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The nucleus
the nucleus
| Question | Answer |
|---|---|
| Nucleus functions please? (3) | 1. Control centre 2. Contains most of cell's genetic material 3. Compartmentalisation of eukaryotic cell |
| Nucleus structure please? (4) | 1. Nuclear envelope 2. Nuclear membrane 3. Nuclear lamina 4. Subnuclear bodies |
| What is the nuclear envelope? | Double membrane enclosing the nucleus |
| Function of the nuclear membrane? | Impermeable to large molecules. Has pores allowing mvt of molecules across |
| What is the nuclear lamina? | Dense fibrillar network adds mechanical support and supports the shape of the nucleus |
| What are subnuclear bodies? | Have multiple roles. Made of unique proteins, RNA & particular parts of chromosomes |
| Approx. length of DNA in nucleus? | 2m |
| Colours of things in conventional fluorescence microscopy? (3) | 1. NPC - Red 2. Nucleolus - Green 3. Chromatin - Blue |
| What is the resolution limit imposed by visible light? | 200nm |
| What does electron microscopy permit? | Spatial resolution of 3-5nm |
| Outer membrane of the nuclear envelope? | Continuous with the rough ER |
| Inner membrane of the nuclear envelope? | Connected to nuclear lamina. Contains several Inner Nuclear Membrane proteins (ass. with nuclear lamina) |
| Function & makeup of nuclear lamina? (3) | 1. Made of intermediate filaments & membrane associated proteins 2. Regulates cellular events (eg DNA replication & cell division) - participates in chromatin organisation 3. Anchors NPCs embedded in nuclear envelope |
| What are laminopathies? | Group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina |
| What is a fibroblast? | Cell contributing to formation of connective tissue |
| Give a few symptoms of laminopathies? (3) | 1. Skeletal/cardiac muscular dystrophy 2. Lipodystrophy 3. Progeria (premature aging) |
| In laminopathies, where are the main mutations? | In Lamin A/C & Nuclear lamina-associated proteins |
| What would a defect in the gene encoding eg emerin lead to? | Defects in filament assembly and and/or attachment to the nuclear envelope |
| What is emerin? | A nuclear lamina-associated protein |
| Examples of Laminopathies? (2) | 1. Emery-Dreifuss muscular dystrophy 2. Hutchinson-Gilford Progeria Syndrome (HGPS) |
| Symptoms and effects of Emery-Dreifuss Muscular Dystrophy? | 1. Joint deformities, heart problems - progressive muscle weakness & wasting 2. Affects skeletal and cardiac muscles |
| Mutation that causes HGPS? | Point mutation in LMNA gene - mutation protein LAD50 |
| What does mutation of the LAD50 protein cause? (3) | LAD50 incorporates abnormally into nuclear lamina - mechanical defects - thickening of lamina - loss of peripheral heterochromatin |
| Symptoms of HGPS? | Early aging |
| How many pairs of chromosomes? | 23 |
| What are chromosome territories? | Discrete individual patches into which DNA is organised |
| Types of DNA in the nucleus? | Euchromatin and heterochromatin |
| What is euchromatin? | Active, open form of DNA that allows transcription factors to bind |
| Euchromatin structure? | DNA wrapped around histone proteins forming nucleosomes |
| What is heterochromatin? | Mostly inactive DNA |
| Types of heterochromatin? | 1. Constitutive - never expressed 2. Facultative - differentially expressed |
| Heterochromatin structure please? | Multiple histones wrapped into 30nm fibre consisting of nucleosome arrays in their most compact form |
| Function of insulator elements? | Organise chromatin fibres in nucleus in separate compartments of higher-order chromatin structure |
| What are nuclear Pore Complexes (NPCs)? | Elaborate multiprotein assemblies that allow mvt of macromolecules between nucleus and cytoplasm |
| What a NPCs freely permeable to? | proteins <40kDa |
| Structure of NPCs? | 8 composite ring of proteins at cytoplasmic surface & similar ring at inner nuclear membrane surface connected by Spoke proteins - composed of 50 nucleoporins |
| How do proteins get into the nucleus? (5) | 1. Protein w/ NLS recognised by importin complexed w/ GTP-binding protein 2. Importin binds to cytoplasmic filaments 3. Complex translocated through pore by sequential binding to pore proteins 4. Protein released 5. Importin-Ran/GTP complex exported |
| NLS and importin? | Importin a has 2 NLS 1. Monopartite NLS 2. Bipartite NLS |
| How do proteins get out of the nucleus? (3) | 1. Proteins targeted for export by nuclear export signals (NESs) 2. NESs recognised by exportins in presence of RNA-GTP - protein directed through NPC to cytoplasm 3. GTP hydrolysis to dissociate target protein into cytoplasm |
| What causes NPC diseases? (2) | 1. Changes in Nucleoporins (NUPs) 2. Changes in carriers(?) |
| What do NPC diseases lead to? | Nuclear/cytoplasmic accumulation of materials |
| Nup214 function? | Facilitates export of NES bearing cargo |
| What can mutation of Nup214 lead to? (2) | Accumulation of proteins in the nucleus & immunosuppression |
| What is NF-kB? | Mutation of Nup214 |
| Triple A syndrome mutations associated with? | Lack of accumulation of ALADIN into the NPC |
| Symptoms of Triple A syndrome? (3) | 1. Muscle control of heart & oesophagus/sphincter 2. Adrenal insufficiency 3. Intellectual disability |
| Triple syndrome cells? | More prone to oxidative damage |
| How does bulk mRNA exit out of the nucleus? (4) | 1. Large complexes attaches NPC by thin filament 2. Reaches pore centre & elongates into 100-150A broad rod 3. Material passes pore centre in rod-form, assuming dumbbell-shaped configuration 5. Spherical particle formed & deposited on cytoplasmic side |
| hTREX mutations cause? (2) | 1. Enhanced formation of R loops 2. High grade tumours |
| What is hTREX? | Transcription/export complex |
| Roles of hTREX? (2) | 1. Stability of mRNA 2. Efficient nuclear export |
Created by:
rubyroo
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