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DNA transposons are also powerful mutagens, T or F



What specialised DNA polymerase enzyme is responsible for replication of telomeres



What are the four different specialised sequences contained within chromosomes

Telomeres, centromeres, replication origins and kinetochores


What happens to the original site from which the DNA transposon was initially excised from

It is repaired by DNA repair mechanisms


Not all of the genetic information in eukaryotes is encoded in the nucleus, where else is some genetic information stored and how

Some genetic information is contained in the mitochondria and chloroplasts in the form of small circular chromosomes


Each de-condensed chromosome occupies a specific region in the interphase nuclei, explain this phenomenon

As genes are transcribed the relative position of the chromosome in the nucleus changes. At interphase transcriptionally inactive regions of/chromosomes become localised at the periphery of the nucleus. In contrast, transcriptional activation of a gene is accompanied by movement of the gene towards the centre of the nucleus


Explain the role of linker histones such as H1

Linker histones act as straps that connect the incoming and outgoing strands of DNA that wrap around the core nucleosome. This helps to stabilise the formation of the 30nm chromatin fibres


Retrotransposons also move throughout the genome/chromosomes, T or F

F – retrotransposons never move. They act through RT converting RNA back to dsDNA at random points in the genome


Define what is meant by a kinetochore

Protein complex that binds to the microtubules in the mitotic spindle


Who discovered chromosomes in 1902

Sutton and Boveri


What are the two constituent parts of each nuclear chromosome

Linear DNA molecule and proteins that confer specialised functions called chromatin


Give an example of a specialised histone that mediates the attachment of the chromosome to the kinetochore inner plate



During which specific stage of the cell cycle can chromosomes easily be distinguished

Metaphase of mitosis


Telomeres define chromosome ends and maintain chromosome integrity, T or F



Explain how the chromatin is indirectly linked to the microtubules during chromosome segregation

The CENP-A histone containing chromatin physically binds to the kinetochore inner plate. An interaction between the kinetochore inner and outer plates links this chromatin to the microtubules of the mitotic spindle


What are alpha-satellite DNA repeats that are found within centromeres

Alpha-satellite DNA repeat sequences are repeat sequence elements around 170bps that act as specific binding sites for a set of specialised histones localised to centrometic sequences. These act as target interaction proteins for kinetochores


Which type of transposons make up the majority of transposons

Retroviral retrotransposons


How do retroviral retrotransposons act

Function via the production of an RNA intermediate


What is the main benefit of carrying mobile genetic sequence information around

Acts as a genome shuffling mechanism that breaks up and reassembles the genome, providing new combinations of DNA sequences and facilitating rapid genomic evolution


What is significant about the N-terminals of core histones

These project out from the nucleosome core and are free to interact with other proteins. These tails are rich in lysine residues and facilitate regulation of chromatin structure and function. They interact with proteins that effect the ability of the chromatin to be de-condensed, re-condensed and transcribed


The organised representation of all of the chromosomes in a eukaryote at metaphase is canned the karyotype, T or F



What is meant by the term transposon

Mobile genetic elements that can replicate themselves and jump around the genome


DNA transposons make up the largest proportion of transposable DNA elements in the human genome, T or F

F – they only account for 5%


What are the five main functions of chromatin

Packaging and unfolding DNA in the nucleus, control of DNA replication, repair and recombination, maintenance of chromosome integrity, governing chromosome segregation and the regulation of gene expression


Describe the structure/composition and role of centromeres

Higher order repeat sequences that contain subsets of repeat sequences called alpha-satellites. Centromeres facilitate chromosome segregation during cell division


Retrotransposons are abundant in invertebrate genomes, T or F

F – they are abundant in vertebrates


What are the three types of transposons

DNA Transposons, Retroviral retrotransposons, Non-retroviral PolyA retrotransposons


Structurally and in terms of proteins encoded by them, how are retrotransposons similar to retroviruses and what is a significant difference

Retrotransposons contain DNA sequences that code for envelope and capsid proteins just like retroviruses do. However, these proteins are usually defective but without preventing the replication capability of the retrotransposon


Of what order can the telomeric repeat sequences at the ends of chromosomes be



How do retrotransposons act in a similar way to retroviruses

They replicate via RNA intermediates and produce new DNA copies that integrate at new genomic locations. Retrotransposons self-encode the reverse transcriptase enzyme required for this mechanism