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Termination of translation

Termination of translation


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What dissociates first - the last tRNA, mRNA and release factors or the subunits of ribosomes?

I tried searching this from Lehninger but couldn't get a clean answer.


Shigeta's got a point: the ribosome is latched onto the mRNA so those two are intrinsically linked. You're really asking whether the ribosome comes off first or whether the tRNA does, but it's actually the new polypeptide, which makes sense:

The stop codon is recognized by a protein, the polypeptide chain release factor (RF), which triggers the hydrolytic release of the nascent polypeptide chain from the P-site-bound peptidyl-tRNA.

This minireview puts forth a model (see below) where, in E. coli at least, the 50S ribosome subunit is then dissociated from the mRNA/30S subunit/tRNA complex, following which the final tRNA is removed. An in-depth review from a few years later gives more context.


just off the top of my head… since the ribosome is made of 2 large complexes which assemble and clamp onto the mRNA, I'd say it was the tRNA first, then the ribosome and mRNA would detach simultaneously.


Termination

Definition
noun
(general) The process, act, or state of terminating
(biochemistry) A process in which the mRNA synthesis (i.e. transcription) or protein synthesis (i.e. during translation) stops at the terminator site
Supplement
In general, the term termination refers to the state, act, or process of reaching the end or bringing to an end. In biology, the term often denotes to a biological process where a biological entity is being ended or completed. For instance, translation, a step in protein biosynthesis wherein the genetic code carried by mRNA is decoded to produce the specific sequence of amino acids in a polypeptide chain, ends in the so-called termination step. In essence, translation begins when a small subunit of the ribosome binds to the 5′ end of mRNA with the help of initiation factors and then followed by a step wherein the next aminoacyl-tRNA in line binds to the ribosome along with GTP and an elongation factor). The last step is referred to as termination. This is when the A site of the ribosome encounters a stop codon (UAA, UAG, or UGA).
Termination is also the final step in gene transcription (the process of transcribing or making a copy of genetic information stored in a DNA strand into a complementary strand of mRNA).
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Last updated on February 27th, 2021


Processing of tRNAs and rRNAs

Figure 3. This is a space-filling model of a tRNA molecule that adds the amino acid phenylalanine to a growing polypeptide chain. The anticodon AAG binds the Codon UUC on the mRNA. The amino acid phenylalanine is attached to the other end of the tRNA.

The tRNAs and rRNAs are structural molecules that have roles in protein synthesis however, these RNAs are not themselves translated. Pre-rRNAs are transcribed, processed, and assembled into ribosomes in the nucleolus. Pre-tRNAs are transcribed and processed in the nucleus and then released into the cytoplasm where they are linked to free amino acids for protein synthesis.

Most of the tRNAs and rRNAs in eukaryotes and prokaryotes are first transcribed as a long precursor molecule that spans multiple rRNAs or tRNAs. Enzymes then cleave the precursors into subunits corresponding to each structural RNA. Some of the bases of pre-rRNAs are methylated that is, a –CH3 moiety (methyl functional group) is added for stability. Pre-tRNA molecules also undergo methylation. As with pre-mRNAs, subunit excision occurs in eukaryotic pre-RNAs destined to become tRNAs or rRNAs.

Mature rRNAs make up approximately 50 percent of each ribosome. Some of a ribosome’s RNA molecules are purely structural, whereas others have catalytic or binding activities. Mature tRNAs take on a three-dimensional structure through intramolecular hydrogen bonding to position the amino acid binding site at one end and the anticodon at the other end (Figure 3).

The anticodon is a three-nucleotide sequence in a tRNA that interacts with an mRNA codon through complementary base pairing.


Molecular Cell Biology

Translation Termination and mRNA Stability

Eukaryotic mRNA translation termination requires two release factors, eRF1 and eRF3. Translation termination process can influence mRNA half-life. Specifically, it was observed that the N-terminal domain of eRF3, which is not required for translation termination, can interact with Pab1, and this interaction is involved in modulating mRNA stability ( Hosoda et al., 2003 ). Disruption of this interaction results in translation-dependent stabilization of mRNA caused by decreased deadenylation rate ( Hosoda et al., 2003 ). Interestingly, it was further found that certain deadenylase complexes can also bind to the same site on Pab1 that is involved in the interaction with eRF3 ( Funakoshi et al., 2007 ). Thus, it has been postulated that eRF3 can regulate mRNA deadenylation by competitively binding to the Pab1, which then modulates the recruitment and activation of deadenylase complexes ( Funakoshi et al., 2007 ). In addition to the release factors, other proteins that can modulate translation termination can also influence mRNA stability. For example, a recent characterized protein named Tpa1 can interact with the two release factors and regulate the readthrough of stop codons ( Keeling et al., 2006 ). Interestingly, although the detailed mechanisms still remain elusive, knocking out this protein can have decreased deadenylation rate and increased mRNA stability ( Keeling et al., 2006 ). Collectively, these results suggest that mRNA translation termination can results in mRNP conformational changes that can influence mRNA stability, likely via modulating mRNA deadenylation.


