Chromosome Structure Flashcards
What is chromatin?
Is a DNA molecule and the proteins that are associated with it.
what protein is about one-third of all proteins within the chromatin? what charge are these things?
Histones
what are the two important functions of histones?
they attach to the DNA molecule and help compact it into a smaller size, they also help regulate the activity of genes within the chromosome.
how many different histones are there and what are they?
there are five different histones which are H1, H2A, H2B, H3, & H4
which histones interact to form a spherical particle called a histone octamer?
the latter four histones being H2A, H2B, H3, & H4)
what does a histone octamer contain?
two H2A, two H2B, two H3, and two H4 proteins
What does a histone octamer associate with, how big is it, what does it do do?
with a small part of the DNA molecule it is around 146-147bp, it is wrapped around twice on the outside of the histone octamer.
what does a histone octamer and the DNA that it wraps form?
a nucleosome
what are nucleosomes separated by? what is this type of DNA called?
They are separated by a short length of DNA that is not a part of a nucleosome called linker DNA.
how long is linker DNA? what is it associated with?
Linker can be 20-100bp in length it is associated with H1 protein.
What do linker histones and nonhistone proteins do?
They help organize adjacent nucleosomes and have a role in compaction.
what happens to the length of a DNA molecule that is organized into a nucleosome?
It is reduced in length about seven fold
what inhibits gene expression in nucleosomes?
closely spaces nucleosomes inhibit gene expression
to express a gene what needs to be done? what is the protein that catalyzes this reaction?
Nucleosomes need to be either moved farther apart or removed altogether, the proteins that form ATP-dependent chromatin-remodeling complexes.
what is compaction for DNA?
the process of making the DNA molecule within a chromosome smaller.
what is the first step in the compaction process?
organizing the DNA into nucleosomes
Nucleosomes within chromatin are coiled into _____. What does this coiling require?
30nm fibers, it requires linker histone
what are the 30nm fibers arranged into? what binding factor is it?
loop domains, the binding factor is CCCTC (CTCF) or SMC protein
what are chromosomes that occupy distinct locations within the nucleus?
Chromosome territories
what are translocations?
chromosomal abnormalities
what are the advantages of loop domains?
it helps compact the DNA so it will fit in the nucleus, but it doesn’t compact it to much.
what are the highly compacted structures in loop domains called?
heterochromatin
what are less compacted structures in loop domains called?
euchromatin
where is most of the heterochromatin located at?
centromere and telomeres
where are most genes located at?
euchromatin
what happens in cell division? (think of heterochromatin), what are a advantage of this?
all regions of a chromosome becomes as compact as heterochromatin
what is a draw back in compact chromosomes during cell division?
DNA replication and transcription are inhibited in these compact chromosomes
what does euchromatin become after cell division is completed?
it becomes less compact
