Structural support, catalysis of chemical reactions, regulation of substances passage across the cell membrane, protection against disease, and main components of hair, nails, bones, and tissues- these are all functions performed by proteins. Protein synthesis, essential for cell activity, mainly occurs in tiny cellular structures called ribosomes. Ribosomes’ function is so vital that they are found in all kinds of organisms, from prokaryotic bacteria and archaea to eukaryotes. In fact, it's often said life is just ribosomes making other ribosomes! In the following article, we'll look at ribosomes' definition, structure, and function.
Millions of flashcards designed to help you ace your studies
Sign up for freeFree ribosomes and bound ribosomes differ in their structure.
If a cell has an extremely high number of ribosomes and a prominent nucleolus, this cell most likely:
Where can you find ribosomes in a eukaryotic cell?
Which organelle assembles the ribosomal subunits?
Proteins produced by bound ribosomes are destined to:
Which pair of ribosomes are more similar to each other?
Ribosomes are present in:
All the eukaryotic ribosomes are found free in the cytosol
Where are the proteins that compose ribosomal subunits synthesized?
What are ribosomes made of?
The second step of gene expression is ____, where ____ molecules are produced by the _____.
All the eukaryotic ribosomes are found free in the cytosol
Where are the proteins that compose ribosomal subunits synthesized?
What are ribosomes made of?
The second step of gene expression is ____, where ____ molecules are produced by the _____.
Free ribosomes and bound ribosomes differ in their structure.
If a cell has an extremely high number of ribosomes and a prominent nucleolus, this cell most likely:
Where can you find ribosomes in a eukaryotic cell?
Which organelle assembles the ribosomal subunits?
Proteins produced by bound ribosomes are destined to:
Which pair of ribosomes are more similar to each other?
Ribosomes are present in:
Achieve better grades quicker with Premium
Geld-zurück-Garantie, wenn du durch die Prüfung fällst
Did you know that StudySmarter supports you beyond learning?
Review generated flashcards
Start learning or create your own AI flashcards
Team Ribosomes Teachers
Thank you for your interest in audio learning!
This feature isn’t ready just yet, but we’d love to hear why you prefer audio learning.
Why do you prefer audio learning? (optional)
Send FeedbackCell biologist George Emil Palade first observed the ribosomes inside a cell using an electron microscope in the 1950s. He described them as “small particulate components of the cytoplasm”. A few years later, the term ribosome was proposed during a symposium and was later widely accepted by the scientific community. The word comes from “ribo” = ribonucleic acid (RNA), and the Latin word “soma” = body, meaning a body of ribonucleic acid. This name refers to the composition of ribosomes, which are composed of ribosomal RNA and proteins.
A ribosome is a cellular structure not bounded by a membrane, composed of ribosomal RNA and proteins, and
The ribosome’s function in protein synthesis is so critical for all cellular activities that two Nobel prizes have been awarded to research teams that study the ribosome.
The Nobel prize in Physiology or Medicine was awarded in 1974 to Albert Claude, Christian de Duve, and George E. Palade “for their discoveries concerning the structural and functional organization of the cell”. The recognition of Palade’s work included the discovery and description of ribosome structure and function. In 2009 the Nobel prize in chemistry was awarded for the description of the ribosome structure in detail and its function at the atomic level to Venkatraman Ramakrishnan, Thomas Steitz, and Ada Yonath. The press release stated, “The Nobel Prize in Chemistry for 2009 awards studies of one of life’s core processes: the ribosome’s translation of DNA information into life. Ribosomes produce proteins, which in turn control the chemistry in all living organisms. As ribosomes are crucial to life, they are also a major target for new antibiotics”.
Ribosomes comprise two subunits (Fig. 1), one large and one small, with both subunits made up of ribosomal RNA (rRNA) and proteins. These rRNA molecules are synthesized by the nucleolus inside the nucleus and combined with proteins. The assembled subunits exit the nucleus to the cytoplasm. Under a microscope, ribosomes look like small dots that can be found free in the cytoplasm, as well as bound to the continuous membrane of the outer nuclear envelope and the endoplasmic reticulum (Fig. 2).
The following diagram represents a ribosome with its two subunits while translating a messenger RNA molecule (this process is explained in the next section).
How do ribosomes know how to synthesize a specific protein? Remember that the nucleus previously transcribed the information from genes into messenger RNA molecules -mRNA- (the first step in gene expression). These molecules ended up exiting the nucleus and are now in the cytoplasm, where we also find the ribosomes. In a ribosome, the large subunit is located on top of the small one, and in the space in between the two, the mRNA sequence passes through to be decoded.
The ribosome small subunit “reads” the mRNA sequence, and the large subunit synthesizes the corresponding polypeptide chain by linking amino acids. This corresponds to the second step in gene expression, the translation from mRNA to protein. The amino acids needed for polypeptide synthesis are brought from the cytosol to the ribosome by another type of RNA molecule, appropriately called transfer RNA (tRNA).
