Q.Select one which is not true for ribosome
Concept understanding — Ribosome Function Translation
Imagine you are in a large library. The shelves are packed with books, but each book is written in a language you cannot read. To understand the book, you need a translator — someone who can read the original script and then explain it to you in plain, usable words.
In a living cell, the "library" is the nucleus, where DNA — the master blueprint — is stored. The "books" are genes, written in the language of nucleic acids. But the cell doesn't work directly with DNA. It needs to build proteins — the actual workers, tools, and building blocks of the body. So it first makes a working copy of a gene, called mRNA (messenger RNA). This mRNA is like a page torn from the book, still in the nucleic-acid language. Now the cell needs a "translator" to convert that message into the language of proteins. That translator is the ribosome.
What is a ribosome?
A ribosome is a tiny, complex molecular machine made of RNA and proteins. It is not a membrane-bound organelle — it floats freely in the cytoplasm or sits on the rough endoplasmic reticulum. Think of it as a workbench that clamps onto the mRNA and reads its sequence, three letters at a time. Each three-letter "word" on the mRNA is called a codon, and each codon specifies one amino acid — the building block of a protein.
The ribosome has two main parts, or subunits — a large one and a small one. The small subunit holds the mRNA in place, while the large subunit does the actual work of joining amino acids together.
The process of translation: from mRNA to protein
Translation happens in three stages, just like reading a sentence: you start, you read word by word, and you stop.
1. Initiation (the start)
The small ribosomal subunit finds a special "start" codon on the mRNA — usually AUG. A special tRNA (transfer RNA) molecule carrying the amino acid methionine binds to that start codon. Then the large subunit clicks into place. The ribosome is now assembled and ready to read.
2. Elongation (the reading and building)
The ribosome moves along the mRNA, one codon at a time. For each codon, a matching tRNA brings the correct amino acid. The ribosome's large subunit then forms a peptide bond between the new amino acid and the growing chain. The ribosome shifts forward, and the empty tRNA is released. This repeats — like a train moving along a track, adding one carriage at a time.
3. Termination (the stop)
When the ribosome reaches a "stop" codon (UAA, UAG, or UGA), no tRNA matches it. Instead, a release factor protein binds, causing the ribosome to let go of the completed protein chain. The two subunits separate, and the new protein is free to fold into its functional shape.
The word "translation" is exact: the cell is translating from the four-letter language of nucleic acids (A, U, G, C) into the twenty-letter language of amino acids. The ribosome is the translator, and tRNAs are the "dictionaries" that match each codon to its correct amino acid.
Why does this matter?
Without translation, the instructions in your DNA would remain useless. Every enzyme that digests your food, every antibody that fights infection, every muscle fibre that lets you move — all are built by ribosomes during translation. If translation stops, the cell dies.
In medicine, many antibiotics work by targeting bacterial ribosomes. For example, tetracycline blocks the binding of tRNA to the ribosome, stopping the bacteria from making proteins. Human ribosomes are slightly different, so the drug affects bacteria but not us — a beautiful example of how understanding this process saves lives.
Key points to remember (as per NCERT)
- Translation is the process of polymerising amino acids into a polypeptide chain, using the sequence of codons on mRNA as a template.
- The ribosome acts as the site of translation and also as a catalyst for forming peptide bonds (the large subunit has an enzymatic activity called peptidyl transferase).
- Each tRNA has an anticodon that base-pairs with the mRNA codon, and it carries the corresponding amino acid at its other end.
- The energy for forming peptide bonds comes from GTP (guanosine triphosphate), not ATP — a small but exam-relevant detail.
In NCERT Class 12 Biology, translation is described as occurring in the cytoplasm (for prokaryotes) or on the rough endoplasmic reticulum (for eukaryotes, especially for proteins destined for secretion). The ribosome moves along the mRNA from the 5' end to the 3' end, and the polypeptide chain grows from the N-terminus to the C-terminus.
A final intuition
Think of the ribosome as a conveyor belt in a factory. The mRNA is the instruction tape that feeds through the belt. Each station along the belt (each codon) calls for a specific part (a tRNA with an amino acid). The belt moves, parts are added, and at the end, a finished product — a protein — rolls off. That protein will go on to do a specific job: some become structural (like collagen in skin), some become enzymes (like lactase to digest milk), and some become hormones (like insulin to regulate blood sugar).
That is translation — the moment when genetic information becomes a working molecule.
