Lecture 2 Flashcards
The 2 DNA strands have
Opposite polarity
Why AT and CG
due to the nature of pyrimidines and purines by this conformation balance is ensured by maintaining 3 rings.
Nuclear lamina is
Intermediate filaments beneath the inner membrane
Nuclear lamina and outer membrane filaments
Support the nuclear pore complex
When can we view heterochromatin and euchromatin
Feulgen stain under the cytophotometer
Somatic cells only
S phase
Why heterochromatin is hard to transcribe
Tightly coiled and condensed
Are heterochromatin and euchromatin the same in all cells
No, in fact the whole chromosome can become inactivated like dose compensation in females
Growth hormones somatostatin and somatotropin are heterochromatin after 18
Some liver cells are
Polyploidy
2n/4n/8n
Chromatin can be isolated biochemically by
Appears
Contains
Cell lysis in hypotonic solution
Viscous and gelatinous
DNA/RNA/histones/non histones
31/5/36/28
Why the pea embryo rna is so much different in comparison with dna than liver cells
As pea embryo are ready to germinate whenever conditions are suitable
During mitosis the chromosome split is visible due to
.. but not in
.. where it already happened
Condensation
S phase
Centromere replicates at
Anaphase
Chromatin thread is the same as
Chromonemata
Chromomeres are
Bead like structured that are sometimes visible during interphase
Obv in polytene chromosomes
Due to close coiling of chromonemata
Polytene chromosomes z
Very buffed areas in drosophila salivary glands abt 1000 chromatin fibers successive replication but no cytokinesis endomitosis
Large diameter
Centromere
Primary constriction
Non stainable gap
Centromere Has….chromatid…appears…
Very thin as it is uncoiled
Unstained with feulgen so stained with centromeric stain
Centromere function
Spindle fibers attach to it at metaphase to ensure chromosomes arrive to daughter cells without it the chromosomes will be lost
Spindle fibers are
Discontinuous
More than 1 centromere
Dicentric
Tricentric
Holocentric
Acentric
Centromere positions
Meta v
Telo/acro i
Submeta j
S.cerevisae centromeres length
Plasmid importance
100-120bp with 3 essential regions
2um fragments
The centromeres of different chromosomes are …without…
CEN
Interchangable
Having any detectable effect
Region I and III
Region II
In s.cerevisae
Conserved, binding sites for spindle
AT rich 90bp length and nature important than sequence
2ndry constriction must be….
Has……
But not….
They are in….chromosmes
In every chromosome
NOR (nucleolar organising regions)
Every 2ndry constriction has them
5 acrocentric with staellites
13,14,15,21,22
NOR has genes that code for
45 s RNA/ 18 s RNA/28s rRNA/ 5.8 s rRNA
Chromosome+NOR
Nucleolar chromosome
Usually 2 in a diploid cell
Telomeres function
Prevent DNases from degrading the DNA molecule
Prevents ends fusion
Facilitate replication without loss of material
Telomeres are…. repeated
In humans
From 1-4
Short sequence tandemly 500-3000
5’TAG3’
TTAGGG
T or G
Enzyme of telomere
End proteins of telomere
Telomere associated sequence
Telonerase
Sheltrin
Repetitve DNA near the telomeres
Most telomeres terminate with…. Called…. Length
C rich single strand
3’overhang
125-175 bp
10nm ellipsodial beads
DNA in bacterial chromosomes is…and..
Nucleosomes
Circular, contains 50 -vely supercoiled domains
Heterochromatin beneath nuclear lamins around nucleolus is called
Nucleolus associated chromatin
Chromosome duplication occurs in
S phase
How cell distinguishes telomeres from sites of damage
Due to sheltrin proteins
TIN2,TPP1,RAP1 complex
