chromosomal structure- eukaryotes vs prokaryotes

Question 1

How does DNA become supercoiled

Answer 1

• cut is made in circular DNA
  strand rotates 360 degrees
• DNA ligase seals nicks

Question 2

how is bacterial chromosome formed

Answer 2

• DNA is folded and supercoiled with the help of RNA and proteins
• circular unfolded protein turns to 40-50 loops turns to supercoiled and folded

Question 3

bacterial chromosomes

Answer 3

contain circular molecules of DNA segregated into about 50 domains

Question 4

Chromosome structure in prokaryotes

Answer 4

• monoploid
• DNA is condensed more than 1000x

Question 5

chromosome structure in eukaryotes

Answer 5

• diploid
• haploid DNA and genome
• ## total length of diploid genome = 2 meters

Question 6

components of eukaryotic chromosomes

Answer 6

• ONE large linear molecule of DNA
• 5 histones
• a divergent group of non-histone proteins

Question 7

chromatin

Answer 7

DNA + histones + protein
- DNA is one of the most negative molecules in the cell and attracts the positive proteins (and histones)

Question 8

First level of DNA packaging: nucleosomes

Answer 8

• referred to as beads on a string
• nucleosome core- (consistant)
• linker DNA varying in length from 8 to 114 nucleotide pairs (not consistent)

Question 9

nucleosome core and complete nucleosome

Answer 9

consists of 2 molecules each of 4 histones - 8 histones total (octomer)
- complete nucleosome contains histone H1 (fifth histone - like a glue that keeps everything together)

Question 10

Second level of DNA packaging: 30 nm chromatin fiber

Answer 10

• fits all 4 11nm cores into 30nm wide space

Question 11

third level of DNA packaging: inter-phase chromosomes (300nm fibre)

Answer 11

• looped and threaded instead of linear
• in this phase cell doesn’t need to divide (mitosis)
• chromosome scaffold forms when non-histone proteins are anchored
• DNA cannot be too compact because transcription factors have to access it to express your genes

Question 12

simplest vs most complex level of chromosomes

Answer 12

simplest: chromatin is double-stranded helical structure of DNA
most complex: tight coiling of the 250nm fibre produces the chromatid of a chromosome

Question 13

Why are histones significant in proteins

Answer 13

without them DNA would unravel

Question 14

metaphase chromosome

Answer 14

during mitosis the chromosomes undergo another stage of packaging
- DNA is slightly unwound