This concept is a common exam-prep search query, appearing online as "Ribosome Function Translation diagram and explanation", "Ribosome Function Translation NEET questions", or "Ribosome Function Translation: Definition, Diagram & Examples". This concept is directly part of the Molecular Basis of Inheritance chapter in the NCERT/CBSE Class 12 Biology syllabus, and it is also an important topic for NEET and state medical/CET entrance exams, making it worth mastering for both board and competitive-exam preparation.
The statement that is not true for ribosomes is that they have no role in protein synthesis.
- Ribosomes are, in fact, the very site where proteins are assembled inside a cell — this is their defining job.
- They are genuinely built from two subunits that come together to form the working particle.
- They do attach to messenger RNA during translation.
- Several ribosomes can also gather on a single mRNA strand to form a polysome, allowing many copies of a protein to be made together.
Option D is false — ribosomes are the site of protein synthesis, not structures with no role in it.
Every statement about ribosomes here is true except the claim that they play no role in protein synthesis.
A ribosome is a compact, non-membrane-bound particle whose entire purpose in the cell is to build proteins. Saying it has "no role in protein synthesis" contradicts the most basic fact about what a ribosome does, which makes that statement the false one.
The other three statements are all accurate. A ribosome genuinely is made of two subunits that fit together to form the complete working particle. It does attach to messenger RNA, reading the genetic message strand by strand as it builds a protein chain. And several ribosomes commonly gather on one mRNA molecule at the same time, forming a chain called a polysome or polyribosome, which lets multiple copies of the same protein be produced simultaneously.
Ribosomes may occur free in the cytoplasm or attached to the rough endoplasmic reticulum, but in either location their function is always protein synthesis.
The false statement is option D — ribosomes are precisely the site of protein synthesis, so saying they have no role in it is incorrect.
Method: Spotting the Statement That Contradicts the Organelle's Defining Job
When an MCQ lists several claims about an organelle and asks which is false, the fastest route is to anchor first on that organelle's single defining job, then check whether any option directly contradicts it. For the ribosome, that defining job is protein synthesis — it is, almost by definition, the site where amino acids get strung into polypeptides.
Once that anchor is in place, a statement claiming "no role in protein synthesis" doesn't need any further evidence-gathering to reject — it collides head-on with the one fact you're most sure of. The remaining statements (two subunits, attaching to mRNA, forming polysomes) are all secondary structural/functional details that are consistent with, and supportive of, that same core job, so they don't need to be independently verified once you've confirmed they don't contradict the anchor fact.
This "anchor on the defining function, then scan for contradictions" approach is generally faster than trying to independently confirm all four statements from memory."
Showing the 12 most recent of 22 on this concept.
- CBSE 2026Set ANNUAL1 markMCQQ.An example of a non-membrane bound organelle is -(a) Endoplasmic reticulum(b) Ribosome(c) Mitochondria(d) Chloroplast
›Reveal solutionSolution
Ribosomes are the only non-membrane-bound organelle among the four options.
Eukaryotic cells contain both membrane-bound and non-membrane-bound organelles:
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Endoplasmic reticulum — a single-membrane network of tubules and cisternae.
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Mitochondria — double-membrane organelles (outer membrane + inner membrane folded into cristae).
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Chloroplast — also double-membrane, with an internal thylakoid membrane system.
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Ribosome — a dense, roughly spherical particle made of ribosomal RNA and proteins (large + small subunit), found free in the cytoplasm or attached to the ER/nuclear envelope. It has no surrounding membrane at all, which is why it is classed as a non-membrane-bound organelle, alongside structures like the cytoskeleton and centriole.
✓Final answerThe correct option is (b) Ribosome — it is the only one of the four that is not enclosed by a membrane.
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- CBSE 2026Set ANNUAL1 markQ.Write answer in one word/sentence: Write the name of dual functional (met and initiator) genetic code.
›Reveal solutionSolution
AUG is the codon that both codes for methionine and serves as the start codon.
The genetic code is read in triplets called codons. The codon AUG has two roles: it codes for the amino acid methionine (Met), and it also functions as the initiator or start codon that signals the beginning of translation (protein synthesis). Because it performs both jobs, AUG is described as a dual-function codon. (The stop codons UAA, UAG and UGA do not code for any amino acid.)
✓Final answerAUG.
- CBSE 2025Set F1 markMCQQ.Which of the following is a soluble RNA?(a) m-RNA(b) r-RNA(c) c-RNA(d) t-RNA
›Reveal solutionSolution
Transfer RNA (tRNA) is the soluble RNA, also called sRNA.
tRNA (transfer RNA) is the smallest of the RNAs and was originally called soluble RNA (sRNA) because it stays dissolved in the cytoplasm. It acts as an adaptor molecule: one end carries a specific amino acid while its anticodon reads the codon on mRNA, thus delivering the correct amino acid to the ribosome during protein synthesis. mRNA carries the genetic message and rRNA forms part of the ribosome; neither is termed soluble RNA ("c-RNA" is not a standard cellular RNA).
