Ribosome – Types, Structure, Function, and Diagram

What are Ribosomes?

• Ribosomes, first observed by George Palade in 1953 through an electron microscope, are complex molecular machines within living cells. They are instrumental in protein synthesis, also known as translation, where they convert genetic information from messenger RNA (mRNA) into proteins. This process is critical for cellular function and growth.
• The protein synthesis in ribosomes occurs in three distinct stages: initiation, elongation, and termination. During these stages, ribosomal RNA (rRNA) within the ribosomes catalyzes the peptidyl transferase reaction. This reaction is crucial for forming peptide bonds between amino acids, the building blocks of proteins. Once synthesized, these proteins are transported to various cell areas to perform diverse cellular functions.
• Structurally, ribosomes are ribonucleoprotein complexes composed of two subunits: the small (30S) and large (50S) subunits. Each subunit comprises one or more rRNA molecules and numerous ribosomal proteins (RPs or r-proteins). These subunits play distinct roles: the 30S subunit primarily decodes genetic information, while the 50S subunit has a catalytic function, aiding in the formation of peptide bonds.
• The synthesis of proteins in ribosomes begins with the transcription of DNA into mRNA. This mRNA chain carries the sequence of amino acids required to form a specific protein. Ribosomes bind to these mRNA chains and use their sequences to assemble amino acids in the correct order. Transfer RNA (tRNA) molecules play a pivotal role in this process. They carry amino acids to the ribosome and match the mRNA’s codons with their anti-codon stem loops, ensuring the correct amino acid sequence for the growing polypeptide chain.
• Furthermore, ribosomes are classified as ribozymes due to their RNA-based catalytic activity, particularly in peptide bond formation. The protein synthesis process encompasses four phases: initiation, elongation, termination, and recycling. Notably, ribosomes can recognize the completion of translation when they encounter stop codons (UAA, UAG, or UGA) in the mRNA, as these codons do not correspond to any tRNA molecules.
• Intriguingly, ribosomes are closely associated with the rough endoplasmic reticulum in cells, playing a vital role in protein sorting and synthesis for both intracellular and extracellular use. The location of ribosomes within a cell—either floating freely in the cytoplasm or attached to the rough endoplasmic reticulum—determines the type of proteins synthesized.
• Ribosomes are ubiquitous in both prokaryotic and eukaryotic cells, with their structure and function being remarkably conserved across species. This conservation suggests a common evolutionary origin. However, differences in size, sequence, structure, and protein-to-RNA ratio exist among ribosomes from bacteria, archaea, and eukaryotes. These differences are significant in medical science, as they allow certain antibiotics to target bacterial ribosomes without affecting human ribosomes.
• In summary, ribosomes are essential cellular components responsible for protein synthesis. Their function and structure are critical for understanding cellular biology and have significant implications in medicine and biotechnology.

Definition of Ribosomes

Ribosomes are small, complex molecular machines found in all living cells that play a crucial role in protein synthesis. They read genetic information encoded in messenger RNA (mRNA) and assemble amino acids into proteins based on this information. Ribosomes consist of two main subunits, each comprising ribosomal RNA (rRNA) and proteins, and are essential for cellular function and growth.

Ribosomes Size and Shape

• Uniformity in Size and Shape: Ribosomes, essential for protein synthesis in cells, are notable for their consistent size and shape across different species. In higher plants and animal cells, ribosomes typically exhibit an oblate or spheroidal shape. Their diameter ranges from 150 to 200 Ångströms (A0), demonstrating a remarkable uniformity despite the diversity of cell types.
• Size Variation: The size of ribosomes can vary depending on the specific type of cell and its physiological state. For instance, the size may differ between a cell at rest and one undergoing cell division. This variation reflects the dynamic nature of ribosomes in adapting to the cellular environment and requirements.
• Structure and Composition: Ribosomes are composed of two distinct subunits, each varying in size. These subunits come together to form a functional ribosome, which is crucial for translating mRNA into proteins. The ribosomes are not enclosed by a membrane, whether they are free in the cytoplasm or bound to the endoplasmic reticulum.
• Prokaryotic Ribosomes: In prokaryotic cells, ribosomes are typically 70S in size. This size is derived from the combination of a 30S small subunit and a 50S large subunit. The ‘S’ unit, or Svedberg unit, represents the sedimentation rate during ultracentrifugation, indicating the rate at which particles settle in a centrifugal field. Prokaryotic ribosomes have a molecular weight of approximately 2.7×10^6 Daltons and a diameter of about 20 nm. They consist of about 65% ribosomal RNA (rRNA) and 35% ribosomal proteins.
• Eukaryotic Ribosomes: Eukaryotic cells contain ribosomes that are generally larger, with a size of 80S. This size results from the association of a 40S small subunit and a 60S large subunit. The molecular weight of eukaryotic ribosomes is around 4×10^6 Daltons, and their diameter ranges between 25 to 30 nm.

