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How does passing on of information differ between genetic and epigenetic inheritance?

Genetic inheritance passes on exact copies of the original code sequence, whereas epigenetic inheritance usually very limited and may not pass on at all.


Describe position effect variegation.

A breakage event in chromatin leading to previous euchromatin areas (transcribing genes) being incorporated into heterochromatin and vice versa.


What is the position effect in regards to genes.

Position of genes, in euchromatin or heterochromatin, determines whether the gene is expressed or not.


What nucleosomal histone-modifications can be found on lysine and serine?

Lysine: acetylation, monomethylstion-trimethylation
Serine: phosphorylation


Where does most histone modification take place?

On the "relatively unstructured N-terminal "histone tails".


What enzymes are responsible for histone modification?

HATs (histone acetyl transferases) and HDACs (histone deacetylase complexes). Histone methyl transferase and histone demethylases.


How are the histone modification enzymes recruited?

Rough action of gene regulatory proteins.


What's the effect of acetylation of lysine on the histone N-terminal tail?

Loosening of chromatin structure through loss of charge.


What is the main purpose of histone modification?

Attraction of proteins that stretch chromatin appropriately.


What are the functions of histone variants and when are they transcribed?

They mediate added function of the histone such astrascriptional activation, centromere function and kinetochore assembly, FNA repair and rcombination, gene expression and chromosome segregation, transcriptional repression ans X-chromosome activation. They're transcribed throughout the interphase, vs. most histones in S phase.


What is the histone code hypothesis?

The hypothesis of histone covalent modification (extending, mosified histone tails) and variation being a code, read by code-reader complexes that modify bucleosome function (transcription, chromatin form etc.).


How are specific chromatin modifications spread for long distances along a chromosome?

With the aid of a reader-writer complex. A gene regulatory protein binds to free DNA, attaches a histone modifying enzyme (writer). A code-reader protein then reads the modification, a new writer enzyme attaches and so on, creating reader-writer complexes.


How is chromatin remodeling limited?

Through barrier sequences in DNA, ex. HS4. A barrier sequence contains for example a cluster of binding sites for histone acetylase enzymes (acetylases and deacetylases), which moderates the possibility of methylation of lysine.


Explain how histone reader-writer complexes can cause chromatin condensation.

ATP-dependent chromatin remodeling complexes attach to the junction of the reader-writer complex formed as reading enzymes replace writing enzymes. The modification thus spreads along the chromatin.


How are histones involved in centromere formation?

The kinetochore-attaching histone is modified in H3. Other histones around are densely packed.


What defines the centromere?

Repeats of A-T-rich alpha satellite DNA. However, this sequence can be missing and rather it is the protein complex associated with the centromere that seems most essential.


What is the role of the initial seeding event in centromere formation?

It is required for de noco centromere formation. It involves histone with the CENP-A variant of histone H3 and happens in humans readily on the A-T-rich repeating satellite DNA-sequences.


Describe the formation of the centromere.

1. Centric heterochromatin displays banding of CENP-A H3 histone areas with corresponding CENP-A negative areas, dimethylated at lysine 4.
2. Centric chromatin coils form so that CENP-A histone H3 areas contact the inner kinetochore plate.
3. Pericentric heterochromatin starts at either end of centric heterochromatin.


How are the centromeric structures of chromatin inherited in replication?

Modified histone components remain bound to replicated DNA and the bind their appropriate components (CENPA-A H3 remains with the DNA).


How are hetero-eu-patterns transferred to replicated DNA.

Histone modification is activated in replicated DNA by specific regulator sequences and modifying proteins, securing passing on of original structure.


What's an alternative to chromatin-associated protein for epigenetic inheritance?

Networks of signaling molecules that control gene expression.


What is a lampbrush chromosome?

The theorized structure of all eucarytotic chromosomes in interphase. Paired sister chromosomes intertwine. Each chromosome has a structure where bigger loops alternate with shorter, more condensed (wavy chromomeres) areas of chromatin. There are 4 copies of each loop in every diploid cell. Most of the DNA is contained outside of the loops. Proteins forms scaffolding for the chromatin to rest on.


What are polytene chromosomes and what are they useful for in DNA research.

Multiple copies of the same chromosome lined laterally and joined to a large unit. Antibody staining allows for investigating of chromayin associated regulatory proteins.


What is a chromosome puff in relation to polytene chromosomes?

A stretch of uncondensed polytene chromosome, visible through microscopy.


What can be said about homologuous chromosome position in the nucleus in general and during very active transcription.

The position of the two homologuous chromosomes don't necessarily coincide but during active transcription they diffuse to nuclear neighbourhoods for gene expression.


How is the eu-heterochromatin barrier enforced?

By barrier proteins:
1. Tethering to nuclear pore complex
2. Binding to nucleosomes
3. Recruitment of histone-modifying enzymes hinders heterochromatin zone from spreading


How are reactions in the nucleus effectivated?

Through macromolecular forming of distinct biochemical environments (proteins polymerize with attached components).


Name two purposes for the highly condensed form of DNA in chromosomes.

1. Easy separation of sister chromatids (they're disentangled)
2. Keeps fragile DNA from breaking during sister chromatid separation


What is the role of condensins?

The condensin proteins aid in compactin of DNA into chromosomes.


What are the different levels of DNA packing in chromosomes?

1. DNA double helix
2. Bead-on-a-string chromatin
3. 30 nm chromatin fibre
4. chromatin fiber waves 300 nm
5. condensation of waving