✓Final answer(D) t-RNA.
- CBSE 2024Set E1 markMCQQ.What is the meaning of charging of t-RNA?(a) Linking of amino acid with cognate t-RNA(b) Attachment of t-RNA with ribosome(c) Translation of RNA(d) Modification of RNA
›Reveal solutionSolution
Charging (aminoacylation) of tRNA is the linking of a specific amino acid to its correct (cognate) tRNA.
Before translation, each amino acid must be attached to the correct transfer RNA:
- The enzyme aminoacyl-tRNA synthetase joins a specific amino acid to its cognate (matching) tRNA, using ATP energy.
- This activated, amino-acid-bearing tRNA is said to be 'charged' or aminoacylated.
- The charged tRNA then carries its amino acid to the ribosome, where the anticodon reads the mRNA codon and the amino acid is added to the growing polypeptide.
So charging refers to linking of the amino acid with its cognate tRNA, not to ribosome binding or RNA modification.
✓Final answer(a) Linking of amino acid with cognate t-RNA.
- CBSE 2024Set ANNUAL1 markQ.Write the type of RNA which brings aminoacids and reads the genetic code.
›Reveal solutionSolution
tRNA is the adaptor molecule that reads the codon on mRNA (via its anticodon) and delivers the corresponding amino acid during translation.
Transfer RNA (tRNA) has a clover-leaf secondary structure with an anticodon loop at one end that base-pairs with a complementary codon on the mRNA, and an amino-acid-acceptor end (3' CCA end) that is charged with the specific amino acid corresponding to that codon (by the enzyme aminoacyl-tRNA synthetase). By simultaneously reading the mRNA codon and carrying the matching amino acid, tRNA acts as the 'adaptor' molecule that translates the genetic code into a polypeptide sequence during protein synthesis.
✓Final answertRNA (transfer RNA).
- CBSE 2024Set ANNUAL1 markMCQQ.For initiation of protein synthesis ribosome binds to the ................ codon of messenger RNA.(a) AUG(b) UGA(c) AGU(d) UAG
›Reveal solutionSolution
Translation begins when the ribosome assembles on the mRNA at the initiation (start) codon AUG.
During translation, the small ribosomal subunit binds to the mRNA and scans for the start codon AUG, which also codes for methionine (or N-formylmethionine in prokaryotes) - the first amino acid of the growing polypeptide. Once the initiator tRNA pairs with AUG, the large ribosomal subunit joins to form the complete initiation complex, and elongation of the polypeptide chain begins. UAA, UAG and UGA are stop codons that terminate translation, not initiate it.
✓Final answer(a) AUG.
- CBSE 2024Set ANNUAL1 markMCQQ.Anticodon is present on :(a) mRNA(b) tRNA(c) rRNA(d) DNA
›Reveal solutionSolution
tRNA carries the anticodon that pairs with the mRNA codon during translation.
A codon is a triplet of bases present on mRNA that specifies an amino acid. The complementary triplet that recognises and base-pairs with this codon is called the anticodon, and it is located in the anticodon loop of transfer RNA (tRNA). During translation, the tRNA charged with a specific amino acid brings its anticodon to pair with the mRNA codon at the ribosome, ensuring the correct amino acid is added to the growing polypeptide chain.
✓Final answer(b) tRNA.
- CBSE 2024Set ANNUAL1 markMCQQ.During protein synthesis, peptide bonds are formed at the –(a) Nucleus(b) Nucleolus(c) Ribosomes(d) Lysosomes
›Reveal solutionSolution
Peptide bonds are formed on ribosomes during translation, catalysed by the peptidyl transferase activity of the large ribosomal subunit.
Protein synthesis (translation) occurs on ribosomes — ribonucleoprotein particles made of a large and small subunit assembled from rRNA and proteins. The mRNA is read codon by codon at the ribosome; aminoacyl-tRNAs bring in specific amino acids that base-pair with codons at the ribosomal A site. The peptidyl transferase activity (a catalytic function of the large subunit's rRNA, making the ribosome a ribozyme) then catalyses formation of the peptide bond between the amino acid held in the A site and the growing polypeptide chain in the P site.
