The Cell Nucleus Flashcards
The function of the nucleus
- Store and maintain the cell’s DNA
- DNA replication
- Transcription
- Ribosomal biogenesis
- Controls communication between nucleoplasm and cytoplasm
How is DNA stored as in the nucleus
Stored as chromosomes
How many pairs of chromosomes in the human nucleus?
23
How do you go from DNA to chromosomes ?
• DNA has a negative charge and wraps around the positive charge histone proteins.
How are nucleosomes made more compact?
Nucleosome made more compact by wrapping into 30nm fibre
What is the highest level of compaction of chromosomes?
Metaphase chromosome
Structure of chromosomes
Single molecule of DNA
Telomeres: protect chromosome ends
Centromere: needed during cell division
Origins of replication
How are chromosomes identified?
Size Banding pattern Centromere position G banding:chromosomes partially digested and stained with giemsa G dark: gene poor, heterochromosome rich G light: gene rich, euchromatin rich
Euchromatin
- Location for active genes
- Less condensed
Majority of genome is made up of euchromatin
Heterochromatin
- Gene poor
- Found near centromeres and telomeres
- Highly condensed- resistant to gene expression
- Associated with the nuclear envelope
About 10% of the genome is heterochromatin
Nuclear compartments(Chromosome territory)
DNA and control access to DNA
Nuclear compartments(Replication factories)
nascent DNA production
Nuclear compartments(Transcription factors)
nascent RNA production
Nuclear compartments(spliceosome)
irregular domains containing splicing factors
Nuclear compartments(Nucleoli)
ribosome biogenesis
Nuclear compartments(PML nuclear bodies)
possible nuclear depot
What occurs at DNA replication factories and what do the factories contain?
DNA replication takes place here
Factories contain all the enzymes and other factors required to produce two new DNA strands.
What does RNA transcription factories contain?
RNA polymerase II
Template DNA strand
Newly synthesised mRNA
What does the nucleolus transcribe?
Transcription of rRNA to produce large 45S rRNA precursor
What does the nucleolus modify rRNA into?
Modification of rRNA into 18S, 5.8S and 28S rRNA
Assembly of ribosomal subunits
18S rRNA and 33 proteins-small ribosomal unit
5.8S, 28S and 5S rRNA and 49 proteins- Large ribosomal subunit.,
How many rRNA genes are copied per haploid gene?
200
Where are the rRNA genes located?
The genes are located in tandem copies on the acrocentric chromosomes
Why does the cell need so many copies of rRNA?
A single mRNA can be translated so many times to give amplification of the final protein product
The ribosomal RNA molecule is not translated into protein, the ribosomal RNA molecule is the final product and the cell requires many ribosomes
What is the nuclear envelope made up of?
Two lipid bilayer
What type of molecules can diffuse through nuclear pores?
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 histones, proteins etc.
Large molecules must be exported actively
