L.9 Nuclear Structure

Name 8 structures of the nucleus

1. Nucleolus

2. Nuclear pores

3. Nuclear envelope

4. Nuclear laminal matrix

5. Chromatin diffuse

6. Chromatin condensed

7. Nuclear bodies

8. Kargo/nucleo-plasm

Nucleus bonded by?

Membrane complex (nuclear envelope)

Components of nuclear envelope

• Inner and outer membranes

• Perinuclear space (between)

Outer membrane shares a common boarder with ?

• ER (associated ribosomes)

• Perinuclear space

Inner membrane integrated with

Nuclear lamina and matrix

What is the nuclear lamina/matrix

Coats inside, adds structural integrity

Nucleolus function (secondary)

• houses 46 chromosomes

How many Gb of info in nucleolus? Gigacodons?

• 33 Gb

• 10 gigacodons

Describe interphase nucleus

• Highly condensed heterchromatin connected with Amina and inner membrane

• non-coding/normal state

What is heterochormatin

Very dense DNA

What is non-condensed DNA-protein complex called

Euchromatin

Describe euchromatin

• non-condensed protein-DNA

• Fills most of nucleus

• Contain actively transcribed DNA

• Cell type specific

Individual chromosomes form ____, which can be seen by ____.

• chromosomal territories

• FISH (fluorescence)

Structure of nucleolus

• largest structure in nucleus

• 1-6/cell

• Granular component, fibrilar centre, dense fibrilar component

Functions of parts of nucleolus

• granular component →rRNA transcription

• Dense fibrillar component → rRNA processing (create RNA)

Major function of nucleolus

rRNA transcription and pre-ribosome processing and assembly

Structure of nucleus determined by

Proteins of nuclear lamina and nuclear matrix

Describe nuclear lamina and matrix

Intra-nuclear cytoskeleton structure network

What does the nuclear lamina/matrix enable?

Chromosome territories

What are nuclear bodies? What do they do?

• memernbaens structres in nuclei of eukaryotes

• Dynamic structures that grow/shrink in response to metabolic needs

4 types of nuclear bodies

1. Cajal bodies

2. Nuclear speckles

3. Paraspeckles

4. PML bodies

Describe cajal bodies

• 1-10/ nucleus

• Manufacture some specialized RNA molecules

Describe nuclear speckles

Enriched in pre- mRNA splicing factors

Describe paraspeckels

• Alter in response To changes in cellular metabolic activity and stress

• Rapid response

• 10-30/muscle

Describe PML bodies

• unknown function

• Composition varies

• Implanted in cell processes (telomere lengthening/ DNA damage response)

When do you see more PML bodies

Cancer

Label the structures

A- cytoplasmic ring

B- cytoplasmic filaments

C- nuclear basket

D- nuclear pore

E- nuclear ring

Type of symmetry of nuclear pores

Eightfold rotational

What is the nuclear pore complex

• npc is largest protein complex in cell

• Easily recognized by 2M*

• Entry/exit of nucleus

Average of ____ NPC in envelope

2000

What is classical nuclear import/export

Through NPC, cargo with classical NLS/NES drives active transport

Importing cargo through NPC requires ____ which occurs via ____. Export requires ___, via _____

• classical NLS

• Importing-proportional*/importin B heterodomer

• NES

• Exporting

Active transport through NPC driven by ____

Gradient of RanGTP and RanGDP (across nucleus)

Classic NLS is ___

Stretch of basic residues

What can pass freely through NPC/across envelope?

• metabolites

• Small ions/molecules

What requires active transport through NPC?

• large macromolecules

  • Protein

  • M/tRNA

  • Ribosomes subunits

  • Viruses

What is an NLS

Nuclear localization sequences

Nuclear pore import step 1

1. Proteins show NLS and recognized by cytoplasmic receptor molecule (importin), forms complex

Step 2 nuclear pore import

Binding/ regcognition → docking with fibres (form cytoplasmic ring)

Step 3 nuclear nuclear pore import

Docking recruits accessory proteins (GTPases and NTF2) to promote interaction, hydrolyze

Step 4 nuclear pore import

• hydrolysis of RanGTP → RanGDP

• Allow for movement through pore

• Release cargo

Steps of nuclear pore export

1. Cargo has nuclear export signal (NES) recognized by exportin

2. Complex associates with basket

3. Docking recruits energy creating Ran-GTPase (hydrolysis) for energy

4. Export into cytoplasm form RanGTP/RanGTP energy

Roughly how many proteins in NPC

~30

Pro and con of NPC complexity

• higher specificity

• Higher chance of error

Dysfunction if NPC associated with ____. Examples

• many diseases

• ALS, FTD, Alzheimer’s triple A syndrome, many cancers

Which nuclear structres play roles in breakdown/reassembly in mitosis?

Envelope and lamina

What triggers prophase?

End of GZ*, activate cyclin-dependant kinases

Example of cyclin-dependant kinases

CDK1

What promotes lamina tearing/NE fragmentation

Microtubule stretching

What happens what nuclear membrane breaks down

NE- associate proteins translocation to kinetic horse, distribute with ER fragments, dissolve in cytoplasm

NE reassembly When/how

• anaphase

• SUN 1, LAP 2 around condensed chromatin

• Nuclear laminsjoin at periphery in telophase

NE breakdown because of ___, what has what function?

• lamin kinase

• Phospholylates lamin A,B and C →depolymerization lamin matrix

What happens to lamin A, B, and C after phosphorylation

B- associate with membrane vesicles

A,C- dispersed

When decomdonsation of chromosomes in daughter cells being (telophase) what occurs coincidentally

• phosphates removed from laminate protein by activated lamin phosphatase

  • polymerization of lamina

    • Membrane bound lamin B= nuclatiensile

What is nucleation site? Why?

• membrane bound lamin B

• Already there, didn’t disappear

Alternative route out of nucleus

Via ER