Biology · Cell: The Unit of Life · NEET
Because they meet three self-rule points: (1) they carry their own single circular DNA molecule, (2) they have their own 70S ribosomes and the machinery to make some proteins, and (3) they divide by fission (split on their own) from pre-existing organelles. This lets them make some of their own proteins and multiply by themselves. The word 'semi' is used because they are only partly independent, not fully.
Their own DNA is small. It codes for only a few of the proteins they need. Most of the other proteins are coded by the DNA in the cell nucleus, made by cytoplasmic 80S ribosomes, and then imported into the organelle. So the organelle depends on the nucleus for most of its proteins. That dependence is why it is 'semi' (partly) and not fully autonomous.
Yes. This is a very common trap. Both have their OWN 70S ribosomes plus RNA, so they CAN synthesize some proteins inside themselves. NEET 2016 tested this exact point: the statement saying they 'lack protein synthesizing machinery' is FALSE. They contain the machinery; they just cannot make all of their proteins alone.
Both contain a single circular, double-stranded, naked DNA molecule (no histone proteins around it, like bacterial DNA). Both contain 70S ribosomes, the same smaller ribosome type found in prokaryotes. The rest of the eukaryotic cell uses 80S ribosomes. This bacteria-like feature is strong evidence for the endosymbiotic origin idea.
No. Only mitochondria and chloroplasts (plastids) are semi-autonomous. Lysosomes, Golgi, ER and vacuoles have NO DNA and NO ribosomes of their own, so they cannot self-divide or make their own proteins. This is why NEET links semi-autonomous strictly to the two double-membrane organelles that have DNA.
They multiply by fission, meaning one organelle splits into two, forming new organelles from pre-existing ones. They are not built fresh from scratch by the cell each time. This 'division of pre-existing organelles' point, combined with their own DNA and 70S ribosomes, is the full definition NEET wants.
Mitochondria and chloroplast are: (i) Semi-autonomous organelles (ii) Formed by division of pre-existing organelles and they contain DNA but lack protein synthesizing machinery. Which one of the following options is correct?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Only mitochondria and chloroplasts (plastids). No other cell organelle is semi-autonomous because no other one has its own DNA and ribosomes.
They have their own circular DNA, their own 70S ribosomes (so they make some of their own proteins), and they divide by fission from pre-existing organelles.
Their DNA is small and codes for only a few proteins. Most of their proteins are coded by the nuclear DNA and imported, so they still depend on the nucleus.
70S ribosomes, the same smaller type found in prokaryotes, unlike the 80S ribosomes in the rest of the eukaryotic cell.
No. This is a NEET trap. They DO have 70S ribosomes and RNA, so they can synthesize some proteins on their own.
