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The mRNA carries the message from the DNA, which controls all of the cellular activities in a cell. If a cell requires a certain protein to be synthesized, the gene for this product is “turned on” and the mRNA is synthesized through the process of transcription (see RNA Transcription ). The mRNA then interacts with ribosomes and other cellular machinery ( [link] ) to direct the synthesis of the protein it encodes during the process of translation (see Protein Synthesis ). mRNA is relatively unstable and short-lived in the cell, especially in prokaryotic cells, ensuring that proteins are only made when needed.

A diagram showing mRNA as a long strand with sets of 3 letters grouped; the left of the mRNA is labeled 3-prime, the right is labeled 5-prime. An oval labeled ribosome small subunit sits under the mRNA and spans 3 of the 3-letter groups. A larger dome (labeled ribosome large subunit) sits on top of the mRNA at this same region. The large subunit has 3 gaps where rectangles labeled tRNA sit. These rectangles each sit on a group of 3-letters on the mRNA at one end and contain an amino acid on the other end. The tRNA on the left has a single amino acid. The tRNA in the middle has a growing pepetide chain of many amino acids. The tRNA on the right as no amino acids and is leaving the ribosome.
A generalized illustration of how mRNA and tRNA are used in protein synthesis within a cell.

rRNA and tRNA are stable types of RNA. In prokaryotes and eukaryotes, tRNA and rRNA are encoded in the DNA, then copied into long RNA molecules that are cut to release smaller fragments containing the individual mature RNA species. In eukaryotes, synthesis, cutting, and assembly of rRNA into ribosomes takes place in the nucleolus region of the nucleus, but these activities occur in the cytoplasm of prokaryotes. Neither of these types of RNA carries instructions to direct the synthesis of a polypeptide, but they play other important roles in protein synthesis.

Ribosomes are composed of rRNA and protein. As its name suggests, rRNA is a major constituent of ribosomes , composing up to about 60% of the ribosome by mass and providing the location where the mRNA binds. The rRNA ensures the proper alignment of the mRNA, tRNA, and the ribosomes; the rRNA of the ribosome also has an enzymatic activity ( peptidyl transferase ) and catalyzes the formation of the peptide bonds between two aligned amino acids during protein synthesis. Although rRNA had long been thought to serve primarily a structural role, its catalytic role within the ribosome was proven in 2000. P. Nissen et al. “The Structural Basis of Ribosome Activity in Peptide Bond Synthesis.” Science 289 no. 5481 (2000):920–930. Scientists in the laboratories of Thomas Steitz (1940–) and Peter Moore (1939–) at Yale University were able to crystallize the ribosome structure from Haloarcula marismortui , a halophilic archaeon isolated from the Dead Sea. Because of the importance of this work, Steitz shared the 2009 Nobel Prize in Chemistry with other scientists who made significant contributions to the understanding of ribosome structure.

Transfer RNA is the third main type of RNA and one of the smallest, usually only 70–90 nucleotides long. It carries the correct amino acid to the site of protein synthesis in the ribosome. It is the base pairing between the tRNA and mRNA that allows for the correct amino acid to be inserted in the polypeptide chain being synthesized ( [link] ). Any mutations in the tRNA or rRNA can result in global problems for the cell because both are necessary for proper protein synthesis ( [link] ).

A diagram of the 2-dimentional tRNA which is a single long strand of RNA folded into a plus shape with loops on the sides and bottom. The regions where the tRNA is folded so that there are 2 parts of the strand forming the linear portions of the plus are held together by hydrogen bonds labeled intramolecular pairing. The loop at the bottom has a set of 3 letters that are complimentary to 3 letters on the mRNA. The top part of the plus has a single stranded end at the 3-prime end; this is attached to an amino acid. B) The 3-dimentional structure looks like single strand folded into a double stranded structure with a bend in the middle.
A tRNA molecule is a single-stranded molecule that exhibits significant intracellular base pairing, giving it its characteristic three-dimensional shape.
Structure and Function of RNA
mRNA rRNA tRNA
Structure Short, unstable, single-stranded RNA corresponding to a gene encoded within DNA Longer, stable RNA molecules composing 60% of ribosome’s mass Short (70-90 nucleotides), stable RNA with extensive intramolecular base pairing; contains an amino acid binding site and an mRNA binding site
Function Serves as intermediary between DNA and protein; used by ribosome to direct synthesis of protein it encodes Ensures the proper alignment of mRNA, tRNA, and ribosome during protein synthesis; catalyzes peptide bond formation between amino acids Carries the correct amino acid to the site of protein synthesis in the ribosome
  • What are the functions of the three major types of RNA molecules involved in protein synthesis?

Rna as hereditary information

Although RNA does not serve as the hereditary information in most cells, RNA does hold this function for many viruses that do not contain DNA . Thus, RNA clearly does have the additional capacity to serve as genetic information. Although RNA is typically single stranded within cells, there is significant diversity in viruses. Rhinoviruses, which cause the common cold; influenza viruses; and the Ebola virus are single-stranded RNA viruses. Rotaviruses, which cause severe gastroenteritis in children and other immunocompromised individuals, are examples of double-stranded RNA viruses. Because double-stranded RNA is uncommon in eukaryotic cells, its presence serves as an indicator of viral infection. The implications for a virus having an RNA genome instead of a DNA genome are discussed in more detail in Viruses .