What you'll learn:

The mRNAs that are synthesized by the process of transcription contain the required information for the synthesis of proteins. This is contained in the form of a codon that is a three-nucleotide arrangement that codes for a particular amino acid. There are 64 codons out of which, 61 codons code for amino acid and three are stop codons. Translation begins from the 5’ end of start codons that is AUG/ GUG/ UUG.

The tRNAs help to guide the correct addition of amino acids to form polypeptide according to the codon present in the mRNA. This is done with the help of enzymes called aminoacyl-tRNA synthetases that charge the tRNA with specific amino acids based upon the codon they recognize. Ribosomes are protein and RNA complexes that catalyze the peptide bond formation by bringing the mRNA and tRNAs together. There are two subunits of ribosomes: large and small and their association during the process of translation is important to form the A, P, and E sites of ribosomes. Acylated tRNA enters the ribosome by entering the A site. When mRNA moves, it results in several biochemical reactions that lead to the synthesis of peptide bond with the incoming amino acid attached with the tRNA. After which, the deacylated tRNA moves into the E site.

The translation process involves three steps: initiation, elongation, and termination. The initiation step involves the association of large and small subunits of ribosomes with the help of initiation factors so as to accommodate the charged initiator tRNA in the P-site. During the elongation stage, charged tRNA with amino acids enter the A site, followed by the formation of peptide bond between the amino acids in the P-site and the A-site, thereby releasing the deacylated tRNA from the E-site. The ribosome then moves to the next codon and the same process continues. This stage is facilitated by various elongation factors. Finally, the termination stage of translation begins upon the encounter of the stop codon. It is described in detail in the following section.


After the sigma is removed, RNA Polymerase continues to unzip template and coding strands of the the DNA, and R-nucleotides are bonded via phosphodiester linkages using the code provided by the template strand of DNA. The incoming DNA enters into an intake portal and is unzipped by a zipper. As the DNA passes the zipper, the hydrogen bonds reattach between the coding and template strand and the DNA double helix leaves through an exit portal. R-nucleotides enter in through another intake portal and are combined via complementary base pairing to the template strand of DNA. The R-nucleotides are bonded together via phosphodiester linkages. R-nucleotides are continuously added to the 3’ end of the developing RNA strand. The 5’ end of the RNA strand leaves through another exit portal of the RNA Polymerase.

Elongation phase of transcription


Termination of translation - Biology

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Once an mRNA is translated, the ribosome needs to dissociate from the RNA and release the newly made polypeptide chain. 

Translation is terminated when a stop codon, UAA, UAG, or UGA, is encountered. There are no complementary tRNAs that correspond to stop codons.

Instead, when a stop codon is positioned on the A site of the ribosome, it is recognized by proteins called release factors, RF1 or RF2.

This binding forces the enzyme peptidyl transferase in the ribosome to catalyze the addition of a water molecule instead of an amino acid to the peptidyl-tRNA.

As a result, the P-site amino acid detaches from its tRNA, releasing the newly made polypeptide into the cytoplasm. 

Next, a third release factor, RF3, bound to GDP joins the ribosome.

On the ribosome, RF3 replaces GDP with GTP. This exchange brings about a conformational change in RF3, which triggers the dissociation of RF1 and RF2 from the ribosome.

Then, RF3 catalyzes GTP hydrolysis, which allows the ribosomal subunits to dissociate from each other and from the mRNA.

The disassembled ribosomal subunits bound to an initiator tRNA, can now join a new mRNA for another round of translation.

9.6: Termination of Translation

The large ribosomal subunit has several important structures essential to translation. These include the peptidyl transferase center (PTC) - which is the site where the peptide bond is formed - and a large, internal, water-filled tube through which the nascent polypeptide moves. This latter structure is called the Peptide Exit Tunnel, and it begins at the PTC and spans the body of the large ribosomal subunit. During translation, as the nascent polypeptide chain is synthesized, it passes through the peptide exit tunnel. It then emerges out in the solvent side, where the peptide chain is subsequently folded into a protein.