Characteristics of Ribosome

1. Fundamental Nature of Ribosomes:
   • Ribosomes are integral cellular structures involved in protein synthesis across all living organisms. They are ubiquitous in both prokaryotic and eukaryotic cells, underscoring their essential role in biological processes.
2. Composition and Structure:
   • Constituents: Ribosomes are composed of ribonucleic acid (RNA) and proteins. The RNA component is known as ribosomal RNA (rRNA).
   • Subunits: Each ribosome consists of two distinct subunits: a smaller subunit and a larger subunit. These subunits work in tandem during the process of protein synthesis.
3. Functional Sites and Genetic Code Translation:
   • Ribosomes possess specific binding sites for molecules involved in protein synthesis. They are responsible for reading the genetic code carried by messenger RNA (mRNA) and translating it into a sequence of amino acids, forming proteins.
4. Cellular Location:
   • Ribosomes are located either scattered throughout the cytoplasm or attached to the endoplasmic reticulum, forming the rough endoplasmic reticulum. This distribution is significant for their role in protein synthesis.
5. Prokaryotic Ribosomes (70S):
   • Size and Composition: Prokaryotic ribosomes, smaller than their eukaryotic counterparts, are approximately 20 nm in diameter and composed of 65% rRNA and 35% ribosomal proteins.
   • Subunits and rRNA: The 70S ribosome comprises a 50S large subunit and a 30S small subunit. The 30S subunit contains 16S rRNA, while the 50S subunit includes 5S and 23S rRNAs.
6. Archaeal Ribosomes:
   • Similarity to Bacterial Ribosomes: Archaeal ribosomes are structurally similar to bacterial ribosomes, with 70S ribosomes composed of 50S and 30S subunits. However, at the sequence level, they resemble eukaryotic ribosomes.
7. Eukaryotic Ribosomes (80S):
   • Size and Formation: Eukaryotic ribosomes are larger, measuring about 25-30 nm. Their formation occurs in both the cytoplasm and the nucleolus.
   • Subunits and rRNA: The 80S ribosome consists of a 60S large subunit and a 40S small subunit. The 40S subunit houses 18S rRNA, while the 60S subunit contains 5S, 5.8S, and 28S rRNAs.
   • Mitochondrial and Chloroplast Ribosomes: Eukaryotic semi-autonomous organelles like chloroplasts and mitochondria contain 70S ribosomes, similar to prokaryotic ribosomes, indicating a bacterial ancestry.

Types of Ribosomes

Types of Ribosomes Based on Sedimentation Coefficients

Ribosomes, pivotal for protein synthesis in cells, are classified based on their sedimentation coefficients, denoted as “S”. This classification is crucial for understanding the functional and structural differences in ribosomes across various cellular types.

