Name: how ribosomes build proteins
Uploaded: 2026-06-01T06:27:55.836Z
Duration: 1 min 27 s
Channel: JoVE

K12 Standards

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

North Carolina 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.1.3

Ribosomes

The subunits of eukaryotic ribosomes are protein-synthesizing structures formed inside the nucleolus.The eukaryotic ribosome is called an 80S ribosome. It is made up of two subunits: a large 60S subunit and a small 40S subunit.The 60S subunit consists of 28S, 5.8S, and 5S rRNAs and about 49 proteins.The 40S subunit consists of an 18S rRNA and about 33 proteins.Both subunits are exported from the nucleus through the nuclear pores. They join on an mRNA to make proteins&#x2014;either free in the cytosol or attached to the outer nuclear envelope or the rough endoplasmic reticulum.The mRNA binding site is located in the small subunit. The three tRNA binding sites, E, P, and A, are formed at the interface of the two subunits.During translation, the initiator tRNA binds directly to the P, or peptidyl, site. During the elongation stage, new tRNAs enter the A or aminoacyl site, and empty tRNAs leave from the E or exit site.The rRNA in the large subunit also catalyzes peptide bond formation between amino acids, allowing the growing polypeptide chain to form.

ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein&#x2014;such as secretory cells in the human pancreas&#x2014;can contain millions of ribosomes.Ribosome Structure and AssemblyRibosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus&#x2014;a part of the nucleus that specializes in ribosome production. Within the nucleolus, rRNA is combined with proteins imported from the cytoplasm. The assembly produces two subunits of a ribosome&#x2014;the large and the small subunits. These subunits then leave the nucleus through pores in the nuclear envelope. At the start of translation, mRNA binds to a site on the small subunit, and subsequently, a large subunit is also recruited. This step forms a functional ribosome.Ribosomes may assemble in the cytosol&#x2014;called free ribosomes&#x2014;or while attached to the outside of the nuclear envelope or endoplasmic reticulum&#x2014;called bound ribosomes. Generally, free ribosomes synthesize proteins used in the cytoplasm, while bound ribosomes synthesize proteins that are inserted into membranes, packaged into organelles, or secreted from the cell.Protein SynthesisRibosomes synthesize proteins by bringing together mRNA and transfer RNA (tRNA). Specialized nucleotides of the tRNA, called anticodon loop, bind to the codon of the mRNA. The tRNA carries an amino acid on the other end. In this way, the genetic code from mRNA is translated into a chain of amino acids, one codon at a time. When mRNA binds to the small subunit of the ribosome, tRNA binds to one of three binding sites on the large subunit of the ribosome. The binding sites are called the A (aminoacyl-tRNA), P (peptidyl-tRNA), and E (exit) sites. As the mRNA is translated, new tRNAs are added at the A site; they move to the P site and are released at the E site. Ribosomes catalyze the formation of peptide bonds between adjacent amino acids, resulting in a polypeptide. The growing polypeptide chain threads through an exit tunnel in the large subunit. When the protein synthesis is complete, the ribosomal subunits dissociate.

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Education

JoVE Core

Cellular Processes

Cell Structure and Function

KEY TERMS AND CONCEPTS

how ribosomes build proteins

Ribosomes build proteins by reading messenger RNA, or mRNA, and linking amino acids in the right order. Both prokaryotic and eukaryotic cells contain ribosomes. Cells that make large amounts of protein, such as secretory cells in the human pancreas, can have millions of them.

Ribosomes are made of ribosomal RNA, or rRNA, and proteins. In eukaryotic cells, rRNA is transcribed from genes in the nucleolus, a part of the nucleus that specializes in making ribosomes. There, rRNA combines with proteins that are imported from the cytoplasm. This assembly forms the large and small ribosomal subunits. The subunits then leave the nucleus through pores in the nuclear envelope.