This tunnel formed by the 23S ribosomal RNA creates a large hydrophilic surface, containing tiny hydrophobic patches. The dimensions of the tunnel (approximately 10 nm × 1.5 nm) can accommodate growing, unstructured polypeptide chains, as well as solvent molecules. The interior of the peptide exit tunnel is not complementary to any peptide. Hence, the polypeptide chain does not “stick” to the walls and can easily slide through. Once it reaches a location in the exit tunnel where there is sufficient space, the nascent peptide chain starts to fold and may successfully form some α-helical regions. However, the majority of protein folding occurs once the polypeptide exits the ribosome.


What is Transcription?

Transcription generally refers to the written form of something. In biology, transcription is the process whereby DNA is used as a template to form a complementary RNA strand – RNA is the “written” form of DNA. This is the first stage of protein production or the flow of information within a cell. DNA stores genetic information, which is then transferred to RNA in transcription, before directing the synthesis of proteins in translation. Three types of RNA can be formed: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA).

Transcription occurs in four stages: pre-initiation, initiation, elongation, and termination. These differ in prokaryotes and eukaryotes in that DNA is stored in the nucleus in eukaryotes, and whereas DNA is stored in the cytoplasm in prokaryotes. In eukaryotes, DNA is stored in tightly packed chromatin, which must be uncoiled before transcription can occur. The production of mRNA from RNA in eukaryotes is particularly more complicated than it is in prokaryotes, involving several additional processing steps.

Pre-initiation, or template binding, is initiated by the RNA polymerase σ subunit binding to a promoter region located in the 5’ end of a DNA strand. Following this, the DNA strand is denatured, uncoupling the two complementary strands and allowing the template strand to be accessed by the enzyme. The opposing strand is known as the partner strand. Promoter sequences on the DNA strand are vital for the successful initiation of transcription. Promoter sequences are specific sequences of the ribonucleotide bases making up the DNA strand (adenine, thymine, guanine,and cytosine), and the identity of several of these motifs have been discovered, including TATAAT and TTGACA in prokaryotes and TATAAAA and GGCCAATCT in eukaryotes. These sequences are known as cis-acting elements. In eukaryotes, an additional transcription factor is necessary to facilitate the binding of RNA polymerase to the promoter region.

RNA polymerase catalyzes initiation, causing the introduction of the first complementary 5’-ribonucleoside triphosphate. Remember that each DNA nucleotide base has a complement: adenine and thymine, and guanine and cytosine. However, the ribonucleotide base complements differ slightly as RNA does not contain thymine, but rather a uracil, and so adenine’s complement is uracil. After the introduction of the first complementary 5’-ribonucleotide, subsequent complementary ribonucleotides are inserted in a 5’ to 3’ direction. These ribonucleotides are joined by phosphodiester bonds, and at this stage, the DNA and RNA molecules are still connected(see Figure 1).

Figure 1: Initiation of transcription. RNAP® refers to RNA polymerase.

Chain elongation occurs when the σ subunit dissociates from the DNA strand, allowing the growing RNA strand to separate from the DNA template strand. This is facilitated by the core enzyme (see Figure 2).

Figure 2: Elongation in transcription

Termination occurs when the core enzyme encounters a termination sequence, which is a specific sequence of nucleotides which acts as a signal to stop transcription. At this point, the RNA transcript forms a hairpin secondary structure by folding back on itself with the aid of hydrogen bonds. Termination in prokaryotes can be assisted by an additional termination factor known as rho(ρ). Termination is complete when the RNA molecule is released from the template DNA strand. In eukaryotes, termination requires an additional step known as polyadenylation in eukaryotes, whereby a tail of multiple adenosine monophosphates is added to the RNA strand.

Figure 3: The main events in each stage of transcription


Functional anatomy of eRF1

The function of class-1 RFs suggests that they should have four distinct sites ( Frolova et al., 1999 ). There should be a ribosome-binding site (RBS), a termination codon recognition site (TCRS), a peptidyl-tRNA interaction site (PRIS) and an RF3- or eRF3-binding site [(e)RF3-BS]. The three-dimensional structure of human eRF1 ( Song et al., 2000 ) can be used for a tentative assignment of these sites to different regions of the molecule (Figure 1).

