Question

Splicing begins: a. as transcription occurs. b. after transcription is complete. c. as translation occurs. d. after translation is complete.

Short answer

Splicing occurs after transcription is complete (option b). It is a crucial step in the maturation of the mRNA molecule for the removal of non-coding sequences (introns) before translation can occur.

Step-by-step solution

Brief introduction to Transcription, Translation, and Splicing

Transcription is the process where genetic information from DNA is copied into a messenger RNA (mRNA) molecule. Translation is the process where the genetic information in mRNA is used as a template to synthesize proteins. Splicing is the process where non-coding sequences called introns are removed from pre-mRNA, and the protein-coding sequences called exons are joined together to create the mature mRNA molecule that will be used for translation.

Identify when Splicing occurs

Splicing occurs before translation as it is a crucial step in the maturation of the mRNA molecule and the removal of non-coding sequences. It takes place after transcription is complete, as the pre-mRNA molecule is generated and needs to be processed further.

Select the correct answer

Based on the information above, the correct answer is: b. after transcription is complete.

Key concepts

Understanding Transcription

Transcription is the first step in the journey from gene to protein, where the blueprint of genetic information encoded within DNA is rewritten into messenger RNA (mRNA). This process occurs within the cell nucleus and involves several key enzymes, most notably RNA polymerase. The RNA polymerase binds to a specific region of the DNA, called the promoter, and unwinds the DNA strands.

As it moves along the DNA, the enzyme assembles a strand of mRNA by matching RNA nucleotides with their complementary DNA partners. This forms an mRNA strand that is essentially a mirror image of the gene's DNA sequence, albeit with uracil replacing thymine. Once the entire gene has been transcribed and a termination sequence is reached, the RNA polymerase releases the newly formed pre-mRNA for further processing.

Decoding Genetic Information Through Translation

Translation is the process of synthesizing proteins from the mRNA template. This occurs in the cytoplasm of the cell where ribosomes, the cell's protein-making machinery, read the sequence of mRNA nucleotides in sets of three bases known as codons. Each codon specifies a particular amino acid, the building block of proteins.

The Role of tRNA

Transfer RNA (tRNA) molecules match their anticodon sequences to the mRNA codons, adding the appropriate amino acids to the growing polypeptide chain in the correct sequence. This chain folds into a specific three-dimensional shape to form a functional protein. The process continues until a stop codon is reached, signaling the end of the protein synthesis.

The Essentials of mRNA Processing

Once transcription is complete, the pre-mRNA undergoes several modifications before it can be translated into a protein. This set of modifications is known as mRNA processing and includes capping, polyadenylation, and splicing.

Capping and Polyadenylation

A 5' cap is added to the front end of the mRNA molecule, which is crucial for mRNA stability and for the initiation of translation. At the other end, a poly-A tail is added, which also aids in stability and export from the nucleus.

Importance of Splicing

Most importantly for our discussion, splicing removes introns, non-coding regions, from the pre-mRNA and joins the coding segments, exons, to form a continuous sequence that correctly codes for a protein. This process ensures that the genetic instructions carried in the mRNA accurately reflect the functional protein product.

Wrapping Your Mind Around Genetic Information

Genetic information is the set of instructions found in the DNA of every organism that directs the formation of proteins needed for life. This information is stored in the sequence of nucleotides along the DNA strands. The four nucleotides — adenine (A), thymine (T), cytosine (C), and guanine (G) — are arranged in specific patterns to encode the genetic instructions.

These instructions dictate everything from physical attributes to the metabolic processes essential for survival. Understanding transcription and translation, as well as mRNA processing, is key to comprehending how genetic information leads to the diversity of life and the functioning of cells. All these processes, from the initial transcription to the final translation, collectively ensure that the genetic code is accurately expressed in the form of functional proteins.