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Principles of Biology
50
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Translation
Translation is the process by which a cell assembles proteins from the genetic code.
The Rosetta stone.
To translate from one language to another, you need a set of comparative rules that act as a template. The
Rosetta stone is concrete evidence of how languages were first translated in early human cultures. By
displaying the same story in different languages, it served as a template for comparison, a reference for how to
get from one language to another. In cells, microscopic structures called ribosomes serve as key sites that
support the translation of the mRNA language into the protein language.
Archiv/Photo Researchers/Science Source.
Topics Covered in this Module
Translating DNA into Proteins
Major Objectives of this Module
Describe the molecular structures involved in translation.
Explain the process of translation in detail.
Explain how post-translational processes prepare proteins for their functions.
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Principles of Biology
50 Translation
How does a genetic code with only four nucleotides provide the information
needed to generate proteins containing up to 20 different amino acids? For
this process to occur, many enzymes with specific structures and function
are required.
Translating DNA into Proteins
Translation is the process of converting the information stored in mRNA into
protein (Figure 1). Proteins are made up of a series of amino acids. With the
help of adapter molecules called transfer RNAs (tRNAs) the appropriate
amino acid is added for each set of three adjacent nucleotides in the mRNA,
called a codon (Figure 2). Transfer RNAs transfer amino acids from a pool of
cytoplasmic amino acids to the growing polypeptide.
Figure 1: Translation of mRNA into protein.
mRNA carries genetic information required for the synthesis of a specific
protein as a series of three-nucleotide units called codons. In the process
of translation, a sequence of nucleotides in a molecule of mRNA is
converted to a sequence of amino acids in a polypeptide. A strand of
mRNA is translated into a linear protein strand. Translation occurs in the 5′
to 3′ direction on the mRNA strand.
© 2014 Nature Education All rights reserved.
Figure Detail
contents
Figure 2: Transfer RNA (tRNA) links codons in mRNA to amino acids
in proteins.
tRNAs are adaptor molecules that base pair with codons in the mRNA.
They bring the amino acids corresponding to each codon and facilitate
their addition to the growing polypeptide.
© 2014 Nature Education All rights reserved.
Figure Detail
Why is a codon made up of three nucleotides, and not one or two
nucleotides? For gene expression to occur successfully, different
arrangements of the four mRNA nucleotides A, G, C, and U must determine
the sequence of the amino acids that make up a protein. How are 20
different amino acids encoded using only 4 nucleotides? Since there are 20
amino acids and only 4 possible nucleotides, the relationship between a
nucleotide in the mRNA sequence and an amino acid in the protein
sequence cannot be one-to-one. If two nucleotides coded for an amino acid,
they would only encode a maximum of 16 amino acids (42=16). However, if
three nucleotides code for an amino acid, 64 variations (43=64) are possible.
Experiments with short stretches of synthetic mRNA demonstrated that a
codon is made up of three adjacent nucleotides.
Since there are 64 possible codons and only 20 amino acids, most amino
acids are coded for by multiple codons (Figure 3). There are also three stop
codons, UAA, UAG, and UGA, which do not code for any amino acid but
instead signal the termination of translation. Just as there are stop codons,
there is also a start codon. The codon AUG codes for the amino acid
methionine (Met), but if encountered in conjunction with other signals, AUG
also indicates the start of translation.
Figure 3: Table of codons.
Three-letter sequences of nucleotides, called codons, code for amino
acids. To find a specific codon in the table, start by finding the first letter
on the left side of the table. Then find the second letter along the top and
the third letter along the right side of the table.
© 2013 Nature Education All rights reserved.
Figure Detail
Test Yourself
If a mutation changed the third nucleotide of a codon where the first nucleotide is U and the
second nucleotide is C, what do you expect the result would be for the polypeptide generated?
Submit
The genetic code is nearly universal to all known species on Earth. There
are a few exceptions such as mitochondria, chloroplasts and some
prokaryotes. However, it is clear that the exceptions are very few and affect
very few codons. Furthermore, all known genetic codes are more similar
than different to each other, which supports the assertion that all life started
from a common ancestor.
Transfer RNA carries amino acids to the ribosome, the site of protein
synthesis.
