The cell nucleus Flashcards
What are the 5 functions of the nucleus?
- Stores and maintains the cells DNA - As chromosomes.
- DNA replication
- Transcription - to make RNA from DNA.
- Ribosomal biogenesis - It is the process of making ribosomes. In prokaryotic cells, it takes place in the cytoplasm with the transcription of many ribosome gene operons. In eukaryotes, it takes place both in the cytoplasm and in the nucleolus.
- Controls communication between the nucleoplasm and the cytoplasm - controls what goes in an out using the nuclear membrane.
How is DNA stored in the nucleus?
DNA is stored as chromosomes.
How many pairs of chromosomes are there in the nucleus? Therefore how many are there in total?
- There are 23 pairs of chromosomes.
- That makes 46 chromosomes in total.
What is a nucleosome?
- A nucleosome is a basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound in sequence around eight histone protein core 1.65 times.
- They form the fundamental repeating units of eukaryotic chromatin.
How are nucleosomes made more compact?
- The nucleosome along with a H1 histone forms the chromatosome.
- The chromatosome folds up to form a 30nm fibre.
- This 30nm fibre forms loops that are 300nm in length.
- The 300nm fibres is then compressed and folded to produe a 250nm wide fibre.
- This tight folding of the 250nm fibre produces the chromatid of a chromosome.
Why are chromosomes neutrally charged?
- The DNA has a negative charge because of the negativity charged phosphate groups.
- The histones are positively charged.
- This makes an overall neutral charge.
What is the most compact form of chromosomes?
Anaphase chromosomes.
What are chromosomes? What are the three structural elements?
- They are a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
- They have 3 structural elements:-
- Telomeres - protect chromosome ends.
- Centromere - needed during cell division.
- Origins of replication - It is a particular sequence in a genome at which replication is initiated.
How are chromosomes identified?
3 key features used to identify chromosomes -
- Size
- Banding pattern
- Centromere position
Chromosomes that are partially digested are stained with Giemsa. This forms Giemsa banding -
- G dark - gene poor, tend to be heterochromatin rich.
- G light - gene rich, tend to be euchromatin rich.
Give information on heterochromatin.
- Gene poor.
- Found near centromeres and telomeres.
- Highly condensed (highly packaged) - usually resistant to gene expression.
- Often associated with the nuclear envelope.
- In a typical cell 10% of the genome is heterochromatin.
- It is the genetically inactive DNA.
Give information on euchromatin.
- Location for active genes.
- Less condensed.
- The majority of the genome is made up of euchromatin.
- It is involved in transcribing RNA to produce proteins.
What is spectral karyotyping?
Spectral karyotyping (SKY) is a laboratory technique that allows scientists to visualize all of the human chromosomes at one time by “painting” each pair of chromosomes in a different fluorescent colour.
What are the 6 different nuclear compartments and what are their functions?
- Chromosome territories - store DNA and control access to DNA.
- Replication factories - nascent DNA production.
- Transcription factories - nascent RNA production.
- Spliceosome - irregular domains containing splicing factors.
- Nucleolus - ribosome biogenesis.
- PML (promyelocytic leukemia) nuclear bodies - possible nuclear depot.
Nascent meaning - just coming into existence and beginning to display signs of future potential.
Biogenesis meaning - the synthesis of living substances by living organisms.
What occurs in DNA replication factories? What do the factories contain?
- DNA replication takes place in replication factories.
- The factories contain all the enzymes and other factors required to produce two new DNA strands.
What does RNA replication factories contain?
The factories contain RNA polymerase II, template DNA strand and newly synthesised messenger RNA.
What is the largest substructure in the nucleus?
The nucleolus.
What are the 3 functions of 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 ribosomal subunit.
- 5.8S, 28S (and 5S) – large ribosomal subunit.
What are the three distinct zones in a nucleolus that you can identify under an electron microscope? What are their functions?
- Fibrillar centre (FC) - Ribosomal RNA genes are transcibed.
- Dense fibrillar component (DFC) - It contains the protein fibrillarin which is important in rRNA processing.
- Granular component (GC) - Involved in the processing and assembly of ribosomes.
What is the nuclear envelope made up of?
It is made up of two lipid bilayers.
What connects the nucleoplasm and the cytoplasm?
The nuclear envelope contain nuclear pores which allows communication between the nucleoplasma and the cytoplasm.
