Period: _____ Date: _________________
How Cells Make Protein: Translation
During transcription , RNA polymerase attaches to the beginning of a gene (a segment of DNA that gets
translated into a protein). A sequence of bases known as a promoter in the DNA “tells” the RNA polymerase
where to bind.
The RNA polymerase then pries open the DNA. One strand of the DNA serves as a template that allows
complementary RNA nucleotides to form hydrogen bonds with it. As a matching RNA nucleotide binds with
its complementary DNA partner, the RNA polymerase catalyzes a sugar-phosphate bond between one RNA
nucleotide and the next, creating an RNA polymer.
When the RNA polymerase reaches the end of the gene, it releases the RNA. In a prokaryotic cell, the
RNA is then ready for action. In a eukaryotic cell, that RNA is usually modified, and then has to find its
way out of the nucleus and into the cytoplasm.
Briefly summarize the process of transcription in six steps:
2. RNA pol. pries
reaches the end
of the gene.
messenger RNA is a code. The ribosome translates this code into protein. This code is called the
GENETIC CODE. It's a universal code, pretty much the same in all living things. In this code, THREE RNA
bases code for ONE amino acid. These three bases are known as a CODON (from "code + one").
As with any cellular process, translation gets carried out without any "higher intelligence." There's no
one in the cell who can read, think, etc. The translator in this process is transfer RNA (tRNA)
tRNAs (7, at right) are bilingual molecules. One end of a tRNA consists of 3
RNA bases that complement an RNA codon. These three bases are called an
"anti-codon." (8) The other end carries an specific amino acid (6).
The process of translation starts with a molecule of messenger RNA coming
out of the nucleus and entering the cytoplasm (shown at 1). Next, a ribosome (2)
attaches to the mRNA, and starts moving along its length. The mRNA sits on the
ribosome in a way that exposes the mRNA codons (shown at 5). The
complementary match between codon (5) and tRNA anticodon (8) ensures that
only the correct amino acid (6) will be brought by a tRNA (7) to the ribosome.
The ribosome catalyzes peptide bonds between adjacent amino acids, resulting in
the formation of a protein (4).
4. Translation Overview
Key to diagram. Use the text above ("tRNAs, anticodons, and translation") to identify all the parts in the diagram.
Summarize the process of translation in 5 steps.
5. Ribosome reaches
the end of mRNA and
releases the protein
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