1. 70S Ribosomes:
   • Size and Sedimentation Coefficient: 70S ribosomes are relatively smaller with a sedimentation coefficient of 70S.
   • Molecular Weight: These ribosomes have a molecular weight of approximately 2.7 × 10^6 daltons.
   • Location: They are predominantly found in prokaryotic cells, including bacteria and blue-green algae. Intriguingly, 70S ribosomes are also present in the mitochondria and chloroplasts of eukaryotic cells, reflecting a symbiotic evolutionary origin.
   • Functional Significance: The presence of 70S ribosomes in prokaryotic cells and organelles like mitochondria and chloroplasts underscores their role in protein synthesis in varied cellular environments.
2. 80S Ribosomes:
   • Size and Sedimentation Coefficient: In contrast to 70S ribosomes, 80S ribosomes are larger, with a sedimentation coefficient of 80S.
   • Molecular Weight: These ribosomes have a higher molecular weight, roughly 4 × 10^6 daltons.
   • Location: 80S ribosomes are primarily located in eukaryotic cells, encompassing both plant and animal cells. Notably, the ribosomes found in mitochondria and chloroplasts are smaller than the cytoplasmic 80S ribosomes.
   • Composition: In yeast, for example, the 80S ribosome contains 79 distinct ribosomal proteins, with 12 being unique to the species. This composition highlights the complexity and specificity of eukaryotic ribosomes in protein synthesis.
3. Comparative Analysis:
   • Prokaryotic vs. Eukaryotic Ribosomes: The 70S ribosomes are characteristic of prokaryotic cells, while eukaryotic cells typically contain 80S ribosomes. This difference is not just in size but also in molecular composition and weight, reflecting the evolutionary divergence between prokaryotic and eukaryotic organisms.
   • Mitochondrial and Chloroplast Ribosomes: The presence of 70S ribosomes in mitochondria and chloroplasts of eukaryotic cells is a fascinating aspect, suggesting a bacterial lineage of these organelles. This aspect is crucial in studying cellular evolution and function.

Types of Ribosomes Based on Locations

Ribosomes, essential for protein synthesis, can be classified based on their location within the cell. They are categorized as either “free” or “membrane-bound,” with each type playing a distinct role in protein synthesis.

1. Free Ribosomes:
   • Location and Movement: Free ribosomes are located in the cytosol, the fluid component of the cell’s cytoplasm. They are characterized by their ability to move freely within this area, although they are excluded from the cell nucleus and other organelles.
   • Protein Synthesis and Destination: Proteins synthesized by free ribosomes are typically released into the cytosol. These proteins are generally used within the cell itself.
   • Environmental Considerations: The cytosol is a reduced environment rich in glutathione, which means that disulfide bonds, formed by oxidized cysteine residues, are not typically produced in this environment.
2. Membrane-bound Ribosomes:
   • Formation and Location: Membrane-bound ribosomes become associated with membranes when they synthesize proteins required by certain organelles. In eukaryotic cells, this association occurs with the endoplasmic reticulum (ER), specifically the rough ER.
   • Protein Synthesis and Processing: As these ribosomes synthesize polypeptide chains, the chains are directly inserted into the ER. This vectorial synthesis allows for the proteins to be subsequently transferred to their final destinations via the secretory pathway.
   • Function of Synthesized Proteins: Proteins produced by membrane-bound ribosomes are typically destined for the plasma membrane or are secreted out of the cell through exocytosis. This indicates a specialized role for membrane-bound ribosomes in synthesizing proteins for export or membrane incorporation.
3. Spatial Distribution and Functional Flexibility:
   • Dynamic Location: The existence of a ribosome as free or membrane-bound is not fixed but depends on the presence of an ER-targeting sequence in the synthesized protein. Therefore, an individual ribosome may alternate between being free in the cytosol and membrane-bound, based on the protein it synthesizes at a given time.
   • Structural Similarity: Despite their different locations and roles, free and membrane-bound ribosomes share the same structure. This uniformity underscores the versatility of ribosomes in protein synthesis across different cellular environments.
4. Classification as Non-membranous Organelles:
   • Organelle Definition: While ribosomes are often described as organelles, they are distinct in that they lack a phospholipid membrane, a common feature of many other organelles.
   • Non-membranous Nature: Due to their particulate, non-membranous nature, ribosomes are sometimes classified as “non-membranous organelles,” highlighting their unique status within the cell.

Ribosome Animation Video

Location of Ribosome

Ribosomes, crucial for protein synthesis, are located either in the cytosol or attached to the endoplasmic reticulum (ER) in both plant and animal cells. Their location is pivotal in determining the type of proteins they synthesize and their subsequent roles within the cell.

