Lecture 18- Regulation of Gene Expression II

Question 1

eukaryotic transcription is more complex than prokaryotic transcription

Answer 1

packaging of DNA into chromatin provides additional opportunities for regulation of gene expression in eukaryotes

Question 2

eukaryotic DNA is packaged into chromatin

Answer 2

net result of condensation during interphase and mitosis: each DNA molecule has been packaged into a mitotic chromosome that is 10,000x shorter than its fully extended length

Question 3

interphase packaging of DNA

Answer 3

short region of DNA double helix -> “beads on a string” form of chromatin -> chromatin fiber of packed nucleosomes

Question 4

“beads on a string” chromatin

Answer 4

• linker DNA is “string”
• core histones of nucleosome is “bead”, 11 nm diameter
• histone H1 binds to linker DNA
• nucleosome includes ~200 nucleotide pairs of DNA
• nuclease digests linker DNA -> released nucleosome core particle
• -dissociates with high concentration of salt into histome octamer and 147 nucleotide pair DNA double helix
• octamers further dissociate into H2A, H2B, H3, and H4

Question 5

eukaryotic DNA is packaged into chromatin

Answer 5

• tight packaging of chromatin inhibits transcription
• open chromatic facilitates transcription
• proteins that influence chromatin structure can regulate gene expression
  1. chromatin remodeling complexes
  
  2. histone modification enzymes

Question 6

chromatin remodeling complexes

Answer 6

-uses energy of ATP to reposition the DNA wrapped around the nucleosomes
A. phosphorylates ATP to catalyze nucleosome sliding (tightens DNA) -> condensed chromatin, DNA is less accessible to other proteins -> INHIBITS transcription
B. phosphorylates ATP in repeated rounds of nucleosome sliding (loosens DNA) -> decondensed chromatin, DNA more accessible to other proteins -> FACILITATE transcription