Translation begins when mRNA binds to a site on the small subunit. The large subunit is then recruited, and the full ribosome becomes functional. Ribosomes can assemble in the cytosol as free ribosomes, or they can attach to the outside of the nuclear envelope or the endoplasmic reticulum as bound ribosomes. Free ribosomes usually make proteins used in the cytoplasm. Bound ribosomes usually make proteins that are inserted into membranes, packaged into organelles, or secreted from the cell.

Ribosomes work with transfer RNA, or tRNA, to match each mRNA codon with the correct amino acid. The anticodon loop of tRNA pairs with the codon on mRNA, while the other end carries an amino acid. On the large subunit, tRNA moves through three sites: A, P, and E. New tRNAs enter at the A site, shift to the P site, and leave through the E site. Ribosomes also catalyze peptide bond formation between neighboring amino acids, which creates a polypeptide. The growing chain passes through an exit tunnel in the large subunit, and the ribosomal subunits separate when protein synthesis is finished.

How Ribosomes Build Proteins

what are cells?

Cell Membrane, DNA, and Organelles

Cells are the basic units of life, from a bacterium made of one cell to a human made of trillions. Even though organisms can differ greatly, their cells share key features that support life. A cell has a plasma membrane, which is a lipid bilayer that separates the cytoplasm from the outside environment. It also contains DNA, the genetic material that carries instructions for the cell. In prokaryotic cells, DNA is found in a region called the nucleoid. In eukaryotic cells, DNA is enclosed...

cell size

Why Cell Size Is Limited

Cell size is limited by surface area and diffusion. Cells vary widely in size, both between organisms and within the same organism. Bacterial cells are usually 1 to 10 micrometers wide, and the smallest bacteria can be 0.1 micrometers in diameter. That is about a thousand times smaller than most eukaryotic cells, which are typically 10 to 100 micrometers across. A cell takes in nutrients and water through diffusion across the plasma membrane or through channels in the membrane. The membrane...

eukaryotic compartmentalization

Cell Organelles and Microenvironments

Eukaryotic cells use membrane-bound organelles to keep cell processes organized. The nucleus and mitochondria are two key examples. Because biological membranes are selectively permeable, they create controlled spaces inside each organelle. These small microenvironments support specialized jobs and separate them from the surrounding cytosol. Different organelles maintain different internal conditions. In animal cells, lysosomes keep an acidic environment that helps their enzymes digest...

prokaryotic cells

Prokaryotic Cell Structures

Prokaryotic cells are small, single-celled organisms found in the domains Archaea and Bacteria. Bacteria include familiar species such as Salmonella and E. coli. Archaea include extremophiles, which are organisms that live in harsh environments like volcanic springs. Prokaryotic cells share several basic features with eukaryotic cells. They are surrounded by a plasma membrane, contain cytoplasm, and have ribosomes that make proteins. Their genetic material is a single, circular DNA molecule.

cytoplasm

Cytoplasm and the Cell’s Internal Framework

The cytoplasm is the cell’s internal space that holds organelles and the cytoskeleton. It is suspended in the cytosol, an aqueous fluid made of water, ions, salts, and many organic molecules. Together, these parts create the environment where key cell activities happen. The cytoplasm is also a major site for protein synthesis and folding. The water-based cytosol helps proteins fold correctly. Hydrophobic amino acid side chains tend to hide in the protein core, while hydrophilic amino acids...

endoplasmic reticulum

ER in Protein and Lipid Transport

The endoplasmic reticulum is a membrane network in eukaryotic cells. It is continuous with the outer membrane of the nucleus. This connection helps link nuclear and cytoplasmic processes and supports efficient movement inside the cell. mRNA can move from the nucleus to ribosomes, which helps protein synthesis happen efficiently. The ER is a major site for making, processing, and distributing biomolecules. The rough endoplasmic reticulum has ribosomes attached to its surface. These ribosomes...

