This step occurs during translation, the process of converting the mRNA code into a protein. Each three-base sequence on mRNA, called a codon, specifies a particular amino acid. The tRNA molecule has an anticodon that matches the codon on the mRNA. This pairing ensures that the correct amino acid is added to the growin...
2. DNA is copied by RNA polymerase
This step is known as transcription, the process of creating mRNA from a DNA template. The enzyme RNA polymerase binds to the DNA and separates the two strands, using one strand as a template to synthesize a complementary mRNA molecule. This mRNA molecule carries the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm, where protein synthesis takes place.
3. Large and small rRNA join with mRNA
This step occurs during the initiation phase of translation. The ribosome, composed of two subunits (large and small), binds to the mRNA. The small subunit contains the binding site for mRNA, while the large subunit contains the binding sites for tRNA and the growing polypeptide chain.
4. mRNA leaves the nucleus
This step follows transcription and precedes translation. After the mRNA is synthesized in the nucleus, it must leave the nucleus and enter the cytoplasm where ribosomes are located. The mRNA passes through nuclear pores, small channels in the nuclear membrane, and travels to the ribosomes.
The Correct Order of Protein Synthesis
The correct order of steps in protein synthesis is:
- **DNA is copied by RNA polymerase (Transcription)**
- **mRNA leaves the nucleus**
- **Large and small rRNA join with mRNA (Initiation of Translation)**
- **Codons are read and the anticodon matches the complementary base (Elongation of Translation)**
Therefore, the answer is **2,4,3,1**.
Explanation of the Order
The sequence of events in protein synthesis is essential for the accurate production of proteins. The process begins in the nucleus with the copying of DNA into mRNA (transcription). This mRNA then travels to the cytoplasm, where it encounters ribosomes. Ribosomes are composed of rRNA and protein and are responsible for translating the mRNA code into a protein. The binding of the ribosome to the mRNA initiates translation, and the ribosome reads the codons on the mRNA one by one. Each codon specifies a particular amino acid. tRNA molecules bring the corresponding amino acids to the ribosome, where they are added to the growing polypeptide chain. This process, known as elongation, continues until the ribosome reaches a stop codon on the mRNA, signaling the termination of translation.
Key Concepts
Here are some key concepts related to protein synthesis:
- **Transcription:** The process of copying DNA into mRNA. This step takes place in the nucleus.
- **Translation:** The process of converting mRNA into a protein. This step takes place in the cytoplasm.
- **Ribosomes:** Cellular organelles composed of rRNA and protein. Ribosomes are responsible for translating mRNA into protein.
- **tRNA:** A type of RNA molecule that carries amino acids to the ribosome during translation. Each tRNA molecule has an anticodon that matches a specific codon on the mRNA.
- **Codon:** A three-base sequence on mRNA that specifies a particular amino acid.
- **Anticodon:** A three-base sequence on tRNA that matches a specific codon on mRNA.
Importance of Protein Synthesis
Protein synthesis is an essential process for all living organisms. Proteins are the building blocks of cells and tissues and perform a wide variety of functions, including:
- **Structural support:** Proteins provide structure and support to cells and tissues.
- **Enzymes:** Proteins catalyze biochemical reactions, speeding up metabolic processes.
- **Hormones:** Proteins act as chemical messengers, regulating various bodily functions.
- **Antibodies:** Proteins play a crucial role in the immune system, defending against pathogens.
- **Transport:** Proteins transport molecules across cell membranes and throughout the body.
Conclusion
Protein synthesis is a complex but highly regulated process that ensures the accurate production of proteins essential for life. Understanding the steps involved in protein synthesis and the factors that influence this process is crucial for understanding the workings of living cells and organisms.