1. Ribosomes in the Cytosol:
   • Free Ribosomes: Many ribosomes exist freely within the cytoplasmic matrix of cells. These ribosomes are not attached to any membrane and are involved in synthesizing proteins that typically serve functions within the cell itself.
   • Polysomes: Multiple ribosomes can attach to a single mRNA strand, forming a structure known as a polysome. This arrangement enhances the efficiency of protein synthesis.
2. Ribosomes Attached to the Endoplasmic Reticulum:
   • Rough Endoplasmic Reticulum (RER): In cells actively involved in protein synthesis, ribosomes are attached to the ER, forming the rough ER. This association is crucial for the synthesis of proteins destined for secretion or for incorporation into cell membranes.
   • Cell Types with High RER Activity: Cells like pancreatic cells, plasma cells, hepatic parenchymal cells, and others exhibit a high density of ribosomes attached to the RER, reflecting their high protein-synthesizing activity.
3. Distribution in Specific Cell Types:
   • Yeast, Reticulocytes, and Lymphocytes: These cells, along with meristematic plant tissues, embryonic nerve cells, and cancerous cells, contain a large number of ribosomes, indicative of their high protein synthesis requirements.
   • Cells with Predominant Free Ribosomes: Cells such as erythroblasts and developing muscle cells have a significant number of free ribosomes, emphasizing their role in synthesizing proteins for intracellular use.
4. Quantitative Aspects of Ribosomes:
   • Prokaryotic Cells: In E. coli, for instance, ribosomes constitute about 25% of the total cellular mass, with approximately 10,000 ribosomes per cell.
   • Eukaryotic Cells: In mammalian cultured cells, there can be as many as 10 million ribosomes per cell, highlighting the extensive protein synthesis machinery in these organisms.

Structure of Ribosome

1. Basic Composition and Structure:
   • Ribosomes are complex molecular machines composed of ribonucleic acid (RNA) and proteins. The RNA component, known as ribosomal RNA (rRNA), combines with various ribosomal proteins to form the structure of the ribosome.
   • Structurally, ribosomes consist of two distinct subunits: a smaller subunit and a larger subunit. These subunits collaborate in the process of protein synthesis, with each playing a specific role.
2. Functional Components and Sites:
   • The small subunit is responsible for reading genetic information and binding to messenger RNA (mRNA). The larger subunit facilitates peptide bond formation and binds to aminoacylated transfer RNAs (tRNAs).
   • Ribosomes have three key sites for tRNA binding and peptide synthesis: the A (aminoacyl) site, the P (peptidyl) site, and the E (exit) site. These sites are crucial for the sequential addition of amino acids to the growing peptide chain.
3. Subunit Morphology and Interaction:
   • The larger subunit of the ribosome is dome-shaped, while the smaller subunit has an oblate-ellipsoid cap shape. The larger subunit contains features such as protuberance, stalk, and ridge, with the P and A sites for tRNA binding.
   • The smaller subunit includes a head, cleft, and platform, fitting over the larger subunit like a cap. The cleft provides space for mRNA between the two subunits.
4. Subunit Association and Disassociation:
   • The association of the ribosomal subunits is influenced by the concentration of magnesium ions (Mg++). A higher concentration of Mg++ ions keeps the subunits attached, while a decrease leads to their separation.
   • In bacterial cells, the subunits exist freely in the cytoplasm and unite only during protein synthesis. Under certain conditions, ribosomes can form dimers (monosomes) or aggregate on mRNA to form polyribosomes or polysomes.
5. Ribosomal Composition:
   • Ribosomes are composed of nearly equal amounts of proteins and RNA. Both subunits contain these components and are linked through interactions between the proteins of one subunit and the rRNAs of the other.
   • The RNA component of ribosomes is synthesized in the nucleolus, where ribosomes are initially assembled.
6. Location and Variability:
   • Ribosomes are located in two primary areas within the cell: scattered in the cytoplasm and attached to the endoplasmic reticulum (ER), forming the rough endoplasmic reticulum.
   • Both free and bound ribosomes are similar in structure and function in protein synthesis. The RNA content in ribosomes varies between 37 to 62%, with the remainder being proteins.
7. Diversity Across Organisms:
   • Prokaryotic cells possess 70S ribosomes, comprising a 30S small subunit and a 50S large subunit. Eukaryotic cells have 80S ribosomes, consisting of a 40S small subunit and a 60S large subunit.
   • Ribosomes found in the chloroplasts and mitochondria of eukaryotes resemble prokaryotic ribosomes, with 70S particles composed of large and small subunits.
8. RNA Structure and Antibiotic Targeting:
   • The RNA in ribosomes is arranged in various tertiary structures, forming loops that extend from the core without altering the overall structure.
   • The differences between eukaryotic and bacterial ribosomes are exploited in the development of antibiotics, allowing for the targeting of bacterial infections without harming human cells.

