In protein synthesis which of the following occur

In prokaryotes, multiple RNA polymerases can transcribe a single bacterial gene while numerous ribosomes concurrently translate the mRNA transcripts into polypeptides. In this way, a specific protein can rapidly reach a high concentration in the bacterial cell.

Bacterial species typically have between 60 and 90 types. Serving as adaptors, each tRNA type binds to a specific codon on the mRNA template and adds the corresponding amino acid to the polypeptide chain. As the adaptor molecules of translation, it is surprising that tRNAs can fit so much specificity into such a small package.

Mature tRNAs take on a three-dimensional structure when complementary bases exposed in the single-stranded RNA molecule hydrogen bond with each other Figure 3. The anticodon is a three-nucleotide sequence that bonds with an mRNA codon through complementary base pairing. At least one type of aminoacyl tRNA synthetase exists for each of the 20 amino acids. Figure 3. Translation is similar in prokaryotes and eukaryotes.

Here we will explore how translation occurs in E. The initiation of protein synthesis begins with the formation of an initiation complex. Because of its involvement in initiation, fMet is inserted at the beginning N terminus of every polypeptide chain synthesized by E. This interaction anchors the 30S ribosomal subunit at the correct location on the mRNA template. At this point, the 50S ribosomal subunit then binds to the initiation complex, forming an intact ribosome.

Figure 4. Translation in bacteria begins with the formation of the initiation complex, which includes the small ribosomal subunit, the mRNA, the initiator tRNA carrying N-formyl-methionine, and initiation factors. Then the 50S subunit binds, forming an intact ribosome.

In prokaryotes and eukaryotes, the basics of elongation of translation are the same. The P peptidyl site binds charged tRNAs carrying amino acids that have formed peptide bonds with the growing polypeptide chain but have not yet dissociated from their corresponding tRNA.

The E exit site releases dissociated tRNAs so that they can be recharged with free amino acids. Elongation proceeds with single-codon movements of the ribosome each called a translocation event.

During each translocation event, the charged tRNAs enter at the A site, then shift to the P site, and then finally to the E site for removal. Peptide bonds form between the amino group of the amino acid attached to the A-site tRNA and the carboxyl group of the amino acid attached to the P-site tRNA. The formation of each peptide bond is catalyzed by peptidyl transferase , an RNA-based ribozyme that is integrated into the 50S ribosomal subunit.

The amino acid bound to the P-site tRNA is also linked to the growing polypeptide chain. Several of the steps during elongation, including binding of a charged aminoacyl tRNA to the A site and translocation, require energy derived from GTP hydrolysis, which is catalyzed by specific elongation factors.

Amazingly, the E. On aligning with the A site, these nonsense codons are recognized by release factors in prokaryotes and eukaryotes that result in the P-site amino acid detaching from its tRNA, releasing the newly made polypeptide. The small and large ribosomal subunits dissociate from the mRNA and from each other; they are recruited almost immediately into another translation init iation complex.

In summary, there are several key features that distinguish prokaryotic gene expression from that seen in eukaryotes. These are illustrated in Figure 6 and listed in Table 1. Figure 6. Post-translational modifications include:. During elongation in translation, to which ribosomal site does an incoming charged tRNA molecule bind? Which of the following is the amino acid that appears at the N-terminus of all newly translated prokaryotic and eukaryotic polypeptides? Skip to main content. Mechanisms of Microbial Genetics.

Search for:. Protein Synthesis Translation Learning Objectives Describe the genetic code and explain why it is considered almost universal Explain the process of translation and the functions of the molecular machinery of translation Compare translation in eukaryotes and prokaryotes. Think about It How many bases are in each codon? The cytosol is filled with closely packed sheets of endoplasmic reticulum membrane studded with ribosomes.

At the bottom left is a portion of the nucleus and its nuclear envelope. Image courtesy of Prof. Orci University of Geneva, Switzerland. Merging cultures in the study of membrane traffic. Nature Cell Biology 6 , doi Each mRNA dictates the order in which amino acids should be added to a growing protein as it is synthesized.

In fact, every amino acid is represented by a three-nucleotide sequence or codon along the mRNA molecule. Figure 7: The ribosome and translation A ribosome is composed of two subunits: large and small. During translation, ribosomal subunits assemble together like a sandwich on the strand of mRNA, where they proceed to attract tRNA molecules tethered to amino acids circles.

A long chain of amino acids emerges as the ribosome decodes the mRNA sequence into a polypeptide, or a new protein. Each tRNA molecule has two distinct ends, one of which binds to a specific amino acid, and the other which binds to the corresponding mRNA codon.

During translation , these tRNAs carry amino acids to the ribosome and join with their complementary codons. Then, the assembled amino acids are joined together as the ribosome, with its resident rRNAs, moves along the mRNA molecule in a ratchet-like motion. The resulting protein chains can be hundreds of amino acids in length, and synthesizing these molecules requires a huge amount of chemical energy Figure 8.

