Nucleus, Chromosomes & Chromatin Flashcards
Nuclear envelope
double membrane enclosing DNA
Outer nuclear membrane
continuous with ER
Inner nuclear membrane
carries nuclear specific protein
Nuclear lamina
fibrous network that provides structural support to the nucleus
Nuclear pore complexes
- channels through which polar molecules and macromolecules pass through the nuclear envelope
- large multi-protein complexes with 8-fold symmetry around central channel
Nuclear localisation signal (NLS)
- tag for nuclear protein
- 1 or 2 short sequences with positively charged Lys residues
Nuclear transport receptors
Importins - into nucleus
Exportins - out of nucleus
What energy drives nuclear transport?
GTP hydrolysis - Ran GTP
Ran-GEF
in nucleus
Ran-GAP
in cytoplasm
Nucleolus is site of and is a:
- site of ribosome biogenesis
- is an aggregation of rRNA gene clusters
Ribosome structure:
- 2/3 RNA, 1/3 protein
- 1 small & 1 large subunit
rRNA gene organisation
tandem arrays
5.8S, 18S and 28S rRNAs transcribed as single:
pre-rRNA which is then cleaved to give rise to 3 mature rRNAs
5S rRNA
encoded by separate gene
Where are ribosomes assembled and exported to
assembled in nucleus and exported into cytoplasm
pre-ribosomal particles
exported from nucleus via nuclear pores to yield active ribosomal subunits
Compartmentalisation
- transcription in nucleus
- translation in cytoplasm
Where do ribosomal proteins assemble
on pre-rRNAs in nucleolus
Prokaryotic chromosome structure
circular with 1 origin of replication
E.coli chromosome
~ 4.6 million bases encoding 4300 different proteins
Eukaryotic genes contain:
introns and exons
Is there correlation between genome size and evolution?
No
Eukaryotic chromosome structure
linear
