Question

The site of active ribosomal RNA synthesis is (a) Nucleolus (b) Mitochondria (c) Cytoplasm (d) All of these

Short answer

The site of active ribosomal RNA synthesis is (a) Nucleolus

Step-by-step solution

Understanding the problem

The first step is to understand what is being asked. We need to know where ribosomal RNA (rRNA) is actively synthesized within the cell. rRNA is a type of RNA, which is essential for the function of ribosomes, offering the site for the synthesis of proteins. The synthesis site of rRNA is therefore critical in understanding the process of protein synthesis

Evaluating each option

Now let's evaluate each of the given options: - (a) Nucleolus: This part of the cell is known to play a role in the synthesis of ribosomes and is also found within the nucleus where DNA transcribes rRNA. Thus, the Nucleolus could indeed be a site of active rRNA synthesis. - (b) Mitochondria: This organelle, often described as the 'powerhouse' of the cell, functions in energy metabolism by producing ATP, and has its own DNA, but is not known to be directly involved in rRNA synthesis. - (c) Cytoplasm: This is the site of protein production in ribosomes, but not where the ribosome itself, or its rRNA component, is synthesized. - (d) All of these: From the above, it is clear that not all these options are correct.

Selecting the correct answer

From the evaluation in Step 2, it becomes clear that the correct answer is (a) Nucleolus, since this is the location in the cell where active rRNA synthesis is known to occur

Key concepts

Nucleolus

The nucleolus is a fundamental component of the cell nucleus, primarily associated with ribosomal RNA (rRNA) synthesis. It is characterized by its dense structure and is found within the nucleus of eukaryotic cells.

Functionally, the nucleolus has the key role of orchestrating the production of the components of ribosomes, which are the cellular machines responsible for protein synthesis. Inside the nucleolus, the rRNA is transcribed from DNA, then combined with proteins imported from the cytoplasm to form the ribosomal subunits. These subunits are later exported to the cytoplasm where they assemble into complete ribosomes. Hence, the nucleolus is essential for cellular growth and proliferation because its primary function is to produce the ribosomes that are necessary for translating genetic information into proteins.

Research has further revealed that nucleoli are involved in various cellular processes, including cell cycle regulation and response to stress. It's a multifaceted organelle, integral not only to the synthesis of ribosomal RNA but also to overall nuclear architecture and function.

Protein synthesis

Protein synthesis is a fundamental biological process where cells construct proteins based on the genetic information carried in DNA. This process occurs in two main stages: transcription and translation.

During transcription, a messenger RNA (mRNA) molecule is created from a DNA template. This mRNA carries the genetic code from the DNA in the nucleus to the ribosomes, which are located in the cytoplasm. In the ribosomes, translation occurs, which is the reading of the mRNA sequence to produce a chain of amino acids that will fold into a functional protein.

Each set of three nucleotides on the mRNA, known as a codon, corresponds to specific amino acids, the building blocks of proteins. Transfer RNA (tRNA) molecules bring these amino acids to the ribosomes in the correct sequence. Through the peptidyl transferase activity of the ribosomal RNA, amino acids are linked together to form a polypeptide chain. After folding and processing, this polypeptide becomes a functional protein that can carry out a myriad of roles in the cell, from catalyzing reactions as enzymes to providing structural support.

Cell organelles

Cell organelles are specialized structures within a cell that serve various functions necessary for the cell's survival and operation. They can be likened to the organs of the body, each performing specific roles and working together to keep the cell functioning properly.

Some notable organelles include:

• Nucleus: This is the control center of the cell, housing the cell's DNA and the nucleolus. It is responsible for managing gene expression and replication of DNA during cell division.
• Mitochondria: Known as the 'powerhouse' of the cell, these organelles generate most of the cell's supply of adenosine triphosphate (ATP), required for energy-consuming activities within the cell.
• Ribosomes: These are sites of protein synthesis, found floating freely in the cytoplasm or bound to the endoplasmic reticulum (ER), forming the rough ER due to their studded appearance.
• Endoplasmic Reticulum (ER): The ER is involved in the synthesis of lipids and proteins; the rough ER with ribosomes synthesizes proteins, while the smooth ER, which lacks ribosomes, synthesizes lipids.
• Golgi apparatus: This structure modifies, sorts, and packages proteins and lipids for storage or transport out of the cell.
• Lysosomes: These contain digestive enzymes to break down macromolecules, damaged cell components, and pathogens.

Each type of organelle has a specific composition and set of functions, together contributing to the cell's overall metabolism, structure, and regulation. Understanding the role of these organelles is crucial for comprehending the intricate web of cellular processes.