The cell nucleus Flashcards
What are the functions of the nucleus?
- Store and maintain the cell’s DNA
- Transcription
- Ribosomal biogenesis (synthesis of ribosomes)
- Controls communication between the nucleoplasm and the cytoplasm
Basic features of a chromosome
A single molecule of DNA Linear (in eukaryotes) Contains genes Contains a number of Structural elements: •Telomeres •Centromere •Origins of replication
During mitosis why do the chromosomes condense?
Allows the chromosomes to be separated evenly during anaphase
What are the 3 key features scientists use to identify chromosomes?
- Size
- Banding pattern
- Centromere position
What technique is used to produce the banding pattern on the chromosomes?
G-banding (Giemsa banding)
What are the features of the dark bands (G dark bands) produced on the chromosomes by G banding?
Gene poor, tend to be heterochromatin rich
What are the features of the Light bands (G light bands) produced on the chromosomes by G banding?
Gene rich, tend of be euchromatin rich
What are the 2 arms on a chromosome called?
p arm (short arm) q arm (long arm)
What is a Metacentric chromosome?
Chromosome where the lengths of p and q arms are very similar. (Centromere towards middle of chromosome).
What is a Submetacentric chromosome?
Chromosome where the length of q arm is longer than the length of p arm. (Centromere closer to one end of Chromosome).
What is an Acrocentric Chromosome?
Chromosome with a very short p arm which only contains repetitive DNA and rRNA genes
Features of Heterochromatin
- Gene poor
- Found near centromeres and telomeres
- Highly condensed – usually resistant to gene expression
- Often associated with the nuclear envelope
Features of Euchromatin
- Location for active genes
- Less condensed
- Majority of the genome is made up of euchromatin
Where is Heterochromatin found with the cell nucleus
Around periphery of the nuclear membrane as well as around nucleolus
Where is Euchromatin found within the cell nucleus?
Found within the interior of the cell nucleus
What is Fluorescent in situ hybridisation?
Technique used to visualise and map specific portions of a cell’s DNA.
Whole chromosome probes (single strands of DNA that are complementary to a certain sequence on the chromosome) are labelled using fluorescent dyes.
This means when they bind to the particular sequence on the chromosome the chromosome becomes coloured.
It can also be used to see where each of the different chromosomes are located within the interphase nucleus
What is a chromosome territory?
Chromosome territories are specific regions within the interphase nucleus in which certain chromosomes are located
Within a chromosome territory do the elements of a chromosome still remain separate?
yes, the Chromosome arms and bands are distinct and mutually exclusive (don’t really overlap, apart from slightly at centromere, or interact) within the chromosome territory
If a particular gene contains euchromatin does it mean that the gene will always be found within the interior of the nucleus?
No, even though a gene contains lots of euchromatin in certain cell types it may not be within the interior of the nucleus but will have a preference for that area.
How much of the human genome is comprised of euchromatin?
Around 90%
How much of the human genome is comprised of heterochromatin?
Around 10%
What is immunofluorescence?
Technique in which specific antibodies bound to a fluoresecent dye then bind to their specific antigen on the target cell. This allows for visualization of the distribution of antigen within the target cell. Can be used to check distribution of specific protein within interphase nucleus.
Are there any patterns present with the way that particular chromosomes organise themselves within chromosome territories?
There can be depending on the cell type. e.g. In mouse lymphocytes chromosome 12 is located next to chromosome 14 which is located next to chromosome 15. (This is called a triple cluster).
Examples of nuclear compartments within the interphase nucleus?
- Chromosome territories: store DNA and control access to DNA
- DNA replication factories: nascent (new) DNA production. Contain all the enzymes and replication factors required for DNA replication
- RNA transcription factories: nascent RNA production. Contain RNA polymerase II, template DNA strand and newly synthesised mRNA
- Spliceosome: irregular domains containing splicing factors
- Nucleoli: ribosome biogenesis
- PML nuclear bodies: possible nuclear depot
What is the nucleolus?
Largest substructure within the nucleus
Functions of the nucleolus
- Transcription of rRNA genes to produce large 45S rRNA precursor
- Cleavage/modification of rRNA precursor into 18S, 5.8S and 28S rRNA
- Assembly of ribosomal subunits 18S –small ribosomal subunit and 5.8S, 28S (and 5S) – large ribosomal subunit
What are the 3 zones within the nucleolus?
Fibrillar center (FC): Where the ribosomal RNA genes are located Dense fibrillar component: where the rRNA transcripts are synthesised (production of rRNA precursor) Granular component: Processing and assembly of newly synthesised rRNA transcripts into the ribosomal subunits
What is the nuclear envelope?
Membrane that separates the nucleus from the cytoplasm
Features of the nuclear envelope
Contains 2 lipid bilayers
Contains many nuclear pore complexes
Contains the nuclear lamina
What functions do nuclear lamina proteins provide?
Help stabalise the shape of the nucleus.
They also have a role in regulation of gene expression
