Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Cell Biology > Section 6B: Protein sorting between cytoplasm and nucleus > Flashcards

Section 6B: Protein sorting between cytoplasm and nucleus Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Nuclear-Cytosol Transport (from nucleus into cytosol):

A
  • processed mRNA (has to be in nucleus when first generated)
  • enzymes come and read DNA code to make RNA (transcription)
    -tRNAs
  • assembled ribosomes
  • transcriptional regulators (has to let massive things go through nuclear envelope
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where are ribosomes made?

A

they are made in the nucleus and immediately need to leave nucleus to go into the cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Nuclear-Cytosol Transport (from cytosol to nucleus):

A
  • ribosomal proteins for
    assembling the ribosome
  • DNA polymerase
  • DNA repair proteins
  • RNA polymerase
  • Transcription factors
  • mRNA processing enzymes
  • Histones
  • etc
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Molecules are diverse:

A
  • Some extremely large
    (ribosome)
  • Some of very small
    (small proteins)
  • Some even smaller
    (ATP)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the whole point of the nucleus?

A
  • to surround DNA to prevent/allow things to go in and out
  • wrong thing entering DNA will cause DNA damage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

The Nuclear Envelope

A
  • double, continuous bilayer
  • outer membrane continuous with ER
  • Lamina
  • Nuclear pore
  • controls bidirectional transport between nucleus and cytosol
  • 3000-4000 pores/nucleus in mammalian cells
  • 5000 macromolecules in both directions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a Lamina?

A

nuclear skeleton underlying inner bilayer - gives shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a Nuclear Pore?

A

“hole” that crosses both inner and outer bilayers
- number of define proteins (nuclear porins) that fit together to form a passageway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The Nuclear Pore Complex (NPC)

A

Disordered region of channel
- Made up of proteins (nucleoporins) that are disordered – lack secondary structure
- Forms a “barrier” that larger
molecules (>60 kDa) cannot
pass without assistance
- Large molecules thus require active transport involving:
1. recognition of nuclear
signal
2. Interaction with cytosolic
fibrils
3. Passage through NPC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

< 5kDa

A

free diffusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

5 - 60 kDa

A

diffusion decreases with size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

> 60 kDa

A

active transport needed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do you keep something small from coming in and out?

A
  • opening is full of proteins that likes to stick together thus, makes it hard for other things to go into complex
  • but allow giant things to go through
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Nuclear pore complex is a _______ gate

A

selective
- some proteins need to be in the nucleus and others out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Nuclear pore complex forms a gate that controls transport

A
  • prevents the free movement of molecules
  • large molecules cannot diffuse through without Active Transport
  • intermediate molecules can diffuse through, but very slowly
  • super small molecules can diffuse through easily
  • Central nucleoporins have unstructured domains that line the pore
  • Creates a meshwork that slows diffusion
  • Proteins >60 kDa must be actively transported in and out of the nucleus
  • Nuclear pore complex is a selective gate: some proteins need to be in the nucleus and others out
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What targets a protein to the nucleus?

A

Nuclear Localization Signal (NLS)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the job of the Nuclear Localization Signal (NLS)?

A

it carries a code inside a protein to tell it what to do

17
Q

What happens when you artificially attach a nuclear localization sequence to GFP?

A

it will drag the whole thing into the nucleus

18
Q

Nuclear Import Receptors

A
  • looks for Nuclear Localization Signal (NLS)
  • be able to bind to these fibre that come out of the NPC
  • NPC often does not interact with transport “cargo” protein directly; they need an intermediate called Nuclear Import Receptors
19
Q

What do Nuclear Import Receptors do?

A

bind to cargo (e.g. proteins being transported into the nucleus) and bridge these into the NPC

20
Q

Nuclear Export Signals and Receptors

A
  • Nuclear export also occurs through signal peptide sequences: nuclear export signal
  • Nuclear export signal is recognized by nuclear export receptors (aka karyopherins)
  • Example function: export pre-assembled ribosomes and mRNA (these are proteins that patrol the nucleus)
21
Q

What causes directionality?

A
  • Active Transport
  • Low concentration from cytosol to high concentration to nucleus)
22
Q

How do certain proteins accumulate in the nucleus?

A

There has to be something (GTPase) that
causes ACTIVE transport and
establishes DIRECTION of
transport

23
Q

GTPase “switches”

A
  1. ON state: bound to GTP
  2. OFF state: bound to GDP
24
Q

What is the protein to turn GTPase ON?

A

GEF

25
Q

What is the protein to turn GTPase OFF?