How do transfer RNA molecules add the correct amino acid to the growing
protein? The mRNA and tRNAs are brought together by a protein-RNA
complex called a ribosome. Each tRNA molecule has a specific amino acid
at one end and a nucleotide triplet, known as an anticodon, at the other
(Figure 4). The nucleotides in the anticodon base pair with the
complementary codons on the mRNA in an antiparallel orientation. For
example, the codon 5′–GCU–3′ will pair with the anticodon 3′–CGA–5′ and
bring the tRNA for alanine (Ala) into the ribosome.
Figure 4: Schematic of tRNA.
tRNAs are short molecules that are around 80 nucleotides long. In this
schematic, the anticodon is highlighted at the bottom, and the amino acid
corresponding to the tRNA appears at the top.
© 2014 Nature Education All rights reserved.
tRNA molecules are created by transcribing information stored in DNA. In
eukaryotes, tRNA is generated in the nucleus and then exported to the
cytoplasm to carry out its role in translation. In both prokaryotes and
eukaryotes, a tRNA molecule is used over and over. It picks up an amino
acid, adds it to a growing polypeptide chain, leaves the ribosome and is
ready to pick up another amino acid and begin the process again.
The process of matching a specific tRNA with the appropriate amino acid is
carried out by a family of enzymes called aminoacyl-tRNA synthetases
(Figure 5). There is a different synthetase for each of the 20 amino acids.
Each synthetase contains an active site that fits only a specific combination
of tRNA and amino acid. In addition, each synthetase is able to bind all of the
tRNAs that code for its amino acid. The covalent attachment of the tRNA and
the amino acid requires the hydrolysis of ATP. A tRNA to which an amino
acid has been added is called an aminoacyl-tRNA or a charged tRNA. After
charging, the aminoacyl-tRNA is released from the synthetase and is ready
for translation.
Figure 5: Formation of an aminoacyl-tRNA.
Enzymes called aminoacyl-tRNA synthetases facilitate the covalent
bonding of the appropriate amino acid to each tRNA molecule. In the first
step (upper left), the enzyme catalyzes the linkage of ATP to an amino
acid specific to each aminoacyl-tRNA synthetase. After the release of a
pyrophosphate group, an amino acid-AMP intermediate remains bound to
the enzyme (upper right). In the next step, the uncharged tRNA
corresponding to the specific amino acid enters the active site of the
enzyme (lower right), where it is linked to the amino acid, producing the
charged tRNA and releasing AMP in the process (bottom). The charged
tRNA leaves the active site, and the enzyme becomes available again
(lower left).
© 2014 Nature Education All rights reserved.
Test Yourself
What would you expect the result to be if a cell contains a mutation that knocks out a
particular aminoacyl-tRNA synthetase?
Submit
A ribosome is made up of a small subunit and a large subunit. A ribosome
has three sites that the tRNA moves through as translation occurs. The
growing polypeptide chain is held by the tRNA in the P site (Peptidyl-tRNA
binding site). The charged tRNA carrying the next amino acid to be added
enters at the A site (Aminoacyl-tRNA binding site). A peptide bond is formed
between the growing chain and the next amino acid to be added. This
reaction moves the growing polypeptide to the tRNA in the A site. The tRNA
in the A site now moves to the P site, and the tRNA in the P site moves to
the E site (Exit site), where it is released from the ribosome (Figure 6).
Figure 6: The three sites in the ribosome.
Charged tRNA enters the ribosome in the A site, moves to the P site as a
new peptide bond is formed between its amino acid and the growing
polypeptide chain, and finally exits through the E site after its amino acid
has been transferred.
© 2014 Nature Education All rights reserved.
Figure Detail
The ribosome keeps the mRNA and tRNA close to each other and brings the
next amino acid to the carboxyl end of the growing polypeptide. Without the
ribosome, the hydrogen bonding between the tRNA and mRNA would be too
weak to hold it there long enough for a peptide bond to form. The ribosome
catalyzes the peptide bond formation that adds the amino acid to the
polypeptide. Experiments have supported the hypothesis that it is the
ribosomal RNA (rRNA) and not the ribosomal proteins that contains the
catalytic site for the peptide bond formation function of ribosomes.
