Cell nucleus Flashcards
What are the functions of the cell nucleus?
store and maintain cell's DNA DNA replication Transcription Ribosomal biogenesis controls communication between the nucleoplasm and the cytoplasm
How is DNA stored as and how many pairs are there in the human nucleus?
chromosomes
23 pairs
How does DNA form chromosomes?
DNA has a negative charge so wraps around the positive charge histone proteins
How are nucleosomes made more compact?
by wrapping into 30nm fibre
what is the highest level of compaction of chromosomes?
metaphase chromosome
What is the structure of chromosomes?
single molecule of DNA linear contains genes telomeres centromeres origins of replication
How are chromosomes identified?
G banding: chromosomes partially digested and stained with giesma G dark: gene poor, heterochromosome rich G light: gene rich, euchromatin rich Size Unique banding pattern Centromere position
heterochromatin
Gene poor
Found near centromeres and telomeres
highly condensed - resistant to gene expression
associated with nuclear envelope
About 10% of the genome is heterochromatin
Euchromatin
location of active genes
less condensed
majority of the genome is made up of euchromatin
Nuclear compartments (chromosome territory)
store DNA and control access to DNA
Nuclear compartments (replication factories)
nascent DNA production
Nuclear compartments (transcription factories)
nascent RNA production
Nuclear compartments (spliceosome)
irregular domains containing splicing factrors
Nuclear compartments (nucleoli)
ribosome biogenesis
Nuclear compartments (PML nuclear bodies)
possible nuclear depot
what occurs at DNA replication factories and what do they contain?
DNA replication takes place here
They contain all the enzymes and other factors required to produce two new strands
what do RNA transcription factories contain?
RNA polymerase II
Template DNA strand
Newly synthesised messenger RNA
What occurs in the nucleolus?
Transcription of rRNA genes to produce large 45s rRNA precursor
cleavage/ modification of rRNA into 18s, 5.8s and 28s rRNA
assembly of ribosomal subunits: 18s (small subunit) and 5.8s,28s and 5s (large ribsomal subunit)
How many rRNA genes are copied per haploid gene and where are they located?
200
the genes are located in tandem copies on the acrocentric chromosomes
Why does the cell need so many copies of rRNA chromosomes?
a single mRNA can be translated so many times to give amplification of the final protein product
the ribosomal RNA molecules is not translated into protein, the rRNA molecule transcribed is the final product and the cell requires many ribosomes
What does the nuclear envelope consist of?
2 lipid bilayer
what types of molecules can diffuse through nulear pore?
movement strictly controlled and only small water soluble molecules can diffuse through the pore
exports from the nucleus include ribosomal subunits and mRNA
imports include histoness, proteinss, etc
large molecules must be exported actively
