D 2.2

What is gene expression?

The process of building a gene product (protein) that the organism can use.

What stays unchanged during gene expression?

The genome.

What changes during gene expression?

The transcriptome and proteome.

How do epigenetic tags link genotype to phenotype?

They activate or silence genes, changing which proteins are made.

What are epigenetic tags?

Chemical modifications that activate or repress transcription.

Do epigenetic tags change DNA sequence?

No — they are reversible and do not modify DNA code.

What happens when cytosine in a promoter is methylated?

: Transcription is repressed.

What does histone methylation or acetylation do?

Can activate or repress transcription depending on the modification.

Do epigenetic tags remain after mitosis?

yes

Do epigenetic tags remain after meiosis?

No — except in genomic imprinting.

What is genomic imprinting?

Epigenetic tags that remain during gamete formation and are passed to offspring.

What can imprinting do to gene expression?

“Turn off” a strong gene that normally dominates.

What is a promoter?

DNA sequence where RNA polymerase binds to start transcription.

What are transcription factors?

Activator or repressor proteins that bind DNA to control transcription.

What is an enhancer?

DNA sequence where activators bind to increase transcription.

What is a silencer?

DNA sequence where repressors bind to decrease transcription.

How do transcription factors regulate genes?

By switching RNA polymerase “on” or “off.”

What does the 5’ cap do?

Protects mRNA from degradation.

What does the poly‑A tail do?

Increases mRNA stability; longer tails = more translation.

What happens when the poly‑A tail shortens?

mRNA is degraded by nucleases.

How do hormones affect gene expression?

They influence transcription rate and mRNA stability.

How does lactose affect gene expression in E. coli?

Lactose deactivates the repressor → genes for lactose metabolism are expressed.

How does estrogen affect gene expression?

Enters cells → binds receptors → activates genes for progesterone receptors.

Why are identical twins used to study epigenetics?

Same genome → differences in phenotype are due to environment.

Why do different cells have different proteins?

They express different mRNAs due to epigenetic regulation.

What determines phenotype?

The proteins produced from gene expression.

What is the transcriptome?

All mRNA molecules produced in a cell.

What is the proteome?

All proteins produced in a cell.

What controls which genes are expressed?

Epigenetic tags + transcription factors.

What environmental factors can influence gene expression?

Diet, hormones, stress, chemicals, and external cues.