Ch 7: The Cell Nucleus Flashcards
- What contents are in an interphase eukaryotic cell nucleus?
①the chromosomes, which are present as highly, extended nucleoprotein fibers, termed chromatin
②one or more nucleoli, which are irregular, shaped electron-dense structures that function in the synthesis of ribosomal RNA and the assembly of ribosomes
③the nucleoplasm, the fluid substance in which the solutes of the nucleus are dissolved
④the nuclear matrix, which is a protein-containing fibrillar network
- What is the structure and function of nuclear envelope?
consists of two cellular membranes arranged parallel to one another and separated by 10 to 50 nm. The nuclear envelope serve as a barrier that keeps ions, solutes and macromolecules from passing between the nucleus and cytoplasm
. The categories of highly repeated DNA sequences and moderately repeated DNA sequences .
Highly repeated sequences include satellite DNAs, minisatellite DNAs, and microsatellite DNAs
Moderately repeated DNA sequences : repeated DNA sequences with coding functions & lack coding function
The functions of three types of RNA polymerases in eukaryotic cells.
RNA polymeraseⅠ synthesizes the larger ribosomal RNAs；RNA polymeraseⅡ synthesizes messenger RNAs and most small nuclear RNAs
RNA polymeraseⅢ synthesize transfer RNAs and the 5S ribosomal RNA
What are the composition, structure and functions of nuclear lamina?
composed of polypeptides，called lamins
The inner surface of the nuclear envelope is bounded by integral membrane proteins to a thin filamentous meshwork
The nuclear lamina provides mechanical support to the nuclear envelope and serves as a site of attachment for chromatin fibers at the nuclear periphery
How can proteins be recognized and transported into nucleus?
Nuclear protein contain a nuclear localization signal. It is recognized by transport receptors importins
What are the four structural levels of chromatin(DNA packing)?
Nucleosome, 30 nm fiber, Looped domains, Metaphase chromosome
What is the structure of nucleosome?
Each nucleosome contains a nucleosome core particle （10nm in diameter）consisting of 146 base pairs of supercoiled DNA wrapped 1 and ¾ round around a disk-shaped complex of eight histone molecules
What are the two kinds of heterochromatin?
①Constitutive heterochromatin, which remains in the compacted state in all cells at all times, it consists primarily of repeated sequences
②Facultative heterochromatin is chromatin that has been specifically inactivated during certain phases of an organism’s life or in certain types of differentiated cells
What are the X chromosome inactivation rules?
①heterochromatization of X chromosome in female mammals occurs during early embryonic development
②heterochromatization in the embryo is a random process，the paternal X have the same chance to be inactivated with the maternal X
③reactivation of the heterochromatized X chromosome occurs in germ cells prior to the onset of meiosis
- What are on the tips of each DNA molecule, to protect the integrity of DNA？
Telomere
Centromere
marked indentation on a mitotic chromosome that serves as the site of kinectochore formation.
Centromere is the residence of highly repeated DNA sequences that serve as the binding sites for specific proteins.
Telomere
an unusual stretch of repeated sequences, which forms a “cap” at each end of a chromosome.
What are the components of eukaryotic cell ribosome?
several molecules of rRNA with dozens of ribosomal proteins
Which kind of rRNA is not transcribed inside nucleolus?
5srRNA
