Protein Synthesis
1. Transcription to translation
a. they transfer information from a sequence of nucleotides into a sequence of amino
acids
b. During transcription, the phase preceding protein synthesis, the cell creates the
various types of RNA that make protein synthesis possible
c. mRNA/messenger RNA is a molecular message that specifies the sequence of
amino acids in a protein.
d. rRNA/ribosomal RNA partially makes up the ribosome. Think of ribosomes as
“protein factories” that can make any kind of protein.
e. tRNA/transfer RNA brings amino acids to the ribosomes
2. Making protein
a. Proteins are polymers of amino acid
3. Messenger RNA (mRNA) codes for proteins
a. mRNA is a polymer of RNA nucleotides.
messenger RNA
b. mRNA’s function is to specify the order of amino acids in a protein. Note that if you
need to review how the genetic code works, you can do so in the previous tutorial.
c. Within the coding portion of mRNA, every three nucleotides make up a codon.
d. Each codon codes for one amino acid.
e. Some codons serve as punctuation. The codon “AUG,” for example, signals the start
of a polypeptide chain. Three other codons indicate the chain’s end.
4. Transfer RNA (tRNA) brings amino acids to the ribosome
a. On the bottom of the tRNA is an anti-codon: 3 RNA nucleotides that complement the
codons in RNA
b. The top of the tRNA has an amino acid binding site.
c.
5. Translation
a. During translation, ribosomes “read” the mRNA, translating the sequence of codons
in the mRNA into a sequence of amino acids in a protein.
b. The ribosome is wrapped around the mRNA in a way that exposes the mRNA
codons to the cytoplasm.
c. The tRNA in the “P” site is holding on to the growing polypeptide, which now consists
of three amino acids.
d. The tRNA in the “A” site has just entered the ribosome. It’s temporarily held in place
by hydrogen bonds between the tRNA’s anticodon and the mRNA’s codon. Imagine
that before this tRNA became temporarily stuck, dozens of other tRNAs might have
bumped into the “A” site. But because their anti-codon didn’t complement the mRNA
codon, each one bounced away.
e. What’s the next move? With the correct tRNA in place, the ribosome acts like an
enzyme and binds the amino acid in the “A” site to the polypeptide in the “P” site.