chromosomes + chromatin Flashcards
what is a nucleosome
DNA bound to central octamer of histone proteins
how many DNA molecules does 1 chromosome have. And how many DNA molecule after replication
1 chromosome = 1 DNA molecule
after replication = 2 DNA molecules (sister chromatids)
what do chromasomes fold into
compartments: A (open) B(closed).
What are TADS
(topologically associated domains) - self interacting genomic region
they are chromatin within the compartments
what are the levels of organisation of a chromosome
- nucleosome
- domain - chromatin domains
- territories - TADS form
what controls the chromatin domains
- histone modifications
- histone varients
- chromatin assoc proteins
Which histones are in the nucleosome
H2A, H2B, H3, H4
H1 differs in species and tissues outside
what do nucleosomes do during transcription
they slide down DNA to open it and expose the DNA to allow transcription.
when nucleosomes close together TFs cant bind
Affects of methylation and acetylation on transcription
increased methylation - nucleosomes tight so TFs cant bind (ch3 groups block)
increased acetylation - nucleosomes loose packed so Tfs can bind ( acetyl groups cause repulsion)
what are LADS and where is it common in
(lamina assoc domains) = parts of chromatin that interact with lamina. has lots of methylated H3 histone
common mod in heterochromatin
what are NADS
nucleolar assoc domains
name the architectural proteins (that the DNA loops in TADS are maintained by)
- histones
- chromatin remodelling enzyme
- Zinc finger
- cohesins
what do chromatin remodelling enzymes do
promotes euro + heterochromatin
what does zinc finger do
mediates DNA looping + regulates transcription
zinc atoms stabilize folds and it is a protein motif
Baso regulates gene organization and expression
what do cohesins do
bind sister chromatids together (mitosis)
Def of epigenetics
changes in gene expression by chromatin modification without changing DNA seq
name some histone modifications
- acetylation
- methylation
- phosphorylation
- deamination
- ubiquitination
What are protamines
In sperm head
replace histones late in the haploid phase of spermatogenesis
Where is heterochromatin found
telomeres and centromeres
What is karyotype, karyogram, idiogram
Karyotype: number and visual appearance of chromosomes in nucleus
Karyogram: chromsomes in homologous pairs and numbered according to LENGTH AND CENTROMERE POSTION
Idiogram: representation of karyotype as a diagram
Types of chromosomes
metacentirc
submetacentric
acrocentric
telocentric
Group c chromosomes 6-12 are what type and X
submetacen tric
Group G 21-22 are what type and y
acrocentric
Group F 19-20 what type
metacentric
Group A 1-3 what type
1 and 3 metacentric 2 submetacentrixc
Group B Group D 13-15 what type
acrocentric
Group B what type 4-5
submetacentric
Grouo E 16-18
16 metacentric but 17 18 submetacentric
What is karyotype evolution due to
chromosomal aberratiosn
duplicTIONS, DELETIONS inversions= results in loops in meiosis
What happens when loops are formed during crossing over
Deltions and duplications occur on the gamete chromosomes for example which means fertility reduced
Bc of the iversion eg, crossing over tried to occur at correct place but in order to do so they have to form loops and in the process duplicate or delete dome bases
How can karyotype aberrations cause new species
If 2 homologous chromosomes have the same defect then fertilty same- homozygous for the defect
RESPRODUCTIVLY ISOLATED
Can carry this onto next geenration
What is robersonian translocation
fusioon of 2 acrocentric chromosomes - cause extra 21
Can cause down syndrome as inherited from from generations ago
Autopolypoploidy and allopolyploidy
Auto= all chromosomal set from same species
Allo=Chromosomal sets from close species combines
Why are polyplloidies frequent in plants
bc asexual repo is very frequent and they have no sex chromsomes
Whuch are the chrmosomes in growing oocytes NOT IN MAMMALS
Lampbrush chromsomes - prod morphogens
Loops of deciondensed chromsomes
Produce mRNA and non coding rRNA
OOplasmic granules? for segreation
What is replication withou cell divisionn
ENDOREPLICATION
Causes polyploid cells
eg polytene chromosomes in secretory cells dipteren larvae
