Ch. 3 - The Nucleus Flashcards
Nucleus
The command center of the cell
Contains the code for all of a cell’s enzymes and proteins
Stores the genetic information
Largest structure within a cell
What are the components of the nucleus?
Nuclear envelope
Chromatin
Nucleolus
Chromatin
A mass of DNA and associated proteins
Two types can be distinguished via microscopy, heterochromatin and euchromatin
Nucleolus
Specialized subdomain of the nucleus
Contains the genes for pre-rRNA
Nuclear envelope
Forms a selectively permeable barrier between nuclear and cytoplasmic components
Two concentric membranes separated by a perinuclear space
Perinuclear space
The narrow space between the two concentric membranes of the nuclear envelope
This space and the outer nuclear membrane are continuous with the RER
Nuclear lamina
A highly organized meshwork of proteins that is closely associated with the inner nuclear membrane
Stabilizes the nuclear envelope
Lamins
Class of intermediate filament proteins that bind to membrane proteins and associate with chromatin in nondividing cells
Nuclear pore complexes
Bridge the inner and outer nuclear membranes
Regulate movement of macromolecules between the nucleus and cytoplasm in both directions simultaneously
Nucleoporins
Various core proteins of a nuclear pore complex
Eightfold symmetry around the lumen
How is heterochromatin visualized with the light microscope? Electron microscope?
Intensely basophilic clumps (light)
Coarse, e- dense material (e-)
How is euchromatin visualized with the light microscope? Electron microscope?
Lightly stained basophilic areas (light)
Finely dispersed granular material (e-)
Heterochromatin
Highly condensed chromatin
DNA is tightly coiled
Less accessible for transcription
Euchromatin
Finely dispersed chromatin
Contains regions of the DNA undergoing active transcription
More prominent in metabolically active cells
Typically more active in protein synthesis
Nucleosome
The structural unit of DNA and histones
Has a core of 8 small histones wrapped around DNA of ~150 bp
Barr body
A small, dense mass of heterochromatin present in females but not in males
Aka “sex chromatin”
One of the two X chromosomes
Chromatid
Each long DNA double helix and its associated proteins
Chromosome
Two chromatids held tougher by complexes of cohesin proteins
The members of each chromosomal pair are called _______ because, although from different parents, they contain allele of the same genes.
homologous
Cells of most tissues (somatic cells) are considered _______ because they contain pairs of chromosomes.
diploid
Diploid cell are referred to as _______.
2n
Germ cells are _______, with half the diploid number of chromosomes, each pair having been separated during meiosis.
haploid
Germ cells
Sperm cells and mature oocytes
Haploid
Karotyping
Chromosomal analysis where the condensed chromosomes of one nucleus may be photographed by light microscopy and rearranged to produce a karotype in which stained chromosomal bands can be analyzed
What causes the intense basophilia of the nucleolus?
Densely concentrated rRNA that is transcribed, processed, and complexed into ribosomal subunits in the nucleoli
Cell cycle
Regular sequence of events that result in new cells
What are the four distinct phases of the cell cycle?
- G1 phase (part of interphase)
- S phase (part of interphase)
- G2 phase (part of interphase)
- M-phase (and cytokinesis)
M phase
Cell division that results in clones
G1 phase
The time gap between mitosis and DNA replication
Cellular content is duplicated, not chromosomes
Period of active RNA and protein synthesis
Cell volume, reduced in half by mitosis, is returned to normal volume
S phase
Synthesis phase
The period of DNA synthesis
Chromosome duplication
Histone synthesis
G2 phase
The gap between DNA duplication and the next mitosis
Cell grows and prepares for mitosis by accumulating proteins needed
Checks for errors
What are the phases of M phase?
- Mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
G0 phase
Postmitotic cells that stop differentiating and specialize
In a state of arrest
Stem cells live in this phase
Mitogens or Growth factors
Protein signals from the extracellular environment that activate cycling in post mitotic G0 cells
Bind to cell surface receptors and trigger a cascade of kinase signaling in the cells
Prophase
Nucleolus disappears and chromosomes are visible
At the centromere, kinetochores serve as a site for microtubule attachment