Ribosomes that are free in the cytosol or bound to a membrane have the same structure and can interchange their location. Proteins produced by free ribosomes are usually used within the cytosol (like enzymes for sugar breakdown) or are destined for mitochondria and chloroplasts membranes or imported to the nucleus. Bound ribosomes generally synthesize proteins that will be incorporated into a membrane (of the endomembrane system) or that will exit the cell as secretory proteins.
The endomembrane system is a dynamic composite of organelles and membranes that compartmentalize the interior of a eukaryotic cell and work together to perform cellular processes. It includes the outer nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, the plasma membrane, vacuoles, and vesicles.
Cells that continuously produce a lot of proteins can have millions of ribosomes and a prominent nucleolus. A cell can also change the number of ribosomes to achieve its metabolic functions if needed. The pancreas secretes large amounts of digestive enzymes, thus pancreatic cells have abundant ribosomes. Red blood cells also are rich in ribosomes when immature, as they need to synthesize hemoglobin (the protein that binds to oxygen).
Interestingly, we can find ribosomes in other parts of a eukaryotic cell, besides the cytoplasm and the rough endoplasmic reticulum. Mitochondria and chloroplasts (organelles that transform energy for cellular use) have their own DNA and ribosomes. Both organelles most likely evolved from ancestral bacteria that were engulfed by the ancestors of eukaryotes through a process called endosymbiosis. Therefore, as previous free-living bacteria, mitochondria and chloroplasts had their own bacterial DNA and ribosomes.
Ribosomes are often referred to as the “cell factories” due to their protein-building function. Because there are so many (up to millions!) ribosomes inside a cell, you can think of them as the workers, or machines, that actually do the assembly job in the factory. They get copies or blueprints (mRNA) of the assembly instructions (DNA) from their boss (nucleus). They do not make the protein components (amino acids) themselves, these are in the cytosol. Therefore, ribosomes only link the amino acids in a polypeptide chain according to the blueprint.
Protein synthesis is essential for cell activity, they function as diverse vital molecules, including enzymes, hormones, antibodies, pigments, structural components, and surface receptors. This essential function is evidenced by the fact that all cells, prokaryotic and eukaryotic, have ribosomes. Although bacterial, archaeal, and eukaryotic ribosomes differ in subunits size (prokaryotic ribosomes are smaller than eukaryotic ones) and specific rRNA sequences, they all are composed of similar rRNA sequences, have the same basic structure with two subunits where the small one decodes mRNA, and the large one joins amino acids together. Thus, it seems that ribosomes evolved early in the history of life, which also reflects the common ancestry of all organisms.
Sign up for free to gain access to all our flashcards.
What are 3 facts about ribosomes?
Three facts about ribosomes are: they are not delimited by a bilayered membrane, their function is to synthesize proteins, they can be free in the cytosol or bound to the rough endoplasmic reticulum membrane.
What are ribosomes?
Ribosomes are cellular structures not bounded by a bilayered membrane and whose function is to synthesize proteins.
What is the function of ribosomes?
The function of ribosomes is to synthesize proteins through the translation of mRNA molecules.
Why are ribosomes important?
Ribosomes are important because they synthesize proteins, which are essential for cell activity. Proteins function as diverse vital molecules including enzymes, hormones, antibodies, pigments, structural components, and surface receptors.
Where are ribosomes made?
Ribosomal subunits are made in the nucleolus inside the cell nucleus.
At StudySmarter, we have created a learning platform that serves millions of students. Meet the people who work hard to deliver fact based content as well as making sure it is verified.
Lily Hulatt is a Digital Content Specialist with over three years of experience in content strategy and curriculum design. She gained her PhD in English Literature from Durham University in 2022, taught in Durham University’s English Studies Department, and has contributed to a number of publications. Lily specialises in English Literature, English Language, History, and Philosophy.
Get to know Lily
Gabriel Freitas is an AI Engineer with a solid experience in software development, machine learning algorithms, and generative AI, including large language models’ (LLMs) applications. Graduated in Electrical Engineering at the University of São Paulo, he is currently pursuing an MSc in Computer Engineering at the University of Campinas, specializing in machine learning topics. Gabriel has a strong background in software engineering and has worked on projects involving computer vision, embedded AI, and LLM applications.
Get to know Gabriel
Vaia is a globally recognized educational technology company, offering a holistic learning platform designed for students of all ages and educational levels. Our platform provides learning support for a wide range of subjects, including STEM, Social Sciences, and Languages and also helps students to successfully master various tests and exams worldwide, such as GCSE, A Level, SAT, ACT, Abitur, and more. We offer an extensive library of learning materials, including interactive flashcards, comprehensive textbook solutions, and detailed explanations. The cutting-edge technology and tools we provide help students create their own learning materials. StudySmarter’s content is not only expert-verified but also regularly updated to ensure accuracy and relevance.
Learn moreSave explanations to your personalised space and access them anytime, anywhere!
By signing up, you agree to the and the of Vaia.
Already have an account? Log in
Sign up to highlight and take notes. It’s 100% free.
The first learning app that truly has everything you need to ace your exams in one place
The first learning platform with all the tools and study materials you need.
