nucleus

All eukaryotic cells possess nuclei, membrane-enclosed organelles that contain chromatin and the nucleolus (labelled tem).

During cell division, the nucleus organizes chromatin into chromosomes that align for segregation along the spindle apparatus. During non-reproductive phases of the cell cycle, nuclear DNA is uncoiled for transcription into pre-mRNA by RNA polymerase II (Pol II) and RNA polymerase III (Pol III) transcribes tRNA genes, 5S-rRNA genes, and genes encoding several other small RNAs. Following pre-mRNA processing, which includes capping, pre-mRNA splicing, alternative splicing, and polyadenylation, the mature mRNA is transported through nuclear pores into the cytoplasm.

Ribosomes (em2), comprising large intracellular aggregates of several RNAs and scores of proteins, are assembled in the nucleolus. Nuclear and rER ribosomes are the site of translation of genetic coding into polypeptides and proteins. The outer nuclear membrane is continuous with the membrane of the ER.

Џ beautiful Flash 8 animation - Inner Life of the Cell, which shows nuclear membrane with nuclear pore complexes, and Interpretation: Inner Life of the Cell Џ

. animation - spinning nucleus : art - nuclear membrane and nuclear pores : animation - nucleolus heterochromatin : ball-stick - dna double helix : animation - adenine tyrosine H bonds : animation - cytosine guanine H bonds : animation - start of transcription :Virtual Cell Textbook - Cell Biology :

• A • adhesion • C • cell membranes • cellular adhesion molecules • cellular signal transduction • centrioles • chemotaxis • chloroplast • cilia & flagella • communication • concentration gradients • cytokine receptors • cytoplasm • cytoskeleton • E • energy transducers • endoplasmic reticulum • endosomes • exosome • F • flagella & cilia • G • Golgi apparatus • GPCRs • H • hormones • I • ion channels • L • lysosome • M • meiosis • microtubules • mitosis • mitochondrion • N • Nitric Oxide • neurotransmission • neuronal interconnections • nuclear membrane • nuclear pore • P • pinocytosis • proteasome • pumps • R • receptor proteins • receptor-mediated endocytosis • S • second messengers • signaling gradients • signal transduction • spindle • structure • T • transport • two-component systems • V • vacuole • vesicle •