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Biomolecules & Cells > Cytosol Nucleus Tracking > Flashcards

Cytosol Nucleus Tracking Flashcards

1
Q

Slide 4

A

Scanning EM image of nucleus nuclear envelope, cytoplasm

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2
Q

What is the perinuclear space with?

A

Endoplasmic Reticulum

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3
Q

How many nuclear membranes are there?

A

“2” - outer & inner!

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4
Q

What else is in the nuclear envelope?

A

Pore complexes!

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5
Q

Fibrous Lamina (or Nuclear Lamina)

A

A meshwork of intermediate filament proteins lining the inner aspect of the inner nuclear membrane

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6
Q

Which materials are exchanged between the nuclear and cytoplasmic compartments?

A 
Slide 6
Nuclear proteins (in)
Ribosomal proteins (in)
Ribosomal subunits (out)
mRNA (out)
tRNA (out)
Shuttling proteins (out)
Ions (both)
ATP (both)
Smallecules (
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7
Q

Nuclear Envelope Components (Start presentation here?)

A

Nuclear Membranes
Nuclear Lamina
Nuclear Pore Complex
Slide 10 is helpful

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8
Q

Outer Nuclear Membrane

A

Continuation of RER, has ribosomes on its outer surface

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9
Q

Inner Nuclear Membrane

A

Associated with Nuclear Lamina & Chromatin

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10
Q

Pore Membranes

A

Connect the two!

Associated with pore complexes!

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11
Q

Nuclear Lamina

A

Slide 11 & 12

Made of 10 nm-diameter fibers (characteristic of IFs)

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12
Q

Components of a nuclear lamin IF

A

Variable Head & Tail Domains

Highly Conserved alpha-helical rod domains (responsible for dimerization), then higher polymerization into IFs

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13
Q

What makes Lamin IFs different from cytoplasmic IFs

A

They have more repeats in the rod domains

They have NLS

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14
Q

What happens to the nuclear lamina during mitosis?

A

The lamina proteins get phosphorylated, causing them to disassemble into free-floating dimers.

They later re-assemble by being dephosphorylated.

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15
Q

What proteins does the lamina interact with in the inner nuclear membrane?

A 
LBR
Emerin
POM121
gp210
Myne-1
Nurim
Nuclear Pore Complex
MAN1
LAPs
HETEROCHROMATIN
60 - 80 proteins, total
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16
Q

What are the two types of lamins that make up the Nuclear Lamina?

A

A-Type

B-Type

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17
Q

Nuclear Pore Complex

A

Slide 15

Slide 16 - Pretty!!!! (dissolved membrane away with detergent, but the pore complexes remain)

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18
Q

Nuclear Pore Complex Components

A 
Slide 17!!!!
Cytoplasmic Fibrils
Cytoplasmic Ring
Nuclear Ring
Nuclear Basket
Distal Ring
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19
Q

What proteins make up a Nuclear Pore Complex?

A

Nucleoporins (many have FG repeats)
Integral Membrane Proteins (gp210, POM121)
Associated Proteins (Ran, Lamins)
Others not well characterized

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20
Q

Mechanisms of Nuclear Transport

A

Diffusion

Active Nuclear Transport

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21
Q

Diffusion

A

Chemical and electrical gradient equilibrium
Works in NPC for smallecules like ions and ATP
Limited by permeability of membrane and diameter of pores

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22
Q

Rate of Diffusion

A 
Inversely proportional to square root of the molecular mass.
Some molecules (like histones) can diffuse, but not as quickly as you'd like, so there are alternative mechanisms.
23
Q

Diffusion Size Cutoffs

A

60 kDa and above can’t diffuse into nucleus

24
Q

Some molecules concentrate in the nucleus, even though they could freely diffuse. Why?!

A

They bind to thangs in the nucleus. Ex: Cations that bind to negatively-charged DNA

25
Q

Active Nuclear Transport

A

Faster uptake for larger molecules that could diffuse, but slowly.
Uptake of molecules to large to diffuse
Requires ATP or GTP

26
Q

NLS code

A

PKKKRKV
Pro-Lys-Lys-Lys-Arg-Lys-Val
KKKRK is the most important
Mess up something in there, and the NLS won’t werq
Discovered from the SV40 Large T Antigen (viral)

Also, hella basic

27
Q

What happens when you covalently attach to albumin or gold?

