Biology · Cell: The Unit of Life · NEET
It is a cell that has no true nucleus. The DNA is not kept inside a nuclear membrane. It also has no membrane-bound organelles like mitochondria, ER, Golgi or lysosomes. Only bacteria and cyanobacteria (blue-green algae) are prokaryotes. NEET always contrasts this with eukaryotes, which DO have a true nucleus and organelles.
No. They have NO well-defined (true) nucleus. Instead the DNA lies in a region called the nucleoid, which is not surrounded by any membrane. So NEET says prokaryotes lack a nuclear membrane, nucleolus and true nucleus. Do not confuse nucleoid (region) with nucleus (organelle).
Because it is NOT enveloped by a nuclear membrane and is NOT wrapped around histone proteins the way eukaryotic DNA is. NCERT calls it 'naked' for this reason. Remember: prokaryotic DNA is naked, double-stranded and circular. In eukaryotes the negatively charged DNA wraps around a positively charged histone octamer to form nucleosomes — prokaryotes do not do this.
Nucleoid is the region in a prokaryote where the single circular DNA lies, with NO membrane around it. Nucleus is a true membrane-bound organelle found in eukaryotes, with a nuclear envelope and nucleolus. Nucleoid = no membrane; nucleus = double-membrane. This exact idea is tested in NEET (70S ribosome organism has DNA not enclosed in a nuclear membrane).
They have NO membrane-bound organelles (no mitochondria, ER, Golgi, lysosome, plastids). They DO have ribosomes (70S), which are non-membrane-bound, and a mesosome, which is just an infolding of the plasma membrane. NEET trap: 'In prokaryotes only RER are present' is WRONG — prokaryotes have no ER at all.
Prokaryotes have 70S ribosomes, made of a 50S large subunit and a 30S small subunit. Eukaryotes have 80S (60S + 40S). Note S = Svedberg unit (sedimentation), so the subunit numbers do NOT simply add up (50 + 30 is written as 70, not 80). Ribosomes are the only 'organelle' shared by both prokaryotes and eukaryotes.
Double-stranded. It is a double-stranded, circular, naked DNA. This also applies to plasmids (the extra small circular DNA) — they are double-stranded too. A very common NEET trap is calling plasmids 'single-stranded'; that is the WRONG option.
Mycoplasma (PPLO). All prokaryotes have a cell wall around the cell membrane EXCEPT Mycoplasma. Mycoplasma is also the smallest living cell (about 0.3 micrometre) and can pass through filters smaller than 1 micron. NEET repeats this fact almost every year.
A mesosome is a special membranous structure formed by the infoldings (extensions) of the plasma membrane into the cell. Its functions: cell wall formation, DNA replication and distribution to daughter cells, respiration and secretion. It has been asked directly in NEET 2023 and 2025 — memorise its functions.
They are stored reserve materials lying free in the cytoplasm. They are NOT bound by any membrane. Examples: phosphate granules, cyanophycean granules and glycogen granules. NEET trap: inclusion bodies do NOT ingest food particles — that statement is wrong.
Which of the following nucleic acids is present in an organism having 70S ribosomes only?
A specialised membranous structure in a prokaryotic cell which helps in cell wall formation, DNA replication and respiration is:
Which of the following are characteristics of prokaryotic cells? (a) Ribosomes are made of 50S and 30S subunits; (b) They can have plasmids; (c) They contain mesosome; (d) They have peroxisomes.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Bacteria (like Mycobacterium, Bacillus, Pseudomonas) and cyanobacteria / blue-green algae (like Nostoc, Oscillatoria). Also archaea such as methanogens. Yeast (Saccharomyces) is NOT a prokaryote — it is a fungus, so it is eukaryotic.
Prokaryotic cells are generally small, about 0.5 to 5 micrometres. Mycoplasma is the smallest at about 0.3 micrometre, while bacteria are larger. They multiply faster than eukaryotic cells.
No. Prokaryotes lack the endomembrane system (no ER, no Golgi, no lysosome) and lack membrane-bound organelles. Any NEET option giving these to a prokaryote is wrong.
No. The genomic DNA is the single main circular chromosome in the nucleoid. A plasmid is a smaller, extra circular DNA outside the genomic DNA. Both are double-stranded. Plasmids replicate independently, are transferable, and give the bacterium special traits.
Eukaryotic cytoplasmic ribosomes are 80S. But mitochondria and chloroplasts inside eukaryotes also have 70S ribosomes, which is one clue that these organelles evolved from ancient prokaryotes (endosymbiosis).
