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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.

polycistronic

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

Spliceosome

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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

a 28 years old woman come to your clinic with complain of fever painful genital blisters which express clear fluid when ruptured burning sensation around the bristers what is the diagnosis?
Ramadhani Reply
genital herpes caused by a virus called herpe simplex virus
Doris
what is the reference between selective medium and differential medium?
Tony Reply
the micro flora of air is transient why
Princess
Hello.... Am new here
essien Reply
welcome essien
Muhammad
welcome essien
Beka
classification of gram positive
lissa Reply
classify gram positive
lissa
catalase test is done to differentiate between staph and strep. as staph is catalase positive while strep is catalase negative then staph is differentiate further on coagulase positive and coagulase negative. staph aureus is coagulase positive while staph epidermidis is coagulase negative.
Muhammad
gram positive staph is further differentiated on sensitivity test and manitol salt fermentation test while gram positive strep is differentiated on hemolysis pattern
Muhammad
more about gramm positive
lissa
please
lissa
ok
Blessing
am back any gist
Blessing
taxonomy
Rahul
can i use the graph of bacterial growth for my master's thesis?
Christoph Reply
facultative anaerobic bavteria gives uniform turdibity in nutrient broth why?
Princess Reply
oils and waxes are not sterilized in autoclave
Princess
what is the function of paraffin
Muhammad
@ MAHI because they can grow all over the media from surface to the bottom as they can utilize oxygen or conduct fermentation in its absence.
Online
2.@MAHI Autoclave uses steam under pressure. The steam cannot penetrate through oil and wax. Thus, dry heat sterilization is preferred than autoclave .
Online
thnku
Nadiya
how nutirent agar can converted into blood agar
Princess
thank you
Princess
take a nutrient agar ........and add 5ml blood and put in it ...........!
Nadiya
nutrient agar +blood 5ml+ distilled water =blood agar .
Nadiya
mixed wellllll
Nadiya
hi
Rahul
why agar is not a neutrient source?
Shimul
because it's a general purpose agar only use for growing bacteria
Richa
way is antigen
opaleye
what is antigen
opaleye
antigen is a foreign body that cause activation of antibody?
ASNAKE
Antigen is a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.
Shimul
thanks for that
opaleye
what is pharmacology
Luyenu
a science that studies about the drug
ASNAKE
hello ever one
Sayid
y
Abdul
Work hard
Anigor
y
Abdul
thanks alot
Luyenu
What is the major different between gram positive and gram negative bacteria.
Asikur
bacteria kya hai
Mala
content of their cell wall
Doris
koi mujhse basic microbiology ki study k Lea book suggest kro .
Richa
Harley prescott
Vikas
what are the five predisposing factors of opportunistic infections
Asher Reply
1. long term exposure to diseases, that the body immunity weakens.
prosper
2. Nature Of some diseases to weaken body immunity such as, AIDS.
prosper
3. Use of immuno-suppresive drugs.
prosper
anyone... need a hand here 🙋😞
prosper
Low immune is the major cause eg for kaposis sarcoma
Davismith
suitable conditions e.g temp,
Muhammad
what os gnormal flora
kifayat Reply
morphological and genetic classification of bacteria
Potter Reply
what is the morphogical
Bupe
h
Sudhir
morphologycal is defined as relating to the branch of biology that deals with the form of living organisms,and with relationship between their structures.
Nadiya
relating to the form or structure of things .
Nadiya
what is the meaning of lessions
oluwa
i am frim Afghanistan.
wahidullah Reply
iam from iraq
Haidar
and i'm from pakistan
Muhammad
Nice
Amina
what's about the qualification
Muhammad
Hlo
Asiya
Hmm
Number
Almustafa Muhammad from Nigeria
Mujtafa
am ustaz Abdulsalam from Ghana
ustaz
am Bupe Chifita from Zambia