The C domain (domain 3) of eRF1 is unlikely to be a RBS for a number of reasons. First, removal of this domain from human eRF1 enhances, rather than reduces, the termination activity in vitro ( Frolova et al., 2000 ), meaning that this region cannot be essential for ribosome binding. Secondly, the C domain is the most rapidly evolving part of eRF1 ( Inagaki and Doolittle, 2001 ), while the ribosome structure is highly conserved. Thirdly, although there is substantial sequence divergence between the C domains of eRF1 and aRF1 ( Inagaki and Doolittle, 2001 ), aRF1 is still able to terminate at animal ribosomes ( Dontsova et al., 2000 ).

Presumably, the binding of eRF1 to the A-site is stabilized by interactions with both ribosomal subunits. This is supported by the observation that mutations in the GGQ and NIKS minidomains of eRF1, most probably located at the large and small ribosomal subunits, respectively (see below), reduce the binding of eRF1 to the ribosome ( Seit-Nebi et al., 2001 Frolova et al., 2002 ). Furthermore, truncation of the N (N-terminal, or domain 1) or the M (middle, or domain 2) domain causes a gradual loss of RF activity in vitro ( Frolova et al., 2000 ), probably due to distortions of RBSs.

The ribosomal functional sites are composed mainly of rRNAs (see Ramakrishnan, 2002 ), suggesting that RBSs of class-1 RFs bind primarily to rRNA sequences rather than to ribosomal proteins. This notion is consistent with the charge distribution along the consensus polypeptide chains of eRF1 and aRF1. There are two clusters of positively charged amino acid residues around positions 180 and 60–70, where the GGQ and NIKS motifs are mapped ( Kisselev et al., 2000 ). This suggests that these two regions comprise two RBSs, which interact with rRNA in either of the two ribosomal subunits.

The existence of the RF1 RBS toward the PTC of the prokaryotic ribosome is manifested by the isolation of short RNA sequences (aptamers) containing 5′-ACCU-3′ and 5′-GAAAGC-3′ sequences identical to the 23S rRNA consensus sequences present in the PTC. These aptamers bind to RF1 and inhibit RF1 activity ( Szkaradkiewicz et al., 2002 ).

The TCRS of class-1 eRFs is located at the N domain, as follows from: (i) in vivo genetic data with yeast eRF1 ( Bertram et al., 2000 ) and in vitro biochemical data with human eRF1 ( Frolova et al., 2002 Seit-Nebi et al., 2002 ), in which site-directed mutagenesis of some positions at the N domain causes profound alterations of the stop codon recognition profile for mutant eRFs (ii) stop codon specificity of the hybrid eRF1 mentioned above ( Ito et al., 2002 ) and (iii) data revealing cross-linking between the first U of the stop codons and the N domain of human eRF1 ( Chavatte et al., 2002 ). However, the exact sequence and structure of TCRS in eukaryotes remain obscure.

For stop codon recognition by eRF1, two types of models have been proposed, a ‘protein-anticodon’ ( Nakamura et al., 2000 ) and a ‘cavity’ ( Bertram et al., 2000 Inagaki et al., 2002 ) model. In the first case, a linear sequence of amino acids decodes a stop codon, while in the second case a combination of amino acid residues from different parts of the polypeptide chain clustered in space around a stop codon decodes it. Attempts to reveal a ‘protein-anticodon’ for eRF1 have failed so far. In contrast, two regions of the N domain represented by two loops containing highly conserved YxCxxxF (positions 125–131) and NIKS (positions 61–64) motifs (Figure 2) play a critical role in stop codon recognition ( Seit-Nebi et al., 2002 ). Amino acid substitutions in these regions profoundly affect the pattern of stop codon recognition probably due to an interplay between these two loops, which are ∼15 Å apart in the crystal sructure of eRF1 ( Song et al., 2000 ). Furthermore, in yeast, eRF1 mutations affecting stop codon recognition are scattered between positions 51 and 132 of the polypeptide chain ( Bertram et al., 2000 ). In silico analysis ( Inagaki et al., 2002 ) of eRF1 sequences does not support a ‘protein-anticodon’ model as well.

