Name: translation begins with ribosome assembly
Uploaded: 2023-04-30T18:28:45.000Z
Duration: 2 min 33 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.1.5

Initiation of Translation

On the mRNA, the start site for translation is crucial. If translation were to begin one nucleotide before or after the start codon, every codon that follows in the mRNA will be misread, synthesizing a non-functional sequence of amino acids.
Translation begins with the codon AUG, and an initiator tRNA that carries the amino acid Methionine or, the chemically modified formylmethionine in bacteria.&#160;
The initiator tRNA also contains conserved nucleotides that are recognized by proteins called eukaryotic initiation factors, or eIFs.&#160;
Together with eIF2 and GTP, the initiator tRNA binds the P site of the small ribosomal subunit forming the eukaryotic pre-initiation complex.
This complex recognizes the mRNA by interacting with initiation factors eIF4E bound to the 5&#8217; cap, and eIF4G bound to the poly(A) tail-binding proteins.
Powered by ATP hydrolysis, the complex then moves from 5&#697; to 3&#697; direction, with the tRNA anticodon searching for the first AUG sequence on the mRNA.
Upon codon-anticodon recognition, GTP is hydrolyzed and the initiation factors dissociate, allowing the large ribosomal subunit to join the complex and form an intact ribosome.
Now, a new tRNA, carrying the second amino

initiation of translation

Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are all required to assemble on the initiation codon of mRNA. This process consists of several steps that are mediated by different eIFs.
First, the initiator tRNA must be selected from the pool of elongator tRNAs by eukaryotic initiation factor 2 (eIF2). The initiator tRNA (Met-tRNAi) has conserved sequence elements including modified bases at specific positions. This makes Met-tRNAi different from other
tRNAs carrying Methionine.
Next, the eIF2/GTP/Met-tRNAi ternary complex and other eIFs bind to the small ribosomal subunit to form a 43S preinitiation complex. Before the preinitiation complex binds the mRNA, to make sure that a correctly processed mRNA is translated, the cell uses initial recognition of the 5&#8217; cap of the mRNA by the eIF4E subunit of eIF4F.
Most eukaryotic mRNAs are monocistronic, that is, they encode only a single protein. Once the preinitiation complex is bound to the mRNA, the complex moves forward to search for the first AUG triplet, which is usually 50&#8211;100 nucleotides downstream of the 5&#8242;-terminal cap.
During this scan, the nucleotides adjacent to the start codon affect the efficiency of codon recognition. If the recognition site is substantially different from the consensus recognition sequence (5&#697;-ACCAUGG-3&#697;), the preinitiation complex may skip over the first AUG triplet in the mRNA and continue scanning to the next AUG. This phenomenon is known as &#8220;leaky scanning.&#8221; Several viruses, such as the human papillomavirus, use leaky scanning as the predominant mechanism during translation. Other cells also frequently use this to produce multiple proteins from the same mRNA molecule.
Bacterial ribosomes can assemble directly on a start codon that lies several nucleotides downstream of the Shine-Dalgarno sequence. So, a single molecule of bacterial mRNA can code for several different proteins, which makes bacterial mRNAs polycistronic.

Initiating translation is complex because it involves multiple molecules. Initiator tRNA, ribosomal subunits, and eukaryotic initiation factors (eIFs) are ...

Education

JoVE Core

Cell Biology

Unit 1

Translation: RNA to Protein

KEY TERMS AND CONCEPTS

translation begins with ribosome assembly

Translation begins when a ribosome assembles on an mRNA molecule and starts reading its code. During this first stage of protein synthesis, the cell prepares the machinery needed to build a protein from amino acids.

The small ribosomal subunit binds to the mRNA first. It helps position the message so the ribosome can find the correct start site. Then the initiator tRNA, which carries the first amino acid, pairs with the start codon on the mRNA.

After the start codon is matched, the large ribosomal subunit joins the complex. This creates a complete ribosome ready for elongation, the stage where the protein chain grows. Translation initiation is a key step because it sets the reading frame and starts protein production in the right place.

Translation Begins with Ribosome Assembly

translation-begins-with-ribosome-assembly

translation

How Cells Build Proteins from mRNA

Translation is the cell process that builds proteins from messenger RNA, or mRNA. It comes after transcription and is the final step in gene expression. Ribosomes, which are made of protein and specialized RNA, carry out this process with help from transfer RNA, or tRNA, and other proteins. The result is a chain of amino acids called a polypeptide. Proteins are called the building blocks of life because they make up much of an organism, from muscle fibers and hair to parts of the immune system.

