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Eukaryotic genes that encode polypeptides are composed of coding sequences called exon s ( ex -on signifies that they are ex pressed) and intervening sequences called intron s ( int -ron denotes their int ervening role). Transcribed RNA sequences corresponding to introns do not encode regions of the functional polypeptide and are removed from the pre-mRNA during processing. It is essential that all of the intron-encoded RNA sequences are completely and precisely removed from a pre-mRNA before protein synthesis so that the exon-encoded RNA sequences are properly joined together to code for a functional polypeptide. If the process errs by even a single nucleotide, the sequences of the rejoined exons would be shifted, and the resulting polypeptide would be nonfunctional. The process of removing intron-encoded RNA sequences and reconnecting those encoded by exons is called RNA splicing and is facilitated by the action of a spliceosome containing small nuclear ribonucleo proteins (snRNPs). Intron-encoded RNA sequences are removed from the pre-mRNA while it is still in the nucleus. Although they are not translated, introns appear to have various functions, including gene regulation and mRNA transport. On completion of these modifications, the mature transcript , the mRNA that encodes a polypeptide, is transported out of the nucleus, destined for the cytoplasm for translation. Introns can be spliced out differently, resulting in various exons being included or excluded from the final mRNA product. This process is known as alternative splicing . The advantage of alternative splicing is that different types of mRNA transcripts can be generated, all derived from the same DNA sequence. In recent years, it has been shown that some archaea also have the ability to splice their pre-mRNA.

Comparison of Transcription in Bacteria Versus Eukaryotes
Property Bacteria Eukaryotes
Number of polypeptides encoded per mRNA Monocistronic or polycistronic Exclusively monocistronic
Strand elongation core + σ = holoenzyme RNA polymerases I, II, or III
Addition of 5’ cap No Yes
Addition of 3’ poly-A tail No Yes
Splicing of pre-mRNA No Yes
  • In eukaryotic cells, how is the RNA transcript from a gene for a protein modified after it is transcribed?
  • Do exons or introns contain information for protein sequences?

Part 2

In the emergency department, a nurse told Mark that he had made a good decision to come to the hospital because his symptoms indicated an infection that had gotten out of control. Mark’s symptoms had progressed, with the area of skin affected and the amount of swelling increasing. Within the affected area, a rash had begun, blistering and small gas pockets underneath the outermost layer of skin had formed, and some of the skin was becoming gray. Based on the putrid smell of the pus draining from one of the blisters, the rapid progression of the infection, and the visual appearance of the affected skin, the physician immediately began treatment for necrotizing fasciitis. Mark’s physician ordered a culture of the fluid draining from the blister and also ordered blood work, including a white blood cell count.

Mark was admitted to the intensive care unit and began intravenous administration of a broad-spectrum antibiotic to try to minimize further spread of the infection. Despite antibiotic therapy, Mark’s condition deteriorated quickly. Mark became confused and dizzy. Within a few hours of his hospital admission, his blood pressure dropped significantly and his breathing became shallower and more rapid. Additionally, blistering increased, with the blisters intensifying in color to purplish black, and the wound itself seemed to be progressing rapidly up Mark’s leg.

  • What are possible causative agents of Mark’s necrotizing fasciitis?
  • What are some possible explanations for why the antibiotic treatment does not seem to be working?

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Key concepts and summary

  • During transcription , the information encoded in DNA is used to make RNA.
  • RNA polymerase synthesizes RNA, using the antisense strand of the DNA as template by adding complementary RNA nucleotides to the 3’ end of the growing strand.
  • RNA polymerase binds to DNA at a sequence called a promoter during the initiation of transcription .
  • Genes encoding proteins of related functions are frequently transcribed under the control of a single promoter in prokaryotes, resulting in the formation of a polycistronic mRNA molecule that encodes multiple polypeptides.
  • Unlike DNA polymerase, RNA polymerase does not require a 3’-OH group to add nucleotides, so a primer is not needed during initiation.
  • Termination of transcription in bacteria occurs when the RNA polymerase encounters specific DNA sequences that lead to stalling of the polymerase. This results in release of RNA polymerase from the DNA template strand, freeing the RNA transcript .
  • Eukaryotes have three different RNA polymerases. Eukaryotes also have monocistronic mRNA, each encoding only a single polypeptide.
  • Eukaryotic primary transcripts are processed in several ways, including the addition of a 5’ cap and a 3′- poly-A tail , as well as splicing , to generate a mature mRNA molecule that can be transported out of the nucleus and that is protected from degradation.

