Cell nucleus Flashcards
What are the functional elements of a chromosome?
a chromosome is a single molecule of DNA
- linear in eukaryotes
- contains genes
functional elements
- origin of replication = site of replication, rewired to initiate DNA replication during the S phase
- centromere = needed during cell division
- telomeres = are at each end of the chromosome, used to protect the ends of chromosomes
What is the function of centromeres?
are megabases of repetitive DNA, major component is the alpha satellite DNA in humans
- all chromosomes have different satellite DNA configurations = at the centre of centromeres
function - locks sister chromatids together
- is the attachment site for chromosomes to the mitotic spindle via a protein structure called the kinetochore
What is the centromere composed of?
kinetochore outer plate
- formed from special proteins
- binds the mitotic spindle (spindle microtubules)
kinetochore inner plate
- formed by kinetochore proteins bound to the alpha satellite DNA
heterochromatin - type of chromatin
- formed on the alpha satellite DNA
What is the function of telomeres?
made up of tandem repeat bases = TTAGGG
- join at the end of each chromosome and form a loop
- protects chromosomes by preventing lost of DNA during each replication/cell division by being lost instead = end replication problem
joins where the first RNA primer was removed from
- cannot be fused together to the rest of the strand because there was no initial strand = primer started transcription
What are the origins of replication?
eukaryotes
- have multiple origins of replication
- have a large genome/chromosome = require multiple origins to allow replication simultaneously, happens at a reasonable rate
prokaryotes
- have a single origin of replication
- do not have an especially large genome = one origin allows them to replicate at a reasonable rate
What is the specific characteristic of chromosomes which allow for identification?
G banding within the chromosomes
- G-banding is a technique used to produce thin, alternating bands along the length of the entire chromosome
- creates unique patterns on each homologous set and allows for their identification
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 are the three identifying characteristics of chromosomes?
size
- chromosome 1 is the largest whilst chromosome 21 and 22 are the largest
banding pattern
- G dark - heterochromatin
- G light - euchromatin
centromere position
- each arm of the chromsome is called p or q
- check where p and q are in relation to the centromere portion
metacentric - centromere is roughly in the centre of the arms
submetacentric - centromere is offset towards the p or q arm (uneven arm length)
acrocentric - no genetic material in the p arm ecept for rRNA
What is karyotyping?
karyotype
- is an individual’s collection of chromosomes
- refers to a laboratory technique that produces an image of an individual’s chromosomes
- is used to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells
- is used to look for abnormal numbers or structures of chromosomes.
spectral karyotyping
- full colour map of chromosomes
How are the types of chromatin and chromosomes positioned in the nucleus during interphase?
- electron microscopy
at interphase they are decondensed to enable visualisation
heterochromatin - stains dark
- positioned at the periphery and towards the edge
euchromatin - stains light
- positioned in the interior
chromsomes
- chromosome arms and bands are distinct and mutually exclusive
- chromosomes form non-overlapping domains in the interphase nucleus
How do sub-compartments exist in the nucleus?
sub-compartments exists despite the absence of internal membranes
What are the different sub-compartments within the nucleus?
chromosome territories
- store DNA and control access to DNA
replication factories
- nascent/new DNA production
transcription factories
- nascent/new RNA production
spliceosome
- irregular domains containing splicing factors
nucleoli
- ribosome biogenesis
PML nuclear bodies: possible nuclear depot
What is the nucleolus? How does it function?
is the largest sub-structure of the nucleus
- is the self organising nuclear compartment
- site of ribosome subunit production
RNA polymerase transcribes the precursor rRNA
rRNA is processed to 18S, 5.8S and 28S RNA molecules by endonuclease and exonuclease cleavage
5S is transcribed in the nucleoplasm by RNA polymerase III and transported to the nucleolus
rRNA folded and associate with 79 ribosomal proteins to assemble the 40S and 60S ribosomal subunits (eukaryotic)
subunits are transported to the cytoplasm
What are the distinct sections/features of the nucleolus?
shown by electron microscopy
- fibrillar centre = holds RNA polymerase and rRNA genes
- dense fibrillar component = RNA transcripts/transcription
- granular component = processing and assembling takes place
What are NORs?
nucleolar organising regions = NORs
- site/location of rRNA genes
What is the difference between mRNA and rRNA?
mRNA
- a single mRNA can be translated multiple times to give amplification of the final product
- can be reused until it is degraded
rRNA
- cell has multiple copies of the rRNA genes
- is not translated into proteins because it is the final product
- required to synthesise the many ribosomes required
