http://www.ck12.org Chapter 26. Biochemistry
RNA, the DNA refolds into the original double helix. The mRNA is exported to the cytoplasm (outside the nucleus)
for further processing.
Amino acids will link with specific transfer RNA molecules for proper placement in the protein chain. The tRNA is
a small coiled molecule that accepts an amino acid on one end and matches up to a specific three-base portion of the
mRNA on the other end. The tRNA interacts with the mRNA so as to put the amino acids in the proper sequence
for the developing protein. After adding the amino acid to the sequence, the tRNA is cleaved from the amino acid
and recycled for further participation in the process. Because we are converting from one "language" to another (a
sequence of mRNA bases into a sequence of amino acids), this part of the process is referred to astranslation.
FIGURE 26.21
The process of assembling amino acids into a protein takes place in the ribosome. This structure consists of two
subunits, each of which is composed of both proteins and ribosomal RNA (rRNA). The two subunits clamp together
on the mRNA and catalyze the formation of the amide linkages in the growing protein. When protein synthesis is
complete, the two subunits dissociate and release the completed protein chain.
The process of protein synthesis is fairly fast. Amino acids are added to the growing peptide chain at a rate of about
3-5 amino acids per second. A smaller protein (100-200 amino acids) can be produced in a minute or less.
Lesson Summary
- Nucleotides contain a pentose sugar, a nitrogen-containing base, and one or more phosphate groups.
- Nucleic acids, such as DNA and RNA, are composed of long strands of nucleotides bonded together through
their phosphate groups. - DNA generally exists as two complementary strands connected by hydrogen bonds into a double helix struc-
ture. - DNA contains the genetic information for the production of proteins.
- The transcription process produces a strand of messenger RNA from DNA.
- During translation, messenger RNA interacts with the ribosome and transfer RNA to produce a protein.