16. Regulation of Expression

Eukaryotic Chromatin Modifications

Histone Methylation and Acetylation

2.   Histone acetylation and histone methylation

 No. This is a modification of chromatin that does not entail a change in the DNA sequence. 

Consider that epigenetics pertains to alterations in chromatin other than changes in the underlying DNA sequence.

Which of the following statements is not associated with epigenetic inheritance?

 positioning related genes near each other 

 No. You are probably thinking of prokaryotic operons. 

 No. Even if this were true, it would not be a general mechanism of gene regulation. 

 No. Genetic recombination usually occurs only during meiosis and is not a general mechanism of gene regulation. 

 allowing unpacked genes to be eliminated from the genome 

 No. With certain rare exceptions, eukaryotes tend not to eliminate genes from their genome. 

Consider how each of the choices might affect the ability of RNA polymerase to transcribe RNA.

In eukaryotes, DNA packing seems to affect gene expression primarily by __________.

Activate transcription in that region, RNA Polymerase can easily interact with DNA.

Repressed transcription in that region, RNA Polymerase cannot easily interact with DNA.

No change in chromatin structure or transcription rates.

Histone acetylation is associated with:

Epigenetics

Histone Acetylation

 causing tighter packing of the chromatin at the target gene, thereby inhibiting transcription 

 No. Acetylation promotes a more open chromatin structure, making DNA more accessible for transcription. 

 causing looser packing of the chromatin at the target gene, thereby inhibiting transcription 

 No. Acetylation causes looser packing of the chromatin, but this makes the DNA more accessible for transcription 

 causing tighter packing of the chromatin at the target gene, thereby enhancing transcription 

 No. Acetylation causes looser packing of the chromatin. Tightly packed chromatin is less easily transcribed. 

 causing tighter packing of the chromatin at the target gene, thereby inhibiting translation 

 No. Acetylation causes looser packing of DNA. DNA packing does not affect translation. 

 causing looser packing of the chromatin at the target gene, thereby enhancing transcription 

How does acetylation affect gene expression?

A scientist clones a regulatory gene that is involved in controlling the expression of other genes and discovers that the regulatory gene encodes an enzyme that acetylates histones. It is likely that this enzyme regulates gene expression by __________.

 No. Looped domains are higher-order structures in which the DNA is more tightly packed. 

No. Heterochromatin refers to clumps of tightly packed chromatin observed in the interphase nucleus.

 No. Genes are functional units of heredity. The "beads" are structural units of DNA packaging. 

 No. The nucleoid is the region in a prokaryotic cell that contains the bacterial chromosome. 

Review the structure of eukaryotic chromatin.

In the "beads on a string" structure of unfolded chromatin, the "beads" are __________.

 No. The chromatin arrangement inhibits the access of the RNA polymerase to the promoter of the gene. 

 No. This would promote greater packaging of DNA into nucleosomes. 

 No. Although removal of methyl groups may serve to activate genes that have been turned off by DNA methylation, this would not help to lessen the coiling of chromatin and give access to the DNA by transcription factors and RNA polymerase.  

What process can facilitate the relaxation of DNA packaging?

The expression of a gene located in a tightly coiled region of DNA can be promoted by __________.

Histones in that region are deacetylated.

DNA is methylated in the regulatory region of the gene.

The chromatin structure is tightly packed.

Which of the following causes transcription to be increased for a specific gene?

Transcriptional repression by methylation of DNA involves the methylation of which nucleotide?

Chromatin Remodeling in Eukaryotes

 No. Histone acetylation is sometimes associated with enhancement of transcription, but both DNA methylation and histone deacetylation tend to repress transcription. 

 No. DNA methylation is involved in setting up patterns of genomic imprinting. 

 No. Transcription factors are protein complexes. DNA methylation and histone deacetylation generally repress transcription. 

 No. An enhancer is a nucleotide sequence in the DNA. 

What is normally associated with DNA methylation? What is normally associated with histone acetylation?

In some cases, DNA methylation and removal of acetyl groups from histones (i.e., deacetylation) combine to __________.

DNA Methylation

Eukarytotic Gene Regulation Chromatin and Transcription Factors

Animation: DNA Packing

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Bozeman Science

1. Introduction to Biology

2. Chemistry

3. Water

4. Biomolecules

5. Cell Components

6. The Membrane

7. Energy and Metabolism

8. Respiration

9. Photosynthesis

10. Cell Signaling

11. Cell Division

12. Meiosis

13. Mendelian Genetics

14. DNA Synthesis

15. Gene Expression

17. Viruses

18. Biotechnology

19. Genomics

20. Development

21. Evolution by Natural Selection

22. Evolution of Populations

23. Speciation

24. History of Life on Earth

25. Phylogeny

26. Prokaryotes

27. Protists

28. Plants

29. Fungi

30. Overview of Animals

31. Invertebrates

32. Vertebrates