organisation of euk genome

Question 1

describe the three levels of condensation

Answer 1

level 1) nucleosome : DNA is coiled around an octomer of histone proteins, forming a nucleosome core (beads on string). Multiple nucleosomes are packed together to form 10nm chromatin fibre

level 2) solenoid : DNA is further coiled to form 30nm chromatin fibre

level 3) looped domains and chromosome : scaffold proteins condense the solenoid to form looped domains. Looped domains can further fold and coil to form chromosome.

Question 2

what is the role of condensation? x2

Answer 2

1) to organise and pack the giant DNA into structures that will facilitate their segregation into daughter nuclei
2) condensation ensures that DNA does not get entangled and break during separation at anaphase

Question 3

what are the 4 functions of telomeres

Answer 3

1) protect DNA from degradation by forming t-loops which is a cap that protects the overhangs of linear chromosomes from degradation by exonucleases. the cap also prevents damaged DNA from being recognised
2) maintain stability of DNA as t-loops prevent chromosome tips from fusing to the ends of other chromosomes
3) Prevent loss of genes by preventing important genes from being eroded due to the end replication problem.
4) Regulate replicative cell senescence because when telomeres shortened to a critical length, the hayflick limit, the cell enters cell senescence

Question 4

how does telomerase maintain telomere length