The PRIS should be located near both the peptidyl-tRNA in the ribosomal P-site and the PTC of the large ribosomal subunit. In contrast, the TCRS should interact with the decoding site of the small ribosomal subunit. From the distance between the anticodon of tRNA and its CCA end (∼75 Å), one can expect a similar distance between the PTC and the decoding site. As TCRS is assigned to part of the N domain (see above) and the C domain is not essential for the termination reaction ( Frolova et al., 2000 ), the most probable location for PRIS is at the tip of the M domain. This suggestion gets support from a number of experimental data. All class-1 RFs, regardless of their origin and codon specificity, share the common Gly–Gly–Gln tripeptide (GGQ motif) ( Frolova et al., 1999 ). In eRF1, it is located at the extremity of the M domain forming a highly exposed minidomain ( Song et al., 2000 ) (Figure 1). In prokaryotes, the GGQ loop of Escherichia coli RF2 is poorly resolved in the electron density, indicating that it is mobile ( Vestergaard et al., 2001 ). The idea that the invariant GGQ motif is located at the PTC, mimics the CCA end of tRNA and forms a part of the PRIS ( Frolova et al., 1999 ) is supported by the fact that glycine residues of the GGQ in eukaryotic and bacterial factors are indispensable for the RF activity when tested both in vitro and in vivo ( Frolova et al., 1999 Song et al., 2000 Mora et al., 2003 ). For example, GAQ mutants of RF1 and RF2 are between four and five orders of magnitude less efficient in the termination reaction than their wild-type counterparts, although their ability to bind to the ribosome is fully retained ( Zavialov et al., 2002 ).

The essential role of the glycyl residues in the GGQ motif is also emphasized by observations in animal cell–virus systems. Expression of the human cytomegalovirus (HCMV) UL4 gene is inhibited by translation of a 22 codon upstream open reading frame (uORF2) (reviewed in Janzen and Geballe, 2001 ). The peptide product of uORF2 acts in a sequence-dependent manner to inhibit uORF2 peptidyl-tRNA cleavage. It has been shown by site-directed mutagenesis ( Janzen et al., 2002 ) that Gly183 and Gly184 of the GGQ motif and Pro21 and Pro22 of the uORF2 (the C-terminal residues of the polypeptide) are essential for full inhibition of downstream translation. These data are consistent with the idea that the C-terminal part of the nascent polypeptide in peptidyl-tRNA is able to interact with the GGQ tripeptide at the PTC. It also suggests that this interaction potentially can obstruct translation termination via a particular structure of the C-terminus of the nascent peptidyl-tRNA.

The third amino acid residue of GGQ is also important, but some glutamine mutants retain in vitro a substantial RF activity ( Seit-Nebi et al., 2000 , 2001 Mora et al., 2003 ). This is in line with the finding ( Zavialov et al. 2002 ) that although GGA mutants of RF1 and RF2 from E.coli are significantly impaired in the termination step, they are much more active than their GAQ counterparts. This could suggest that the role of Gln185 is in conserving the spatial structure of the GGQ minidomain ( Seit-Nebi et al., 2001 ).

Taken together, these data are hard to reconcile with the proposal ( Song et al., 2000 ) that the function of the glutamine is to orient a water molecule toward peptidyl-tRNA at the PTC of the ribosome. Therefore, the catalytic mechanism of the termination reaction remains unclear.

The Gln252 residue in the GGQ motif of RF2 (E.coli) was found to be N 5 -methylated ( Dinçbas-Renqvist et al., 2000 ), which increases the termination efficiency of RF2, that again points to a critical role for GGQ in termination.

When the GGQ motif is located at the PTC, then the distance between the GGQ tripeptide and the TCRS should be ∼75 Å. In the crystal structure of human eRF1, the distance spanned by the NIKS motif, which cross-reacts with the first base (U) of the stop codon ( Chavatte et al., 2002 ), and the GGQ motif is ∼100 Å ( Song et al., 2000 ). However, it can be reduced substantially by interactions between eRF1 and the ribosome, and the YxCxxxF motif, rather than the NIKS loop, may be the major TCRS, giving a distance between PRIS and TCRS of ∼75 Å ( Seit-Nebi et al., 2002 ).

The signalling between the stop codon and PTC may involve conformational alterations not only of RFs themselves but also of rRNA sequences, since it is believed (see Caskey, 1980 ) that the catalytic reaction is carried out by PTC (which is now known to be composed of rRNA) rather than by class-1 RFs. Presumably, the GGQ minidomain opens the PTC to allow the entry of a water molecule, whereas chemical groups of certain rRNA nucleotides catalyse the cleavage reaction.

eRF1 and the class-2 RF, eRF3 (see below), interact via their C-terminal domains (see Kisselev and Buckingham, 2000 ). Clearly, the C domain of eRF1 is an eRF3-BS (Figure 1). It probably also binds other proteins. There are some other proteins, Upf1p, Upf2p and Upf3p ( Wang et al., 2001 and references therein), Mtt1p ( Czaplinski et al., 2000 ) and Itt1p ( Urakov et al., 2001 ), that bind to unknown regions of eRF1. The biological significance of these interactions has been discussed elsewhere ( Wang et al., 2001 ).

