Lecture 2/3/25 Flashcards
Why are the R groups of histones facing each other?
To stabilize the histone core structure, keeping DNA wrapped around nucleosomes.
What part of the amino acid chain does DNA interact with?
The positively charged lysine and arginine residues on histone tails.
At what point in the cell cycle do chromosomes condense?
During prophase of mitosis.
How does chromosome condensation happen?
H1 histone stabilizes linker DNA, promoting chromatin compaction into higher-order structures.
What is the difference between trans and cis movement of histones?
Cis movement shifts histones along the same DNA region; trans movement relocates histones to a different DNA region.
What are the effects of ubiquitination?
H2A ubiquitination represses transcription, while H2B ubiquitination activates transcription.
What do chromodomains do?
They recognize and bind methylated histones, often leading to transcriptional repression.
What do bromodomains do?
They recognize and bind acetylated histones, promoting transcription by loosening chromatin.
What do HAT proteins do?
Histone acetyltransferases (HATs) add acetyl groups to histones, loosening chromatin and activating transcription.
What do HDAC proteins do?
Histone deacetylases (HDACs) remove acetyl groups, tightening chromatin and repressing transcription.
At what point in the cell cycle are histones made?
During the S phase to package newly replicated DNA.
How are histones distributed during DNA replication?
H3-H4 tetramers stay on one strand, while H2A-H2B dimers are removed and reassembled on both strands.
What happens to H2A and H2B during replication?
They are displaced from DNA and later reassembled onto the newly synthesized strands.
What must be done to new histones added to the DNA strands?
They must be post-translationally modified (acetylation, methylation, phosphorylation) to match parental histones.
