Nucleus Flashcards
1
Q
What is the nucleus
A
- A memebrane bound organelle in eukaryotic cells containing DNA
- And the cells control centre
2
Q
Define eukaryote
A
- An organism whose cells have a memebrane-bound nucleus
- Including animals, plants, fungi and othe unicellular organisms
3
Q
What is part of the structure of the nucleus
A
- Contains DNA arranged in chromosomes
- Surrounded by the nuclear envelope/membrane
- Nuclear lamins support the nuclear membrane
4
Q
Define DNA
A
- A polymer composed of two polynucleotide chains that coil around each other to form a double helix
- Carries genetic instructions for development, functioning, growth, and reproduction
5
Q
What is the nuclear envelope/membrane
A
- It is made up of a phospholipid bilayer that surround the nucleus
- Which encloses the genetic material
- Outer membrane is continuous with rough ER
- Inner membrane contains proteins that act as anchoring sites for chromatin and for the nuclear lamina
- The space inbetween the membranes is called perinuclear space, where proteins made get transported to
6
Q
What is nuclear lamina
A
- It is in the nuclear side of the inner nuclear membrane
- Meshwork of interconnected protein subunits called nuclear lamins
- The lamins are intermediate filament proteins plymerised into 2D lattice
- Gives shape and stability to envelope
- attached to nuclear pore complexes NPC and integral proteins on the inner membrane
7
Q
Why does the nuclear envolope contain pores
A
- To control the movement of substances in and out of the nucleus
- E.g. RNA is selectively transported into the cytoplasm
- Proteins are selectively transported into the nucleus
- Regulating gene expression
8
Q
Why is the nucleus important
A
- Separates fragile chromosomes from cell contents – crucial for proper function of cell
- DNA replication, transcription and RNA processing - all in the nucleus
- Separates RNA transcription in the nucleus from translation machinery in the cytoplasm
9
Q
What is the nucleolus
A
- When one or more nucleoli are found inside the nucleus
- Most prominent in cells that are synthesising large amounts of protein
- Sites at which ribosomes are reassembled and ribosomal RNA is transcribed
10
Q
What happens to the nuclear envelope during mitosis
A
- Nucleus disassembles, lamina depolymerises & NPCs disperse in cytosol (phosphorylation of lamins and NPC proteins)
- Some NPC proteins bound to nuclear import receptors – important in reassembly of NPCs at end of mitosis
- Nuclear envelope membrane proteins disperse throughout ER membrane
- Later in mitosis, nuclear envelope reassembles close to surface of daughter chromosomes (dephosphorylation of lamins)
10
Q
What is around and inside nuclear pores
A
- Nuclear basket
- Inside are proteins called neoporins that create eightfold rotaional symmetry
- Inside the neoporins is filled with numerous repeats of unstructured phenylalanine-glycine proteins that create a mesh inside the NPC
- The mesh acts as a sieve - restricting diffusion of large macromolecules but smaller ones can pass through
11
Q
How do large macromolecules go through NPCs
A
- They need import or export signals
- Other proteins contain both nuclear localisation signals (NLS) and nuclear export signals (NES)
- Relative rates of import and export determine steady-state localisation
12
Q
What are nuclear localisation signals
A
- Responsible for the selectivity of active nuclear import process
- Most commonly - 1 or 2 short sequences rich in lysine and arginine (+ charge) in aa - sequence varyies for different proteins
13
Q
What are nuclear import receptors
A
- They are karyopherins (proteins that are involved in transporting molecules between the cytoplasm and the nucleus)
- Nuclear localization signals must be recognized by nuclear
transport receptors (import or export receptors) to get in or out - Receptors can use adaptor proteins that form an import
receptor/NLS bridge (for proteins that dont fit into an import receptor) - Have FG binding sites
14
Q
What happens in the NPC when cargo has to go through
A
- Nuclear import receptors recognise nuclear localisation signals on the cargo proteins and bind (or use an adaptor protein to bind)
- The FG (phenylalanine and glycine) binding sites on the import receptors bind to FG repeats found in the NPC mesh
- This binding disrupts interactions between the repeats dissolving the mesh
- Allowing the receptor-cargo complex to diffuse into the NPC pore
