chromatin & chromosomes

what mediates the relaxing of dna?

topoisomerase

bacterial (chromosomal) dna

-instead of nucleus, bacterium has a nucleoid region

-dna forms loop domains (supercoiled) each of which is anchored by dna binding proteins

bacterial dna- supercoiled

topoisomerases catalyze changes in chromatin configuration

-most: top. - supercoild dna, nucleoid associated proteins (NAPs) hold in proper conf.

plasmids

small circular piece of dna that replicates independently 

-conjugation: plasmids replicated, and copies transferred to another bacterium 

(+) vs (-) supercoil

+: overrotated

-: under

plamids do not contain essential genes but survival genes

-resistance factors: proteins that protect against antibiotics

-fertility factors: proteins that enable them in conjugation w/ other bac. more eff.

supercoiling

-dna wound around 8 histone proteins: nucleosome

-chromatosome: nucleosome plus H1 (histone 1 protein locks the dna around the histones)

-stretch of linker dna connects chromoatosomes

-scaffold proteins help hold dna together

-chromatin: combo of dna and proteins

human acrocentric chrom

13,14,15,21,22 (important for Robertsonian translocation)

structure of chromosome

p arm telomere

centromere

q arm telomere

4 types of chrom

metacentric: normal

submetacentric: shorter p, longer q

acrocentric: very short p, much longer q

telocentric: only q

*conf only acquired after s phase

a chromosome is defined by

the number of centromeres

polycentric chromosomes - some organisms

chromosomes have centromeres distributed along the chromosome; spindle fibers attach all along the chromosome

chromosome has characteristic repeated sequence

centromere has a lot of repeated sequences

diff organi. have diff centromeric sequences

specific histones make up the centromere

contain variant form of histone H3 (CENH3) and adopt a characteristic chrom, confi. - what allows them to serve their function

spindle fibers

kinetochore (specialized protein structure)

spindle fibers bind w/ kinet. so 2 members of each homologous chrom. pair can get pulled apart

anaphase

telomeres must be stabalized

human telomere repeat sequence: 5”-TTAGGG-3”

-one strand projects beyond the other strand- protection of telomere protein binds to the single stranded dna

-multi protein complex (shelterin) binds telomeres and keeps them from being repaired (non-homologous end joining, end-to-end fusion)

euchromatin & heterochromatin

-euch: less condensed dna region (still supercoiled), most genes located here active

-hetero: more condensed, genes usually inactive 

-chrom can break + rearrange themselves: if rearrangement moves a gene too close to hetero region, can silence gene (position effect)

-moving dna from areas of euch to hetero viceversa drastically changes expression level but not sequence, genes go from active to inactive   

inversion of chrom

flipping of genes changes gene expression 

position effect

remove a segment + put histone in another location which changes expression

humans have 46 chrom

arranged in 23 pairs

-22 are autosomes (1: largest, 22: smallest)

-1 pair sex chrom: xx and xy

karyotype

refers to picture or individual’s chrom status

-total # of chrom, sex chrom, any abnormalities (normal F: 26, xx)

M w/ down syn: 47, xy,, +21

F w/ turner syn: 45, x

M missing chrom 6: 45, xy, -6sa

aneuploidy

not having standard # of chrom for your species

-nullisomy: no copies of specific chom

monosomy: 1 copy of a specific chrom

disomy: 2 copies

trisomy: 3 copies

tetrasomy: 4

polyploidy

having 1 or more extra full sets of chrom

-haploid: having 1 set

diploid: 2 sets

triploid: 3 sets

tetraploid: 4 sets