Chemical Composition of Ribosomes

The chemical composition of ribosomes, crucial for their function in protein synthesis, can be systematically analyzed in terms of their constituent components: ribosomal RNAs (rRNAs), ribosomal proteins, and metallic ions.

1. Ribosomal RNAs (rRNAs):
   • Ribosomes in different organisms contain varying types of rRNA, essential for their structure and function.
   • 70S Ribosomes:
     • These ribosomes, typically found in prokaryotic cells, consist of three types of rRNA: 23S, 16S, and 5S rRNA.
     • The 50S ribosomal subunit, which is the larger subunit, contains both 23S and 5S rRNA.
     • The smaller 30S ribosomal subunit houses the 16S rRNA.
   • 80S Ribosomes:
     • Common in eukaryotic cells, these ribosomes are composed of four types of rRNA: 28S, 18S, 5S, and 5.8S rRNA.
     • The larger 60S ribosomal subunit includes 28S, 5S, and 5.8S rRNAs.
     • The 18S rRNA is present in the smaller 40S ribosomal subunit.
2. Ribosomal Proteins:
   • Ribosomal proteins vary among different organisms and contribute to the structure and function of ribosomes.
   • In bacteria, the composition of ribosomal proteins differs across species.
   • For instance, in Escherichia coli (E. coli), there are 55 distinct ribosomal proteins identified, including core proteins (CP) and split proteins (SP).
3. Metallic Ions:
   • Ribosomes also contain divalent metallic ions, which play a crucial role in maintaining the structure and facilitating the function of ribosomes.
   • Key metallic ions include magnesium (Mg++), calcium (Ca++), and manganese (Mn++).

What is Plastoribosomes and mitoribosomes?

Plastoribosomes and mitoribosomes are specialized ribosomes found within eukaryotic cells, specifically in plastids and mitochondria, respectively.

Plastoribosomes:

• Location: These are situated within plastids, predominantly in chloroplasts of plant cells.
• Type: They are of the 70S type, akin to prokaryotic ribosomes.
• Function: Plastoribosomes play a pivotal role in protein synthesis within plastids.
• Similarity: Plastoribosomes exhibit a closer resemblance to prokaryotic ribosomes, underscoring the evolutionary lineage of chloroplasts from ancestral cyanobacteria.

Mitoribosomes:

• Location: Mitoribosomes are localized within the mitochondrial matrix.
• Type: They also belong to the 70S category.
• Function: Mitoribosomes are instrumental in synthesizing proteins that are essential for mitochondrial functions, utilizing precursors provided by the mitochondria.
• Similarity: While mitoribosomes share certain characteristics with prokaryotic ribosomes, they are not as closely related as plastoribosomes. This reflects the evolutionary history of mitochondria, which are believed to have originated from an ancestral prokaryote.

In summary, both plastoribosomes and mitoribosomes are eukaryotic cell-specific ribosomes that exhibit similarities with prokaryotic ribosomes, highlighting the endosymbiotic origins of plastids and mitochondria.

High-resolution structure of Ribosomes

The intricate architecture of ribosomes has been elucidated with remarkable precision through high-resolution structural studies. These studies have been instrumental in mapping the atomic resolutions of ribosomes from various organisms, providing invaluable insights into their functional and structural nuances.

