join the ap-bio course

๐ŸŽ–๏ธfiveable certificate upon completion

โฑ๏ธ 2 min read

๐Ÿ“ย ย 

ap bio

ย โ€ขย 

study guide

ย โ€ขย 

Unit 6

6.5 Regulation of Gene Expression

#operons

#epigeneticchanges

#prokaryotes

#eukaryotes

#regulatorysequences


written by

Samantha Himegarner

samantha himegarner

published on april 3, 2020

Last updated on May 31, 2020

Regulatory Sequences

There are sequences of DNA that have control over increasing or decreasing the expression of certain genes in the organism; essentially, they can turn a gene "on" or "off." These sequences are known as โ€œregulatory sequences,โ€ and they interact with proteins to do so. The genes that are expressed determine the phenotypes of the cell and/or organism. There are also different levels of expression that can affect this.ย 

Epigenetic Changes

DNA can be modified to change what will and will not be expressed as well. These changes are called โ€œepigeneticโ€ changes and are often reversible. Gene regulation occurs in both eukaryotes and prokaryotes, though the groups of genes that are regulated are different.

Operons

Prokaryotes utilize operons to regulate gene expression. An operon is a cluster of genes with a single promoter. Lac operons, which are present in E. coli cells, are a good example of inducible operons. Inducible operons allow the expression of the gene by default and only turn off when the protein it creates is no longer needed. When the protein is needed again, it turns back on and continues to express the gene.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-02%20at%209.22.31%20PM.png?alt=media&token=4bae86ca-e275-4220-9860-1e647a8e17c7

Image courtesy of LumenLearning.

It is regulated by a lac repressor and a catabolic activator protein (CAP). The lac repressor normally will block transcription, but when it senses the presence of lactose, it stops repressing so that the gene can be expressed. The CAP detects glucose, and activates transcription when glucose is low. Both the CAP and the lac repressor detect indirectly. The presence of cAMP lets the CAP know that glucose levels are low, whereas the lac repressor senses the lactose isomer allolactose. lacZ, lacY, and lacA are the genes that are expressed, and can be used for metabolism.

Fiveable

join more students

create an account on fiveable

Repressibleย Operons

Trp operons are also found in E. Coli, but they are repressible operons. This means they only turn on when needed (instead of the expression as default). When the repressor is bound to tryptophan, it blocks the expression of the operon. It is only turned on when the trp levels are low. When the repressor is not bound, the operon works very similarly to the lac operon described above. There is a promoter, operator, and various genes that are transcribed as a single mRNA.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FOSC_Microbio_11_07_trp.jpg?alt=media&token=57096028-82b0-4fb5-ab8c-29b5cfda816e

Image courtesy of LumenLearning.

Watch AP Bio live streams here.

Fiveable Logo

2550 north lake drive
suite 2
milwaukee, wi 53211

92% of Fiveable students earned a 3 or higher on their 2020 AP Exams.

*apยฎ and advanced placementยฎ are registered trademarks of the college board, which was not involved in the production of, and does not endorse, this product.

ยฉ fiveable 2020 | all rights reserved.