The Cell Nucleus Flashcards
What are the functions of the nucleus?
- to store and maintain a cell’s DNA
- DNA replication
- transcription
- ribosomal biogenesis
- controls communication between the nucleoplasm and the cytoplasm
What 3 key features to scientists use to identify chromosomes?
- SIZE
- BANDING PATTERN
- CENTROMERE POSITION
List some differences between Heterochromatin and Euchromatin.
HETEROCHROMATIN:
- gene poor
- found near centromeres and telomeres
- highly condensed, usually resistant to gene expression
- often associated with the nuclear envelope
EUCHROMATIN:
- location for active genes
- less condensed that heterochromatin
- majority of the genome is euchromatin
What is the difference in the spatial location of gene-rich vs. gene-poor chromosomes?
The gene-poor chromosomes are at the periphery of the nucleus, while the gene-rich are in the interior.
What are nuclear compartments?
They are subnuclear compartments that exist within the nucleus , despite the absence of internal membranes.
List 6 nuclear compartments and their functions.
- CHROMOSOME TERRITORIES: they store DNA and control access to it. Chromosome arms and bands are distinct and mutually exclusive. Chromosomes form non-overlapping domains in the interphase nucleus.
- REPLICATION FACTORIES: Has replication factories, where nascent DNA (lagging strand) is produced
- TRANSCRIPTION FACTORIES: Contains RNA pol II, template DNA for nascent mRNA(lagging strand) production
- SPLICEOSOME: irregular domains containing splicing factors
- NUCLEOLI: ribosome biogenesis
- PML NUCLEAR BODIES: possible nuclear depot
Nucleolus is the largest substructure in the nucleus. What are 3 functions of the nucleolus?
- transcription of rRNA genes to produce a large 45S precursor
- cleavage/modification of rRNA into 18S, 5.8S and 28S rRNA
- assembly of ribosomal subunits (18S, 5.8S, 5S and 28S)
What are the three distinct zones in a nucleolus that you can identify under an electron microscope, and what are their functions?
- Fibrillar Centre (FC): ribosomal RNA genes
- Dense Fibrillar Component (DFC): rRNA transcripts
- Granular Component (GC): processing and assembly
Describe the nuclear pores and movement through them.
The nuclear envelope contains nuclear pores, which is how communication between the nucleoplasm and the cytoplasm occurs.
Movement through the nuclear pores is strictly controlled and only small water soluble molecules can diffuse freely through the pore.
NUCLEAR EXPORT:
ribosomal subunits and mRNA proteins require a nuclear export signal
NUCLEAR IMPORT:
histones, DNA/RNA polymerase and other nuclear proteins - proteins require a nuclear localisation sequence
What is a chromosome?
- A single molecule of DNA
- Linear (in eukaryotes)
- Contains genes
- Structural elements:
- Telomeres: protect chromosome ends
- Centromere: needed during cell division
- Origins of replication
Describe G-banding.
Chromosomes partially digested and stained with Giemsa
G dark – gene poor, tend to be heterochromatin rich
G light – gene rich, tend of be euchromatin rich
What is:
metacentric, submetacentric, acrocentric?
- Metcentric - centromere is in the middle of the chromosome.
- Submetacentric - centromere is on one side of the chromosome, causing a short arm (p) and a long arm (q).
- Atrocentric - When the centromere is on one end of the chromosome, causing a very short arm. The short arm is the satelite DNA (tandemly repeating non-coding DNA) and has rRNA genes.
What is Karyotyping?
What is spectral karyotyping?
A test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells. Spectral involves the use of fluorescent (can be colourful).
How are chromosomes organised in the nucleus? (metaphase and interphase)
metaphase chromosomes
DNA tightly packed (condensed)
interphase chromosomes DNA more relaxed (decondensed)
Why does the cell need so many copies of the ribosomal RNA genes?
- Compared to single copy gene – a single mRNA molecule can be translated many times to give amplification of the final protein product.
- The ribosomal RNA molecule is not translated into protein, the ribosomal RNA molecule transcribed is the final product and the cell requires many ribosomes.
