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BIO SCI 99 Study Guide - Midterm Guide: Nucleosome, Histone H2B, Chromatin

Biological Sciences
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Lecture4. DNA Packaging
DNA packaging What’s the problem?
1. Human cells contain 46 chromosomes. Their combined length is nearly two meters. All of
this DNA must be packed into a nucleus with a diameter as small as 7 microns, while
ensuring organized access to its information.
2. Do prokaryotes and viruses have the same problem?
Levels of DNA compaction
1. Terminology: chromatin.
2. Technique: DNA gel electrophoresis and SDS-PAGE. Just know the general concepts and how
to interpret the gels.
3. Nucleosome level
i) The basic unit of condensation.
ii) What are the components of a nucleosome?
iii) Be able to interpret the chromatin digestion experiment (Figure 10-1).
iv) What are the functions of: the core histones (H2A, H2B, H3, H4), the histone octamer,
the linker histone (H1), the histone N-terminal tails?
v) Acetylation of the N-terminal tails is generally associated with opening chromatin and
allowing transcription. It is thought that acetylation weakens nucleosome-nucleosome
interaction (which are mediated through interactions between N-terminal tails).
4. 30 nm filament level
i) What is the relationship between the core histones, the linker histone and the 30 nm
5. Next level: Looping of the 30 nm filament along a chromosomal protein scaffold.
6. And higher levels of compaction that are still being worked out…rosettes?
7. Top level: the chromosome
8. What effect does DNA packing have on gene expression?
9. Compare the gene transcription levels between genes on naked DNA, beads-on-a-string
DNA (DNA bound with core histones), and 30 nm filament DNA.
10. Be able to interpret Figure 10-10.
11. How do prokaryotes compact their DNA? Looking for two main points here
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