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. It ensures the proper alignment of the mRNA and the ribosomes during protein synthesis and catalyzes the formation of the peptide bonds between two aligned amino acids during protein synthesis.
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. Although RNA is not used for long-term genetic information in cells, many viruses do use RNA as their genetic material. Show Answer Answer d. Show Answer Answer c. Show Answer Answer a. A virus may use RNA as its genome. A rRNA is a major component of ribosome.
B mRNA is a copy of the information in a gene. Show Answer True. Show Answer False. How do complementary base pairs contribute to intramolecular base pairing within an RNA molecule? Nissen et al. Licenses and Attributions. CC licensed content, Shared previously. Short nucleotides , stable RNA with extensive intramolecular base pairing; contains an amino acid binding site and an mRNA binding site. The cytosol is filled with closely packed sheets of endoplasmic reticulum membrane studded with ribosomes.
At the bottom left is a portion of the nucleus and its nuclear envelope. Image courtesy of Prof. Orci University of Geneva, Switzerland.
Merging cultures in the study of membrane traffic. Nature Cell Biology 6 , doi Each mRNA dictates the order in which amino acids should be added to a growing protein as it is synthesized. In fact, every amino acid is represented by a three-nucleotide sequence or codon along the mRNA molecule.
Figure 7: The ribosome and translation A ribosome is composed of two subunits: large and small. During translation, ribosomal subunits assemble together like a sandwich on the strand of mRNA, where they proceed to attract tRNA molecules tethered to amino acids circles. A long chain of amino acids emerges as the ribosome decodes the mRNA sequence into a polypeptide, or a new protein.
Each tRNA molecule has two distinct ends, one of which binds to a specific amino acid, and the other which binds to the corresponding mRNA codon. During translation , these tRNAs carry amino acids to the ribosome and join with their complementary codons. Then, the assembled amino acids are joined together as the ribosome, with its resident rRNAs, moves along the mRNA molecule in a ratchet-like motion. The resulting protein chains can be hundreds of amino acids in length, and synthesizing these molecules requires a huge amount of chemical energy Figure 8.
Figure 8: The major steps of translation 1 Translation begins when a ribosome gray docks on a start codon red of an mRNA molecule in the cytoplasm. A second tRNA molecule, bound to two, connected amino acids, is attached to the 4 th , 5 th , and 6 th nucleotide from the left.
It no longer has amino acids bound to its terminus. In step 4, the tRNA molecule that formerly had two connected amino acids attached to its terminus, has now accumulated four amino acids total.
Different colored spheres represent different amino acid types, and the four spheres are connected end-to-end in a chain. A tRNA to the right has one amino acid attached to its terminus. A tRNA molecule carrying a single amino acid is shown approaching the ribosome from the cytoplasm. In step 5, the ribosome is shown to have moved along the length of the mRNA molecule from left to right. A long chain of approximately 19 amino acids is connected to the end of the tRNA molecule.
Five tRNA molecules carrying a single amino acid each are seen floating freely in the cytoplasm surrounding the mRNA molecule. In step 6, the ribosome is disassociated from the mRNA molecule. The amino acid chain has disassociated from the tRNA and is floating freely in the cytoplasm as a complete protein molecule.
The illustrated ribosome is translucent and looks like an upside-down glass jug. The mRNA is composed of many nucleotides that resemble pegs aligned side-by-side along the molecule, in parallel. Each type of nucleotide is represented by a different color yellow, blue, orange, or green.
The first three nucleotides, bound to the ribosome, are highlighted in red to represent the stop codon. In step 2, a tRNA molecule is bound to the stop codon. At the end of the tRNA molecule opposite this point of attachment is an amino acid, represented as a sphere. In step 3, a tRNA bound to a single amino acid is attached to the 7 th , 8 th , and 9 th nucleotide from the left.
In eukaryotic cells, however, the two processes are separated in both space and time: mRNAs are synthesized in the nucleus, and proteins are later made in the cytoplasm. This page appears in the following eBook. Aa Aa Aa. Ribosomes, Transcription, and Translation. Figure 1: DNA replication of the leading and lagging strand. The helicase unzips the double-stranded DNA for replication, making a forked structure. Figure 3: RNA polymerase at work. What Is the Function of Ribosomes?
This Escherichia coli cell has been treated with chemicals and sectioned so its DNA and ribosomes are clearly visible. Figure 7: The ribosome and translation. A ribosome is composed of two subunits: large and small.
Figure 8: The major steps of translation. Cellular DNA contains instructions for building the various proteins the cell needs to survive. In order for a cell to manufacture these proteins, specific genes within its DNA must first be transcribed into molecules of mRNA; then, these transcripts must be translated into chains of amino acids, which later fold into fully functional proteins.
Although all of the cells in a multicellular organism contain the same set of genetic information, the transcriptomes of different cells vary depending on the cells' structure and function in the organism. Cell Biology for Seminars, Unit 2. Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually.
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