High-Resolution Structures of Ribosomes from Various Organisms:

1. Prokaryotic Ribosomes:
   • 50S Subunit: This is the large subunit of prokaryotic ribosomes. High-resolution structures have been determined for this subunit from two organisms:
     • Archaeon Haloarcula marismortui: An extremophilic archaeon known for its resilience in high-saline environments.
     • Bacterium Deinococcus radiodurans: A bacterium renowned for its extraordinary resistance to ionizing radiation.
   • 30S Subunit: Representing the small subunit of prokaryotic ribosomes, its high-resolution structure has been delineated from:
     • Bacterium Thermus thermophilus: A thermophilic bacterium that thrives at elevated temperatures.
2. Eukaryotic Ribosomes:
   • 60S Subunit: This is the large subunit of eukaryotic ribosomes. Its high-resolution structure has been mapped from:
     • Tetrahymena thermophila: A model ciliated protozoan used extensively in molecular and cellular biology research.
   • 40S Subunit: The small subunit of eukaryotic ribosomes has its high-resolution structure determined from:
     • Tetrahymena thermophila.

In essence, the high-resolution structures of ribosomes, derived from diverse organisms, have paved the way for a deeper understanding of ribosomal functions, interactions, and evolutionary relationships. These structures, determined with atomic precision, stand as a testament to the advancements in structural biology and the collaborative efforts of the global scientific community.

Ribosome biogenesis 

Ribosome biogenesis is a complex and coordinated process that encompasses the synthesis and assembly of ribosomal components. In eukaryotic cells, this intricate process occurs both within the nucleus, specifically the nucleolus, and the cytoplasm.

Key Aspects of Ribosome Biogenesis:

1. Ribosomal Subunits: Eukaryotic ribosomes are denoted as 80S, comprising two distinct subunits: the larger 60S and the smaller 40S. These subunits are differentiated by their ribosomal RNA (rRNA) and protein constituents.
2. Ribosomal Protein Synthesis: Ribosomal proteins undergo synthesis through a two-step process. Initially, their encoding genes are transcribed within the nucleus. The resultant transcripts are then exported to the cytoplasm, where they undergo translation, yielding ribosomal proteins. Upon maturation, these proteins are transported back to the nucleus, specifically targeting the nucleolus.
3. rRNA Production: The rRNAs, namely 18S, 28S, and 5.8S, are transcribed as a unified precursor, termed 45S pre-rRNA, within the nucleolar organizer region. This transcriptional activity is facilitated by RNA polymerase I. Post-transcriptional modifications lead to the separation of these rRNAs. Conversely, the 5S rRNA is transcribed as pre-5S rRNA by RNA polymerase III in the nucleoplasm, external to the nucleolus. Subsequent processing guides it to the nucleolus.
4. Subunit Assembly: Within the nucleolus, the 5S rRNA associates with the 28S and 5.8S rRNAs, orchestrating the formation of the 60S large subunit. The 18S rRNA, on the other hand, collaborates with ribosomal proteins to constitute the 40S small subunit. These assembled subunits are then channeled from the nucleolus to the cytoplasm.
5. Final Assembly: In the cytoplasm, the 60S and 40S subunits converge, culminating in the formation of the functional 80S ribosome, primed for its role in protein synthesis.

