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MCAT Content / Genetic Code / Messenger Rna Mrna

Messenger RNA (mRNA)

Topic: Genetic Code

Messenger RNA or mRNA is a type of RNA that is formed by transcription of DNA and encodes a protein.

During transcription, a DNA sequence is copied into a complementary RNA molecule. In eukaryotes, this occurs in the nucleus. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that enzymes can convert back and forth from DNA to RNA. Unlike DNA replication, transcription results in a RNA complement that substitutes the RNA uracil (U) in all instances where the DNA thymine (T) would have occurred. You can see this represented in the figure below:

MCAT Messenger RNA (mRNA)

The RNA molecule that is copied from a DNA sequence is called a transcript. Some transcripts are used as structural or regulatory RNAs, and others encode one or more proteins. If the transcribed gene encodes a protein, the result of transcription is messenger RNA (mRNA), which will then move to ribosomes in the cytoplasm and be used to create a protein in the process of translation.

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Key Points

• Messenger RNA or mRNA is formed from a DNA sequence in a process known as transcription.

• mRNA is complementary to the template strand of DNA it is copied from, except the RNA-specific nucleotide uracil replaces thymine. The mRNA sequence is exactly the same as the non-template strand of DNA

• mRNA is used by ribosomes in the cytoplasm to synthesize a polypeptide chain (protein).

Key Terms

Messenger RNA (mRNA): An RNA molecule that is copied from a DNA sequence during transcription and is used to create a protein during translation.

Transcription: The process of converting a specific sequence of DNA into a new RNA molecule.

Complementary: Describes the pairing between specific nucleotides in DNA and RNA.

Uracil (U): A nucleotide specifically found in RNA that replaces the thymine found in DNA.

Transcript: A RNA molecule that is copied from a DNA sequence during transcription.

Ribosome: A macromolecule composed of RNA and proteins, located in the cytoplasm or on the rough endoplasmic reticulum, that uses an mRNA sequence to produce a polypeptide chain during translation.

Translation: The process where RNA is used to create a new polypeptide chain (protein).

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