Problem 191 - Objective Biology for NEET

Question

Assertion: Mitochondria and chloroplast are semi-autonomous cell organelle. Reason: Both contain DNA, RNA and ribosome.

Step-by-Step Solution

Answer

Yes, the reason correctly supports the assertion. Mitochondria and chloroplasts are semi-autonomous cell organelles because they contain their own DNA, RNA, and ribosomes.

Step 1: Understand the Assertion

The assertion states that mitochondria and chloroplasts are semi-autonomous cell organelles. This concept refers to their ability to act to some extent independently within the cell.

Step 2: Analyze the Reason

The reason provides evidence for the claim by stating that both organelles contain their own DNA, RNA, and ribosomes. These components are crucial for their independent functioning, such as synthesizing proteins and replicating their own DNA to replicate themselves.

Step 3: Match the Reason to the Assertion

Having established what each organelle can do and why, the next step is to determine if the reason indeed supports the assertion. Since DNA, RNA, and ribosomes are essential for autonomy and both mitochondria and chloroplasts contain these, the reason supports the assertion.

Key Concepts

Mitochondria

Known as the 'powerhouse of the cell', mitochondria are integral to energy production. Inside these organelles, a process called cellular respiration occurs. Here, glucose and other nutrients are converted into adenosine triphosphate (ATP), which cells use as a primary energy currency.

Mitochondria have their own circular DNA, much like bacterial DNA, which is why they are seen as semi-autonomous. This DNA allows them to produce some of their own proteins and enzymes necessary for their function. However, they depend on the cell's nuclear DNA for the full range of proteins they require. Importantly, mitochondria can replicate, grow, and divide independently of the cell, underlining their semi-autonomy.

Chloroplast

Chloroplasts are essential for photosynthesis, a process that captures sunlight to create glucose, providing energy for plants as well as oxygen for the environment. Similar to mitochondria, chloroplasts have their own DNA, which allows them to synthesize some proteins required for photosynthesis.

They have a complex structure, including an outer membrane, an inner membrane, and stacks of thylakoids where the light-dependent reactions occur. The presence of chloroplast DNA gives plants the edge to regulate photosynthesis processes and aids in the organelle's self-replication – factors contributing to their semi-autonomous status.

Cellular DNA

Cellular DNA is the genetic material found within the nucleus of eukaryotic cells. It encodes the instructions needed to construct and regulate all of the cell's proteins and cellular activities. In contrast to organelle DNA, nuclear DNA is linear and complex, requiring an array of proteins to carefully manage its replication and transcription into RNA.

Even semi-autonomous organelles such as mitochondria and chloroplasts depend on many proteins encoded by nuclear DNA, establishing a dynamic interdependence between them and the cell nucleus. These organelles cannot function without the contribution of nuclear DNA, as it provides the additional proteins and instructions necessary for their operation.

Ribosomes

Ribosomes are molecular machines that synthesize proteins by translating messenger RNA (mRNA) into amino acid sequences. These sequences ultimately fold into functional proteins. Both eukaryotic cells and semi-autonomous organelles possess ribosomes, but the ones found in organelles are slightly different, similar to those found in bacteria.

The presence of ribosomes within mitochondria and chloroplasts empowers them with the ability to make some of their own proteins. Therefore, ribosomes are critical to the semi-autonomous nature of these organelles, allowing them to produce essential components for their unique functions within the cell.