lecture 2 nucleus structure and function

Main difference between prokaryotes & eukaryotes:

• Eukaryotes have a membrane-bound nucleus.

• Prokaryotes have a nucleoid region with less DNA packaging and no nuclear membrane.

Nuclear size

• varies based on cell type, increases in development & cancer cells.

Functions of the Nucleus

• Compartmentalization of genetic material

• Regulation of cellular activities:

Regulation of cellular activities controls :

• metabolism

• protein synthesis

• cell division.

Compartmentalization of genetic material:

• Site of DNA replication, transcription, and RNA processing.

• Produces components for translation (ribosomes, mRNA, tRNA).

Nucleoplasm:

• Highly organized, containing over 30 specialized subdomains.

Nucleolus:

• Largest & most prominent subdomain.

• Produces ribosomes by transcribing rRNA and assembling ribosomal subunits.

• Size and number depend on cell activity (more active cells = larger nucleoli).

Chromosomal Organization:

• Chromosomes are arranged in discrete subdomains.

Actively transcribed genes

• (euchromatin) are at the edges of chromosomal territories.

Interchromosomal channels

•  prevent unwanted interactions.

Nuclear Speckles:

• Contain mRNA splicing factors.

• Highly dynamic, growing/shrinking based on transcription activity.

Nuclear Matrix

• Protein network that supports nuclear shape and organization.

• Anchors nuclear subdomains and enzymes involved in gene expression.

• Composition & function are still being studied.

 Nuclear Envelope

• Separates nuclear contents from cytoplasm.

• Regulates molecule exchange (e.g., mRNA and proteins).

• Maintains nuclear integrity and spatially organizes gene expression.

3 main components of nuclear envelope

• Nuclear Membranes

• Nuclear Lamina

• Nuclear Pore Complex (NPC)

Nuclear membrane

• Inner & outer membranes, with a perinuclear space between them.

• Outer membrane is continuous with the rough ER.

Nuclear lamina

• Fibrous protein network (lamins) on the inner surface of the inner membrane.

• Provides mechanical support and connects chromatin to the envelope.

• Mutations in lamin genes cause diseases like Hutchinson-Gilford Progeria Syndrome (premature aging).

Nuclear Pore Complex (NPC):

• Regulates transport of molecules in/out of the nucleus.

• Composed of ~40 proteins (nucleoporins), forming a large, 8-fold symmetrical structure.

• Small molecules move freely, but larger ones require active transport.

what are the components of the nuclear pore complex

• Central Scaffold

• FG Nucleoporins

• Y-Complexes

• Cytoplasmic Filaments

• Nuclear Basket

Central Scaffold

• Anchors NPC to the nuclear envelope.

• Forms a large, aqueous central channel (~20-40 nm).

FG Nucleoporins

• Lined with phenylalanine-glycine (FG) repeats that create a sieve-like mesh.

• Selectively allow small molecules while blocking larger ones (>40 kDa).

Y-Complexes

• Located on cytoplasmic & nuclear sides.

• Connect to cytoplasmic filaments & nuclear basket.

Cytoplasmic Filaments

• Extend into the cytoplasm, involved in protein recognition & import.

Nuclear Basket

• Located on the nucleoplasmic side.

• Regulates import & export of molecules.