While the function of ribosomes is the same in prokaryotes and eukaryotes,
the proteins and RNAs that make up their ribosomes are different. Humans
have taken advantage of some of the differences between bacterial and
human ribosomes to develop antibiotics that are safe for human
consumption but kill harmful bacteria by disrupting bacterial protein
synthesis. We have discovered these antibiotics in microbes, which use them
to disrupt competing bacteria's protein synthesis. For example, tetracyclines,
a family of antibiotics produced by Streptomyces bacteria, bind to the small
ribosomal subunit in competing bacteria and alter its structure so that an
aminoacyl-tRNA cannot bind to the A site. We now prescribe these
antibiotics as a treatment for bacterial infections. Unfortunately, many strains
of the bacteria targeted by tetracyclines have developed a resistance to
tetracycline by producing a protein that protects the bacteria's ribosomes
from binding the antibiotic. The factors that influence the action of antibiotics
and the evolutionary counter-measures of the bacteria they target are areas
of great interest and importance at the intersection of basic biology and
human health.
Enzymes mediate translation.
Like transcription, translation has three phases: initiation, elongation and
termination. Each phase requires protein factors that aid in the process. And
energy, provided by hydrolysis of guanosine triphosphate (GTP), is
required for initiation, elongation and termination.
Initiation occurs when the small ribosomal subunit binds to the mRNA at the
5′ end and scans the mRNA in a 3′ direction until it reaches the start codon
(Figure 7). A specialized initiator tRNA, with the anticodon 3′-UAC-5′, pairs
with the start codon, 5′-AUG-3′, at the P site of the ribosome. In prokaryotes,
an AUG must be preceded by a specific sequence in order to be interpreted
as the start codon. This sequence is recognized by an mRNA binding site in
the small ribosomal subunit and helps position the start codon in the P site.
In eukaryotes, the first AUG encountered by the ribosome is the start codon,
but translation initiation normally also requires the 5′ cap that is added during
mRNA processing following transcription. The initiator tRNA is charged with
methionine (Met) in eukaryotes and with a chemically modified methionine,
N-formylmethionine (fMet), in prokaryotes. Once the start codon is found,
proteins known as initiation factors facilitate the binding of the large
ribosomal subunit to the small ribosomal subunit. GTP is hydrolyzed to
provide energy for the assembly of the subunits to form the translation
initiation complex.
Figure 7: Initiation of translation.
The small ribosomal subunit binds the mRNA, and the initiator tRNA binds
the start codon. The recognition of the start codon is facilitated by an
initiation factor protein. Two other initiation factors prevent the large
ribosomal subunit from binding before the arrival of the initiator tRNA.
Upon binding of the initiator tRNA to the mRNA, GTP is hydrolyzed, and
the large subunit binds to the small subunit to form the translation initiation
complex.
© 2014 Nature Education All rights reserved.
Synthesis of the polypeptide always occurs in the same direction, with the
initial methionine at the amino end, known as the N-terminus. Each amino
acid is added at the carboxyl end of the previous amino acid. The end of a
polypeptide sequence is thus known as the C-terminus.
During elongation, amino acids are added to the C-terminus of the growing
polypeptide. Elongation is a three-step process that requires the participation
of GTP and proteins called elongation factors. First, the aminoacyl-tRNA
with the anticodon matching the next codon on the mRNA is brought to the A
site by an elongation factor. Many tRNAs are present around the ribosome,
but only the aminoacyl-tRNA with the appropriate anticodon will remain at
the A site (Figure 8). When correct base pairing between the mRNA codon
and aminoacyl-tRNA anticodon occurs, the elongation factor hydrolyzes
GTP, which releases the aminoacyl-tRNA into the ribosome.
Next, the large ribosomal subunit catalyzes the formation of a peptide bond
between the carboxyl end of the growing polypeptide in the P site and the
amino group of the amino acid in the A site. This moves the growing
polypeptide to the tRNA in the A site and unlinks the polypeptide from the
tRNA currently in the P site. Energy from GTP hydrolysis is not required in
this step.
Finally, the tRNA with the growing polypeptide chain is translocated from the
A site to the P site. The uncharged tRNA that was in the P site is
translocated to the E site, where it is released from the ribosome. The
ribosome moves along the mRNA with the attached tRNAs, and the next
codon is brought into the A site. This step is facilitated by another elongation
factor, which requires the hydrolysis of GTP each time a translocation event
occurs.
Figure 8: Elongation.
