An Interactive Introduction to Organismal and Molecular Biology, 2021

PROTEIN SYNTHESIS OVERVIEW | 133
Protein synthesis consists of two main processes: transcription and translation. During the process of
transcription—which occurs in the nucleus—an mRNA molecule is created by reading the DNA. Note that
DNA never “becomes” RNA; rather, the DNA is “read” to make an RNA molecule. The mRNA leaves the
nucleus and then, through the process of translation, the mRNA is read to create an amino acid sequence
which folds into a protein.
Consider what the terms “transcribe” and “translate” mean in relation to language. To “transcribe”
something means to rewrite text again in the same language while to “translate” something means to rewrite
the text in a different language. Similar to these meanings, in biology, DNA is transcribed into RNA: both
DNA and RNA are made of nucleic acid (i.e., the same “language”). With the assistance of proteins, DNA is
“read” and transcribed into an mRNA sequence. To read RNA and create protein, though, we refer to it as
being translated: RNA is made of nucleic acid and protein is made of amino acid (i.e., different “languages”).
Therefore, DNA is transcribed to create an mRNA sequence, and then the mRNA sequence is translated to
make a protein.
DNA and RNA
The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the
genetic material in all living organisms, ranging from single-celled bacteria to multicellular mammals. It is in the
nucleus of eukaryotes and in the organelles, chloroplasts, and mitochondria. In prokaryotes, the DNA is not
enclosed in a membranous envelope.
The cell’s entire genetic content is its genome, and the study of genomes is genomics. In eukaryotic cells but
not in prokaryotes, a DNA molecule may contain tens of thousands of genes. Many genes contain information
to make protein products (e.g., mRNA). Other genes code for RNA products. DNA controls all of the cellular
activities by turning the genes “on” or “off.”
The other type of nucleic acid, RNA, is mostly involved in protein synthesis. The DNA molecules never
leave the nucleus but instead use an intermediary to communicate with the rest of the cell. This intermediary
is the messenger RNA (mRNA). Other types of RNA—like rRNA, tRNA, and microRNA—are involved in
protein synthesis and its regulation.