DNA Structure and Replication Flashcards
(28 cards)
What are the two forms of chromatin?
Chromosomes can shuttle between euchromatin and heterochromatin forms.
What is the role of DNA packaging?
DNA packaging organizes and protects DNA; it also regulates DNA expression.
What is a nucleosome?
A nucleosome consists of DNA wrapped around a histone.
What is linker DNA?
Linker DNA is where the DNA is not wrapped around the histones.
What are histones made of?
Histones are made of 8 subunits called octamers.
How much DNA does each octamer bind?
Each octamer binds to about 147 bp of DNA.
What are the lengths of linker sequences?
Linker sequences are about 38 - 53 bp.
What structure do histones form?
Histones coil around each other to save space and make a solenoid structure.
What is found in the central part of a chromosome?
The central part of a chromosome contains non-histone scaffold protein components.
What do solenoids do?
Solenoids make loops around the central part of the chromosome.
How is DNA replicated?
DNA is replicated by semi-conservative replication, where there is one old strand and one new strand.
What is the role of DNA polymerase?
DNA polymerase forms the new strand by incorporating free nucleotides or d NTPs.
How does polymerase link nucleotides?
Polymerase links the 3’ C of an existing nucleotide to the 5’ C of a new nucleotide.
What type of chromosome do prokaryotes have?
Prokaryotes have a single circular chromosome.
What are the three steps of DNA replication?
DNA replication proceeds in three steps: initiation, elongation, and termination.
What occurs during the initiation of prokaryotic DNA replication?
The DNA molecule unwinds and the two strands separate. Primase synthesizes an RNA primer that allows DNA polymerase to bind.
What happens during the elongation phase of prokaryotic DNA replication?
Replication forks are formed and move along the molecule. Two helicases work in either direction, and DNA ligase joins fragments together.
What is the outcome of prokaryotic DNA replication?
Two identical circular chromosomes have formed.
How does eukaryotic DNA replication initiate?
Multiple origins of replication form making replication bubbles. Primase causes an RNA primer to be made, allowing DNA polymerase to bind at the 3’ end.
What occurs when replication bubbles meet in eukaryotic DNA replication?
The newly copied DNA is joined together.
What is the role of DNA ligase in eukaryotic DNA replication?
DNA ligase sticks together Okazaki fragments and fixes the strands once the bubbles meet.
What is the function of exonucleases in eukaryotic DNA replication?
Exonucleases catalyze the removal of a single nucleotide (dNMP) if errors in transcription are identified.
What happens after the RNA primer is removed in eukaryotic DNA replication?
There is a gap that DNA polymerase cannot fill. The telomerase enzyme binds to the overhanging DNA, makes a primer, and completes the rest.
What is assembled after DNA replication in eukaryotes?
New nucleosomes are assembled with either a parental or new H3-H4 tetramer, completing the structure with a pair of H2A - H2B dimers.
