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By the end of this section, you will be able to:
  • Discuss why every cell does not express all of its genes
  • Describe how prokaryotic gene regulation occurs at the transcriptional level
  • Discuss how eukaryotic gene regulation occurs at the epigenetic, transcriptional, post-transcriptional, translational, and post-translational levels

For a cell to function properly, necessary proteins must be synthesized at the proper time. All cells control or regulate the synthesis of proteins from information encoded in their DNA. The process of turning on a gene to produce RNA and protein is called gene expression    . Whether in a simple unicellular organism or a complex multi-cellular organism, each cell controls when and how its genes are expressed. For this to occur, there must be a mechanism to control when a gene is expressed to make RNA and protein, how much of the protein is made, and when it is time to stop making that protein because it is no longer needed.

The regulation of gene expression conserves energy and space. It would require a significant amount of energy for an organism to express every gene at all times, so it is more energy efficient to turn on the genes only when they are required. In addition, only expressing a subset of genes in each cell saves space because DNA must be unwound from its tightly coiled structure to transcribe and translate the DNA. Cells would have to be enormous if every protein were expressed in every cell all the time.

The control of gene expression is extremely complex. Malfunctions in this process are detrimental to the cell and can lead to the development of many diseases, including cancer.

Prokaryotic versus eukaryotic gene expression

To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different manners.

Prokaryotic organisms are single-celled organisms that lack a cell nucleus, and their DNA therefore floats freely in the cell cytoplasm. To synthesize a protein, the processes of transcription and translation occur almost simultaneously. When the resulting protein is no longer needed, transcription stops. As a result, the primary method to control what type of protein and how much of each protein is expressed in a prokaryotic cell is the regulation of DNA transcription. All of the subsequent steps occur automatically. When more protein is required, more transcription occurs. Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.

Eukaryotic cells, in contrast, have intracellular organelles that add to their complexity. In eukaryotic cells, the DNA is contained inside the cell’s nucleus and there it is transcribed into RNA. The newly synthesized RNA is then transported out of the nucleus into the cytoplasm, where ribosomes translate the RNA into protein. The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation occurs only outside the nucleus in the cytoplasm. The regulation of gene expression can occur at all stages of the process ( [link] ). Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors ( epigenetic    level), when the RNA is transcribed (transcriptional level), when the RNA is processed and exported to the cytoplasm after it is transcribed ( post-transcriptional    level), when the RNA is translated into protein (translational level), or after the protein has been made ( post-translational    level).

Questions & Answers

what is Alimentary canal?
Princess Reply
what is commenialism
jamex Reply
Do you mean commensalism?,it is a feeding relationship that has to do with two different species feeding, that is one is benefiting and the other is unaffected.
hamidat
commensalism is a feeding relationship that has to do with different species feeding, one is gaining and the other is unaffected.
hamidat
what is the work of phloem tissue
Rose Reply
What is osmoregulation?
Jacklin
osmoregulation is the maintenance of internal body through the aid of water
favour
mention four characteristics of enzymes
Leah
mention four characteristics of enzymes
Agorong
The phloem tissue is responsible for the distribution of manufactured food in the shoot.
hamidat
Enzymes speed up the rate of chemical reactions,they are catalytic protein.
hamidat
to transport the manufactured food
Ronald
A skeleton is any film structure that gives mechanical support to the body and provides protection to the softer parts of the body.
Patrick Reply
nice
Kabir
A skeleton is a frame or bony part of a body that aid in the movement of different parts of the body.
hamidat
What is a skeleton?
Chipo Reply
is a bone without meat
Stanley
is a frame work of d body that provide support nd rigidity 4 d body
tunz
is a structure of the body without the organs and the skin
Rose
what is an electron microscope?
Chr Reply
is a microscope that is used to study small organisms in the cell.
Rose
is a microscope which uses electricity to magnify
jamex
okay
Rose
what is commenialism
jamex
what is an antigen?
Luyando
an antigen is any thing that reduces the action of a gene
hamidat
what is biochemist
Lenard Reply
biochemistry:-is the study of chemical reaction with living organisms
Kabir
HOW MANY DNA STRANDS DOES CORONA VIRUS HAVE?
Baramox
GO AND ASK GOOGLE.
hamidat
what are the scientific method
Precious Reply
describe the functioning of the Golgi body in animal cells
Naiga Reply
used to package minerals in the cell
Rose
what features does red blood have that allows it to effectively move through the blood and transport oxygen? list at least four features and explain how they help RBC's carry out their functions.
Alice Reply
has nucleus, haemoglobin
favour
what is biology
kenneth Reply
it's the study of living organisms and their interactions with one another and the environment
Precious
Biology is the study of life.
hamidat
is the study of living organisms and there structure
Rose
describe the structure of DNA
Mafashion Reply
it a double helical structure negatively charged as a results of a phosphate backbone and the two strands are joined together by hydrogen bonds
Ebenezer
Bring out clearly the process of clothing
Irene Reply
How is the region of unwinding called
Irene
what is hoemositasis
Violet
homeostasis is the regulation of a constant internal environment
hamidat
what is DNA replication
jamex
is de maintance of constant internal environment
jamex
is an unfavourable conditions cost by capavic bacteria
hashim Reply
no idea
hamidat
no idea
Precious
Describe the following terms used in nutrition, parasitism, saprophytic, symbiosys
Meymo Reply
parasitism involves gaining and losing
hamidat
a saprophyte does not cause harm to it Host.
hamidat
in symbiosis the two organisms are benefiting
hamidat

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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