Figure 8: The major steps of translation 1 Translation begins when a ribosome gray docks on a start codon red of an mRNA molecule in the cytoplasm. A second tRNA molecule, bound to two, connected amino acids, is attached to the 4 th , 5 th , and 6 th nucleotide from the left. It no longer has amino acids bound to its terminus. In step 4, the tRNA molecule that formerly had two connected amino acids attached to its terminus, has now accumulated four amino acids total.

Different colored spheres represent different amino acid types, and the four spheres are connected end-to-end in a chain. A tRNA to the right has one amino acid attached to its terminus. A tRNA molecule carrying a single amino acid is shown approaching the ribosome from the cytoplasm. In step 5, the ribosome is shown to have moved along the length of the mRNA molecule from left to right.

A long chain of approximately 19 amino acids is connected to the end of the tRNA molecule. Five tRNA molecules carrying a single amino acid each are seen floating freely in the cytoplasm surrounding the mRNA molecule. In step 6, the ribosome is disassociated from the mRNA molecule.

The amino acid chain has disassociated from the tRNA and is floating freely in the cytoplasm as a complete protein molecule. The illustrated ribosome is translucent and looks like an upside-down glass jug.

The mRNA is composed of many nucleotides that resemble pegs aligned side-by-side along the molecule, in parallel. Each type of nucleotide is represented by a different color yellow, blue, orange, or green. The first three nucleotides, bound to the ribosome, are highlighted in red to represent the stop codon.

In step 2, a tRNA molecule is bound to the stop codon. At the end of the tRNA molecule opposite this point of attachment is an amino acid, represented as a sphere. In step 3, a tRNA bound to a single amino acid is attached to the 7 th , 8 th , and 9 th nucleotide from the left. In eukaryotic cells, however, the two processes are separated in both space and time: mRNAs are synthesized in the nucleus, and proteins are later made in the cytoplasm. This page appears in the following eBook.

Aa Aa Aa. Ribosomes, Transcription, and Translation. Figure 1: DNA replication of the leading and lagging strand. The helicase unzips the double-stranded DNA for replication, making a forked structure.

Figure 3: RNA polymerase at work. What Is the Function of Ribosomes? This Escherichia coli cell has been treated with chemicals and sectioned so its DNA and ribosomes are clearly visible.

In biology, a codon refers to the trinucleotides that specify for a particular amino acid. What is the Genetic Code? Come join us now!

The copy of a DNA segment for gene expression is located in its coding region. It consists of two major sites: 1 anticodon arm and 2 acceptor stem. The anticodon arm contains the anticodon that complementary base pairs with the codon of the mRNA.

The acceptor stem is the site where a specific amino acid is attached in this case, the tRNA with amino acid is called aminoacyl-tRNA. Rather, it serves as one of the components of the ribosome.

The ribosome is a cytoplasmic structure in cells of prokaryotes and eukaryotes that are known for serving as a site of protein synthesis.

The ribosomes can be used to determine a prokaryote from a eukaryote. Prokaryotes have 70S ribosomes whereas eukaryotes have 80S ribosomes. Both types, though, are each made up of two subunits of differing sizes. The larger subunit serves as the ribozyme that catalyzes the peptide bond formation between amino acids.

The A aminoacyl site is where aminoacyl-tRNA docks. The P peptidyl site is where peptidyl-tRNA binds. The E exit site is where the tRNA leaves the ribosome.

Transcription is the process by which mRNA template , encoding the sequence of the protein in the form of a trinucleotide code, is transcribed from DNA to provide a template for translation through the help of the enzyme, RNA polymerase.

Thus, transcription is regarded as the first step of gene expression. But unlike DNA replication, transcription needs no primer to initiate the process and, instead of thymine, uracil pairs with adenine. The steps of transcription are as follows: 1 Initiation, 2 Promoter escape, 3 Elongation, and 4 Termination. The first step, initiation, is when the RNA polymerase, with the assistance of certain transcription factors, binds to the promoter of DNA. This leads to the opening unwinding of DNA at the promoter region, forming a transcription bubble.

A phase of abortive cycles of synthesis occurs resulting in the release of short mRNA transcripts about 2 to 15 nucleotides. The next step is for the RNA polymerase to escape the promoter so that it can enter into the elongation step.

During elongation, RNA polymerase traverses the template strand of the DNA and base pairs with the nucleotides on the template noncoding strand. This results in mRNA transcript containing a copy of the coding strand of DNA, except for thymines that are replaced by uracils. The sugar-phosphate backbone forms through RNA polymerase. The last step is termination. In eukaryotes, the mRNA transcript goes through further processing.

It goes through polyadenylation , capping , and splicing. Translation is the process in which amino acids are linked together in a specific order according to the rules specified by the genetic code. It occurs in the cytoplasm where the ribosomes are located.

Following protein synthesis are events, e.