The nucleus is where transcription (DNA → mRNA) occurs, not translation; the nucleolus is the site of rRNA synthesis and ribosome assembly, not peptide-bond formation; lysosomes contain hydrolytic enzymes for degradation and play no role in protein synthesis.
✓Final answer(c) Ribosomes.
- CBSE 2024Set ANN1 markMCQQ.Which of these cell organelles is not covered by a membrane ?(a) Golgi bodies(b) Endoplasmic reticulum(c) Ribosomes(d) Vacuoles
›Reveal solutionSolution
Ribosomes are not membrane-bound; Golgi bodies, endoplasmic reticulum and vacuoles are all surrounded by a membrane.
Cell organelles are broadly grouped into membrane-bound (Golgi apparatus, endoplasmic reticulum, mitochondria, plastids, vacuoles, lysosomes) and non-membrane-bound (ribosomes, cytoskeleton, centrioles). Ribosomes are minute particles made of ribosomal RNA and proteins, found free in the cytoplasm or attached to the rough ER and the outer mitochondrial/plastid membranes. They lack any surrounding membrane of their own, unlike the Golgi bodies (a system of membrane-bound cisternae), the ER (a network of membranous tubules/cisternae), and vacuoles (single-membrane-bound sacs).
✓Final answerRibosomes.
- CBSE 2024Set ANNUAL1 markMCQQ.Which of the following organelles does not surrounded by any membrane ?(a) Ribosome(b) Nucleus(c) Mitochondria(d) Endoplasmic reticulum
›Reveal solutionSolution
Ribosomes are non-membranous cell organelles made of RNA and protein (ribonucleoprotein particles).
Cell organelles are broadly divided into membrane-bound (nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, plastids, vacuoles) and non-membrane-bound organelles. Ribosomes, found either freely in the cytoplasm/matrix or attached to the endoplasmic reticulum or the outer membrane of the nuclear envelope, are composed of ribosomal RNA and proteins and are NOT bound by any membrane. This is why they can be considered ribonucleoprotein particles rather than true membranous organelles. The nucleus, mitochondria and endoplasmic reticulum are all bound by one or two membranes.
✓Final answer(a) Ribosome
- CBSE 2023Set CG1 markMCQQ.The process of protein synthesis with the help of m-RNA is called(a) Translation(b) Transcription(c) Reverse transcription(d) Replication
›Reveal solutionSolution
Protein synthesis using an mRNA template is translation — option (a).
Concept — the three stages of gene expression:
- Transcription (b): DNA → mRNA (copying a gene into messenger RNA).
- Translation (a): mRNA → protein. Ribosomes read the mRNA codons (three bases at a time), tRNA brings the matching amino acids, and a polypeptide is built.
- Reverse transcription (c): RNA → DNA (in retroviruses, by reverse transcriptase).
- Replication (d): DNA → DNA (copying the genome before cell division).
Because the question specifies protein synthesis with the help of m-RNA, the process is translation.
✓Final answer(a) Translation.
- CBSE 2023Set ANNUAL1 markMCQQ.In which cell organelles synthesis of protein takes place(a) Golgi complex(b) Ribosomes(c) Mitochondria(d) Plastids
›Reveal solutionSolution
Ribosomes are the cell organelles where protein synthesis (translation) takes place.
This is a fundamental fact from the Cell: The Unit of Life chapter regarding the functions of different cell organelles.
Ribosomes and protein synthesis: ribosomes are small, dense, granular structures made of ribosomal RNA (rRNA) and proteins, and are not bound by any membrane. They occur as free particles in the cytoplasm or attached to the endoplasmic reticulum (rough ER) and outer membrane of the nuclear envelope. During translation, the ribosome reads the sequence of codons on a messenger RNA (mRNA) molecule and, with the help of transfer RNA (tRNA) bringing in specific amino acids, links these amino acids together by peptide bonds to build a polypeptide chain. Several ribosomes can attach to a single mRNA strand simultaneously, forming a polyribosome (polysome), which increases the rate of protein production.
Why the other options are wrong:
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The Golgi complex processes, packages and modifies proteins/lipids after synthesis, and is involved in secretion — it does not synthesise proteins itself.
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Mitochondria are the site of aerobic respiration and ATP production ("powerhouse of the cell"), though they do contain their own small ribosomes (70S) for a very limited amount of self-synthesis of a few mitochondrial proteins — but the general answer expected at this level for "site of protein synthesis" is the ribosome.
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Plastids (e.g., chloroplasts) are mainly the site of photosynthesis in plant cells.
✓Final answerThe correct answer is (b) Ribosomes.
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