Question

Assertion: Chloroplast can synthesize proteins Reason: Chloroplast contains ribosomes.

Short answer

Yes, the assertion is correct. Chloroplasts can synthesize proteins because they contain ribosomes, the part of the cell responsible for protein synthesis.

Step-by-step solution

Understanding the role of chloroplasts

Chloroplasts are organelles found in plant cells that are most known for carrying out photosynthesis. However, they also carry out other functions, such as protein synthesis.

Understanding the role of ribosomes

Ribosomes are parts of the cell responsible for protein synthesis. They convert genetic material into proteins by reading the sequence of the mRNA.

Connect the function of ribosomes to chloroplasts

Chloroplasts contain ribosomes. This allows them to read mRNA sequences and synthesize proteins.

Key concepts

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy. This happens primarily in the chloroplasts within plant cells. These chloroplasts contain chlorophyll, a green pigment that captures light energy.

The process occurs in two main stages called the light-dependent reactions and the Calvin cycle. During the light-dependent reactions, sunlight is absorbed and used to split water into oxygen, protons, and electrons. This reaction takes place in the thylakoid membranes of the chloroplasts.

• Light-dependent reactions generate ATP and NADPH, which are energy carriers.
• Oxygen is released as a byproduct.

Next, in the Calvin cycle, which occurs in the stroma of the chloroplasts, the ATP and NADPH produced are used to convert carbon dioxide into glucose, a form of sugar. This sugar provides energy and building blocks for growth and development. Overall, photosynthesis is crucial because it forms the base of the food chain by providing energy for plants and, indirectly, all other living organisms.

Ribosomes

Ribosomes are vital molecular machines found in all living cells, responsible for protein synthesis. They translate genetic information from mRNA into proteins by using a sequence of nucleotides as a blueprint.

Each ribosome is composed of two subunits, a small and a large one, each made of proteins and ribosomal RNA (rRNA). These subunits work together to read mRNA sequences and assemble amino acids in the correct order to make a specific protein.

• Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum.
• In chloroplasts, ribosomes enable the organelle to synthesize certain proteins independently.

The ribosomes within chloroplasts are similar to those found in bacteria, supporting the theory of endosymbiosis. This theory suggests that chloroplasts originated from ancient symbiotic bacteria. This independence allows chloroplasts some autonomy in managing their own protein needs, crucial for their multifunctional roles in the cell.

Protein Synthesis

Protein synthesis is a fundamental biological process in which cells construct proteins based on genetic instructions. It begins with transcription, the process where DNA is transcribed into messenger RNA (mRNA) in the cell nucleus.

Once mRNA is produced, it travels to the ribosomes, where translation occurs. Ribosomes read the sequence of mRNA nucleotides in groups of three, called codons, each specifying an amino acid. Transfer RNA (tRNA) brings the correct amino acids to the ribosome in accordance with the mRNA sequence.

• The sequence of amino acids determines the final protein structure and function.
• Proteins can act as enzymes, structural components, or signal molecules.

In the context of chloroplasts, they possess their own ribosomes and genetic material, enabling them to synthesize some proteins independently. This feature supports their roles in photosynthesis and other functions necessary for the plant's survival and adaptation.