Transcription is the process where the DNA sequence of a gene is copied into a messenger RNA (mRNA) molecule. It involves RNA polymerase enzymes linking nucleotides together to form an RNA strand using a DNA strand as a template. Transcription has three stages - initiation, elongation, and termination. In eukaryotes, the mRNA also undergoes processing after transcription such as splicing and addition of a 5' cap and poly-A tail. Transcription is regulated individually for each gene.
• Define transcription• Define translation• What are the 3 steps.pdfarihantelehyb
• Define transcription
• Define translation
• What are the 3 steps of translation?
• Define the “genetic dogma”
• What is the function of Transfer RNA?
• What is the function of RNA polymerase?
• What is the function of DNA polymerase?
• Define “splicing of RNA”
• What is an exon?
• What component of the cell does the translation?
• What molecule in the cell does transcription?
• What are the functions of: operon, promotor?
• What is the difference between inducible operon and repressible operon?
Solution
• Define transcription
Transcription is the process of making an RNA copy of a gene sequence. This copy, called a
messenger RNA (mRNA) molecule, leaves the cell nucleus and enters the cytoplasm, where it
directs the synthesis of the protein, which it encodes. Here is a more complete definition of
transcription.
• Define translation
Translation is the process of translating the sequence of a messenger RNA (mRNA) molecule to
a sequence of amino acids during protein synthesis. The genetic code describes the relationship
between the sequence of base pairs in a gene and the corresponding amino acid sequence that it
encodes. In the cell cytoplasm, the ribosome reads the sequence of the mRNA in groups of three
bases to assemble the protein. Here is a more complete definition of translation:
• What are the 3 steps of translation?
Step # 1. Initiation:
Initiation of translation in E .coli involves the small ribosome subunit, a mRNA molecule, a
specific charge initiator tRNA, GTP, Mg++ and number of proteinaceous initiation factors (IFs).
These are initially part of the small subunit and are required to enhance binding affinity of the
various translational components (Table 8.1). Unlike ribosomal proteins, IFs are released from
the ribosome once initiation is completed.
Step # 2. Elongation:
Once both subunits of the ribosome are assembled with the mRNA, binding site for two charged
tRNA molecules are formed. These are designated as the ‘P’ or peptidyl and the ‘A’ or
aminoacyl sites. The charged initiator tRNA binds to the P site, provided that the AUG triplet of
mRNA is in the corresponding position of the small subunit. The increase of the growing
polypeptide chain by one amino acid is called elongation.
Step # 3. Termination:
Termination of protein synthesis is carried out by triplet codes (UAG, UAA, UGA; stop codons)
present at site A. These codons do not specify an amino acid, nor do they call for a tRNA in the
A site. These codons are called stop codons, termination codons or nonsense codons. The
finished polypeptide is still attached to the terminal tRNA at the P site, and the A site is empty.
• Define the “genetic dogma”
A theory in genetics and molecular biology subject to several exceptions that genetic information
is coded in self-replicating DNA and undergoes unidirectional transfer to messenger RNAs in
transcription which act as templates for protein synthesis in translation
• What is the function of Transfer RNA?
The tRNA molecule, or tr.
Protein synthesis is the process whereby biological cells generate new proteins. Translation, the assembly of amino acids by ribosomes, is an essential part of the biosynthetic pathway, along with generation of messenger RNA (mRNA), aminoacylation of transfer RNA (tRNA), co-translational transport, and post-translational modification. Protein biosynthesis is strictly regulated at multiple steps. They are principally during transcription (phenomenon of RNA synthesis from DNA template) and translation (phenomenon of amino acid assembly from RNA). The cistron DNA is transcribed into the first of a series of RNA intermediates. The last version is used as a template in synthesis of a polypeptide chain. Protein will often be synthesized directly from genes by translating mRNA. A proprotein is an inactive protein containing one or more inhibitory peptides that can be activated when the inhibitory sequence is removed by proteolysis during post translational modification. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide) that specifies its insertion into or through membranes, i.e., targets them for secretion. The signal peptide is cleaved off in the endoplasmic reticulum. Preproteins have both sequences (inhibitory and signal) still present. In protein synthesis, a succession of tRNA molecules charged with appropriate amino acids are brought together with an mRNA molecule and matched up by base-pairing through the anti-codons of the tRNA with successive codons of the mRNA. The amino acids are then linked together to extend the growing protein chain, and the tRNAs, no longer carrying amino acids, are released. This whole complex of processes is carried out by the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. The ribosome latches onto the end of an mRNA molecule and moves along it, capturing loaded tRNA molecules and joining together their amino acids to form a new protein chain.
