Chromatin Structure Flashcards
What is “Fine Control”?
Interaction of cis-acting DNA sequences (promoters and enhancers) with RNA polymerase and transcription factors
What is “Course Control”?
Changes in structure of chromatin to prevent or enable ACCESS of RNA polymerase and transcription factors
What are 2 cis-acting DNA sequences?
Promoters and Enhancers
What is the difference between genome and epigenome?
Genome = totality of DNA in an organism Epigenome = totality of DNA and DNA modifications and associated proteins
Why is the 30nm fiber important?
It is the fundamental fiber of both metaphase chromosomes and interphase chromatin
What is the difference between 10nm fibers and 30nm fibers?
In the 10nm fiber, some DNA is accessible. In the 30nm fiber, most of the DNA is folded into the interior and therefore not accessible to RNA polymerase and transcription factors
What is the histone octamer composed of?
2 units each of H2A, H2B, H3, and H4
What is the nucleosome core composed of?
Histone octamer, 146 bp DNA, 1.75 turns
How was the nucleosome core discovered?
Resulted from a limit digest of chromatin by micrococcal nuclease
What is the main role of H1?
Facilitates folding of 10nm fiber into 30nm fiber
What is the structural difference between chromatin containing H1 vs. chromatin without H1?
With H1: nucleosomes have regular zigzag orientation
Without H1: beads on string
Describe the structure of chromatin
Histones on the inside, DNA on outside wrapped around the histone octamer, particulate structure
What did experiments with micrococcal nuclease reveal about chromatin structure?
- ) Chromatin structure may not be as uniform as thought, may be more particulate
- ) Less micrococcal nuclease = more nucleosomes complexed together
What are transgenic marker genes?
Genes used to determine if a piece of DNA has been successfully inserted into the genome of the host organism
What are selectable markers?
Genes that protect the transformed organism or cell from a selective agent (usually an antibiotic)
What is a screenable marker?
Genes that give transformed cells an identifiable characteristic to distinguish them from untransformed cells but do not confer resistance to the selective agent
What are 3 examples of screenable markers?
- ) GFP: fluoresces green when excited with UV light
- ) Luciferase: converts energy of ATP into light
- ) B-Galactosidase: converts colorless substrates into colored compounds that can be easily detected
What are reporter genes?
Genes usually attached to regulatory sequences of another gene of interest to test the effects of the regulatory sequence; can be used to measure gene activity
What are insulators?
Boundaries between domain of the gene and the enhancer (or silencer) so that the gene can no longer feel the activating (or repressing) effects
What are Domain Boundaries?
Special nucleoprotein structures formed by proteins at specific sites along chromosome
How is inappropriate activation avoided?
Organisms use DNA insulators to block activation of unrelated genes by nearby enhancers
What is the function of insulator proteins?
Recruit histone acetyltransferases that acetylate flanking nucleosomes; acetylation inhibits histone modifications required for the propagation of transcriptionally silent condensed chromatin
What is the function of boundary elements?
To relate structural organization of chromatin fiber to informational organization of the DNA
What are position effects?
The modification of gene expression when genes are relocated to new environments by rearrangement or transformation
What is important about the site of insertion?
It helps determine the level of expression of the transgene
How is repression facilitated?
By the association of genomic sequences with the inner nuclear lamina through lamin binding proteins
Why are transcriptional neighborhoods (TNs) important?
They contain a collection of transcriptional machinery and help provide an environment for the initiation, hyperactivation, and maintenance of transcription
What is the function of architectural proteins (APs)?
They bend DNA and compact chromatin
