lecture 1 - the nucleus Flashcards
What are the 3 general functions of the nucleus?
- storage of DNA
- Transcription of RNA from DNA
- Mechanical element as it is stiffer than the rest of the cell
What is one key component of eukaryotic cells?
genetic material is compartmentalised
What are the benefits of compartmentalisation?
- Protect DNA – critical information storage
- Increase surface area for membrane-localised reactions
- Increase efficiency of transcription and synthesis
- More ways to regulate gene expression
What is a significant structure if the nuclear double membrane?
Its continuous with the double membrane
what is one theory about how the nucleus may have evolved?
- DNA in prokaryotes is tethered
- over time the tethering increases until nucleus is bound
What is the nuclear lamina?
thin plate, slice or layer that is related to intermediate filaments to form meshwork on inner nuclear membrane
What are the two types of nuclear lamina?
A/C and B
What are the main diseases caused when the lamina is destroyed?
muscular dystrophy and progeria
What holds the inner membrane and outermembrane of the nucleus together?
LINC complex
What are the names of the proteins that hold together the inner membrane?
SUN/KASH proteins
What are the names of the proteins that hold together the outer membrane to the cytoskeleton
nesprins
What do nesprins do?
- connect to different cytoskeleton elements ( i.e either actin, intermediate filaments or microtubules)
What are the 6 proteins that make up the nuclear matrix in the nucleus?
- NuMa
- Titin
- Spectrin
- PLF
- Nuclear actin
- Motor proteins
Role of NuMa
Organisation of chromatin
Role of titin
binds chromosomes and lamina
Role of Spectrin
elastic component of lamina
Role of PLF
pore linked filaments
Role of nuclear actin
short filaments or monomeric
Role of motor proteins
nuclear myosin , kinesins
What are chromosomes?
DNA - protein complex specially packaged for cell division
What is chromatin?
complex of DNA, RNA and proteins
What is Euchromatin
“true” chromatin • Less visible by microscopy • Not so densely packed • Majority of the genome (~90%) • Localised in central part of nucleus
What is heterochromatin
- “different” chromatin
- Looks dark under the microscope
- Tightly-packed condensed DNA
- Localised around lamina and nucleoli
How are chromosomes arranged in the nucleus?
arranged discretely
What are other names for euchromatin/heterochromatin?
A/B chromatin
What are LADS?
Lamina - associated domains
Where is the most little RNA production found in the nucleus?
n LADs (heterochromatin) than away from lamina (euchromatin)
What molecules need to be exported out of the nucleus?
- mRNA – messenger (genes)
- rRNA – ribosomal
- tRNA – transfer (protein synthesis)
- Assembled ribosomal subunits
What molecules need to be imported from the cytoplasm into the nucleus?
- RNA polymerase
• Ribosomal proteins
• Transcription factors
• All other structural proteins (lamins, histones, etc)
How is the nuclear pore complex composed?
- ring structure with 8 fold symmetry
- 30 different Nuclear Pore proteins ( NUPs)
What is the central channel composed of?
FG*-Nups that form selective barrier to transport
What lies on the Nuclear pore complex on the cytosolic side?
Fibrils
What lies on the Nuclear pore complex on the nuclear side?
Nuclear basket
What are the two types of movement through the NPC (nuclear pore complex)
- passive transport
- facilitated transport
What type of molecules can get into the nucleus via passive transport
small molecules and proteins
What molecules need facilitated transport to get into the nucleus?
RNAs, larger proteins and macromolecular complexes
How can facilitated transport get the energy to pump molecules into the nucleus?
Facilitated transport requires energy
• ATP hydrolysis for mRNA
• GTP hydrolysis for proteins, tRNA, and ribosomes
What is the mRNP?
mRNA-protein complex
Includes processing, capping, splicing proteins as well as export factors
How does the nucleus prevent the mRNP from returning to the nucleus?
ATP hydrolysis release of Dbp5 in cytoplasm and mRNP remodelling prevents movement back into the nucleus
How do nuclear import proteins, importins, transport cargo into the nucleus?
- Bind cargo proteins in cytoplasm
* Interact with FG-Nups
How is the Cargo released from the importins once in the nucleus?
Cargo release enabled by Ran-GTP binding to importin-b
Conformational change that
results in complex coming apart
What are the name of proteins which provide nuclear exportation?
Exportins
how are the exporting released from the cargo in the cytoplasm
Ran-GTP hydrolysed to Ran-GDP in cytoplasm
conformational change that results in complex degradation
What are GTPases?
- molecular switches
- bind to Ran, Ras, Rho, and other families
- conformational change in the GTPasebind or unbind proteins
What does RAN - GAP do?
GTP hydrolysis to GDP
What does RAN- Geff do?
GTP loading after hydrolysis
What is an NLS and an NES?
Nuclear localisation signal (NLS) and Nuclear export signal (NES)
Where are NLS or NES ‘s found?
A nuclear localization signal or sequence (NLS) is an amino acid sequence that ‘tags’ a protein for import into the cell nucleus
What makes up a Nuclear localisation signal?
- Protein motif typically 8 amino acids long
- Can occur anywhere in the protein
- Many basic residues such as lysine (K), arginine (R), and proline (P)
- Binds to importins
What makes up an nuclear export signal?
- Sequence with four hydrophobic amino acids (most often leucine, L)
- E.g. LxxxLxxLxL, where x is any other amino acid
- Binds to exportins
What are the major functions of the nucleolus?
- Transcription of rRNA
- Assembly of ribosomal subunits
what is the nucleolus composed of?
• Segments of 10 chromosomes encoding rRNA genes • Proteins for processing rRNAs • Ribsomal subunit proteins • Small nucleolar RNA (snoRNA) oligonucleotides that help process rRNAs
What are other less known functions of the nucleolus?
Sensing and responding to stress
• Cell cycle regulationCancer
size of canal bodies
0.2 – 2 mm diameter
size of PML bodies
0.1 – 1 mm diameter
size of speckles
20 nm – 1 mm diameter
Function of Cajal bodies
RNA processing
• Genome organization (chromosome domain boundaries)
Function of PML bodies
- Often associated with Cajal bodies
* DNA repair, cell proliferation, programmed cell death
Function of Speckles
Gene transcription
• mRNA processing (splicing to make various versions of genes)