• Define transcription• Define translation• What are the 3 steps.pdfarihantelehyb
• Define transcription
• Define translation
• What are the 3 steps of translation?
• Define the “genetic dogma”
• What is the function of Transfer RNA?
• What is the function of RNA polymerase?
• What is the function of DNA polymerase?
• Define “splicing of RNA”
• What is an exon?
• What component of the cell does the translation?
• What molecule in the cell does transcription?
• What are the functions of: operon, promotor?
• What is the difference between inducible operon and repressible operon?
Solution
• Define transcription
Transcription is the process of making an RNA copy of a gene sequence. This copy, called a
messenger RNA (mRNA) molecule, leaves the cell nucleus and enters the cytoplasm, where it
directs the synthesis of the protein, which it encodes. Here is a more complete definition of
transcription.
• Define translation
Translation is the process of translating the sequence of a messenger RNA (mRNA) molecule to
a sequence of amino acids during protein synthesis. The genetic code describes the relationship
between the sequence of base pairs in a gene and the corresponding amino acid sequence that it
encodes. In the cell cytoplasm, the ribosome reads the sequence of the mRNA in groups of three
bases to assemble the protein. Here is a more complete definition of translation:
• What are the 3 steps of translation?
Step # 1. Initiation:
Initiation of translation in E .coli involves the small ribosome subunit, a mRNA molecule, a
specific charge initiator tRNA, GTP, Mg++ and number of proteinaceous initiation factors (IFs).
These are initially part of the small subunit and are required to enhance binding affinity of the
various translational components (Table 8.1). Unlike ribosomal proteins, IFs are released from
the ribosome once initiation is completed.
Step # 2. Elongation:
Once both subunits of the ribosome are assembled with the mRNA, binding site for two charged
tRNA molecules are formed. These are designated as the ‘P’ or peptidyl and the ‘A’ or
aminoacyl sites. The charged initiator tRNA binds to the P site, provided that the AUG triplet of
mRNA is in the corresponding position of the small subunit. The increase of the growing
polypeptide chain by one amino acid is called elongation.
Step # 3. Termination:
Termination of protein synthesis is carried out by triplet codes (UAG, UAA, UGA; stop codons)
present at site A. These codons do not specify an amino acid, nor do they call for a tRNA in the
A site. These codons are called stop codons, termination codons or nonsense codons. The
finished polypeptide is still attached to the terminal tRNA at the P site, and the A site is empty.
• Define the “genetic dogma”
A theory in genetics and molecular biology subject to several exceptions that genetic information
is coded in self-replicating DNA and undergoes unidirectional transfer to messenger RNAs in
transcription which act as templates for protein synthesis in translation
• What is the function of Transfer RNA?
The tRNA molecule, or tr.
Protein synthesis is the process whereby biological cells generate new proteins. Translation, the assembly of amino acids by ribosomes, is an essential part of the biosynthetic pathway, along with generation of messenger RNA (mRNA), aminoacylation of transfer RNA (tRNA), co-translational transport, and post-translational modification. Protein biosynthesis is strictly regulated at multiple steps. They are principally during transcription (phenomenon of RNA synthesis from DNA template) and translation (phenomenon of amino acid assembly from RNA). The cistron DNA is transcribed into the first of a series of RNA intermediates. The last version is used as a template in synthesis of a polypeptide chain. Protein will often be synthesized directly from genes by translating mRNA. A proprotein is an inactive protein containing one or more inhibitory peptides that can be activated when the inhibitory sequence is removed by proteolysis during post translational modification. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide) that specifies its insertion into or through membranes, i.e., targets them for secretion. The signal peptide is cleaved off in the endoplasmic reticulum. Preproteins have both sequences (inhibitory and signal) still present. In protein synthesis, a succession of tRNA molecules charged with appropriate amino acids are brought together with an mRNA molecule and matched up by base-pairing through the anti-codons of the tRNA with successive codons of the mRNA. The amino acids are then linked together to extend the growing protein chain, and the tRNAs, no longer carrying amino acids, are released. This whole complex of processes is carried out by the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. The ribosome latches onto the end of an mRNA molecule and moves along it, capturing loaded tRNA molecules and joining together their amino acids to form a new protein chain.
