Genetics - 12

nucleoid

compact double

Hu and HNS proteins

small positively charged proteins that can bond ionically to the phosphate backbone of DNA

bacteria is supercoiled and has 3 distinct parts

Linking number

the number of turns or times two strands of DNA cross over each other

topoisomers

identical molecules that differ only in linking number

topoisomerases

enzymes that cut one or both strands of DNA and wind or unwind the helix before resealing the ends

What direction does supercoiling occur

opposite of the underwinding

Polytene chromosomes

many stranded chromosome with distinctive banding that has undergone numerous rounds of DNA replication without separation

chromomeres

bands on chromosomes

puff region

localized uncoiling and visible manifestations of a high level of gene activity

Lampbrush chromosomes

have extensive looping

chromatin

decondensed DNA

histones

positively charged proteins associated with DNA

chromatin remodeling

chromatin changing its structure

acetylation

opens up chromatin fibers

methylation

associated with increased gene activity

histone tails

important for histone modification such as acetylation, methylation, and phosphorylation

euchromatin

uncoiled and active

heterochromatin

condensed and inactive

c banding

only centromeres are stained

g banding

differential staining along length of chromosome

satellite DNA

highly repetitive with short repeats

Centromeres

heterochromatic region at which sister chromatids remain attached after replication and site where spindle fibers attach

Telomeric DNA

short tandem repeats that contribute to the stability and integrity of the chromosome

Middle repetitive sequences

recognized by Cot analysis, referred to as minisatellites

Short interspersed elements (SINES) and long interspersed elements (LINES)

dispersed throughout genome, generated via retrotransposons an RNA intermediate

pseudogene

nonfunctional gene with sequence homologous to known structural gene present elsewhere in the genome