Mutation Effects

Objectives

• Describe beneficial mutations
• Give examples of harmful mutations
• Explain gene expression
• Summarize the regulation of the lac operon

The majority of mutations have neither a positive nor negative effect. These are neutral mutations.

Beneficial mutations are essential for evolution to occur. They help organisms adapt to changes in the environment.

Mutations in bacteria allow them to survive antibiotics. Mutations lead to antibiotic-resistant strains of bacteria.

Harmful mutations may cause

• a genetic disorder
• cancer

All of your cells have the same genes, but they do not all have the same proteins.

Using a gene to make protein is gene expression.

Regulation of Gene Expression

• Chemical and structural modification of DNA
• Transcription
• Translation
• Post-transcription modification

Regulation of Gene Expression

• RNA transport
• mRNA degradation
• Post-translational modification

Gene regulation when transcription occurs involves controlling how much RNA is made.

A regulatory protein (transcription factor) regulates gene expression by binding to DNA.

Types of Regulatory Proteins

• Activator
• Repressor

Additional proteins carry out more roles.

Most prokaryotic gene regulation isn't as complicated.

Operon

An operon is a region of DNA that consists of one or more genes that code for proteins for a specific function.

Operon includes

• Promoter
• Operator (region where regulatory proteins bind)

lac operon

The lac operon consists of

• A promoter
• An operator
• 3 genes for enzymes to digest lactose
• (regulated by lactose)

When lactose is absent a repressor protein binds to the operator. This blocks the binding of polymerase to the promoter.

When lactose is present the repressor protein does not bind, allowing the polymerase to bind and begin transcription....

As a result, the lac genes are expressed, and lactose is digested.

This is simple compared to eukaryotic gene regulation.

Enhancers are distant regions of DNA that loop back to interact with a promoter.

The sequence TATAAA (TATA box) is commonly found in the promoter region.

Homeobox genes regulate development. They code for proteins that switch on a series of developmental genes.

In insects, hox genes ensure that limbs are in the correct locations.

Cancer causing mutations occur

• in tumor suppressor genes
• in proto-oncogenes