The process by which an RNA copy of a gene is made or it’s a DNA dependent RNA synthesis.
Transcription resembles replication
In its fundamental chemical mechanism
Its polarity (direction of synthesis)
Its use of a template
Transcription differs from replication
It does not requires a primer
It involves only limited segments of a DNA molecule
Within transcribed segments only one DNA strand serves as a template for synthesis of RNA.
Lecture notes from biology of cells and molecules course 1200, Transcription and translation lecture notes overview of transcription and translation process in eukaryotic and prokaryotic cells.
Transcription and synthesis of different RNAs
Processing of RNA transcript
Catalytic RNA
RNA splicing and Spliceosome
Transport of RNA through nuclear pore
Translation and polypeptide synthesis
Posttranslational modification
Protein trafficking and degradation
Antibiotics and inhibition of protein synthesis.
Replication,transcription,translation complete the central dogma of life.How mRNA,tRNA,rRNA act on ribosomes for protein synthesis.Difference between eukaryotes and prokaryotes
The process by which an RNA copy of a gene is made or it’s a DNA dependent RNA synthesis.
Transcription resembles replication
In its fundamental chemical mechanism
Its polarity (direction of synthesis)
Its use of a template
Transcription differs from replication
It does not requires a primer
It involves only limited segments of a DNA molecule
Within transcribed segments only one DNA strand serves as a template for synthesis of RNA.
Lecture notes from biology of cells and molecules course 1200, Transcription and translation lecture notes overview of transcription and translation process in eukaryotic and prokaryotic cells.
Transcription and synthesis of different RNAs
Processing of RNA transcript
Catalytic RNA
RNA splicing and Spliceosome
Transport of RNA through nuclear pore
Translation and polypeptide synthesis
Posttranslational modification
Protein trafficking and degradation
Antibiotics and inhibition of protein synthesis.
Replication,transcription,translation complete the central dogma of life.How mRNA,tRNA,rRNA act on ribosomes for protein synthesis.Difference between eukaryotes and prokaryotes
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Transcription- an overview of DNA transcription (article) | Khan Academy.pdf
1. ·
·
·
In transcrip!on, the DNA sequence of a gene is
transcribed (copied out) to make an RNA molecule.
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Key points:
Transcrip!on is the first step in gene
expression. It involves copying a gene's
DNA sequence to make an RNA
molecule.
Transcrip!on is performed by enzymes
called RNA polymerases, which link
nucleo!des to form an RNA strand (using
a DNA strand as a template).
Transcrip!on has three stages: ini!a!on,
elonga!on, and termina!on.
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Overview
of transcrip!on
Science AP®/College Biology
Gene expression and regula!on
Transcrip!on and RNA processing
2. In eukaryotes, RNA molecules must be
processed a#er transcrip!on: they are
spliced and have a 5' cap and poly-A tail
put on their ends.
Transcrip!on is controlled separately for
each gene in your genome.
Introduc!on
Have you ever had to transcribe something?
Maybe someone le# a message on your
voicemail, and you had to write it down on
paper. Or maybe you took notes in class,
then rewrote them neatly to help you review.
As these examples show, transcrip!on is a
process in which informa!on is rewri"en.
Transcrip!on is something we do in our
everyday lives, and it's also something our
cells must do, in a more specialized and
narrowly defined way. In biology,
transcrip!on is the process of copying out
the DNA sequence of a gene in the similar
alphabet of RNA.
Overview of transcrip!on
3. Transcrip!on is the first step in gene
expression, in which informa!on from a gene
is used to construct a func!onal product
such as a protein. The goal of transcrip!on is
to make a RNA copy of a gene's DNA
sequence. For a protein-coding gene, the
RNA copy, or transcript, carries the
informa!on needed to build a polypep!de
(protein or protein subunit). Eukaryo!c
transcripts need to go through some
processing steps before transla!on into
proteins.
