Lecture G14 (Prokaryotes vs Eukaryotes)

In prokaryotes, transcription and translation are coupled

True. They occur simultaneously in the cytoplasm, allowing faster regulation of gene expression

How do prokaryotes reproduce?

By binary fission, an asexual process where the chromosome replicates, the cell elongates, and the membrane pinches inward to form two identical daughter cells

How many origins of replication do bacteria have?

One origin of replication

In prokaryotic replication, how does replication proceed from the origin?

Bidirectionally, forming two replication forks until they meet

Are the fundamental mechanisms of DNA replication similar in prokaryotes and eukaryotes?

Yes, though prokaryotes have one origin and eukaryotes have many

What enzyme starts transcription in prokaryotes by binding the promoter?

RNA polymerase

Do prokaryotes modify mRNA (splicing, 5’ cap, poly-A tail)?

No. mRNA is immediately ready for translation

Why do antibiotics target bacterial ribosomes without harming eukaryotic cells?

Because prokaryotic ribosomes are smaller and structurally different

Two key differences between prokaryotic and eukaryotic cells

Prokaryotes

• no nucleus

• Single circular DNA

Eukaryotes

• nucleus present

• Multiple linear chromosomes

What is an operon?

A cluster of prokaryotic genes under control of a single promoter and operator

What does the operator do?

Acts as a regulatory switch controlling RNA polymerase access to genes

What is the function of a repressor?

A protein that binds the operator to block transcription (negative regulation)

Is the trp operon usually on or off? What turns it off?

Usually on; turned off when tryptophan binds the repressor and activates it

Is the lac operon usually on or off? What turns it on?

Usually off; turned on when allolactose (inducer) inactivates the repressor

What defines negative gene regulation?

A repressor prevents transcription (trp and lac operons both use this)

What activates positive regulation in the lac operon?

CRP bound to cAMP enhances RNA polymerase binding when glucose is low

Inducible operons typically control which type of pathway – catabolic or anabolic?

Catabolic (breakdown pathways; e.g., lactose metabolism)

Repressible operons usually regulate which type of pathway?

Anabolic pathways (e.g., tryptophan synthesis)

How do bacteria adjust gene expression in changing environments?

By regulating transcription to produce only needed enzymes, or via feedback inhibition

Why are operons useful in bacteria?

They allow coordinated regulation of genes that function together in a pathway