Nucleus

Question 1

Functions of nucleus

Answer 1

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

Question 2

Nuclear envelope

Answer 2

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

Question 3

Appearance of nucleus

Answer 3

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)

Question 4

Euchromatin

Answer 4

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

Question 5

Heterochromatin

Answer 5

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

Question 6

Length of DNA in cell

Answer 6

2 meeters (20-25K genes)

Question 7

Facultative vs constitutive heterochromatin

Answer 7

Facultative based on cell fx, usually in center of nucleus

Constitutive rarely transcribed, near nuclear envelope (ex Barr body in females)

Question 8

Chromosome segregation

Answer 8

Each chromosome has “territory”

Can result in “clock-faced” nucleus

Question 9

Signs of high transcriptional activity

Answer 9

EUCHROMATIN
Large nucleolus (many ribosomes)
More nuclear pores

Question 10

Barr body

Answer 10

Inactive X chromosome in females

Always heterochromatin

Question 11

Chromosome packing

Answer 11

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)

Question 12

Nuclear matrix

Answer 12

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

Question 13

Nuclear pore structure

Answer 13

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

Question 14

Nuclear pore transport

Answer 14

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)

Question 15

Nucleolus function

Answer 15

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

• Size proportional to translation activity

Question 16

Nucleolus structure

Answer 16

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