RNA polymerase
The main enzyme involved in transcrip!on is
RNA polymerase, which uses a single-
stranded DNA template to synthesize a
complementary strand of RNA. Specifically,
RNA polymerase builds an RNA strand in the
:
4. 5' to 3' direc!on, adding each new nucleo!de
to the 3' end of the strand.
Stages of transcrip!on
Transcrip!on of a gene takes place in three
stages: ini!a!on, elonga!on, and
termina!on. Here, we will briefly see how
these steps happen in bacteria. You can learn
more about the details of each stage (and
about how eukaryo!c transcrip!on is
different) in the stages of transcrip!on
ar!cle.
1. Ini!a!on. RNA polymerase binds to a
sequence of DNA called the promoter,
found near the beginning of a gene. Each
gene (or group of co-transcribed genes,
in bacteria) has its own promoter. Once
bound, RNA polymerase separates the
DNA strands, providing the single-
stranded template needed for
transcrip!on.
:
5. 2. Elonga!on. One strand of DNA, the
template strand, acts as a template for
RNA polymerase. As it "reads" this
template one base at a !me, the
polymerase builds an RNA molecule out
of complementary nucleo!des, making a
chain that grows from 5' to 3'. The RNA
transcript carries the same informa!on
as the non-template (coding) strand of
DNA, but it contains the base uracil (U)
instead of thymine (T).
[What do 5' and 3' mean?]
:
6. 3. Termina!on. Sequences called
terminators signal that the RNA
transcript is complete. Once they are
transcribed, they cause the transcript to
be released from the RNA polymerase.
An example of a termina!on mechanism
involving forma!on of a hairpin in the
RNA is shown below.
Eukaryo!c RNA
modifica!ons
In bacteria, RNA transcripts can act as
messenger RNAs (mRNAs) right away. In
:
7. eukaryotes, the transcript of a protein-coding
gene is called a pre-mRNA and must go
through extra processing before it can direct
transla!on.
Eukaryo!c pre-mRNAs must have their
ends modified, by addi!on of a 5' cap (at
the beginning) and 3' poly-A tail (at the
end).
Many eukaryo!c pre-mRNAs undergo
splicing. In this process, parts of the pre-
mRNA (called introns) are chopped out,
and the remaining pieces (called exons)
are stuck back together.
End modifica!ons increase the stability of
the mRNA, while splicing gives the mRNA its
correct sequence. (If the introns are not
removed, they'll be translated along with the
exons, producing a "gibberish" polypep!de.)
To learn more about pre-mRNA modifica!ons
in eukaryotes, check out the ar!cle on pre-
:
8. mRNA processing.
Transcrip!on happens for
individual genes
Not all genes are transcribed all the !me.
Instead, transcrip!on is controlled
individually for each gene (or, in bacteria, for
small groups of genes that are transcribed
together). Cells carefully regulate
transcrip!on, transcribing just the genes
whose products are needed at a par!cular
moment.
For example, the diagram below shows a
"snapshot" of an imaginary cell's RNAs at a
given moment in !me. In this cell, genes 1, 2
and 3, are transcribed, while gene 4 is not.
Also, genes 1, 2, and 3 are transcribed at
different levels, meaning that different
numbers of RNA molecules are made for
each.
In the following ar!cles, we'll take a more in-
:
9. depth look at RNA polymerase, the stages of
transcrip!on, and the process of RNA
modifica!on in eukaryotes. We'll also
consider some important differences
between bacterial and eukaryo!c
transcrip!on.
[References]
Sort by: Top Voted
Ques!ons Tips & Thanks
Want to join the conversa!on?
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Anson Chan 6 years ago
more
The hairpin somewhat appears to
look like a tRNA molecule. Am I
wrong in saying that tRNA is formed
from these hairpin structures?
•
Answer Comment
(19
votes)
Upvote
6
more
:
10. emilyabrash
6
years
ago
more
No, you're not wrong. A
tRNA contains hairpins as
well, though the hairpins
play different roles in the
two cases. In transcrip!on
termina!on, the hairpin
causes the RNA
polymerase to stall and the
transcript to separate from
the DNA. In a tRNA,
mul!ple hairpins form and
give the tRNA molecule
the 3D shape it needs to
perform its job of
delivering amino acids.