Elongation requires the hydrolysis of two GTP molecules and involves
matching an amino acid-charged tRNA to a codon in the mRNA, forming a
new peptide bond between the new amino acid and the previous one, and
translocating the ribosome to the next codon.
© 2014 Nature Education All rights reserved.
Elongation continues until a stop codon is reached. The codons UAG, UAA
and UGA do not code for amino acids, and there are normally no tRNAs with
anticodons corresponding to the stop codons; instead, these three codons
are signals to terminate translation. When a stop codon appears at the A
site, a protein shaped like an aminoacyl-tRNA called a release factor enters
the A site and binds to the stop codon. The release factor causes a water
molecule to be added to the polypeptide chain instead of an amino acid. This
breaks the bond between the tRNA and the polypeptide in the P site. The
polypeptide is released through the exit tunnel of the ribosome's large
subunit. The translation assembly breaks apart in a process that requires the
hydrolysis of a GTP molecule (Figure 9).
Figure 10 summarizes the steps of translation. There are several notable
differences in the translation process between prokaryotes and eukaryotes.
In prokaryotes, a single mRNA may have multiple start and stop codons and
can therefore direct the production of multiple polypeptides. Furthermore,
prokaryotic translation may start as soon as a start codon is transcribed from
the DNA since there is no mRNA processing or separation of nucleus and
cytoplasm. In eukaryotes, mRNA is transcribed and processed in the nucleus
and then exported to the cytoplasm for translation. As a result, transcription
and translation are separated in space and time and cannot occur
simultaneously as in prokaryotes. In addition, translation initiation requires
the 5′ cap, so only the AUG nearest the 5′ cap is used as the start codon
even if there are multiple start and stop codons in the mRNA. As a result, a
single mRNA usually directs the production of only one polypeptide in
eukaryotes.
Figure 9: Termination of translation.
Translation terminates when the ribosome encounters a stop codon, and a
release factor (instead of a tRNA) binds to the stop codon in the A site.
The release factor helps separate the complete polypeptide from the last
tRNA. The complete polypeptide is released from the ribosome, and the
ribosomal subunits are disassembled and recycled for translating other
mRNAs. Termination requires the hydrolysis of a GTP molecule.
© 2014 Nature Education All rights reserved.
Figure 10: Putting the steps of translation together.
This figure summarizes the three phases of translation: initiation,
elongation, and termination. Each phase involves a specific set of protein
factors, as well as chemical energy largely supplied by GTP hydrolysis.
© 2014 Nature Education All rights reserved.
Test Yourself
What steps of translation require energy to occur?
Submit
It takes less than a minute for a ribosome to translate an average-size
polypeptide. And multiple ribosomes are able to translate an mRNA molecule
at the same time. Once a ribosome has cleared the start codon, another
ribosome is able to attach to the start site and begin translation. A string of
ribosomes along an mRNA is called a polyribosome (Figure 11).
Polyribosomes allow a cell to make large quantities of protein very quickly.
Figure 11: Polyribosomes.
Multiple ribosomes can translate an mRNA molecule at the same time. In
this figure, each ribosome is synthesizing a polypeptide independently of
the others, resulting in a large number of polypeptide molecules
synthesized using the same mRNA molecule.
© 2014 Nature Education All rights reserved.
Post-translational modifications prepare proteins for their functions.
As translation occurs, the polypeptide folds spontaneously due to its primary
sequence. Frequently, a chaperone protein called chaperonin also aids in
proper folding. However, many proteins require additional modifications after
translation to become fully functional.
There are many types of post-translational modification. Proteolysis is the
cleavage of a regulatory subunit from a polypeptide to convert an inactive
precursor to its active form. Glycosylation is the addition of carbohydrates to
the polypeptide chain to aid in targeting and recognition. Phosphorylation is
the addition of phosphate groups to the polypeptide to alter the shape and
therefore the activity of the protein. And other proteins may not be functional
alone but require assembly with other polypeptides to form a functional multisubunit protein complex.
In addition to post-translational modifications, proteins sometimes must be
targeted to specific locations in the cell to be functional. For example, a
sodium-potassium pump serves no purpose in the cytosol but must be
inserted into the plasma membrane to move ions in and out of the cell. Other
proteins, such as peptide hormones, are ultimately secreted out of the cell.
