Mollecular Flashcards
(21 cards)
what is the charge of the DNA and how it forms the NUCLEUSOME?
Negatively charged DNA loops twice around the positively charged histone octamer to form nucleusome “beads on a string”.
How DNA exists where and in what form?
DNA exists in the condensed, Chromatin form in order to fit into the NUCLEUS.
how does the nucleosome look like?
it looks like beads on a string.
what amino acids are in the Histones?
Histones are rich in the amino acids Lysine and Arginine (remember Histones have LA in them)
what histones are in the nucleosomes ?
H2A, H2B, H3 and H4 ( double each = x2 ) “ remember nucleosomes have all the histones except 1 which is H1”
what does H1 role in the DNA?
H1 binds to the nucleosome and to “linker DNA”, thereby stabilising the chromatin fibre. “ remember it binds so it means stability to the chromatin”.
in what cell cycle and phase, chromosomes are formed?
In Mitosis, DNA condenses to form chromosomes.
synthesis of DNA and Histones ?
DNA and histone synthesis occur during S phase.
condensed and appear darker on EM
Heterochromatin
transcriptionally inactive and sterically inaccessible?
Heterochromatin
HeteroChromatin
Highly Condensed
inactive X chromosomes and they are HeteroChromatin
Barr Bodies
Less Condensed, appears lighter on EM
EuChromatin
Transcriptionally active, sterically accessible
EuChromatin
EuChromatin
Eu= true, “ truly transcribed”
DNA Methylation
favours C “cytosine”.
DNA Methylation
template strand Cytosine and Adenine are Methylated in DNA Replication, which allows Mismatch Repair enzymes to distinguish between Old and New strands in Prokaryotes.
what does DNA Methylation at CpG islands do to the transcription?
DNA Methylation at CpG islands represses transcription. “remember CpG Methylation Makes DNA Mute”
Methylation that causes Reversible repression of DNA transcription?
Histone Methylation
Histone Methylation
Usually reversibly represses DNA transcription, but can Activate it in some cases depending on methylation Location.
Histone Acetylation
makes DNA Active, by relaxing the DNA coiling, allowing for transcription. “ remember Acetylation = Active”
