Nuclear Chromatin, Epigenetic Modifications And Nuclear Transport Flashcards
What are the most abundant proteins associated with eukaryotic DNA?
Histones
Histones are a family of small, basic proteins present in all eukaryotic nuclei.
What are the five major types of histone proteins?
H1
H2A
H2B
H3
H4
These histones are rich in positively charged basic amino acids.
What structure do nucleosomes consist of?
A protein core with DNA wound around its surface
The core is an octamer containing two copies each of histones H2A, H2B, H3, and H4
How many base pairs of DNA are contained in a nucleosome?
147 base pairs
The DNA is wrapped slightly less than two turns around the protein core.
What are histone tails?
amino terminus of 11–37 residues extending from the fixed structure of the nucleosome
What modifications can occur to histone tail lysines?
Acetylation
Deacetylation
These modifications are reversible and act on specific lysines in the N-termini.
What is the effect of acetylation on histone tail lysines?
Neutralizes the positive charge of lysine ε-amino group
This eliminates its interaction with a DNA phosphate group.
What is the term for modifications that influence chromatin structure and processes?
Epigenetic modifications
These include acetylation and methylation of histone tail amino acid side chains.
What is the nuclear pore complex?
A structure that facilitates transport in and out of the nucleus
It is embedded in the nuclear envelope and regulates the exchange of macromolecules.
What directs proteins to the nucleus?
Nuclear-localization signals (NLS)
These signals are rich in lysine.
What is the role of importins?
Transport proteins containing nuclear-localization signals into the nucleus
They recognize and bind to NLS to facilitate nuclear import.
What are nuclear-export signals (NES)?
Signals that stimulate export of proteins from the nucleus
These signals are often leucine-rich.
What is a common mechanism for nuclear export?
Shuttling proteins containing both NLS and NES
This allows proteins to be exported and later re-imported into the nucleus.
Fill in the blank: The histone tail lysines undergo reversible _______ and _______ by enzymes
Acetylation, deacetylation
Fill in the blank: Proteins found in the nucleus contain a _______ that directs their selective transport into the nucleus.
nuclear-localization signal (NLS)
True or False: All proteins in the nucleus are synthesized in the nucleus.
False
All proteins found in the nucleus are synthesized in the cytoplasm.
What is the appearance of chromatin isolated in low-ionic-strength buffer?
What is the appearance of chromatin isolated in low-ionic-strength buffer?
Beads-on-a-string appearance
The ‘beads’ are nucleosomes and the ‘string’ is linker DNA.
What is the range of linker DNA length among species?
15 to 55 base pairs
