Nucleus Flashcards
Describe the nuclear envelope.
Made up of two membranes, with a perinuclear space in between that is continuous with ER lumen. The membranes have pores that allow for transportation. Lined with nuclear lamina- IFs that bind inactive genetic material (heterochromatin).
Why is important from a pathological perspective to know what normal nuclei look like?
Malignincies can cause morphological changes in the appearance of the nuclei that can be seen under microscopy. You can identify these abnormalities via tests like pap smears.
How does the pap smear test work?
Nuclei have normal appearances, and abnormal appearances indicate a problem. A pap smear looks at cells from the cervix for nuclear malignincies.
How can you tell if a cell is metabollicaly active?
Euchromatin is unwound and cannot be seen under microscopy. Heterochromatin is bundled tightly, usually bound to the nuclear lamina at the edge of the nucleus. If the cell is producing a wide variety of proteins, there will be more euchromatin, and the nucleus will appear lighter with a prominent nucleolus.
What is the difference between facultative and constitutive DNA?
Facultative- moves fluidly between eu and heterochromatin as it is used
Constitutive- exists primarily as heterochromatin.
Describe nucleosome organization.
8 histidine subunits (2 of each H2A, H2B, H3, and H4) with 150 bp wrapped around them. helps condense chromosomes. wind (spontaneously) and unwind (energy input) every few seconds.
Describe the condensing organization for DNA from smallest to largest.
DNA is wound into nucleosomes. Nucleosomes are coiled together into a filament called a solenoid. Solenoids are folded over into loops via condensin. When the folding is extensive enough, the DNA appears as metaphase chromatin
What does condensin do?
Facilitates folding of solenoids
How are the chromosomes organized within the nucleus itself?
Scaffolding proteins segregate certain chromosomes into certain parts of the nucleus.
Describe how transportation through the nuclear pore occurs.
In order to be imported into the cell, the protein needs a nuclear localization signal. The protein will bind to the protein importin, which binds to filaments within the nuclear pore called nucleoportin. Importin binds to cargo under high [GTP] and releases it under low [GTP], which corresponds to the concentrations extracellularly and intracellularly.
What do importin and exportin do?
Importin binds to cargo outside the nucleus under high [GTP] and releases it into the nuclear pore under low [GTP]. Exportin does the opposite.
Describe the function of the nucleolus.
The nucleolus transcribes rDNA into rRNA, but does not assemble the ribosome itself. It is exported from the nucleus.
Describe the structural organization of the nucleolus.
Loops the 10 coding regions from 5 chromosomes coding for rRNA. Fibrillar center- rDNA not being transcribed (center nucleolus)
Dense Fibrillar Zone- rDNA being transcribed (border nucleolus)
Granular zone- ribosome packaging/processing (in between dense fibrillar zones)
T/F- There are no proteins assembled in the nucleus?
True- all proteins necessary to transcription are imported