The archaean class-1 RF, aRF1, is structurally ( Kisselev et al., 2000 Song et al., 2000 ) and functionally ( Dontsova et al., 2000 ) similar to eRF1, but so far no aRF3 has been identified. It is, in fact, unlikely that an aRF3-BS exists in aRF1, since most aRF1s are truncated extensively from their C-termini, apparently leaving no room for such an interaction.

RF1, RF2 and mtRF1 differ profoundly in their primary structures from the eRF1/aRF1 family ( Frolova et al., 1994 , 1999 Kisselev et al., 2000 Song et al., 2000 ). Furthermore, the crystal structures of human eRF1 ( Song et al., 2000 ) and E.coli RF2 ( Vestergaard et al., 2001 ) are also dissimilar. Therefore, the functional anatomy of the RF1/RF2/mtRF structural family may be different from that of eRF1/aRF1. It is possible that bacterial RFs change their conformation when they bind strongly to ribosomes programmed with stop codons, an option suggested above for eRF1.


Transcription & Translation AP® Biology Exam Review & Practice

Let’s review what we’ve learned in this AP® Biology Crash Course so far:

• DNA is the genetic “blueprint” of living organisms and the starting point for all proteins. Its information is copied and transferred into RNA to produce proteins.

• Promoter DNAis a segment of DNA that signals the start of genetic coding for a specific gene. RNA polymerase will attach here at the start of transcription for the gene.

• RNA is an important molecule that comes in various types. With regard to transcription and translation, RNA not only copies and moves genetic information, but also turns that information into the resulting proteins.

• RNA polymerase is the molecule that plays the key role in the transcription process. RNA polymerase attaches to the DNA and makes a copy of the genetic information in the form of an mRNA strand.

• mRNA stands for “messenger RNA,” the copy of DNA information that is moved out of the nucleus to give “instructions” in the process of protein formation.

• tRNA stands for “transfer RNA,” and is the molecule that takes mRNA’s instructions and turns individual amino acids into proteins.

Transcription is the process of making RNA from DNA in order to transfer genetic information out of the nucleus and to the site of protein synthesis (the ribosomes). RNA polymerase “rewrites” the DNA information and creates a new copy in the form of mRNA.

Translation is the process by which RNA is used to make proteins. tRNA “reads” the mRNA strand and “translates” it into a chain of amino acids (a protein).

If you think you’re ready to discuss transcription and translation on the AP® Biology Exam, take a stab at this quick practice question:

Q: How are proteins synthesized from genetic information? Describe the processes and the major molecules involved.

A: First, RNA polymerase attaches to the antisense strand at the site of the promoter DNA. The hydrogen bonds between the DNA’s nucleotides break and the helix unwinds, allowing the RNA polymerase to move down the strand, creating a copy of the genetic information in the form of mRNA. This copying of information is the process of transcription. If necessary, the mRNA undergoes capping, splicing, or polyadenylation, and is then moved out of the nucleus via specialized pores.

Once the mRNA reaches the ribosome, the initiation phase of translation begins. tRNA attaches to the first piece of genetic information—the start codon—and begins to assemble amino acids per the mRNA’s genetic instructions. As each piece of the mRNA is “read,” the ribosome moves along the strand and a longer chain of amino acids is created. This is the elongation phase. Finally, when the ribosome has read the entire strand of mRNA and completed the full polypeptide (protein) chain, the process enters the termination phase, at which point the ribosome releases the finished protein. This protein release is the final step of translation.

There you have it: DNA transcription and translation are the two molecular mechanisms by which organisms’ bodies produce new proteins to build real physical components. Do these processes make sense to you? Are there any elements you’re still struggling to understand? Let us know in the comments!

If you’re still trying to wrap your head around the intricacies of DNA, check out our intensive review of DNA for information on its discovery, structure, and functions.

Need help preparing for your AP® Biology exam?

Albert has hundreds of AP® Biology practice questions, free response, and full-length practice tests to try out.


Watch the video: Termination of Translation (July 2022).


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