Genetics - Exam 2 - Gene Regulation

Gene regulation

Control of when, where, and how much a gene is expressed.

Promoter

DNA sequence where RNA polymerase binds to start transcription.

Regulatory sequences

DNA elements that increase or decrease transcription (enhancers, silencers).

Transcription factors

Proteins that bind DNA and influence transcription (activators, repressors).

Effector molecules

Small molecules that interact with transcription factors to turn genes on or off.

Epigenetics

Heritable regulation of gene activity without changing DNA sequence.

Methylation

Addition of methyl groups to DNA, often silencing gene expression.

Lac operon

Bacterial gene system that controls lactose digestion.

LCT gene

Human gene that encodes lactase enzyme.

Explain why gene expression must be regulated

• Genes must be turned on/off at the right place and time.

• Different cells need different proteins depending on their role.

• Regulation conserves energy and resources.

Explain how gene regulation accounts for the physical differences among different cell types and in different environments

• All cells have the same DNA, but express different subsets of genes.

• Regulation allows cells to adapt to environmental changes

Explain the role of promoters, regulatory sequences, transcription factors, and methylation in controlling when and where genes are transcribed

• Promoters → DNA regions where RNA polymerase binds to start transcription.

• Regulatory sequences → Enhancers increase transcription, silencers decrease it.

• Transcription factors → Proteins that bind DNA to turn genes on or off.

• DNA methylation → Chemical tags on DNA that usually block transcription (silence genes).

Describe how bacteria regulate production of β-galactosidase (the enzyme used for digestion of lactose) in bacteria (the lac operon)

• No lactose present → A repressor binds the operator, blocking transcription of β-galactosidase.

• Lactose present → Lactose (allolactose) binds the repressor, causing it to detach → transcription of β-galactosidase begins.

• Glucose present → The cell prefers glucose, so transcription of the lac operon is low.

• Low glucose + lactose present → High cAMP activates CAP protein, which helps RNA polymerase bind → maximum production of β-galactosidase.

Describe how mammals regulate production of lactase (the enzyme used for digestion of lactose) and contrast this mechanism with that of bacteria

• Mammals regulate lactase production based on developmental stage and epigenetic changes (long-term control).

• Bacteria regulate β-galactosidase production based on nutrient availability in the environment (short-term control).

Explain how mutations in regulatory sequences can affect an organism's phenotype and use human lactose digestion as an example

• Mutations in regulatory regions (not coding sequences) can change gene expression without altering the protein itself.

• Phenotype - Populations with these mutations can digest milk into adulthood.