Ribosome Associated Diseases 

1. Ribosomopathies:
   • Ribosomopathies are disorders caused by the improper functioning of ribosomes.
   • These conditions often result from mutations in ribosomal proteins, leading to a range of clinical manifestations, including bone marrow failure and anemia.
2. Congenital Syndromes Due to Defective Ribosome Biogenesis:
   • Several congenital syndromes are linked to defective ribosome biogenesis. These include Diamond-Blackfan anemia (DBA), X-linked dyskeratosis congenita (DKC), cartilage hair hypoplasia (CHH), and Treacher Collins syndrome (TCS).
   • These conditions underscore the critical role of ribosomes in various physiological processes.
3. Diamond-Blackfan Anemia (DBA):
   • DBA is a rare blood disorder characterized by the bone marrow’s inability to produce sufficient red blood cells (RBCs), leading to anemia.
   • The disorder involves abnormal pre-rRNA maturation and is associated with mutations in several ribosomal protein genes.
   • These mutations disrupt the structural components of the ribosome, impacting its function and leading to the clinical manifestations of DBA.
4. X-linked Dyskeratosis Congenita (DKC):
   • DKC is a genetic disorder affecting skin, nails, and mucous membranes, often associated with bone marrow failure.
   • The condition is linked to mutations affecting ribosomal DNA (rDNA) transcription and ribosome assembly.
5. Cartilage Hair Hypoplasia (CHH):
   • CHH is characterized by short stature, fine hair, immune deficiencies, and an increased risk of certain cancers.
   • It is associated with mutations affecting ribosomal RNA processing, highlighting the ribosome’s role in cell growth and division.
6. Treacher Collins Syndrome (TCS):
   • TCS is a condition marked by craniofacial deformities.
   • Mutations affecting ribosomal biogenesis and protein synthesis are implicated in the development of TCS.

Differences Between eukaryotic ribosome and prokaryotic ribosomes

Ribosomes can be found in organisms like bacteria, parasites and various other animals such as microscopic and lower-level organisms are those that are referred to as prokaryotic ribosomes. The ones that reside inside humans and other animals like higher-level animals are the ones that we refer to as the eukaryotic ribosome.

1. Prokaryotes possess 70S ribosomes consisting of a 30S and 50S subunit. In contrast, eukaryotes possess 80S ribosomes comprised of a 40S as well as a 60S subunit.
2. 70S Ribosomes tend to be smaller than 80S ribosomes, whereas the 80S Ribosomes are significantly larger than 70S ribosomes.
3. Prokaryotes possess a 30S subunit that is an RNA 16S subunit. These comprise 1540 nucleotides attached by 21 proteins. The 50S subunit is made by a subunit of 5S RNA which contains 120 nucleotides. the 23S RNA subunit includes 2900 nucleotides, and 31 proteins.
4. Eukaryotes are characterized by 40S subunits with 18S RNA, along with 300 proteins and 1900 nucleotides. The main subunit has 5S RNA, 120 nucleotides, 4700 nucleotides as well as also 28S RNA. 5.8S RNA and 160 nucleotides and 46 proteins.
5. Eukaryotic cells contain chloroplasts and mitochondria as organelles. Those organelles also have ribosomes 70S. Therefore, eukaryotic cells possess various types of the ribosomes (70S as well as 80S) and prokaryotic cells only contain 70S ribosomes.

What is Heterogeneous ribosomes?

• Ribosomes have a compositional heterogeneity that is shared by species and even within same cell, as demonstrated by the presence of mitochondrial and cytoplasmic Ribosomes in the same eukaryotic cell. Some researchers have proposed that the diversity in the composition of the ribosomal proteins of mammals is crucial in the regulation of genes, i.e., the special ribosome hypothesis. This hypothesis is controversial and a subject for ongoing study.
• Heterogeneity in the composition of ribosomes was first suggested to play a role in the controlling the translation of protein production in the work of Vince Mauro and Gerald Edelman. They suggested the ribosome filter hypothesis in order to explain the functions of regulation the ribosomes. Evidence suggests that specialized ribosomes with a specificity to distinct cell populations could alter the way that gene expression is controlled. Certain ribosomal proteins exchange the complex assembled with the cytosolic copies HTML1suggesting structures of in living the ribosome could be altered without the necessity of creating a new ribosome.
• Certain ribosomal protein are essential for the life of a cell, and others aren’t. In the budding yeast, 14/78 of ribosomal proteins are not essential to grow, whereas in humans, this is contingent on the specific cell. Other examples of heterogeneity are post-translational modifications to ribosomal proteins like the acetylation process, methylation as well as phosphorylation. In Arabidopsis and Viral, internal ribosome entrance sites (IRESs) can facilitate translation by ribosomes with distinct compositions. For instance 40S ribosomal units that lack the eS25 in mammalian cells and yeast cells aren’t able to attract CrPV IGR. CrPV IGR.
• Heterogeneity in ribosomal DNA modifications is a key factor in maintaining structural integrity or function. Most modifications to mRNA are located in high-conserved areas. The most commonly used changes to rRNA include the pseudouridylation as well as 2′-O of methylation of ribose.

