Nucleus

histone- protein that binds to DNA nucleosome- protein dna complex containing 8 histone proteins chromatin- repeating nucleosome structure chromosome- region of chromatin that carries info relating to a specific set of genes (1/3 dna, 2/3 protein)- 23 pairs in nucleus sister chromatids-identical copies of the same chromosome

mrna is modified after transcription by adding a 5 prime CAP (modified guanine nucleotide) and 3 prime polyadenylation (adenosine monophosphate molecules) splicing occurs help with- stability of mRNA, binding to the ribosome and translation initiation, export from the nucleus

biggest single organelle in eukaryotic cells contains genetic material- packaged as chromatin nucleolus- darker stained region nuclear envelope is a double membrane (PL bilayer) outer membrane is continuous with endoplasmic reticulum nuclear laminar- part of cytoskeleton, maintaining structure

large quaternary protein structure aqueous channel that connects the nucleoplasm to cytosol nuclear basket- cage like structure nucleoporins- proteins that form the NPC cystosolic fibrils- long fibres that reach out into cytosol that reach out to proteins NPC has 8 fold rotational symmetry, meaning it has 8 nucleoporin proteins that form a ring structure

NPC is formed of nucleoporin 30 different types of NP 500-1000 proteins (big proteins) in each NPC nucleus isn’t static- lots of things moving in and out via NPC- dynamic gap of npc is 9nm - 5KDa protein can pass straight through, 60 KDa can pass through but a bit harder, >60Kda cannot pass- need specialised mechanism

nuclear localisation signal- tell a protein to go into the nucleus recognised by specific nuclear import receptor (importins) NIR bind to FG repeats on nuclearporins in cytosolic domain of npc proteins move through NPC binding sequentially to FG repeats proteins are synthesised on cytosolic ribosomes containing an NLS protein enters nucleus but is still bound to NIR

guanosine triphosphate gtp binding protein- binds to GTP and acts as GTPase (hydrolyses GTP to GDP) GAP- GTPase activating protein, binds to GTP binding protein and induces GTP hydrolysis ^part of recycling/ Ran cycle GEF- guanine exchange factor, binds to GTP BP and causes it to release GDP + replaces it with GTP

protein bound to NIR inside nucleus RAN gtp binds to NIR- conformational change which releases protein ran GTP now bound to NIR exits nucleus through NPC RAN binding protein binds to RAN gtp, releasing NIR and recycling it ran BP and ran GTP bind ran GAP hydrolyses GTP and forms GDP- releases from Ran BP GDP can enter nucleus through NPC GEF translates GDP back to GTP

mature mRNA is complexed with proteins- messenger ribonucleoprotein mRNP export uses nuclear export receptors receptors bind to adaptor proteins adaptor proteins bind to the 5’ (prime) end of mRNA, interacting with the cap binding complex (CBC) adaptor proteins can only bind if the mRNA has been properly processed this complex binds sequentially to FG repeats and is transported out of the nucleus

chromatin exists in 2 forms within our cell heterochromatin is transcriptionally inactive and densely packed (dark regions)- hinders transcriptional machinery euchromatin is transcriptionally active and loosely packed packed full of RNAs and proteins- darkly stained nucleolus is region of nucleus where ribosomes are synthesises (ribosomal biogenesis) very high demand

found in cytosol/ER synthesised in nucleus site of protein synthesis made up of 2/3 rRNA and 1/3 protein made up of large 60S (contains 5S, 5.8S, 28S rRNA + 49 proteins) + small subunit 40S (contains 18S rRNa and 33 proteins) =80S ribosome

unit = S how quickly an organelle sinks to the bottom of a tube when it is centrifuged non linear function influenced by mass, density and shape

high demand on ribosomal biogenesis 4 rRNAs are encoded by more than 200 rRNA genes, split across 6 chromosomes making it easy to synthesis RNA quickly rRNA genes are clustered together on a DNA sequence known as tandem repeats 18S, 5.8S and 28S rRNAs are transcribed in nucloelus by rna poly 1 5S rRNA are transcribed by rna poly 3 in nucleoplasm

speeds up rRNA transcription contain -spacer regions of different coding sequences (non coding dna sequence) -coding sequence (18S, 5.8S, 28S) -can generate rRNA very quickly as sequences are all next to each other -everything is transcribed in chunks 45S pre rRNA formed by spacer regions

-addition of ribosomal proteins (1/3) which enters via nucleoporin (ran cycle) -forms large macromolecular structure (90S pre ribosome- 45S pre rRNA + protein) -90S pre ribosomes are modified to form 3 rRNAs

rna complexes with proteins to help with stability and function snoRNPs are snoRNA complexed with proteins snoRNAs complexed with structural proteins and enzymes modifiy 90S pre ribosome recognise areas of rRNA that require modification- chop them out snoRNA binds to RNA- protein portion of snoRPS will modify small nucleolar ribonucleoproeteins small nucleolar RNAs

methylation of hydroxyl group on ribose sugar- improves stability of rna molecule and acts as a tag so cell knows it can be taken out converting uridine to pseudouridine (isomers) - isomerisation catalysed by psi synthesis, improves affinity of rna to trna during protein synthesis cleavage of 45S pre rRNa

trying to get ride of spacers in 45s rrna snoRNPs contain enzymes- exoribonucleases - that remove ETS (externally transcribed spacers) endoribonucleases remove ITS

5S rRNA (transcribed in the nucleoplasm) combines with 5.8S and 28S rRNA to form the 60S subunit 40S and 60S subunits are transported to the cytoplasm separately and re-combine export through the NPC is reliant on Ran-cycle

reverse process of import protein must bind to Ran GTP and nuclear export receptor (NER) at same time