Key concepts and summary

  • Ribonucleic acid (RNA) is typically single stranded and contains ribose as its pentose sugar and the pyrimidine uracil instead of thymine. An RNA strand can undergo significant intramolecular base pairing to take on a three-dimensional structure.
  • There are three main types of RNA, all involved in protein synthesis.
  • Messenger RNA ( mRNA ) serves as the intermediary between DNA and the synthesis of protein products during translation.
  • Ribosomal RNA ( rRNA ) is a type of stable RNA that is a major constituent of ribosomes. It ensures the proper alignment of the mRNA and the ribosomes during protein synthesis and catalyzes the formation of the peptide bonds between two aligned amino acids during protein synthesis.
  • Transfer RNA ( tRNA ) is a small type of stable RNA that carries an amino acid to the corresponding site of protein synthesis in the ribosome. It is the base pairing between the tRNA and mRNA that allows for the correct amino acid to be inserted in the polypeptide chain being synthesized.
  • Although RNA is not used for long-term genetic information in cells, many viruses do use RNA as their genetic material.

Matching

Match the correct molecule with its description:

___tRNA
___rRNA
___mRNA
A. is a major component of ribosome
B. is a copy of the information in a gene
C. carries an amino acid to the ribosome

C, A, B

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True/false

Ribosomes are composed mostly of RNA.

True

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Double-stranded RNA is commonly found inside cells.

False

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Short answer

What are the differences between DNA nucleotides and RNA nucleotides?

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How is the information stored within the base sequence of DNA used to determine a cell’s properties?

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How do complementary base pairs contribute to intramolecular base pairing within an RNA molecule?

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If an antisense RNA has the sequence 5ʹAUUCGAAUGC3ʹ, what is the sequence of the mRNA to which it will bind? Be sure to label the 5ʹ and 3ʹ ends of the molecule you draw.

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Why does double-stranded RNA (dsRNA) stimulate RNA interference?

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Questions & Answers

what is fermentation example ?
Sonal Reply
is proceess in which an agent couses of an oganic substances breakdown into simpler substance,especially in aneorobic breakdown of suger into alcohol.
Okashat
is it better to study microbiology and then medicine it makes no difference to go directly to medicine?
Jessee Reply
Dray's mathdme cell wall konse color k hote he
Jinal Reply
what is dray's mathdme cell wall
Prabhat
I confused. please help me
Karen
just confused
Raj
l don't understand it please explain it for me.
Karen Reply
epitopes are present on the surface of
Rohit Reply
at the tip of variable region on the antibody...where antigen and antibody binding sites combine...
Fiza
The term that is used refer to moving microbes under a microscope are referred to as?
Lee Reply
Members of the genus Neisseria cause which of the folowing human diseases?
Farah Reply
genital infections
Kamaluddeen
gonorrhoea
sandip
gonorrhoea
Jessee
4. Which of the following specimens should not be refrigerated? a. Urine b. Urogenital swab
Zahraa Reply
urine
Muuse
urine
Agatha
Urine
Tean
urine
Yasser
Urine
Ebtehal
urine
anamika
urine
Puja
urine
Inemesit
urine
Samuel
Urine
Muhammad
Details about McConkey agar
Muhammad
urine
SK
urine
what is bacteria
anamika Reply
a member of large number of unicellular microorganism which have cell wall but lack of cell organelles an oranised nucleus including somewhat can cause disease
Sukhdeep
Bacteria are usually composed of one cell onl to that are neither plants nor animals, microscopic, that may cause diseases or may be beneficial(in gut)... it depends upon their weapons. Nearly all animal life is dependent on Bacteria for their survival
Fiza
thanks
anamika
what factor make bacteria colony large and how could we sterlise it in large scale
fatty
nutrient concentration temp gaseous conc ph ion or salt concentration mositure condition factors contribute to make large colony. by autoclaving we will sterilize bactetia
Sukhdeep
Colony is actually visible growth of Bacteria that is as a result of suitable environment for growth i.e optimal conditions for growth, temperature, moisture etc. there're many methods to get rid of bacteria. If We stop giving them optimal conditions for living Bacteria will die soon .
Fiza
what's the difference between an antigen and a pathogen?
Pathogens are organisms that cause disease in other organisms whereas Antigen is a part of a pathogen that triggers the immune response..
Rajat
so it is the antigen that dendritic cells present to the T cells and not the pathogen itself?
no no antigen are the west product or part of the pathogen. in such case bacteria it self fight with over immune response & in another case bacteria release antigens
vasava
& other antigen like pollan grain, dust particles etc.....
vasava
pathogen are microbes that can infect the body and causw illness....antigens are the part of pathogens that alert the body to an infection
Sukhdeep
antigen is a part of blood and pathogen is foreign particle which causes diseases
Yogyata
antigen could be non microorganism.... where as pathogen is mixroorganism
tadesse
Thanks
Karen
a pathogen is a disease causing organism while an antigen is a protein in the white blood cells which combats pathogens.
Jessee
what type of widal test
sobhit Reply
this test determine for typhoid in this test if H,O antigen are present that indicate the positive test bac. are salmonella typhy
vasava
what h.o denotes
Iqra
o: body of bacteria, h: flagellate
Explain Mould
Chinenye Reply
Explain mycoses and it's classification
Chinenye
why do we have hiccups?
Manisha Reply
shakey diaphragm
Curlisse
The antibody binding site is formed primarily by:
Asalla Reply
How many types of MICROORGANISMS do we have?
Hope Reply
Hello friends
Hope
microorganisms are divided into seven type Bacteria archaea protozoa algae fungi virus and multicellular animal parasites
Raj

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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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