Bupe
what is microbiology
Bupe
is the study of invisible micro organism
Mujtafa
microbiology is the study of very too small organisms which we can't see with naked eyes ......in other words ....study of microorganism is called microbiology.
Nadiya
Hello! How Can Microorganisms Be Isolated From The Skin?.. 5 ways if possible. (briefly)
prosper
from skin swabbing is the prefer method worldwide
Muhammad
thanks Muhammad Nauman very much!
prosper
hi
Meek
hi Meek
prosper
are there any other ways pals?
prosper
hi prosper
Meek
hello Meek Mild.
prosper
Any question or ideas, Meek?😊
prosper
and if a patient have any blister or abscess on the skin then first cut the blister or abscess. inside material is taking by syringe.
Muhammad
in case of fingernail or toenails simply cut a small piece of nail and culture on the appropriate media at a required temperature and time
Muhammad
Again, thanks Mr. Muhammad! I appreciate the help.
prosper
you welcom prosper 😊
Muhammad
what are the media use for skin swab?
Sieh-Mlanwin
blood and macckonkey mostly usededia for skin bacteria
Muhammad
used media*
Muhammad
@ SIEH mostly fungal infection occurs in skin so SDA ( Sabouraud Dextrose Agar) or MEA ( Malt extract agar) are common.
Online
thanks
Sieh-Mlanwin
Microbiologicam source of vitamins
Bachi Reply
what do you mean?
Md
that's example?
Md
hi everyone
Muhammad
such as. c/s media
Md
hmm hlw
Md
just tell me about that ?
Md
where are u from
Muhammad
history of Bactolagy?
Piyush Reply
ask me any question you want on microbiology
Norbuqaari Reply
what is scale up fermenter ? and whict bectetia is benifited in industrial microbilogy ?
Nadiya
can u explain to me wts the meaning of autoclave,and how it doing and ,wt r the equipment to need to do it?
chandi
stem heat under pressure
Nadiya
thnks
chandi
autoclave is a steam heat under pressure .it is use to sterilize the equipment, agar ,petridish broth liquid and many more things....to kill the microbes.......free from microbes
Nadiya
nadiya Scale up studies refers to the act of using results obtained from laboratory studies for designing a prototype and a pilot plant process. do you agree or
Norbuqaari
bectetia is benifited in industrial microbilogy is lactobacilli
Norbuqaari
and
Nadiya
chandi. strong heated container used for chemical reactions and other processes using high pressures and temperatures, e.g. steam sterilization.
Norbuqaari
another
Norbuqaari
who is father of microbiology?
Norbuqaari
anton van leoven hook
chandi
antonie van leeuwenhoek
chandi
thanks
Norbuqaari
what is microbial taxonomy
Ini
what is normal flora
kifayat
normal flora contains the microorganisms which lives on and in our body but can not cause diseases easily....e.g staph. aureus lives on our body they dont cause disease in normal conditions whenever our skin is injured by any cut or wound then they enter into the body and cause diseases
Muhammad
two types of normal flora .... one is the resident normal flora and the other is transient normal flora.....resident normal flora is reside on our body in every condition but transient normal flora changes with the conditions
Muhammad
what is the method used for anaerobic bacteria to grow in the lab other then the candle jar method?
Muhammad
Why those beans water smell
Asiya
wow
Sebewu
hahahaha
Kwame
Asiya Ibrahim please beans water how? please come clear!
Kwame
what is the purpose of gam staining
Norbuqaari Reply
the purpose of gram staining is to differentiate and classified bacteria and other microbes !
Nadiya
the purpose of gram staining is to differentiate between gram negative bacteria and gram positive bacteria
Leah
thanks Nadiya... Thank you Leah Kalasya..Safari njema!
prosper
remember me in yr prayers norbuqaari ! 🙂
Nadiya
what is the virus?
Norbuqaari Reply
an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host.
chandi
chandi sheeth thanks alot
Norbuqaari
😊😊😊
chandi

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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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