Introns are rarer in bacterial pre-tRNAs, but do occur occasionally and are spliced out. After processing, the mature pre-tRNA is ready to have its cognate amino acid attached. The cognate amino acid for a tRNA is the one specified by its anticodon. Attaching this amino acid is called charging the tRNA. In eukaryotes, the mature tRNA is generated in the nucleus, and then exported to the cytoplasm for charging.
Processing of a pre-tRNA. Nucleotides that are cleaved away are shown in green. The anticodon nucleotides are shown in a lighter shade of red. The amino acid phenylalanine is attached to the other end of the tRNA. The amino acid is loaded into the CCA tail at the end of the acceptor stem. Some anticodons form base pairs with several codons by the wobble base pairing.
The secondary structure of a tRNA molecule is shown in figure 2. The ribosome is the protein-synthesizing organelle in the cell, translating the coding sequence on an mRNA molecule into a polypeptide chain. The synthesis of rRNA occurs at the nucleolus. Both rRNA molecules combine with ribosomal proteins to form a small subunit and a large subunit.
The large subunit of rRNA serves as the ribozyme that catalyzes the peptide bond formation. During translation, small subunit and large subunit come together to form the ribosome. The mRNA molecule is sandwiched between the small and large subunit. Each ribosome is composed of three binding sites for the binding of tRNA molecules. They are A, P, and E sites. The A site binds with the aminoacyl-tRNA. The aminoacyl-tRNA contains a specific amino acid.
The aminoacyl-tRNA molecule at the P site is attached to the growing polypeptide chain. Then, the aminoacyl-tRNA molecule moves to the E site. It is the base pairing between the tRNA and mRNA that allows for the correct amino acid to be inserted in the polypeptide chain being synthesized Figure 4.
Any mutations in the tRNA or rRNA can result in global problems for the cell because both are necessary for proper protein synthesis Table 1. Figure 4. A tRNA molecule is a single-stranded molecule that exhibits significant intracellular base pairing, giving it its characteristic three-dimensional shape. Thus, RNA clearly does have the additional capacity to serve as genetic information.
Although RNA is typically single stranded within cells, there is significant diversity in viruses. Rhinoviruses, which cause the common cold; influenza viruses; and the Ebola virus are single-stranded RNA viruses.
Rotaviruses, which cause severe gastroenteritis in children and other immunocompromised individuals, are examples of double-stranded RNA viruses. Because double-stranded RNA is uncommon in eukaryotic cells, its presence serves as an indicator of viral infection. A nucleic acid is purified from a mixture. The molecules are relatively small, contain uracil, and most are covalently bound to an amino acid. Which of the following was purified?
Skip to main content. Biochemistry of the Genome. Search for:. Think about It What are the functions of the three major types of RNA molecules involved in protein synthesis? Key Concepts and Summary Ribonucleic acid RNA is typically single stranded and contains ribose as its pentose sugar and the pyrimidine uracil instead of thymine. An RNA strand can undergo significant intramolecular base pairing to take on a three-dimensional structure.
There are three main types of RNA, all involved in protein synthesis.
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