Comment
(27
votes)
Upvote
Sukidhar9 4 years ago
more
if introns are not important, why are
introns are formed?
•
Answer Comment
(12
votes)
Upvote
tyersome
4
years
ago
…
Good ques!on!
Introns have mul!ple roles
in biology including the
regula!on of gene
expression.
Other introns have
func!ons a#er they are
spliced out from the
:
11. spliced out from the
transcript and can act as
signaling or regulatory
molecules.
Some rela!vely rare types
of introns appear to be
parasi!c DNA molecules
— they insert copies of
themselves into genes and
then splice themselves out
from the RNA presumably
to keep the host cell alive.
It is possible that the more
typical introns originated
from such parasi!c DNA
elements.
This is s!ll an area of
ac!ve research and it is
quite likely that more
func!ons for introns will
be uncovered in the
future.
If you wish to know more,
you could start with this
sec!on of the wikipedia
ar!cle on introns:
h"ps:/
/en.wikipedia.org/wi
ki/Intron#Biological_func!
ons_and_evolu!on
2
comments
(18
votes)
Upvote
:
12. sreelakshmi.s
6 years
ago
mo…
do the presence of introns indicate
something related to evolu!on?
•
Answer Comment
(5
votes)
Upvote
Meggie Lund
6
years
ago
more
Not really. Introns enable
one gene to produce
mul!ple polypep!de
sequences, thereby
crea!ng a more efficient
genome. This will make
more sense if you look at
the examples in the pre-
mRNA processing ar!cle. I
think you're thinking of
pseudogenes, which are
non-coding regions
remaining in an organism's
:
13. See 3 more answers
remaining in an organism's
DNA from ancestral roots.
You're correct in your
conclusion that introns are
non-coding, but just
because a sequence is an
intron in one pre-mRNA
sequence doesn't mean
that it can't be included in
the exon sequence in
another.
1
comment
(10
votes)
Upvote
will.butacu 5 years ago
more
What I don't understand is: If the
Promoter is located at the 5' end of
a gene how does RNA polymerase
start there if it reads from 3' to 5'
and syntetase RNA from 5' to 3?
•
Answer Comment
(4
votes)
Upvote
tyersome
5 years
ago
…
The RNA is actually
synthesized using the
an!sense (complementary)
strand as the template.
2
comments
(4
votes)
Upvote
Priyanka 4 years ago
more
Hi, this isn't men!oned in this
:
14. Hi, this isn't men!oned in this
ar!cle, but I would like to ask,
What is the difference between a
gene and a cistron? Why do we
need the term , cistron, in the first
place?
And what do the terms
monocistronic and polycistronic
mean?
•
Answer Comment
(4
votes)
Upvote
tyersome
4 years
ago
…
Really there isn't much
difference — as far as I
know the existence of the
two terms is an accident of
history — my advice would
be to use gene.
Many prokaryo!c (and a
few eukaryo!c) genes are
transcribed together into a
single mRNA and then
translated separately from
the single mRNA. These
situa!ons are described as
"polycistronic". The more
common condi!on of one
transcript encoding a
single protein is thus
"monocistronic".
Confusingly, the en!re
mul!gene (polycistronic)
unit will o#en be referred
to as an operon. Operons
are typically made up of
genes encoding proteins
that work together in an
:
15. that work together in an
organism and this
structure ensures that they
are all made at the same
!me and in similar
quan!!es.
You can read more about
this here:
h"ps:/
/www.khanacademy
.org/science/biology/gene-
regula!on/gene-
regula!on-in-
bacteria/v/operons-and-
gene-regula!on-in-
bacteria
And for a bit more detail:
h"ps:/
/en.wikipedia.org/wi
ki/Operon
Comment
(4
votes)
Upvote
aryan0904 4 years ago
more
Are there other ways that the
mRNA strand could detach from the
DNA strand instead of the hairpin
turn? And what would happen if the
mRNA nucleo!de accidentally gets
changed instead of the normal one
ie. a muta!on?
•
Answer Comment
(3
votes)
Upvote
tyersome
4 years
ago
…
This is briefly covered in
the next ar!cle — short
answer: yes, but
:
16. answer: yes, but
transcrip!on termina!on
is s!ll being ac!vely
studied and is not
completely understood.
