15 public questions tagged with this topic.
Ribosomal RNA (rRNA) is a key structural and functional component of ribosomes, aiding protein synthesis.
Ref: NCERT Class 12 Chemistry > Chapter 14: Biomolecules > Topic: Nucleic Acids - Types and Functions - DNA, RNA
Protein sorting depends on presence of N-terminal signal sequence or internal transmembrane domain. Secretory proteins like insulin, lysosomal cathepsins, plasma membrane receptors and Golgi glycosyltransferases harbor hydrophobic signals recognized by signal recognition particle leading to Sec61 engagement and translocation into ER lumen or membrane, then onward transport, removed from cytosol. Absence of signal leaves nascent chain completing synthesis on free ribosomes in cytoplasm where folding by Hsp70 and TRiC chaperonin occurs. Cytoskeletal proteins actin forty three kDa forming seven n
Ref: Blobel Nobel Lecture; signal sequence free vs membrane-bound polysomes actin spectrin cytosolic.
Binding of ribosomes to rough ER ensures nascent secretory proteins directly translocate into lumen avoiding cytosolic exposure of hydrophobic stretches. This interaction requires specific receptors beyond Sec61 translocon. Ribophorin I and II are type I transmembrane glycoproteins of sixty and eighty kDa forming part of oligosaccharyltransferase complex, strongly associated with translocon. Their cytosolic domains contact sixty S subunit near polypeptide exit tunnel, increasing ribosome affinity approximately tenfold compared to naked lipid bilayer. After signal sequence inserts into Sec61 ch
Ref: Alberts Ch 12; ribophorin I/II OST subunits anchor 60S to Sec61, increase ER ribosome affinity.
Ribosomes are not membrane-bound organelles; they are freely floating in the cytoplasm or attached to the rough ER.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Human Genome Project and DNA Fingerprinting
Ribosomes are made of ribosomal RNA (rRNA) and proteins, and they facilitate protein synthesis.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Human Genome Project and DNA Fingerprinting
Translation initiation **requires the ribosome, mRNA, and tRNA** to start protein synthesis.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Genetic Code and Translation
Ribosomes **are not membrane-bound organelles**; they are found freely in the cytoplasm or attached to the rough ER in eukaryotes.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Structure Double Helix and Packaging - Nucleosome
The cytoplasm is the semi-fluid matrix and principal arena of cellular reactions. Ribosomes are non-membrane-bound RNA–protein particles occurring freely in the cytoplasm, on rough ER, and within mitochondria and chloroplasts.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles
George Palade first observed ribosomes as dense particles under the electron microscope in 1953. Ribosomes consist of RNA and proteins and are not surrounded by a membrane.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles
Ribosomes are non-membrane-bound structures composed of RNA and proteins. They serve as the sites of protein synthesis in both prokaryotic and eukaryotic cells.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Endomembrane System - ER Golgi Lysosome Vacuole
Prokaryotic ribosomes are approximately 15 nm by 20 nm, are associated with the plasma membrane and contain 50S and 30S subunits, forming a 70S ribosome. Several ribosomes on one mRNA constitute a polysome.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Prokaryotic Cell - Structure and Components
Several ribosomes may attach to a single mRNA to form a polyribosome or polysome. The ribosomes of the polysome translate the mRNA into protein.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Prokaryotic Cell - Structure and Components