Ribosomes build proteins by reading messenger RNA, or mRNA, and linking amino acids in the right order. Both prokaryotic and eukaryotic cells contain ribosomes. Cells that make large amounts of protein, such as secretory cells in the human pancreas, can have millions of them. Ribosomes are made of ribosomal RNA, or rRNA, and proteins. In eukaryotic cells, rRNA is transcribed from genes in the nucleolus, a part of the nucleus that specializes in making ribosomes. There, rRNA combines with...

golgi apparatus

Protein Sorting in the Golgi Apparatus

The Golgi apparatus sorts and modifies proteins after they leave the endoplasmic reticulum (ER). Properly folded and assembled proteins are packaged into vesicles, or small membrane sacs, and moved by microtubule-based motor proteins. These vesicles can fuse into vesicular tubular clusters before reaching the Golgi, which often looks like a ribbon-shaped organelle in eukaryotic cells. Vesicles enter the cis face of the Golgi, the side facing the ER. They pass through a set of pancake-shaped...

peroxisomes

Peroxisomes and Cellular Detoxification

Peroxisomes and mitochondria are two important oxygen-utilizing organelles in eukaryotic cells. Mitochondria carry out cellular respiration, which turns energy from food into ATP. Peroxisomes focus on breaking down substances such as fatty acids and other materials the cell needs to process. A peroxisome is a single membrane-bound organelle. It helps with lipid metabolism and chemical detoxification. Enzymes inside peroxisomes move hydrogen atoms from molecules to oxygen. This reaction...

microtubules

Microtubules in Cells and Cell Movement

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plant cell wall

Plant Cell Walls in Growth and Support

Plant cell walls help plant cells keep their shape, stay protected, and remain supported. As a cell matures, its wall can change based on the cell type. Parenchyma cells in leaves usually have only a thin primary cell wall. These walls are part of how different plant cells take on different jobs. Collenchyma and sclerenchyma cells are found mostly in the outer layers of stems and leaves. Collenchyma cells add strength by partially thickening the primary cell wall. Sclerenchyma cells provide...

plasmodesmata

Plasmodesmata and Plant Cell Communication

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the extracellular matrix

How ECM Supports Animal Tissues

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the nucleus

Nuclear DNA and Cell Control

The nucleus is the control center of a eukaryotic cell. It is a membrane-bound organelle that contains chromosomal DNA. That DNA helps control gene expression and regulate protein production in the cell. Not all cellular DNA has the same role. The DNA in mitochondria and chloroplasts supports functions that are specific to those organelles. Inside the nucleus, DNA structure also affects how genes are regulated. Nuclear DNA is wrapped around proteins called histones. This forms chromatin, a...

tissues

Body Tissues and Their Jobs

Body tissues are groups of cells with similar structure and function. When different tissues work together, they form an organ with a specialized job. Vertebrates have four main tissue types: epithelial, connective, muscle, and nervous tissue. Epithelial tissue is made of thin sheets of cells. It covers the skin and lines internal organs and body cavities. These cells are tightly packed, so they help protect against injury, infection, and water loss. Epithelial tissue may be simple, with one...

gap junctions

Connexins and Cell-to-Cell Signaling

Gap junctions help animal cells send signals and share small materials with nearby cells. They are made of special proteins that form pores between neighboring cells and connect their cytoplasm. Through these channels, cells can exchange ions and other small molecules. These communication channels are found in many invertebrate and vertebrate species. They support important processes such as cell differentiation and development. They are also linked to human diseases, including disorders of...

key terms and concepts

See how ribosomes read mRNA, use tRNA, and assemble amino acids into proteins. Learn the roles of free and bound ribosomes in cells.

How Ribosomes Build Proteins | JoVE K12

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Pennsylvania State Academic Standards

Life Science

Structure and Function

3.1.9-12.A

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Ohio’s Learning Standards and Model Curriculum

Cells

Cell structure and function

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From Molecules to Organisms: Structures and Processes

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SC.912.L.14

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How Ribosomes Build Proteins

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