BIOQUIMICA Flashcards
(15 cards)
Why does DNA exist in chromatin form inside the nucleus?
Because it needs to be compacted to fit inside the cell nucleus.
How is DNA organized in chromatin?
It wraps twice around a histone octamer, forming nucleosomes, giving it a ‘beads on a string’ appearance.
Which protein stabilizes the chromatin fiber?
Histone H1, which binds to the nucleosome and linker DNA.
Why does DNA have a negative charge?
Because of the phosphate groups in its structure.
Why do histones have a positive charge?
Because they contain amino acids like lysine and arginine, which have a positive charge and help bind DNA.
What is heterochromatin, and how does it appear under an electron microscope?
It is the more condensed form of chromatin, appears darker, and is transcriptionally inactive.
Where can examples of heterochromatin be found in the nucleus?
In Barr bodies (inactive X chromosomes) at the periphery of the nucleus.
What is euchromatin, and how does it appear under an electron microscope?
It is the less condensed form of chromatin, appears lighter, and is transcriptionally active.
What effect does DNA methylation have on gene expression?
It usually represses gene transcription.
What happens when CpG islands in a gene promoter are methylated?
Gene transcription is silenced.
What diseases are associated with abnormal DNA methylation?
Aging, carcinogenesis, and Fragile X syndrome.
What effect does histone methylation have on DNA transcription?
It usually represses transcription, but in some cases, it can activate it depending on the location of methyl groups.
What effect does histone acetylation have?
It relaxes chromatin, facilitating gene transcription.
What enzyme is responsible for histone deacetylation, and what is its effect?
Histone deacetylase (HDAC), which causes tighter DNA coiling and reduces transcription.
What disease might be linked to histone deacetylation?
Huntington’s disease, due to altered gene expression.
