Lecture 1/31/25 Flashcards
What is epigenetics?
Heritable gene expression changes that do not alter the DNA sequence.
What are histones?
Proteins that package and organize DNA into nucleosomes.
Do bacteria have histones?
No, but they have histone-like proteins.
How might an endonuclease react with naked DNA versus chromatin?
It cleaves naked DNA easily, but chromatin structure protects DNA from cleavage.
Briefly describe the structure/components of a nucleosome.
A nucleosome consists of DNA wrapped around a histone octamer (H2A, H2B, H3, H4).
What is linker DNA?
DNA between nucleosomes that connects them.
What makes H1 different from other histone proteins?
H1 binds to linker DNA, stabilizing nucleosome structure and promoting chromatin compaction.
Why do histone proteins have a high proportion of lysine and arginine in their N-terminal tails?
These positively charged residues interact with negatively charged DNA, stabilizing chromatin.
How do histones affect gene expression?
Histone modifications regulate DNA accessibility for transcription.
What is used to help nucleosomes move?
Chromatin remodeling complexes reposition nucleosomes using ATP.
What is the difference between chromodomain proteins and bromodomain proteins?
Chromodomain proteins bind methylated histones; bromodomain proteins bind acetylated histones.
What is the ‘histone fold’ and what does it do?
A structural motif in histones that helps form the histone octamer and bind DNA.
What is the difference between trans and cis movement of histones?
Cis movement alters nucleosome spacing; trans movement recruits proteins to modify chromatin.
Why is modification important with histone tails?
Histone tail modifications regulate gene expression and chromatin structure.
What types of histone modifications are there?
Acetylation (loosens chromatin), methylation (activates or represses), phosphorylation, and ubiquitination.
