Lecture 4- Nucleus Flashcards
Histones
Positively charged proteins that form the core of the nucleosome complex (DNA wraps around them)
Nonhistones
Negatively charged proteins that regulate transcription, repair and replicate DNA, and convert chromatin structure
Heterochromatin
Condensed chromatin
Not transcriptionally active
Constitutive Heterochromatin
Contains DNA that is not transcribed
Facultative Heterochromatin
DNA is not transcribed in particular cell being examined but may be transcribed in other cells
Barr Body/Drumstick
Inactivated X chromosome
Euchromatin
Transcriptionally active
Not condensed
Nuclear Lamina
Support inner membrane
During cell division-phosphorylated to dissociate membrane
Post cell division-dephosphorylated to reassemble membrane
How are chromosomes organized in the nucleus?
Each one occupies a discrete region and is anchored by lamina
Replication Factories
Functional bodies where replication takes place inside the nucleus
Nuclear Speckles
Concentrations of mRNA splicing machinery
PML Bodies
Accumulation of transcription factors and chromatin-modifying proteins
Cajal Bodies
Contain coilin protein
What is the Nuclear Pore Complex?
A passageway for macromolecules to go between nucleoplasm and cytoplasm
It requires ATP and GTP
What are the proteins called that transport macromolecules into and out of the nucleus?
Karyopherins (Importin alpha/beta & Exportin)
What is the structure of the Nuclear Pore Complex?
8-fold symmetry around a central canal
8 spokes connect rings to nuclear and cytoplasmic surfaces
Basketlike structure on the nuclear side
How does import through the Nuclear Pore Complex occur?
Importin alpha recognizes NLS
Ran-GDP binds to importin beta and moves through pore
Importin beta separates and is released from Ran-GDP
RCC1 generates Ran-GTP
How does export through the Nuclear Pore Complex occur?
Exportins bind to Ran-GTP and protein and moves through pore
Ran-GTP is separated from exportin and protein
Ran-GAP converts Ran-GTP to Ran-GDP for import
What are the Functional sequences of a Chromosome?
Telomeric Sequence-Located at ends of chromosome and insure integrity
Centromeric Sequence-Involved in separation during Mitosis and Meiosis
Replication Sequence-Start sites for DNA replication
What is the Nucleolus?
A region inside the nucleus where rRNA is transcribed
A nucleus may have more than one nucleolus
What are the regions of a Nucleolus?
Fibrillar Center-Tightly coiled non-transcribed DNA
Dense Fibrils-Active transcription of RNA (contains ribonucleoproteins)
Granules-Contains maturing ribosomes