Mitochondria and chloroplasts are often called semi-autonomous…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Mitochondria and chloroplasts are often called semi-autonomous. Give three features they share that explain the name. Say where in each organelle the DNA lies, and why they cannot be fully independent of the cell.
Need a reminder? The key ideaShow
A mitochondrion has an outer membrane and an inner membrane folded into cristae, an outer compartment and a matrix. The matrix holds circular DNA and 70S ribosomes. Plastids: chloroplasts (chlorophyll), chromoplasts (carotene, xanthophylls), and leucoplasts: amyloplasts (starch), elaioplasts (oils and fats), aleuroplasts (proteins).
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Their own DNA. Each has its own circular DNA: in the matrix of a mitochondrion and in the stroma of a chloroplast.
Step 2. Their own ribosomes. Each has 70S ribosomes, so it can make some of its own proteins.
Step 3. They divide. Mitochondria divide by fission, and chloroplasts divide too.
Step 4. Not fully independent. Their DNA is small. Most of their proteins are made from the genes in the nucleus, so they depend on the cell.
Answer: own circular DNA (matrix; stroma), own 70S ribosomes, and division. They are only semi-autonomous because most of their proteins come from nuclear genes.
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