A

GAP

26
Q

Ran GTPase regulates _______ of nuclear transport

A

directionality

27
Q

Ran GTPase and the
nuclear transport cycle

A
  • Nuclear Import
  • Nuclear Export
28
Q

Nuclear Import:

A
  • In the cytoplasm, Ran-GDP does not bind to nuclear import receptors,
    which allows binding to proteins destined for the nucleus
  • Once past the Nuclear Pore Complex (NPC), the nuclear import
    receptors bind to Ran-GTP (in the nucleus).
  • Ran-GTP forces the nuclear import receptors to release their protein
    cargo
  • Nuclear import receptors bound to Ran-GTP return to cytosol “empty”
29
Q

Ran is bound to GTP in the nucleus and GDP in the cytosol, what does this mainatin?

A

This maintains GRADIENT

29
Q

Nuclear Export:

A
  • In the nucleus, Ran-GTP binds to nuclear export receptors, which allows
    binding to proteins destined for the cytosol.
  • Once past the Nuclear Pore Complex (NPC), the nuclear export
    receptors bind to Ran-GDP (in the cytosol, due to Ran-GAP).
  • Ran-GDP forces the nuclear export receptors to release their protein
    cargo.
  • Nuclear export receptors bound to Ran-GDP return to nucleus “empty”
29
Q

T cells are immune cells that are activated during infection and inflammation

A
  • destroy infected cells
  • Once activated, T-cells need to “turn on” certain genes
  • NF-AT is a transcription factor that turns on genes when T cells
    are activated
  • NF-AT hangs out in cytosol but moves into nucleus once T cells are
    activated
29
Q

RanGTP binding blocks a protein loop
required for binding to cargo

A
  • binding of Ran GTP to the nuclear import receptor causes a change in shape of the nuclear import receptor, changing conformation that no longer makes it possible for the cargo to bind
  • cargo releases
29
Q

Nuclear transport by Ran-GTP
and Ran-GDP gradient: Summary

A
  • There is a Ran-GTP/GDP gradient: because Ran GEF is in the nucleus and Ran GAP is in the cytosol
  • Ran-GTP is high in the nucleus and low in the cytosol
  • Ran-GDP is low in the nucleus and high in the cytosol
  • Ran-GTP binds to nuclear import receptors to deposit cargo proteins in the nucleus
  • Ran-GTP induces binding of nuclear export receptors to cargo proteins
  • GTP hydrolysis in cytosol deposits export cargo in the cytosol
29
Q

Nuclear Import Chart

A
  • Transport Pore: Nuclear Pore Complex (NPC)
  • Sequence recognized on
    CARGO proteins: Nuclear Localization
    Sequence (NLS)
  • Transport receptors: Nuclear Import
    Receptor
  • Effect of binding Ran-GTP
    (in nucleus): Nuclear Import
    Receptor lets go of
    cargo (into nucleus)
  • Effect of Ran-GDP
    (in cytosol): Nuclear Import
    Receptor can bind to
    cargo (in cytosol)
29
Q

Nuclear Export Chart

A
  • Transport Pore: Nuclear Pore Complex (NPC)
  • Sequence recognized on
    CARGO proteins: Nuclear Export Sequence (NES)
  • Transport receptors: Nuclear Export
    Receptor
  • Effect of binding Ran-GTP
    (in nucleus): Nuclear Export
    Receptor can bind to cargo (in the nucleus)
  • Effect of Ran-GDP (in cytosol): Nuclear Export Receptor lets go of cargo (in cytosol)
30
Q

GTP hydrolysis in the cytosol deposits…

A

export cargo in the cytosol

30
Q

Access to the transport machinery can be turned ON and OFF

A

e.g. infection in blood
- only turn on immune cells when there is an infection
- protein changes nuclear or cytosolic localization

31
Q

Control nuclear import during T
cell activation

A
  • T cells are immune cells – responsible for inflammatory response
  • Normally inactive until expose to inflammatory signals or antigens
  • When inactive – NF-AT, a transcription factor is cytosolic (phosphorylated) to keep inflammation genes off
  • When activated – NF-AT is dephosphorylated to move to the
    nucleus – drives gene expression of inflammatory genes
  • Phosphorylation and dephosphorylation are on-off switches to expose nuclear export and nuclear import signals, respectively
  • Low Ca2+ is in resting T cell, High Ca2+ is in activated T cell
  • Low Ca2+ means infection has cleared
  • When Calcineurin is stopped, it no longer has the ability to destroy cells
32
Q

What happens when Calcineurin is stopped?

A

T cells no longer have the ability to destroy cells

32
Q

What does low Ca2+ mean?

A

it means infection has cleared

32
Q

Low Ca2+ is in _______ T cell, High Ca2+ is in _______ T cell

A

resting, activated

Cell Biology (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions