Nucleus Flashcards
Nucleus function
Command centre of the cell, contains the molecular machinery to replicate DNA and to synthesise and process different types of RNA.
Produce ribosomes
Nucleus components
nuclear envelope, chromatin, nuclear pores, nucleolus
Nuclear envelope structure
- two concentric membranes, with narrow perinuclear space
- space and outer nuclear membrane continuous with outer cytoplasmic space and RER.
- inner membrane covered in nuclear lamina
- inner and outer membrane bridged by nuclear pore complexes.
Nuclear envelope function
forms selectively permeable barrier between nucleus and cytoplasm
Nuclear lamina structure + function
Meshwork of intermediate filament called lamin, stabilising the nuclear envelope and bind to membrane proteins and chromatin
Nuclear pore structures and function
Nuclear pore complexes contain nucleoporin proteins- eightfold symmetry around a lumen. Allows ions and molecules to flow through.
Inbound molecules- chromatin proteins, ribosomal proteins, transcription proteins and enzymes
outbound molecules- mRNA, rRNA, ribosomes
Chromatin structure + functions
DNA associated with histones, contain 46 chromosomes.
Structural unit called nucleosome. which has a core of 8 histones and 150 base pairs of DNA.
DNA wrapped around histones is coiled for greater compaction
Histones on DNA like beads on a string
Different types of chromatin
Euchromatin and heterochromatin
Explain nucleosome structures in euchromatin
finely dispersed granular material, histones not closely associated - more transcription
Explain nucleosome structures in heterochromatin
more compact, little or no transcriptional activity
Two types of heterochromatin
constitutive and facultative
Explain constitutive chromatin
generally similar across all cell types and contain mainly repetitive, gene poor DNA sequences.
Present in regions such as centromeres and telomeres
Explain facultative chromatin
contains regions of DNA with genes transcription is variable inactivated in different cells using epigenetic mechanisms
can go through reversibly transitions from compact, transcriptionally silent states to more open, transcriptionally active conformations
What is a Barr body?
One of the two large X chromosomes present in human females, not men
contains facultative heterochromatin
This X chromosome is tightly coiled, whilst the other is uncoiled and transcriptionally active
Nucleolus structure
Generally spherical, basophilic subdomain of the nucleus.
densely concentrated ribosomal RNA (hence very basophilic)
different fibrillar and granular subregions, due to the different stages of rRNA maturation
