<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Describe the steps involved in prokaryotic gene regulation
  • Explain the roles of activators, inducers, and repressors in gene regulation

The DNA of bacteria and archaea is usually (there are a few known exceptions to the circular chromosome in bacteria) organized into a circular chromosome supercoiled in the nucleoid region of the cell cytoplasm. Proteins that are needed for a specific function, or that are involved in the same biochemical pathway, are often times encoded together in blocks called operons . Therefore, operons are single transcription units, encoding for multiple genes. Expression of these genes is organized from a single regulatory region and all genes in the operon are therefore regulated as a single unit. For example, all of the genes needed to use lactose as an energy source are coded next to each other in the lactose (or lac ) operon.

In bacteria, all transcription is controlled through RNA polymerase, a multiprotein complex that recognizes the promoter region and initiates transcription, elongates the transcript, and terminates transcription. Therefore, gene expression can be regulated at any of these steps, initiation, elongation, or termination; however, in bacteria, the majority of the regulation is at the level of transcription initiation.

The role of the promoter

The first level of control of gene expression is at the promoter itself. There are two ways a promoter controls gene expression. First is which RNA polymerase holoenzyme (sigma + Core RNA polymerase) recognizes the promoter. Remember, bacteria have a number of sigma factors many of which control gene expression only under certain conditions, such as Sigma-S during stationary phase. The second level of control is promoter strenght, some promoters are considered "strong", while others are considered "weak". The basis of promoter strength is the specificity the promoter has to RNA polymerase. Each different sigma factor has a different recognition sequence, for example, the sigm-70 protein in E. coli has the recognition sequence 5'-TTGACA-(16-17 nucleotides)-TATAAT-3'. Strong promoters have sequences close to the consensus recognition sequence, weak promoters have sequences more divergent to the consensus.

Regulator proteins

The next layer of control is the addition of regulatory proteins. These proteins can either act to increase transcription, and are often called activators or activator proteins . These proteins bind to the promoter region and aid RNA polymerase to recognize a promoter and initiate transcription. Alternatively, regulatory proteins that inhibit transcription are often referred to as repressors or repressor proteins . Some regulatory proteins can act both as a repressor or an activator depending upon how they interact with RNA polymerase and the promoter. For example the regulatory protein called CAP can act to activate some genes and repress other genes. Therefore the terms "activator" and "repressor" should be used depending upon the situation or condition, and may not truely reflect the role of the protein in question.

Questions & Answers

what is mutation
Janga Reply
what is a cell
Sifune Reply
how is urine form
Sifune
what is antagonism?
mahase Reply
classification of plants, gymnosperm features.
Linsy Reply
what is the features of gymnosperm
Linsy
how many types of solid did we have
Samuel Reply
what is an ionic bond
Samuel
What is Atoms
Daprince Reply
what is fallopian tube
Merolyn
what is bladder
Merolyn
what's bulbourethral gland
Eduek Reply
urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
what is heart
Konadu Reply
how is urine formed in human
Konadu
how is urine formed in human
Rahma
what is the diference between a cavity and a canal
Pelagie Reply
what is the causative agent of malaria
Diamond
malaria is caused by an insect called mosquito.
Naomi
Malaria is cause by female anopheles mosquito
Isaac
Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
Olalekan
a canal is more needed in a root but a cavity is a bad effect
Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
Achor
how are lungs work
Commander
where does digestion begins
Achiri Reply
in the mouth
EZEKIEL
what are the functions of follicle stimulating harmones?
Rashima Reply
stimulates the follicle to release the mature ovum into the oviduct
Davonte
what are the functions of Endocrine and pituitary gland
Chinaza
endocrine secrete hormone and regulate body process
Achor
while pituitary gland is an example of endocrine system and it's found in the Brain
Achor
what's biology?
Egbodo Reply
Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
Alfreda
Biology is the study of how living organisms live and survive in a specific environment
Sifune
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Ucd bis2a intro to biology v1.2. OpenStax CNX. Sep 22, 2015 Download for free at https://legacy.cnx.org/content/col11890/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ucd bis2a intro to biology v1.2' conversation and receive update notifications?

Ask