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Section 5.docx

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Dalhousie University
BIOL 2020
Patrice Cote

Section 5 Nucleus Structure and Function Ch12 (475-485), Ch11 (428-430) DNA nucleus is where DNA is stored in the form of chromatin heterochromatin - tightly bound cannot be transcribed euchromatin - unwound ready to be transcribed replication transcription structure of nucleus and how it allows things to happen Nucleus nuclear envelope: two membranes. inner and outer. many nuclear pores stability inside, maintained by the nuclear matrix nucleoplasm: liquidy stuff in the nucleus nucleolus: darker staining region inside the nucleus; where ribosome are made - chromatin: storage form for DNA Nuclear Membrane - outer membrane is continuous with the ER membrane inner membrane is continuous with the outer-membrane gap between the inner and outer called the inter-membrane space Lamina: intricate layer of filaments (made of intermediate filaments) lamina is on the inside of the inner membrane: strong layer, rigid, structure and stability Integral proteins in the membrane: attached so that they go in the inter- membrane space in order for the nuclear envelope to break down prior to mitosis, the lamins must be phosphorylated. A kinase will do this. nuclear membrane is not permeable to random stuff transport between cytoplasm and nucleus is extremely regulated - things can enter and leave through the nuclear pore thousands of nuclear pores on every nucleus Each nuclear pore contains a nuclear pore complex inside the nuclear pore. it acts as a plug. it is the darkly stained area inside the pore. the proteins that make up the nuclear pore complex are the nucleoporins only need to know 4 different parts to it spoke ring assembly: turquoise in diagram. connects through the inner membrane to the outer membrane nuclear basket: dark blue. looks like a basket. hangs down into the nucleoplasm. asymmetrical. it is only inside the nucleus. doesn’t go outside at all. cytoplasmic filaments. red filaments that extend out into the cytoplasm. wave around like tentacles in the cytoplasm. central transporter: pink tunnel on the inside. 8 - fold symmetry (from top view or from bottom view) Nuclear Localization Signals (NLSs) Lysine (K) Arginine (R) Proline (P) sequence of specific amino acids that tells the cell its supposed to go inside the nucleus. these sequences can vary, can be at any part of the protein. usually has a lot of positive amino acids. rich in K, R, P. Transport Receptors even they have a NLS, they must be escorted by a chaperone importins- into the nucleus exportins- out of the nucleus importins: 3 subunits: NLS protein attaches to alpha importin then to beta importin. step1 : they all clump together and make a group. NLS on the bottom, then a, then b. (receptor cargo) step 2: the receptor cargo complex docks on a cytoplasmic filament step 3: conformational change occurs, and it causes the NPC to “swallow” it step 4: once the Receptor-Cargo enters the nucleus, Ran-GTP (a gtp-ase) dissociates the receptor from the cargo (removes alpha and NLS from beta) step 5: Ran-GTP transports importin B back to the cytoplasm and the GTP is hydrolysed by GDP. alpha is stuck inside. so it binds to exportin, which exports it back out to the cytoplasm. Ran-GTP is a GTP-ase. can turn a GTP to a GDP. on when bound to GTP off when bound to GDP can turn GTP off by hydrolyzing GTP - lots of enzymes that catalyze this process. for example, GAP. Ca
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