Fill in the blank

A ________ mRNA is one that codes for multiple polypeptides.


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The protein complex responsible for removing intron-encoded RNA sequences from primary transcripts in eukaryotes is called the ________.


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Short answer

What is the purpose of RNA processing in eukaryotes? Why don’t prokaryotes require similar processing?

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Below is a DNA sequence. Envision that this is a section of a DNA molecule that has separated in preparation for transcription, so you are only seeing the antisense strand. Construct the mRNA sequence transcribed from this template.

Antisense DNA strand: 3’-T A C T G A C T G A C G A T C-5’

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Questions & Answers

Can you give an essay of theta model of DNA replication?
ARYA Reply
Actually Bacterial replication is bidirectional process so when replication start in bacterial DNA two dna forks get formed and both replication again meet on same point in termination position ... so therefore in bacterial dna a greek letter (θ) structure formed which is called theta modal.
what are thermophile's bacteria
evon Reply
bacteria which can survive in high temperature.
why do we study microbiology?
Joyce Reply
For the classification, identification of pathogenic microbes ...
what is pathogenicity
diseases causing activity ...
of microbes..
sorry ability not activity..
I think it's the degree of a pathogen to cause infection
what is prokaryotes
are micro-organisms that have no nucleus e.g bacteria
and they do not possess membrane bound organelles e.g mitochondria
they are single cellular organisms,
all the organelles are embedded in cytoplasm of the cell
They don't possess true nucleus
they're unicellular organisms
they are classified as bacteria and. archaea. bacteria have a cell membrane conposed of peptidoglycan and archaea is composed of psuedomu
organelles are non membraneous as the nucleus
What is the biosynthesis of a bacteria cell
Adesina Reply
biosynthesis is multiple step enzymes catalyze process which occur in bacterial cell
biological way of manufacturing food and utilizes it for growth, multiplication and development
what is microbiology
Kiirya Reply
which organism can not be seen necked eyes is knowm as microbiology
micro can be define as d smallest living organisms dat can not be see wit naked eyes only with the aid of a microscope 🔬
bio means life logy means study
biology can b define as the systematic study of living things
microbiology can be define as the study of tiny organisms, that's according to my understanding
Microbiology is the study of living organisms which cannot be seen by the naked eye but only with the aid of a microscope. These microorganisms can be classified as bacteria, fungi, micro-algae, protozoa and virus.
microbes that can't seen in naked eyes. upto 100micrometer we can see in naked eyes but 1 microns or nanometers are invisible in naked eye.
what is a cell
Oteri Reply
cell can be define as smallest indivisible organism in the body
cell is the smallest unit which makes up the whole body
cell is smallest unit and there are two types prokaryotic cell and eukaryote cell. bacteria a prokaryotic cell which works independently.
nice forum
Which parasite competes with the host for vitamin B12 to cause pernicious anaemia
Diphyllobothrium latum for vit B12
it is also fish tapeworm
Diphyllobothrium sp feed vitB 12
recent trends in microbiology of biofertilizer
Ykomalipriya Reply
using nano technology
what is transposors
Junk DNA, jumping gene.
transposon elements are jumping gene as DNA sequence move from one location to anothet
what is microbiology
Usama Reply
Microbiology is the study of organisms, most of which are too small to be seen with the naked eye, including bacteria, algae, protozoa, and fungi, as well as acellular agents, such as viruses and prions.
what is gram +ve and gram - ve bacteria?
gm- contain lipid layer so it take counter stain during gram staining and pink or red in color but gm + does have thick LPS layer.
what year microbiology started
Robert Koch was the first to detect microorganisms
what appears microorganisms
clear the questions please
was it robert koch or robert hooke?
microbiology word came from microns. study microbes that not recognize in naked eyes.
what are the branch of microbiology
Oyemade Reply
We can basically classify into pure and applied microbiology
what is arabinose operon and it's stucture
Pooja Reply
The L-arabinose operon, also called the ara or araBAD operon, is an operon required for the breakdown of the five-carbon sugar, L-arabinose, in Escherichia coli
kya hum operon ko divide kar skate hain
reactions if viruses to physical and chemical agents?
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
gram negative bacteria hence gonococcal infection
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
not 'things'...'organisms' like bacterias, viruses and fungi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
bacterium is obvio in a singular form but plural of bacterium is bacterias
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
that is microbiology which is deals with microbes only their structure

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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