Instead of remaining in the cytosol, such proteins must pass through the
secretory pathway — endoplasmic reticulum (ER), Golgi apparatus and
plasma membrane.
Regardless of a polypeptide's final destination, translation always begins with
free ribosomes in the cytosol and will continue there unless the growing
polypeptide contains a signal that causes the ribosome to attach to the ER.
Polypeptides that are destined to be integral membrane proteins or secreted
proteins contain a signal peptide, an approximately 20 amino acid
sequence near the N-terminus. This sequence is recognized as it emerges
from the ribosome by a protein-RNA complex known as the signal-
recognition particle (SRP). The SRP escorts the ribosome to a receptor
protein in the ER membrane, and the polypeptide is translocated across the
ER membrane into the ER lumen as translation continues (Figure 12). From
there, the polypeptide passes through the Golgi apparatus to the plasma
membrane, where it is exocytosed (for a secreted protein) or remains
embedded in the membrane (for an integral membrane protein).
Figure 12: Targeting polypeptides to the ER.
A signal-recognition particle (SRP) directs the protein-synthesizing
ribosome to the ER membrane. Translation of the polypeptide continues
as the polypeptide is directly translocated across the membrane.
© 2014 Nature Education All rights reserved.
There are other signal peptides that bring polypeptides to other cellular
structures including the nucleus, mitochondria, chloroplasts and other
organelles. However, for these structures, translation occurs in the cytosol
and then the polypeptide is imported into the appropriate structure.
Test Yourself
How does the sequence of a polypeptide target it to a specific structure within the cell?
Submit
BIOSKILL
Western Blot.
How do scientists determine if a protein is being synthesized? One technique
for detecting a specific protein from a cell sample or tissue is a western blot,
also known as a protein immunoblot.
Proteins are separated using gel electrophoresis. One type of gel
electrophoresis is called SDS-PAGE, which separates proteins by size. Next,
the proteins are transferred to a special blotting paper, generally made of
nitrocellulose. The protein pattern from the gel is the same as the pattern on
the blotting paper. The blot is then "blocked" with nonspecific proteins,
commonly derived from cow's milk, which will cover any open protein-binding
regions left on the paper.
To identify the specific protein of interest, an antibody is added that will only
bind to the specific protein. Once the primary antibody is bound, a secondary
antibody is added that binds to the primary antibody. The secondary antibody
is bound to an enzyme or chemical that becomes visible when the proper
substrate is added (Figure 13).
Figure 13: Western blot.
A specific protein can be visualized by isolating the protein by gel
electrophoresis and using a specific antibody to identify the protein on a
paper blot. In the first step, a mixture of protein is separated by size using
SDS-PAGE electrophoresis. The proteins are then transferred to a
nitrocellulose membrane, and the membrane is probed with an antibody
specific to the protein of interest. The antibody itself may carry a label, or it
may be recognized by a labeled secondary antibody (bottom). In both
cases, the label results in the appearance of a dark band corresponding to
the protein of interest when the membrane is exposed to film.
© 2011 Nature Education All rights reserved.
Figure Detail
Test Yourself
Researchers have created a line of mutant cells that are missing a particular protein. A
western blot is performed to look at a sample of wild-type cells and a sample of the mutant
cells. What do you expect to see on the western blot?
Submit
BIOSKILL
IN THIS MODULE
Translating DNA into Proteins
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
Synthetic Biology: Making Life from
Bits and Pieces
Scientists are combining biology and
engineering to change the world.
PRIMARY LITERATURE
Classic paper: How scientists
discovered the enzyme that turns
RNA into DNA (1970)
RNA-dependent DNA polymerase in virions
of RNA tumour viruses.
View | Download
SCIENCE ON THE WEB
How Small?
See the difference between a coffee bean
and a single atom.
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Principles of Biology
50 Translation
Summary
Describe the molecular structures involved in translation.
Ribosomes are RNA-protein complexes that facilitate translation.
Aminoacyl-tRNA synthetases covalently link amino acids to their appropriate
tRNA molecule(s).
OBJECTIVE
Explain the process of translation in detail.
Translation occurs in three phases: initiation, elongation, and termination.