Addi!onal reading:
h"ps:/
/en.wikipedia.org/wi
ki/Eukaryo!c_transcrip!o
n#Termina!on
h"ps:/
/www.nature.com/s
citable/topicpage/dna-
transcrip!on-426
I'm not completely sure I
understand your second
ques!on — are you asking
what would happen if the
"wrong" base was
incorporated into an
mRNA?
If so, probably not much
since each gene typically
will make mul!ple
transcripts and most
mRNAs have a very short
life!me. (Note that this is
almost certainly something
that happens all the !me
since all biological
processes make errors.)
While I've never see any
evidence that any of this
ever actually happens, it
seems possible that in rare
cases the change might
make an mRNA encode a
toxic protein that could kill
a cell or worse yet trigger
:
17. a cell or worse yet trigger
cancer forma!on. I
suppose if you were
spectacularly unlucky it
might even promote prion
forma!on (a contagious
toxic protein structure).
Comment
(5
votes)
Upvote
Megan Sullivan
6 years
ago
m…
does the hairpin structure come in
to play in transcrip!on?
•
Answer Comment
(1
vote)
Upvote
SpinosaurusRex
6
years
ago
more
A hairpin loop is an
unpaired loop of
messenger RNA (mRNA)
that is created when an
mRNA strand folds and
forms base pairs with
another sec!on of the
same strand. The resul!ng
structure looks like a loop
or a U-shape.
Hairpins are a common
type of secondary
structure in RNA
molecules. In RNA, the
secondary structure is the
basic shape that the
sequence of A, C, U, and G
nucleo!des form a#er
they are linked in series,
such a folding or curling of
:
18. such a folding or curling of
the nucleic acid strand.
mRNA hairpins can be
formed when two
complementary sequences
in a single mRNA molecule
meet and bind together,
a#er a folding or wrinkling
of the molecule. Hairpin
loops can also form in
DNA molecules, but are
most commonly observed
in mRNA.
There are many instances
of the hairpin loop
phenomenon among
nucleic acid strands. One
example of a hairpin loop
is the termina!on
sequence for transcrip!on
in some prokaryotes. Once
a polymerase meets this
loop, it falls of and
transcrip!on ends.
Another more general
example is tRNA, a central
player in protein synthesis,
which is par!ally formed
by hairpin loops. The tRNA
molecule actually contains
three hairpin loops that
form the shape of a three-
leafed clover. One of these
hairpin loops contains a
sequence called the
an!codon, which
recognizes and decodes
the mRNA molecule three
nucleo!des (one codon) at
a !me during transla!on.
This clover-leaf structure
:
19. This clover-leaf structure
supports the eventual
connec!on between every
codon, an!-codon and
amino acid.
h"p:/
/www.nature.com/sci
table/defini!on/hairpin-
loop-mrna-314
Comment
(9
votes)
Upvote
Tzviofen 2 years ago
more
Does the transcribed region always
start with bases TAC, so that the
RNA will start with bases AUG,
which codes for methionine?
•
Answer Comment
(3
votes)
Upvote
RowanH
2 years
ago
…
No, transcrip!on starts
upstream of the AUG, so
the mRNA contains a 5'
untranslated region. Then
ribosomes translate
star!ng from the AUG in
the mRNA. The details of
how they find the AUG is
different in eukaryotes and
prokaryotes.
Comment
(3
Upvote
:
20. Comment
(3
votes)
Upvote
Tammie Derpine
4 years
ago
m…
Won't the RNA have the wrong
sequence if the introns are spliced,
or is it predetermined to omit the
codons in the introns in order to
have the "perfect" code in the
mature RNA?
•
Answer Comment
(3
votes)
Upvote
Jen
4 years
ago
mo…
Introns are actually
noncoding DNA segments
(in other words, they do
not code for proteins), so
splicing them out actually
helps produce a func!onal
protein rather than
poten!ally disrupt protein
func!on. However, this
doesn't mean introns are
useless either; in fact, they
are actually very important
for regula!ng gene
expression.
We've learned a lot about
introns since their
discovery but many
ques!ons about them and
their func!ons s!ll remain
unresolved. You can learn
more about them in the
link below. Hope that
helps!
:
