Question

Which of the following best represents the central dogma of gene expression? a. During transcription, DNA codes for polypeptides. b. During transcription, DNA codes for mRNA, which codes for polypeptides during translation. c. During translation, DNA codes for mRNA, which codes for polypeptides during transcription. d. none of the above

Short answer

The correct answer is option b. During transcription, DNA codes for mRNA, which codes for polypeptides during translation.

Step-by-step solution

Understand the structural relationship

The first step is to understand the structural relationships involved in gene expression. This involves three key components: DNA, mRNA and polypeptides (proteins). DNA carries the genetic information; mRNA is the messenger molecule that takes the information from the DNA; and the proteins are the end products that perform various functions in the cell.

Comprehending the central dogma

Next, you need to understand the central dogma, which is basically the path from DNA, through mRNA, to produce proteins. This process includes two main stages: Transcription, where DNA codes for mRNA, and Translation, where mRNA codes for proteins.

Matching the options with the concept

With your understanding of the central dogma, you then match the options provided in the exercise with the concept. The correct answer will be the one that accurately summarizes this path.

Key concepts

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize a functional gene product. This involves several stages, but the main players are DNA and proteins. It all starts with DNA, which holds the genetic blueprint. Gene expression can be thought of as the way in which these instructions are used to create molecules like proteins that perform essential functions in the body. There are several steps involved in the process:

• Transcription
• Processing of mRNA
• Translation into proteins

This sequence ensures that the genetic code is accurately expressed, allowing cells to perform their specific roles effectively.

Transcription

Transcription is the first major step of gene expression. During transcription, a specific segment of DNA is copied into mRNA by the enzyme RNA polymerase. This process takes place in the nucleus of the cell.
The DNA unwinds to expose the gene that needs to be used, and the RNA polymerase reads the DNA sequence to synthesize a complementary mRNA strand.

• RNA polymerase binds to the promoter region of a gene.
• As it moves along, it synthesizes an mRNA strand complementary to the DNA template.
• The newly formed mRNA detaches from the DNA, and the DNA strands re-anneal.

This mRNA is then processed and transported out of the nucleus to be used in protein synthesis.

Translation

Translation is the process that follows transcription in the path of gene expression. It occurs in the cytoplasm of the cell and involves converting the information from mRNA into a sequence of amino acids, forming a polypeptide chain.
This takes place in the ribosome, which reads the mRNA sequence three bases at a time - each three-base combination is called a codon.

• The ribosome binds to the mRNA strand.
• Transfer RNA (tRNA) molecules, with attached amino acids, bind to the codons on the mRNA according to complementary base pairing.
• The amino acids are joined together in sequence, creating a polypeptide chain.

Once the chain is complete, it folds into a functional protein that can perform various cellular tasks.

mRNA

mRNA, or messenger RNA, serves as the intermediary between the genetic code in DNA and the synthesis of proteins. After transcription, mRNA carries the genetic code from the DNA in the nucleus to the ribosome in the cytoplasm.
It plays a crucial role in translating genetic information into proteins by specifying the sequence of amino acids.

• mRNA is a single-stranded molecule.
• It reflects a complementary sequence to its DNA template.
• It contains codons that dictate the order of amino acids in a protein.

This messenger molecule ensures the flow of genetic information is accurate and efficient, achieving the central task of generating proteins.

DNA

DNA, or deoxyribonucleic acid, is the hereditary material in all cells. It contains the instructions needed for an organism to develop, survive, and reproduce.
In the context of gene expression, DNA is the blueprint from which all genetic information is derived.

• Structured as a double helix with two strands winding around each other.
• Made up of nucleotides: adenine, thymine, cytosine, and guanine.
• Sequences of nucleotides form genes, which code for proteins.

DNA ensures that the genetic code is preserved and transmitted from one generation to the next, enabling all life processes.

Protein Synthesis

Protein synthesis is the final step in the process of gene expression. It is the process by which cells make proteins, and it happens in two stages: transcription and translation.
Proteins are vital for the body since they perform a myriad of functions, such as enzyme activity and structural support.

• Essential for building and repairing tissues.
• Involves DNA, mRNA, ribosomes, and tRNA.
• Results in the formation of a polypeptide chain that folds into a protein.

The accuracy and efficiency of protein synthesis are critical, as proteins need to be correctly formed to function properly within the organism's cells.