Cell Nucleus Flashcards
(28 cards)
What is function of nucleus?
Store + maintain cell’s DNA DNA replication Transcription Ribosomal biogenesis Controls communication between nucleoplasm + cytoplasm
How is DNA stored?
Is stored as chromosomes
Human cells have 23 pairs of chromosomes containing 6 x 10^9 base pairs of DNA
Describe the structure of chromosome?
Single molecule of DNA Linear in eukaryotes Contains genes Telomere= protects ends of chromosome Centromere= needed during cell division Origins of replication= required to replicate DNA of chromosomes within reasonable time frame
Chromosomes + cell cycle
In G1 phase, there are 2 homologs, parental + maternal homolog
During s phase, there is firing of replication origins to get duplication of each of these chromosomes
In G2, cells is tetraploid=> 4 cops of chromosomes
As cell enters M phase, there is change in chromosomes as they become highly condensed
What technique can be used to identify chromosomes?
What does it tell us?
G banding
Chromosomes are partially digested + stained with Giemsa
G dark= gene poor so heterochromatin rich
G light= gene rich so euchromatin rich
What are 2 arms of chromosomes called?
P arm + q arm
P arm is slightly shorter
Q arm is slightly longer
What is meaning of metacentric chromosomes?
Some chromosomes, arms looks relatively similar
What is meaning of submetacentric chromosomes?
In some chromosomes, centromere is towards on end
What is meaning of Acrocentric chromosomes?
P arm is very short which contains repetitive RNA + ribosomal RNA genes
What is Karyotyping used for in human cell?
To identify chromosomal abnormalities
What is heterochromatin?
Gene poor
Found near centromeres + telomeres
Highly condensed so usually resistant to gene expression
Often associated with nuclear envelope
In typical cell, 10% of genome is heterochromatin
What is euchromatin ?
Gene rich
Location for active gene
Les condensed
Majority of genome is made up of euchromatin
What is spectral karyotyping?
Fluorescent in situ hybridisation
Fluorescent markers used
In situ->cells on slide + add probe. You do hybridisation step between probe + DNA. Wherever the DNA happens to be on chromosome or within the nucleus, it will bind + give you a fluorescent signal
How are chromosomes organised in metaphase nucleus?
Metaphase chromosomes, DNA is tightly packed (condensed)
How is chromosome organised in interphase nucleus?
Interphase chromosomes, DNA is more relaxed (decondensed)
What are chromosome territories?
Chromosomes arms + bands are distinct + mutually exclusive
These pattern of chromosome take within cell nucleus is called chromosome territories
Where are gene poor chromosomes located?
Located in periphery of nucleus
Where are gene rich chromosomes located?
Located in interior of nucleus
Functional compartmentalisation of nucleus
Subnuclear compartment exist despite absence of internal membranes
What are DNA replication factories?
Is where DNA replication takes place
Contains all enzymes + other required to produce 2 new DNA strands
What are RNA transcription factories?
Contain RNA polymerase II, template DNA strand + newly synthesised mRNA
Each of these factories will contain general transcription factors that are required to open up DNA + in order to let RNA polymerase to come in + bind
What is nucleolus?
Largest substructure in nucleus
What are 3 distinct zones of nucleolus by electron microscopy?
FC (fibrillar center) - where ribosomal RNA genes are located
DFC( dense fibrillar component)- where rRNA transcripts being made from DNA containing ribosomal genes are
GC (granular component)- processing + assembly
Why does cell need so many copies of ribosomal RNA genes?
Compare to single copy gene- single mRNA molecule can be translated many times to give amplification of final protein product
Ribosomal RNA molecule is not translated into protein, ribosomal RNA molecule transcribed is final product + cell requires many ribosomes
