Question 1

What are the three main mechanisms of epigenetic regulation?

Accepted Answer

Epigenetic regulation occurs through DNA methylation, histone modification, and RNA-based processes. DNA methylation adds methyl groups to specific bases, altering transcription factor binding. Histone modification adds chemical groups to histone proteins, affecting chromatin folding and accessibility. RNA-based processes, including microRNAs and small interfering RNAs, alter chromatin structure and gene translation.

Question 2

How does DNA methylation prevent gene transcription?

Accepted Answer

DNA methylation adds methyl groups to specific DNA bases, which blocks regulatory proteins like transcription factors from binding to DNA. When transcription factors cannot attach to the promoter region, the transcription machinery is prevented from initiating gene transcription, effectively silencing the gene.

Question 3

What is X-chromosome inactivation and why does it occur?

Accepted Answer

X-chromosome inactivation is the random silencing of one X chromosome in female mammals during early development. Females have two X chromosomes while males have one X and one Y. Since the X chromosome contains significantly more genes than the Y chromosome, inactivating one X prevents excess gene expression in females, maintaining balanced expression levels.

Question 4

What are CpG islands and how are they affected in cancer?

Accepted Answer

CpG islands are stretches of cytosine and guanine nucleotides in gene promoter regions. In healthy cells, CpG islands remain unmethylated. However, in cancer cells, CpG islands in tumor suppressor genes and cell cycle regulators become excessively methylated, silencing these protective genes and allowing uncontrolled cell division.

Question 5

How do histone modifications affect chromatin structure and gene expression?

Accepted Answer

Histone modifications add chemical groups such as methyl or acetyl groups to histone proteins that DNA wraps around. These modifications alter how tightly chromatin is folded—either opening it up to make genes more easily transcribed or condensing it to inhibit transcription, thereby regulating gene accessibility and expression.

Question 6

Can epigenetic changes be inherited across generations?

Accepted Answer

Yes, epigenetic modifications are passed down to daughter cells during cell division and can sometimes be inherited through generations of individuals. These heritable changes create long-term phenotypic changes without altering the underlying genetic sequence, allowing environmental factors like diet, stress, and toxic exposure to have lasting effects.

Question 7

How do environmental factors influence epigenetic regulation?

Accepted Answer

Environmental factors such as diet, exposure to toxic substances, and stress can trigger epigenetic changes in gene expression. These factors activate or suppress the three main epigenetic mechanisms—DNA methylation, histone modification, and RNA-based processes—allowing external conditions to alter how genes are expressed without changing the DNA sequence itself.

Regulacja epigenetyczna

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