How are genes used by cells to build proteins?
Select one:
A. The genes in RNA direct the synthesis of proteins directly
B. DNA is transcribed into an amino acid sequence.
C. The genes in RNA direct the synthesis of a DNA molecule, which is used to build a protein
D. The genes in DNA direct the synthesis of an RNA molecule, which is used to build a protein.
The Correct Answer and Explanation is:
The correct answer is:
D. The genes in DNA direct the synthesis of an RNA molecule, which is used to build a protein.
Explanation:
Genes are segments of DNA that contain the instructions for building proteins, which are essential molecules that perform a vast array of functions in living cells. The process by which cells use genes to make proteins involves two main steps: transcription and translation.
- Transcription: DNA to RNA
The first step occurs in the cell nucleus, where the gene’s DNA sequence is copied into a messenger RNA (mRNA) molecule. DNA serves as a template for this process. The enzyme RNA polymerase reads the DNA sequence of the gene and synthesizes a complementary strand of mRNA. This mRNA carries the genetic information from the DNA, but in a form that can leave the nucleus and enter the cytoplasm. This is because proteins are made in the cytoplasm by structures called ribosomes, and DNA itself cannot leave the nucleus. - Translation: RNA to Protein
In the cytoplasm, the mRNA associates with a ribosome, the cellular “machine” that reads the sequence of nucleotides in the mRNA three at a time (each triplet is called a codon). Each codon specifies a particular amino acid. Transfer RNA (tRNA) molecules bring the appropriate amino acids to the ribosome, where they are linked together in the correct order to form a protein chain. This chain then folds into a functional protein.
The other options are incorrect for these reasons:
- A. The genes in RNA direct the synthesis of proteins directly:
Genes are encoded in DNA, not RNA. RNA is a messenger but does not contain the original genetic blueprint. - B. DNA is transcribed into an amino acid sequence:
DNA is transcribed into RNA, not directly into amino acids. The amino acid sequence is determined during translation from mRNA. - C. The genes in RNA direct the synthesis of a DNA molecule, which is used to build a protein:
This reverses the correct flow of genetic information. Genes in DNA direct RNA synthesis; RNA then guides protein synthesis.
In summary, the central dogma of molecular biology states that DNA → RNA → Protein. DNA contains the instructions, RNA transcribes those instructions, and proteins are synthesized based on the RNA code. This flow of information is fundamental to how cells function and produce the molecules necessary for life.