ribosomes

Ribosomes in Protein Synthesis

Ribosomes build proteins by reading messenger RNA, or mRNA, and turning that genetic code into an amino acid chain. Both prokaryotic and eukaryotic cells have ribosomes. Cells that make large amounts of protein, such as secretory cells in the human pancreas, can contain millions of them. Ribosomes are made of ribosomal RNA, or rRNA, and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus, a region of the nucleus that specializes in making ribosomes. There, rRNA joins with...

trna activation

Charging tRNA for Protein Synthesis

tRNA charging is the step that prepares transfer RNA for protein synthesis. In this process, an amino acid is attached to its matching tRNA by an enzyme called aminoacyl-tRNA synthetase. The charged tRNA can then deliver that amino acid during translation. tRNA charging is a key part of how cells build proteins from genetic information. The transcript focuses on the activation of tRNA and the role of aminoacyl-tRNA synthetases in this process. These enzymes help ensure that the correct amino...

Translation begins when a ribosome assembles on an mRNA molecule and starts reading its code. During this first stage of protein synthesis, the cell prepares the machinery needed to build a protein from amino acids. The small ribosomal subunit binds to the mRNA first. It helps position the message so the ribosome can find the correct start site. Then the initiator tRNA, which carries the first amino acid, pairs with the start codon on the mRNA. After the start codon is matched, the large...

termination of translation

How Protein Synthesis Ends

Protein synthesis ends when translation reaches a stop signal on the mRNA. At this stage, the ribosome no longer adds amino acids to the growing polypeptide chain. Instead, the process shifts to releasing the completed protein.

improving translational accuracy

Boosting Protein Translation Fidelity

Protein translation fidelity helps cells build the right protein from an mRNA message. The ribosome must read each codon correctly and add the matching amino acid in order. Even small errors can change the final protein. The transcript explains how accuracy can be improved during translation. It focuses on the steps that help the ribosome choose the correct tRNA and keep the growing peptide chain on track. These controls reduce mistakes while the protein is being made. This topic is important...

nonsense-mediated mrna decay

Nonsense-Mediated mRNA Decay and UPF Proteins

Nonsense-mediated mRNA decay is a cell quality-control process that removes faulty mRNA before it can make a shortened protein. It helps protect cells from errors during gene expression. The pathway depends on UPF proteins, which help identify and trigger the breakdown of the problem message. This process matters when an mRNA contains a premature stop signal, also called a nonsense codon. Instead of allowing translation to continue, the cell recognizes the defective message and targets it for...

molecular chaperones and protein folding

Chaperones Guide Protein Folding

Molecular chaperones help proteins fold into the correct shape. Protein folding is a key step after a protein is made, because shape affects function. If a protein does not fold properly, it may not work as it should. Chaperones do not become part of the final protein. Instead, they assist the folding process and help proteins avoid harmful misfolding. They are especially important when newly made proteins are still fragile and need support as they take on their proper structure. This topic...

the proteasome

Protein Recycling by the Proteasome

The proteasome breaks down proteins inside cells. It helps control which proteins stay active and which are removed. This process is an important part of protein recycling. Proteins can be tagged for destruction before they enter the proteasome. The cell uses this system to remove proteins that are no longer needed or that must be cleared away. The proteasome then cuts them into smaller pieces. This protein breakdown helps the cell stay organized and function properly. By clearing selected...

regulated protein degradation

How Cells Remove Unneeded Proteins

Cells remove unneeded proteins through regulated protein degradation. This process helps control which proteins stay active and which proteins are broken down. Protein degradation is not random. The cell uses signals to mark proteins for removal at the right time. This regulation lets the cell respond to changing needs and keep protein levels balanced. Regulated protein degradation is an important part of molecular biology. It shows how cells maintain control over their internal processes by...

proteins: from genes to degradation

Protein Synthesis and Breakdown

Proteins are made from genes and later broken down when they are no longer needed. This page follows that path from gene information to protein degradation, or protein breakdown. It shows how cells build proteins and how they remove them at the right time. The process begins with genes, which carry the instructions for making proteins. Those instructions are used to produce proteins with specific jobs in the cell. After a protein has done its work, the cell can degrade it instead of keeping it...

key terms and concepts

Learn how translation starts as the ribosome binds mRNA, the initiator tRNA matches the start codon, and the large subunit joins to begin protein synthesis.

Translation Begins with Ribosome Assembly | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Louisiana Student Standards for Science

High School

Life Sciences

From Molecules To Organisms: Structures And Processes

HS-LS1-1

Virginia  Standards of Learning

HIgh School

BIO.2

BIO.2.d

Minnesota Academic Standards in Science

Life Science

3.2.1 9L.3.2.1.1

Alabama Course of Study Science

From Molecules to Organisms: Structures and Processes

9-12.B.1.2

Florida Department of Education

SC.912.L.16

SC.912.L.16.5

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS1-1.

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Translation Begins with Ribosome Assembly

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