Control Of Gene Expression

Flashcards for vocabulary review.

Gene expression

Occurs when a gene is “activated” and used to make mRNA and proteins.

Control of Gene Expression

Enzymes are turned on or off as needed, to respond to changing environmental conditions.

Differentiation allows for

Growth, development and repair in multicellular organisms.

Transcriptional Control

Activates or deactivates genes before or during transcription; most commonly-used method.

Post-transcriptional Control

Activates or deactivates gene products (RNA or proteins) AFTER transcription has occurred.

Regulatory Genes/Sequences

Code for regulatory proteins, which attach to genes to turn them on or off.

Activators

Proteins that initiate transcription.

Repressors

Proteins that prevent transcription.

Co-repressors

Molecules that bind to and help the repressors.

Inducers

Molecules that bind to either activators or repressors to activate or deactivate them.

Transcription factors

General term used to describe eukaryotic proteins that regulate transcription.

Control elements

Sequences to which regulatory proteins​ molecules bind; “Switches” that turn genes on and off.

Promoter region

A sequence just upstream of the start codon to which DNA and RNA polymerase attach. Includes the TATA box in eukaryotes.

Operator

Short sequence of DNA within the promoter that activates or deactivates the gene (switches it on or off) in prokaryotic cells.

Enhancers

Sequences of DNA found far upstream of the promoter that must be activated before transcription can occur; only found in eukaryotic cells.

Operon model

Genes with related functions are located next to each other in the DNA; A single promoter controls the entire set of genes

Tryptophan

An amino acid essential to survival; when it isn't available in the environment, bacteria have to make it themselves.

trp Operon

5 different polypeptides are required to make tryptophan. 5 polypeptides = 5 genes

trp Operon

Because bacteria need a constant supply of tryptophan, this operon is usually turned ON. However, if they have access to tryptophan in the environment, they will switch this gene OFF to conserve resources.

Tryptophan Regulation

Repressible enzymes usually participate in anabolic pathways; Their synthesis is repressed by high levels of the end product

lac Operon

E. coli love to eat lactose. This requires 3 enzymes = 3 genes; Is usually OFF because Lactose is not usually present in the environment.

Regulating The Breakdown Of Lactose

Inducible enzymes usually function in catabolic pathways; Their synthesis is induced by a chemical signal