Lecture 23 Flashcards
What is the function of the nucleus?
1) Storage, replication, and repair of genetic material
2) Expression of genetic material
3) Ribosome Biosynthesis
List the order and size of DNA condensation
1) DNA duplex (2nm in diameter)
2) Nucleosome fiber (10nm in diameter)
3) Chromatin fiber (30nm in diameter)
4) Coiled chromatin fiber (300nm in diameter)
5) Coiled coil (700 nm in diameter)
6) Condensed chromatid (1400nm in diameter)
What factors can damage the quality of DNA and create genetic variation?
UV light exposure
Cellular metabolism
Chemical exposure
Replication errors
Ionization radiation
Describe the expression of the genetic material function of the nucleus?
(What happens here?)
Transcription of mRNAs, tRNAs, rRNAs etc.
Promoter region: controls transcription
RNA splicing before nuclear export of mRNAs
Describe the structure of the nucleus?
What is contained in each structure?
Nuclear envelope: nuclear membrane, nuclear pores, nuclear lamina
Nuclear content: Chromatin, nucleoplasm, nucleolus
Where is the condensed heterochromatin in the nucleus
It’s more to the outer edge of the cell and it’s attached to the lamina
Describe the structure of the nuclear envelope
2 parallel phospholipid bilayers separated by a 10-50nm space
outer nuclear membrane (ONM): binds to ribosomes, continuous with the rough ER (transcription of proteins)
Inner nuclear membrane (INM): has integral proteins and connects to the nuclear lamina (Docking site to stabilize cell structure)
Why is the nuclear envelope so important?
Separate the nuclear content fron the cytoplasm
Separates transcription and translation processes (allows for these processes to be done independently)
Selective barrier: allows limited movement of molecules between the. nucleus and cytoplasm
What is the nuclear lamina? What is its function?
Thin meshwork of filamentous proteins (made of lamins [IFs] that are only found in animal cell, there is something equivalent in plant cells also)
Bound to the inner membrane of nuclear envelope by integral proteins
(next to nucleoplasmic leaflet)
Attachment sites for chromatin (Heterochromatin)
Provides structural support to the nuclear envelope
What is a nuclear pore? Where is it found?
Gateways between the cytoplasm and nucleus (All transport happens here)
3000-4000 pores per nucleus
Found where the inner and outer membrane fuses
Contains a complex protein structure (arrangement of different types of proteins, high density)
What is the nuclear pore complex (NPC)
Composed of nucleoporins (NUPs) (large family of different proteins)
Octagonal symmetry
Projects into the cytoplasm and nucleoplasm
a supermolecular complex: 15-30 times the size of a ribosome (VERY BIG)
How do molecules move through the nuclear pore complex (NPC)
Passive diffusion of molecules 40kDA (40000 grams per mole) or less: rapid, 100 molecules/minute/mole
Regulated movement of larger molecules: Slow, 6 molecules/minute/mole
How does nuclear import occur?
Regulated movement of proteins using an intrinsic amino acid sequence - nuclear localization sequence (NLS)
What is nuclear localization sequence (NLS)?
What/where are the different signals on the protein sequence?
Where does the signal go based on its position on the sequence?
NLS: several positively charged amino acids within the protein sequence
No signal peptide: doesn’t exist on the protein sequence (to cytosol)
Amino-terminal signal: on the end of the protein sequence (to the chloroplasts and mitochondrion)
Internal signal: in the middle of the protein sequence (to the nucleus)
Describe the process/steps of nuclear import
1) Protein with NLS (cargo) interacts with importin protein in the cytoplasm
2) Cargo/importin complex interacts with FG-NUPs at the NPC and enters the nucleoplasm
3) Ran-GTP (G-protein) interacts with importin (releases transcription factor) ; cargo dissociates and stays in the nucleoplasm
4) Ran-GTP/importin complex exits the nucleus through the NPC
5) GTP is hydrolyzed into GDP. Importin released in the cytoplasm to find new cargo
