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Nucleolus
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x

Nucleolus
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x

- Nucleolar organizing center (fibrillar center)
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x

- Pars fibrosa
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x

- Pars granulosa
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x

Perinucleolar heterochromatin
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x

Nuclear envelope
This EM shows the subdivisions of the nucleolus. The palest region, the fibrillar center, contains the nucleolar organizing regions of multiple chromosomes; the pars fibrosa (dense fibrillar component) contains the newly transcribed rRNA; and the pars granulosa contains maturing ribosomes. This nucleolus is partially surrounded by perinucleolar heterochromatin. 35,000x