Question

Which of these statements about mRNA is false? a. It is produced as a larger pre-mRNA. b. It forms associations with ribosomes. c. Its base triplets are called anticodons. d. It codes for the synthesis of specific proteins.

Short answer

The false statement about mRNA is c. Its base triplets are called anticodons. This term actually refers to tRNA, not mRNA. In mRNA, the base triplets are called codons.

Step-by-step solution

Understanding mRNA

mRNA, short for messenger RNA, is a type of RNA that carries the genetic instructions from DNA for the synthesis of proteins, which is a part of gene expression. mRNA is transcribed from the DNA in the nucleus into a preliminary form called pre-mRNA before becoming mature mRNA. This mature mRNA then associates with ribosomes to translate the genetic instructions into proteins.

Examining Each Statement

With the basic understanding of mRNA, we can now examine each answer choice. a. pre-mRNA is the first form of mRNA that is transcribed from DNA. This pre-mRNA then undergoes processing to become mature mRNA. So this statement is true. b. mRNA associates with ribosomes, which are the molecular machines that use the instructions carried by the mRNA to synthesize proteins. So, this statement is also true. c. The mention of "anticodons" in this statement is misleading. Anticodons are a feature of tRNA (transfer RNA), not mRNA. In mRNA, the base triplets that correspond to amino acids in proteins are called codons. So, this statement is false. d. mRNA indeed codes for the synthesis of specific proteins; that's its main function. This statement is therefore true. Therefore, answer c is the false statement about mRNA.

Key concepts

Gene Expression

Gene expression is the process by which the information encoded within DNA is used to produce functional products, usually proteins. It is a critical aspect of biology governing how genetic information is converted into the structure and function needed by cells.
Gene expression primarily involves two major stages:

• Transcription: This is the first stage where a segment of DNA is copied into mRNA by the enzyme RNA polymerase. This mRNA acts as a messenger carrying the genetic code from the nucleus to the cytoplasm of the cell, where it will be translated into protein.
• Translation: The mRNA is then read by ribosomes in the cytoplasm, where ribosomes use the code to build proteins by linking the appropriate sequence of amino acids.

During gene expression, only certain genes are expressed at any given time, allowing cells to perform specialized functions. The control over which genes are expressed can affect everything from cell differentiation to responses to environmental changes.

Ribosomes

Ribosomes are the molecular machines present in all living cells, responsible for producing proteins by reading the sequence of an mRNA molecule. These organelles link amino acids together in the order specified by the coded sequences in mRNA to form a polypeptide chain that will fold into a functional protein.
Even though ribosomes are small, they play a crucial role in cellular function due to their role in protein synthesis:

• Ribosomes consist of two subunits, a large and a small one, each composed of rRNA (ribosomal RNA) and protein.
• They can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming what is known as the rough ER.
• They bind mRNA and tRNA, translating the mRNA code into an amino acid sequence using tRNA molecules that carry specific amino acids.

The association of ribosomes with mRNA during translation highlights their essential role in converting genetic instructions into tangible, functional entities in the cell.

Protein Synthesis

Protein synthesis is the cellular process of constructing proteins from amino acids in a sequence dictated by the sequence of nucleotides in mRNA. This process can be broken down into two main stages: transcription, followed by translation, each crucial to the accurate production of proteins.

• Initiation: The start of translation begins when the small ribosomal subunit binds with the mRNA and finds the start codon, typically AUG, which signals the correct position to begin protein synthesis.
• Elongation: During this phase, ribosomes move along the mRNA, decoding the codons into the corresponding amino acids, which are brought in by tRNA molecules. The ribosome facilitates the formation of peptide bonds between amino acids, building a polypeptide chain.
• Termination: This process concludes when the ribosome reaches a stop codon on the mRNA, which signals the release of the completed polypeptide from the ribosome structure.

The resultant polypeptide chain undergoes folding and modification to become a fully functional protein. Protein synthesis is fundamental to cell function and organism development, and errors in this process can lead to various diseases or developmental issues.