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CTO Quiz 1 > Nucleus > Flashcards

Flashcards in Nucleus Deck (16):
1

Functions of nucleus

Contains DNA (duh)
Assemble ribosomes
Specific transport of RNA, regulatory molecules
Mechanisms for replication and division

2

Nuclear envelope

Double membrane surrounding perinuclear space (continuous with rough ER)
Supported by lamin (inside lumen)
Nuclear pore complexes regulate transport

3

Appearance of nucleus

Mirrors function or dysfunction of cell
ie - fusion, U-shaped or multilobed, active or inactive
Larger and more irregular can be cancer (important to know "normal" for different cell types)

4

Euchromatin

DNA being actively transcribed, dispersed, less densely packed
Lighter in color
Cell transcribing wide variety of proteins

5

Heterochromatin

DNA no transcribed, densely packed
Darker, often anchors to lamin/envelope
Cell is making few proteins (can be large amounts but low diversity)

6

Length of DNA in cell

2 meeters (20-25K genes)

7

Facultative vs constitutive heterochromatin

Facultative based on cell fx, usually in center of nucleus
Constitutive rarely transcribed, near nuclear envelope (ex Barr body in females)

8

Chromosome segregation

Each chromosome has "territory"
Can result in "clock-faced" nucleus

9

Signs of high transcriptional activity

EUCHROMATIN
Large nucleolus (many ribosomes)
More nuclear pores

10

Barr body

Inactive X chromosome in females
Always heterochromatin

11

Chromosome packing

150 bp of helix + histone octamers (4 protein pairs) =
Nucleosome + histone H1 ->
Solenoid +condensins ->
300 nM loop -> 700 nM loop ->
Chromosome

* Chromatin remodeling complexes can make available for transcription (requires ATP)

12

Nuclear matrix

Anchors and structures chromosomes into territories, also replication and splicing proteins

13

Nuclear pore structure

>30 proteins, large complexes
Small molecules pass freely
Crosses both membranes of envelope
Fibrils help guide importins in cytoplasm
"Nuclear cage" in nucleoplasm

14

Nuclear pore transport

Nuclear localization signal on protein -> importins bind and carry (requires high RanGDP vs GTP)
RanGTP high in nucleus -> dissociation

* Polarity driven by RanGTP gradient (hydrolysis enzymes in cytoplasm not nucleoplasm)
* Exportins have opposite polarity (bind in RanGTP, release in GDP)

15

Nucleolus function

Forms ribosomal subunits
rRNA transcribed, proteins imported after translation
Subunits exported to cytoplasm
Also transcribe tRNA

* Size proportional to translation activity

16

Nucleolus structure

Five pairs of chromosomes (10 total) loop rRNA sequences
Fibrillary center - not being transcribed
Dense fibrillary zone - active transcription
Granular zone - active subunit assembly