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By the end of this section, you will be able to:
  • Explain the central dogma
  • Explain the main steps of transcription
  • Describe how eukaryotic mRNA is processed

In both prokaryotes and eukaryotes, the second function of DNA (the first was replication) is to provide the information needed to construct the proteins necessary so that the cell can perform all of its functions. To do this, the DNA is “read” or transcribed into an mRNA    molecule. The mRNA then provides the code to form a protein by a process called translation. Through the processes of transcription and translation, a protein is built with a specific sequence of amino acids that was originally encoded in the DNA. This module discusses the details of transcription.

The central dogma: dna encodes rna; rna encodes protein

The flow of genetic information in cells from DNA to mRNA to protein is described by the central dogma ( [link] ), which states that genes specify the sequences of mRNAs, which in turn specify the sequences of proteins.

A flow chart shows DNA, with an arrow to RNA, which has an arrow to protein.
The central dogma states that DNA encodes RNA, which in turn encodes protein.

The copying of DNA to mRNA is relatively straightforward, with one nucleotide being added to the mRNA strand for every complementary nucleotide read in the DNA strand. The translation to protein is more complex because groups of three mRNA nucleotides correspond to one amino acid of the protein sequence. However, as we shall see in the next module, the translation to protein is still systematic, such that nucleotides 1 to 3 correspond to amino acid 1, nucleotides 4 to 6 correspond to amino acid 2, and so on.

Transcription: from dna to mrna

Both prokaryotes and eukaryotes perform fundamentally the same process of transcription, with the important difference of the membrane-bound nucleus in eukaryotes. With the genes bound in the nucleus, transcription occurs in the nucleus of the cell and the mRNA transcript must be transported to the cytoplasm. The prokaryotes, which include bacteria and archaea, lack membrane-bound nuclei and other organelles, and transcription occurs in the cytoplasm of the cell. In both prokaryotes and eukaryotes, transcription occurs in three main stages: initiation, elongation, and termination.


Transcription requires the DNA double helix to partially unwind in the region of mRNA synthesis. The region of unwinding is called a transcription bubble    . The DNA sequence onto which the proteins and enzymes involved in transcription bind to initiate the process is called a promoter    . In most cases, promoters exist upstream of the genes they regulate. The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all of the time, some of the time, or hardly at all ( [link] ).

Illustration shows a template strand and nontemplate strand of DNA, with a promoter section in red on the template strand. Downstream of the promoter is an RNA polymerase where RNA is being synthesized.
The initiation of transcription begins when DNA is unwound, forming a transcription bubble. Enzymes and other proteins involved in transcription bind at the promoter.


Transcription always proceeds from one of the two DNA strands, which is called the template strand    . The mRNA product is complementary to the template strand and is almost identical to the other DNA strand, called the nontemplate strand    , with the exception that RNA contains a uracil (U) in place of the thymine (T) found in DNA. During elongation, an enzyme called RNA polymerase    proceeds along the DNA template adding nucleotides by base pairing with the DNA template in a manner similar to DNA replication, with the difference that an RNA strand is being synthesized that does not remain bound to the DNA template. As elongation proceeds, the DNA is continuously unwound ahead of the core enzyme and rewound behind it ( [link] ).

Questions & Answers

why are the laws of thermodynamics considered laws of nature and not scientific theories
Yolonda Reply
archea were given their own separate domain because they are?
which of the following is a basic component of all of the others?
which of the following organization levels is the least inclusive
which cell feature is absent in bacterial cells
which metric movies the base unit of measurement by one thousandth (0.001)?
What is biology?
Blessing Reply
List the branches of biology
List the branches of biology
List the branches of biology
List the branches of biology
must all prokaryotic cells posses a cell wall?
chris Reply
what is biology?
Cathy Reply
biology is basically the study of life
that's true
it's the study of living things
What is a celiac disease
Falase Reply
distinguish between properties and characteristics
Elee Reply
what are organelles
organelles are substances that makes up a cell
what is biology
Prevail Reply
biology is science that studies life
it's the study of living and non living things
now that we have an estimate for the diameter of the cell.what estimate can we make about the volume of the cell?
faxhood Reply
why too much insulin result in low blood sugar
Leri Reply
For example, too much exercise can cost you to lose to much weight. Too much insulin will pull to much sugar out of your systemic system into your cells.
difference between DNA and RNA
Eyitayo Reply
DNA is deoxyribonuclaic acid. Deoxy refers to a lack of oxygen. The Ribose moity is missing an OH group. I think it is missing from the second C of the ring. RNA is ribonucleic acid. DNA has our genetic code in on it. RNA is translated from DNA and carries the blue print for protein synthesis.
The OH group on RNA prevents it from being reactive. But it is very unstable though. Would you want such a power tool floating around in your body, no. And you have three types of RNA: mRNA, tRNA and rRNA. Please let me know it this helped?😄
Eric answered this question perfectly
what determines the aeration level in the soil
Shola Reply
what is homeostasis?
Sarita Reply
It means balance in a biological system.
What is biology
Don Reply
Biology z the study of life
what's biology
biology is the study of living nd none living organism
Biology is the study of life
yes Sir
what's cell biology
biology is the study of life
Biology is a science subject that deals with the study of living things and how they interact with there environment
what is asexual reproduction,?
Awoi Reply
A type of reproduction which does not involve the fusion of gametes or a change in the number of chromosomes
Reproduction without sex... In which form a single organism or cell makes a copy of itself.
Please explain the concept of mitosis and meiosis
I guess you could use it for study buddies and brushing up on what you need to
what is mitosis
Asexual reproduction?
why pepsin and trypsin released in active form?
mitosis is the type cell division in which two daughter cells have same no. of chormosomes
chromosome number remains the same in mitosis
Yrr help me.
Physical chemistry..... Koi h jo mujhe physical chem ki notes send kr ske
what is asexual reproduction
what makes golgi body in plants
Abdulkareem Reply
name the membrane of the plants
how can turners syndrome be corrected before birth
which animal survive from being preyed just because of being humble, slow, and not aggressive
Plants have golgi body's also. Plants are eukaryotic cells. And membrane bound organelles are a characteristic of eukaryotic cells. Moreover golgi body's are creatted from the ER. Also do not forget plants have plastids and animal cells do not.

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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