Epigenetics

What is the primary function of DNA methylation in epigenetics?

• To increase the rate of DNA replication

• To regulate gene expression

• To repair damaged DNA

• To facilitate RNA splicing

Answer explanation

The primary function of DNA methylation in epigenetics is to regulate gene expression. By adding methyl groups to DNA, it can silence genes or alter their activity, influencing cellular functions and development.

Histone modification can affect gene expression by:

• Changing the DNA sequence

• Altering the chromatin structure

• Increasing the number of chromosomes

• Deleting histone proteins

Answer explanation

Histone modification alters the chromatin structure, which can either promote or inhibit gene expression. This change in structure affects how tightly DNA is packaged, influencing accessibility for transcription.

Which of the following is a common type of histone modification?

• Phosphorylation

• Glycosylation

• Acetylation

• Methylation

Answer explanation

Acetylation is a common histone modification that alters chromatin structure and regulates gene expression. Phosphorylation and methylation are also modifications, but acetylation is particularly well-known for its role in transcriptional activation.

Non-coding RNAs are primarily involved in:

• Coding for proteins

• Regulating gene expression

• DNA replication

• Protein degradation

Answer explanation

Non-coding RNAs play a crucial role in regulating gene expression by interacting with DNA, mRNA, and proteins, influencing various cellular processes. They do not code for proteins, replicate DNA, or degrade proteins.

What is the role of X-inactivation in female mammals?

• To double the number of X chromosomes

• To silence one of the two X chromosomes

• To activate both X chromosomes

• To delete one X chromosome

Answer explanation

X-inactivation is a process in female mammals where one of the two X chromosomes is silenced to ensure dosage compensation. This prevents an excess of X-linked gene products, making the correct choice 'To silence one of the two X chromosomes'.

Which of the following is a characteristic of microRNAs?

• They are long, coding RNAs

• They are short, non-coding RNAs

• They are involved in DNA replication

• They are proteins

Answer explanation

MicroRNAs are short, non-coding RNAs that play a crucial role in regulating gene expression. They are not long coding RNAs, proteins, or involved in DNA replication, making the correct choice "They are short, non-coding RNAs."

How do microRNAs typically regulate gene expression?

• By binding to DNA and altering its sequence

• By degrading mRNA or inhibiting its translation

• By enhancing protein synthesis

• By modifying histones

Answer explanation

MicroRNAs regulate gene expression primarily by binding to mRNA, leading to its degradation or inhibiting its translation into protein. This mechanism effectively reduces the levels of specific proteins in the cell.

What is the role of long non-coding RNAs (lncRNAs) in gene regulation?

• They code for proteins

• They act as templates for DNA replication

• They regulate gene expression at the transcriptional and post-transcriptional levels

• They degrade mRNA

Answer explanation

Long non-coding RNAs (lncRNAs) play a crucial role in regulating gene expression by influencing transcription and post-transcriptional processes, unlike coding RNAs which produce proteins.

Which of the following statements about X-inactivation is true?

• It occurs randomly in all cells of male mammals

• It results in the formation of a Barr body

• It leads to the expression of both X chromosomes in females

• It is a reversible process

Answer explanation

X-inactivation occurs in female mammals to equalize gene dosage between sexes, leading to the formation of a Barr body from the inactivated X chromosome. The other statements are incorrect.

What is the consequence of histone acetylation on chromatin structure?

• It condenses chromatin, making it less accessible

• It relaxes chromatin, making it more accessible

• It deletes histone proteins

• It causes DNA methylation

Answer explanation

Histone acetylation adds acetyl groups to histones, which relaxes the chromatin structure. This relaxation makes the DNA more accessible for transcription and other processes, facilitating gene expression.