Chromosomes Flashcards
Where is the heterochromatin found?
By the centromere and telomeres
What are telomeres?
The ends of chromosomes have no space for the RNA primers to attach to hence doesn’t get replicated.
Therefore telomeres shorten throughout our lives
Must not be inappropriately degraded or repaired
What is the centromere?
Holds sister chromatids together
What is heterochromatin
Loped around histones and are inactive
What direction does DNA polymerase work ?
3 to 5 prime
What stitches Okazaki fragments?
DNA ligase
DNA polymerase can synthesis dna de novo.
True or false
False it needs an RNA primer
What is the end replication problem?
Shortenning of telomerres
What is telomerase ?
An enzymes which adds repeats to resynthesis the telomere but it’s only present in stem or germ cells
What are centromeres
Repeated DNA sequences which joins sister chromatids together.
What is a kinetochore
Protein complex that binds to the microtubules on the centromere
What form is dna when activates or transcribed?
Euchromatin
What are extragenic sequences?
Repeated DNA sequence which have no biologically function
What is satellite DNA?
In centromeres and telomeres
14 to 500 base pairs with mainly A and T
What is minisatellite dna?
Present in shorter lengths
15 to 100
GC rich
What is the use of minisatellites
Used for paternity tests and DNA fingerprinting
What are the types of highly repeated interspersed DNA?
SINE (short interspersed nuclear elements)
LINE
What is a nucleosome?
DNA wrapped around a core protein of 8 histones with a histones H1 clipping them onto the histones
What is a solenoid structure?
Coiling of nucleosomes
6 nucleosomes per turn
Called a chromatin fibre
How long is a chromatin fibre?
30nm
What happens to a chromatin fibre before becoming a chromosome?
It joins with fibre scaffold complex to form a series of loops to form a chromatin scaffold
When are chromosomes most condense?
Metaphase
Why is heterochromatin important?
Negative DNA becomes neutral due to positive histones
Takes up less space
Becomes inactive as it’s inaccessible
What is metacentric chromosomes?
Where the centromere is near the middle of the chromosome
What is sub metacentric chromosomes?
The centromere is much hugger up the chromosomes to create a distinct p and a arm
What is an acrocentric chromosome?
Where the centromere is so far up that the p arm of the chromosome has no function it is just a telomere really
What is an example of metacentric chromosomes ?
Chromosome 1
What is an example of submetacentric chromosomes ?
Chromosome 12
What is an example of acrocentric chromosomes ?
Chromosome 21
How are chromosomes analysed?
Take blood
Separate out rbc
Culture and incubate
Colchicine added
Separate WBCs
Burst cells using saline
Spread out chromatin on slide
Stain it
What is colchicine ?
Mitotic inhibitor which causes cells to accumulate at metaphase
What is Karotyping?
Preparation of a complete set of metaphase chromosomes in order
Most of our chromosomes are submetacentric.
True or False
True
What is FISH?
Fluorescence in situ hybridisation
The sequence of interest is labelled with a dye
What are the types of Fish probes?
Unique sequence probes
Centromeres probes
Telomeric probes
Whole chromosome probes
What is a unique sequence probe?
Unique sequences are highlighted
What is a centromeric probe?
Helps determine chromosome number
What is a telomeric probe used for?
Detect sub telomeric rearrangements
Often in children with unexplained mental retardation
What is a whole chromosome probe?
Use various probes and fluorescent dyes for each chromosome to create spectral karyotypes to detect translocation Easier to align
FISH can be used on an intact nuclei. True or False
True
What is a bivalent?
The sister undergo recombination
What is recombination?
Exchange of parts of chromosomes between the maternal and paternal copy
What is gametogenesis?
Production of gametes via meisos
What is egg formation called?
Oogenesis
What is sperm formation called?
Spermatogenesis
Difference of timing of gametogenseis
Females are born with all their eggs in meiosis 1(primary oocytes) males make them in puberty
What is x inactivation ?
Females zygotes get 2 X chromosomes one gets randomly switched off so it’s never expressed and hidden deep in heterochromatin
What is the first enzyme needed for dna replication?
RNA primase
To make a complementary segment of rna (a primer)
It allows DNA polymerase to bind onto it
What’s the difference between microsatellites and lines/sines?
Microsatellites repeats are back to back/consecutive
Lines are repeats dispersed throughout the whole genome randomly (not adjacent)