Functions of Ribosome

1. Site of Protein Synthesis:
   • Ribosomes are integral to the process of biological protein synthesis, also known as translation.
   • They are responsible for linking amino acids in the sequence specified by messenger RNA (mRNA) molecules.
2. Catalytic Functions in Peptide Bond Formation:
   • Ribosomes act as catalysts in critical biological processes, including peptidyl transfer and peptidyl hydrolysis.
   • These processes are essential for the formation of peptide bonds, which link amino acids to form proteins.
3. Protection of Nascent Polypeptide Chains:
   • During protein synthesis, ribosomes safeguard the emerging polypeptide chain from degradation by protein-digestive enzymes.
4. Decoding Genetic Messages:
   • A primary function of ribosomes involves decoding the genetic messages carried by mRNA.
   • This decoding is a crucial step in translating the genetic code into functional proteins.
5. Translation Process:
   • Ribosomes facilitate the translation of mRNA into proteins, a process initiated in the cell nucleus with DNA transcription.
   • The mRNA, organized in the nucleus, is transported to the cytoplasm where ribosomes bind to it, initiating protein synthesis.
6. Interaction with tRNA:
   • In the cytoplasm, ribosomal subunits bind around mRNA polymers, and transfer RNA (tRNA) integrates amino acids into the growing protein chain.
7. Diverse Protein Synthesis:
   • Proteins synthesized by free ribosomes are typically used within the cytoplasm itself.
   • Conversely, proteins synthesized by ribosomes bound to the endoplasmic reticulum are often secreted or incorporated into cell membranes.
8. Enzymatic and Initiation Roles:
   • Ribosomes provide essential enzymes, such as peptidyl transferase, and initiation factors for the condensation of amino acids into polypeptides.
9. RNA and mRNA Attachment Sites:
   • Ribosomes contain ribosomal RNA (rRNA) crucial for the attachment of mRNA and tRNA during protein synthesis.

Quiz

Which of the following is the primary function of ribosomes?
a) DNA replication
b) Photosynthesis
c) Protein synthesis
d) Lipid metabolism

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In which cellular location would you primarily find ribosomes?
a) Nucleus
b) Mitochondria
c) Cytoplasm
d) Golgi apparatus

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Which type of RNA is primarily associated with ribosomes?
a) mRNA
b) tRNA
c) rRNA
d) snRNA

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The ribosomes found in prokaryotic cells are of which type?
a) 60S
b) 80S
c) 70S
d) 90S

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Which subunit of the ribosome reads the mRNA?
a) Large subunit
b) Small subunit
c) Both subunits
d) Neither subunit

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Which antibiotic specifically targets bacterial ribosomes?
a) Penicillin
b) Tetracycline
c) Aspirin
d) Ibuprofen

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Ribosomes are made up of which two main components?
a) Lipids and proteins
b) Sugars and lipids
c) Proteins and rRNA
d) mRNA and tRNA

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Which organelle is closely associated with ribosomes for protein synthesis and modification?
a) Lysosome
b) Endoplasmic reticulum
c) Peroxisome
d) Vacuole

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Which of the following is NOT a function of ribosomes?
a) Catalyzing peptide bond formation
b) Assisting in DNA replication
c) Reading the genetic code
d) Facilitating the binding of tRNA to mRNA

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In eukaryotic cells, ribosomes can be found attached to which of the following?
a) Mitochondrial membrane
b) Nuclear envelope
c) Rough endoplasmic reticulum
d) Plasma membrane

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FAQ

References

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3. Noller, H. F., Hoffarth, V., & Zimniak, L. (June 1992). Unusual resistance of peptidyl transferase to protein extraction procedures. Science, 256(5062), 1416–9. https://doi.org/10.1126/science.1604315
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