During initiation, the ribosome forms and the initiator tRNA provides the first
amino acid. During elongation, tRNA molecules bring the appropriate amino
acids to the ribosome using base pairing between the codon on the mRNA
and the anticodon on the tRNA. The amino acid is added to the growing
polypeptide chain. Termination occurs when the stop codon is reached.
OBJECTIVE
Explain how post-translational processes prepare proteins
for their functions.
There are a variety of post-translational processes that may be required for a
polypeptide to become functional. Polypeptides may be cleaved or brought
together. Glycosylation and phosphorylation add specific chemical groups to
the polypeptide.
OBJECTIVE
Key Terms
aminoacyl-tRNA synthetase
An enzyme that charges tRNA molecules with their appropriate amino acid; a
different synthetase exists for each of the 20 amino acids.
anticodon
The region of a tRNA that is complementary to a codon on mRNA.
elongation factor
One of multiple proteins that facilitates the lengthening of a polypeptide during
protein synthesis.
guanosine triphosphate (GTP)
A nucleotide similar to ATP that provides energy during several steps of protein
synthesis.
initiation factor
One of several proteins that facilitate the recognition of the start codon and the
subsequent assembly of the large and small subunits of the ribosome.
polyribosome
String of ribosomes on a single mRNA molecule that allows the cell to make large
quantities of protein rapidly.
release factor
One of several proteins that recognize stop codons and facilitate the detachment
of the completed polypeptide from the ribosome at the end of translation.
ribosome
A protein-RNA complex that facilitates the interaction of mRNA and tRNA; site of
protein synthesis.
signal peptide
A sequence of twenty amino acids near the N-terminus that redirects protein
synthesis to the ER in conjunction with the signal-recognition particle.
signal-recognition particle (SRP)
A protein-RNA complex that recognizes and binds to signal peptides, facilitating
the translocation of free ribosomes to the ER surface.
contents
transfer RNA (tRNA)
A specialized adapter molecule that brings a specific amino acid to the ribosome
during protein synthesis; contains an anticodon complementary to a specific
codon in the mRNA.
IN THIS MODULE
Translating DNA into Proteins
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
Synthetic Biology: Making Life from
Bits and Pieces
Scientists are combining biology and
engineering to change the world.
PRIMARY LITERATURE
Classic paper: How scientists
discovered the enzyme that turns
RNA into DNA (1970)
RNA-dependent DNA polymerase in virions
of RNA tumour viruses.
View | Download
SCIENCE ON THE WEB
How Small?
See the difference between a coffee bean
and a single atom.
page 258 of 989
1 pages left in this module
Principles of Biology
contents
50 Translation
Test Your Knowledge
1. One codon for asparagine has the sequence AAC. What is the sequence of the
anticodon on the aminoacyl-tRNA (in the 5′ to 3′ direction)?
CAA
GUU
GGA
UUG
TTG
2. All polypeptides in eukaryotes have which of the following in common?
All polypeptides start with the same amino acid.
All polypeptides end with the same amino acid.
All polypeptides have the same number of amino acids.
All polypeptides are cleaved before they become active.
None of the answers are correct.
3. Which of the following are post-translational modifications?
glycosylation
phosphorylation
protein cleavage
multiple polypeptides binding together
All answers are correct.
4. Which of the following first binds to the mRNA at the translation initiation site?
GTP
aminoacyl-tRNA synthetase
small ribosomal subunit
large ribosomal subunit
aminoacyl-tRNA
5. How many different aminoacyl-tRNA synthetases exist?
20
21
64
4
16
Submit
IN THIS MODULE
Translating DNA into Proteins
Summary
Test Your Knowledge
WHY DOES THIS TOPIC MATTER?
Stem Cells
Stem cells are powerful tools in
biology and medicine. What can
scientists do with these cells and their
incredible potential?
Cancer: What's Old Is New Again
Is cancer ancient, or is it largely a
product of modern times? Can
cutting-edge research lead to prevention
and treatment strategies that could make
cancer obsolete?
Synthetic Biology: Making Life from
Bits and Pieces
Scientists are combining biology and
engineering to change the world.
PRIMARY LITERATURE
Classic paper: How scientists
discovered the enzyme that turns
RNA into DNA (1970)
RNA-dependent DNA polymerase in virions
of RNA tumour viruses.
View | Download
SCIENCE ON THE WEB
How Small?
See the difference between a coffee bean
and a single atom.
page 259 of 989