Chapter 11.4: Replication of Eukaryotic Chromosomes Flashcards
Define replication unit or replicon
o The DNA running both ways from one origin of replication to the endpoints, where it merges with DNA from adjoining replication forks
What is o The DNA running both ways from one origin of replication to the endpoints, where it merges with DNA from adjoining replication forks?
replication unit or replicon
What is the first step of nucleosome formation during DNA replication?
o Step 1: As DNA replication takes place, nucleosomes assemble rapidly on newly formed daughter DNA molecules. The “new” nucleosomes are a mixture of old (recycled) and newly formed histones, distributed randomly on the two daughter DNA molecules
After o Step 1: As DNA replication takes place, nucleosomes assemble rapidly on newly formed daughter DNA molecules. The “new” nucleosomes are a mixture of old (recycled) and newly formed histones, distributed randomly on the two daughter DNA molecules, what is the next step of nucleosome formation during DNA replication?
o Step 2: The synthesis and transport of histones must be tightly coordinated with DNA synthesis because the nascent DNA becomes incorporated into nucleosomes within minutes of its formation
After o Step 2: The synthesis and transport of histones must be tightly coordinated with DNA synthesis because the nascent DNA becomes incorporated into nucleosomes within minutes of its formation, what is the last step of nucleosome formation during DNA replication?
o Step 3: Histone modifications are labile; they become lost during DNA replication so that new nucleosomes do not have the modification found in the chromatin of the parental cell
What are telomeres?
Composed of special DNA sequences associated with specific proteins, these caps contain no genes but are crucial in preserving the structural integrity of each chromosome
Where do the linear chromosomes of eukaryotic cells terminate?
telomeres
What is the function of telomeres?
Telomeres and an enzyme called telomerase provide a countermeasure to the DNA polymerase limitation of replicating in the 5’-to-3’ direction
• Telomeres consist of particular repetitive DNA sequences that do not encode proteins
• Adds to the end of the telomere to counterbalance the loss of DNA that must occur when linear DNA molecules are copied
What is the repetitive DNA sequence of telomeres in humans?
o Humans: 5’ TTAGGG 3’
Define shelterin
a complex of proteins that folds up the telomeres into a structure that shields single-stranded TTAGGG sequences from nucleases and NHEJ enzymes
What is a complex of proteins that folds up the telomeres into a structure that shields single-stranded TTAGGG sequences from nucleases and NHEJ enzymes?
shelterin
