but provide no selective advantage to the cell
An insertion sequence is a transposable element that typically contains inverted repeats and a coding region for an enzyme called
transposase
The process by which small segments of DNA can insert themselves in multiple locations throughout the genome is called
transposition