Operons are a section of genes that are all transcribed together. The operon is regulated by the promoter and operator sequence upstream of the genes in the operon. Operons are found primarily in prokaryotes.

Operon

Transcription factors are proteins that regulate genes by binding to DNA. They typically bind upstream of an operon to regulate its expression. They can be repressors and prevent RNA Polymerase from transcribing genes or activators and facilitate the binding of RNA Polymerase to transcribe genes. They respond to stimuli in the cell's environment to regulate genes.

Transcription Factors

Promoter sequences are DNA sequences that define where transcription of a gene by RNA polymerase begins. Transcription factor activators can also interact with this sequence to activate transcription. Promoter sequences are typically located directly upstream of the genes they regulate. 

Promoter

An operator is the DNA sequence that is usually downstream of the RNA Polymerase binding site but upstream of the first gene in the operon. The operon interacts with a transcriptional repressor. By binding to the operator sequence, repressors physically block the RNA Polymerase from interacting with the -10 and -35 sequences to transcribe.

Operator Sequence

Gene expression must be regulated in order to express the genes that are needed at the right times so that cellular energy is not wasted. There are many regulatory genes required for gene regulation in eukaryotes and prokaryotes.

University of Wisconsin - Madison

Gene expression refers to the processes of using the genetic code to make proteins.  This process occurs in two steps: transcription and translation. This occurs in all of the classifications of microbial genetics.
Gene expression is also described as the "Central Dogma of Molecular Biology" to describe the transfer of information of the genetic code in cells.

Gene Expression

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Translation is the decoding of mRNA transcripts into proteins. Protein synthesis uses more energy in a cell than any other metabolic process. This overall process is conserved with prokaryotes and eukaryotes with important differences in the proteins and mRNA involved. 

Translation (Protein Synthesis)

Gene Regulation

Mutations in the genetic code occur at the DNA base pair level when a DNA base pair is changed. It may or may not have a noticeable change to the protein that is made due to redundancy in the genetic code. However, a mutation in the DNA can lead to a noticeable phenotype. 

Mutations

Transcription is the process of transcribing the genetic information of DNA into RNA transcripts. This transcript is mobile and is a copy of DNA with RNA nucleotides. This process is largely conserved in prokaryotes and eukaryotes with some significant differences between them.

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