A

GOLD ASS NUCLEUS

28
Q

A few examples of NLS sequences

A 
PKKKRKV
GKKRSKA
KAKRQR
RKRRR
PRRRK
PYLNKRKGKP
KKKKRKREK
KKKRRSREK
29
Q

Second type of NLS

A

Bipartite (discovered in Nucleoplasm)
KR PAATKKAGQA KKKK
Two basic clusters separated by a sequence of about 10 rando amino acids

30
Q

Two step process of nuclear import

A

Step 1 - Energy Independent

Step 2 - ATP Dependent

31
Q

Step 1

A

Fraction A
Binding of NLS-containing substrate to to a nuclear pore complex
NEM-sensitive

32
Q

Step 2

A

Fraction B
Translocation - Moving of the substrate across the pore.
Blocked by non-hydrolyzable GTP analogues

33
Q

Fraction B

A

Contains Ran (Ras-like protein that binds GTP)
Restored import in the presence of ATP and Fraction A.
Recombinant Ran also active.
Blocked by non-hydrolyzable GTP analogues

34
Q

What does this mean?

A

It was primarily Ran-dependent hydrolysis of GTP that provides energy for transport across the pores

35
Q

Fraction A

A 
Heterodimeric complex needed for NLS-mediated import
Karyopherin alpha/Karyopherin beta
Importin alpha/importin beta
NLS receptor/p97
NPC targeting complex

THESE ARE ALL NAMES FOR THE SAME COMPLEX

Typically karyopherin or importin are the running names these days.

36
Q

Karyopherin/Importin Alpha - Important structure

A

N-terminal, C-terminal, IT IS A PROTEIN

Functional shit:

NLS Binding/Contact Surface
Karyopherin/Importin Beta1 binding domain

37
Q

Karyopherin/Importin Beta1 - Important structure

A

The first of a family of karyopherinBetas/ImportinBetas
Involved in SV40 Large T antigen and Bipartite NLS
90 kDa
Binds importin-alpha (via importin beta binding domain)
Binds RAN-GTP
Binds FG repeats in nucleoporins

There is a large family of these proteins. Some mediate import. Some mediate export.

Beta1 needs Alpha (middleman) to bind to the NLS.

Most other karyopherin Betas bind directly to cargo.
They bind to:
Ribosomal proteins
tRNA
Some are involved in export, but rely on an NES for that.

38
Q

NES

A

Nuclear Export Sequence

Very Leucine-rich.
The tRNA one appears on the tRNA itself, not a bound protein

39
Q

“Important things” about Karyopherin/importin(exportin)-Betas

A

Over 20 in the human genome
Each receptor recognizes a different type of targeting signal for import or export
Soluble
Interact with both Cargo (sometimes indirectly) and NPC
Shuttle back and forth through NPC carrying cargo one way, then recycling back without cargo (usually)

40
Q

mRNA export

A

Not completely understood.
Coupled to splicing somehow.
Inhibit splicing, inhibit export.

No karyopherin/importin involved.

41
Q

Ran-GAP

A

Activates the cytoplasmic GTPase so Ran-GDP predominates in cytoplasm

42
Q

Ran-GEF

A

Catalyzes exchange of GDP for GTP.

43
Q

Importins release their cargo when?

A

Upon binding Ran-GTP

44
Q

Exportins bind their cargo when?

A

When they bind to Ran-GTP

45
Q

Exportins release their cargo when?

A

When Ran-GTP is no longer around.

46
Q

NLS and NES signals can be masked.

A

Phosphorylation - conformational change

Phosphorylation - binding to another protein that hides the signal

47
Q

NLS and NES signals can be created

A

Phosphorylation - Conformational change
Phosphorylation - Release fo masking protein
Degradation of bound masking protein

48
Q

What does the nuclear envelope do besides all this?

A

Regulates transcription factors through MAN1 and LEMD3

49
Q

MAN1/LEMD3

A

Brake
Resides in inner nuclear membrane
Downregulates Smad 1/2/3

50
Q

Smads 1/2/3

A

Move into the nucleus (using karyopherins) in response to activation of the TGF-Beta signaling family

51
Q

What happens if you lose half your MAN1?

A

Sclerosing Bone Dysplasias with Skin Abnormalities.
Buschke-Ollendorff Syndrome and Osteopoikilosis
From increased TGF-Beta and BMP signaling in bone and skin

52
Q

Osteopoikilosis and Buschke-Ollendorff

A

Hyperdensities in cortical bone (can be painful)
From overactive BMP and TGF-Beta laying down the cortical bone.
Also has skin effects too.

53
Q

Last slide

A

Um I don’t think it’s on the test.
memorize it maybe?
I think maybe it was just to make this all seem relevant.

Biomolecules & Cells (2 decks)

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