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Cellular Biology and Biochemistry > Moving into the nucleus > Flashcards

Moving into the nucleus Flashcards

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1
Q

What does sub cellular compartmentalisation allow for?

A

Complex control mechanisms

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2
Q

What does localisation to membrane-bound compartments do?

A 
Modulates interactions between proteins
Depends on molecular signals
Increases relative concentrations of species
Regulation of the local environment
Provides a level of control
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3
Q

Where does gated transport take place?

A

At pore complexes

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4
Q

What is the difference between transmembrane and vesicular transport?

A

Transmembrane transport involves direct passage across intact membranes
Vesicular transport does not involve passage across membranes

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5
Q

What does the nucleus separate?

A

Genetic material from the rest of the cell

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6
Q

Which is the most prominent sub cellular compartment?

A

The nucleus

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7
Q

What separates the nucleus from the cell?

A

The nuclear envelope

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8
Q

What is the structure of the nucleus?

A

Nuclear membrane is a phospholipid bilayer
Outer membrane is continuous with the endoplasmic reticulum
Inner membrane has an underlying meshwork of filaments called the nuclear lamina
Nucleolus

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9
Q

What does the nuclear pore complex enable?

A

Enables active bi-directional transport of molecules/proteins

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10
Q

What is the molecular weight of a nuclear pore complex?

A

125 MDa

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11
Q

How more nuclear pore complexes are there in the nucleus?

A

~3000

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12
Q

At what rate can the nuclear pore complex transport protein?

A

1000 per minute

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13
Q

What can move through the nuclear pore complex?

A

Free movement of small molecules

Selective transport of larger proteins

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14
Q

What is a nuclear pore complex made of?

A

500 subunits of 30 individual proteins called nuclear porins

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15
Q

What is the structure of the nuclear pore complex?

A

8-fold symmetric structure that rivets the double nuclear membrane together

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16
Q

What are the 4 classes of nucleoporins?

A

Transmembrane
Core scaffold
Linker
FG

17
Q

What moves through the nuclear pore complex by passive diffusion?

A

Small molecules
Metabolites
Ions

18
Q

What is dependent on energy to travel through the nuclear pore complex?

A 
Proteins
mRNA
tRNA
Ribosomal subunits
Viruses
19
Q

What regulates the export and import of proteins across the nuclear membrane?

A

A cycle of interactions between:
Protein cargo
Nuclear transport receptors (importins and exportins)
Small GTPase Ran

20
Q

What are the three phases to export and import through the nuclear pore complex?

A

Cargo is recognised and bound by nuclear transport receptors
This docks on the pore complex via FG nups and cargo is translocated through the NPC
NTR-cargo dissociated

21
Q

How are cytosolic proteins directed to the nucleus?

A

Nuclear localisation sequences
Can be anywhere in the proteins sequence
Artificial tagging of an NLS is sufficient for relocation

22
Q

What are importins?

A

Formed of importin a and b that form a heterodimer
Importin a recognises the NLS on cargo protein
Importin b interacts with the pore complex via FG repeats
RanGTP bings importin b and triggers release of the cargo
Importins are recycled back to the cytoplasm

23
Q

Describe importin b?

A 
19 helical repeat motifs
1-8 bind RanGTP
7-19 interact with importin a
4-8 interact with nucleoporins
Importin b forms a superhelical structure that wraps around the IBB domain of importin a
24
Q

How is directionality controlled?

A

The RanGTP-GDP gradient

25
Q

Where is RanGDP found?

A

In the cytosol

26
Q

Where is RanGTP found?

A

In the nucleus

27
Q

What are nuclear export sequences rich in?

A

Leucine

28
Q

What is Crm1?

A

Protein export receptor

29
Q

What is NXF1?

A

mRNP export protein

30
Q

Where are proteins that regulate Ran?

A

Localised

31
Q

How else can nuclear import be regulated?

A

Phosphorylation

32
Q

How does phosphorylation promote nuclear import?

A

Increases binding affinity of cargo to importin a
Enhanced recognition of cargo by importin a
Induces conformational change exposing NLS
NLS phosphorylation induces cytoplasmic retension

33
Q

Which protein requires nuclear export the most?

A

mRNPs

mRNA and associated ribonuclear proteins

34
Q

What are the stages to nuclear export of mRNA?

A
  1. Capping
  2. Splicing
  3. 3’end processing
  4. TAP recruitment
  5. Localisation to NPC periphery
  6. Docking
  7. Translocation
  8. Cytoplasmic release
35
Q

What is the main mRNA export factor?

A

NXF1

36
Q

What recruits NXF1?

A

ALY

37
Q

What does NXF1 bind to?

A

FG Nups

38
Q

Is RanGTP gradient used in export of mRNA?

A

No

39
Q

What provides directionality in the export of mRNA?

A

GLE1 and DDX19

Cellular Biology and Biochemistry (22 decks)

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