Function
Translation is the name of the process our cells use to make proteins. Ribosomes are the organelles that can take a copy of our genetic material and translate it into a protein. The original genetic material is DNA, and it is stored in the cell's nucleus. When a specific protein is needed, our cells make a copy of the DNA. This copy is also RNA, but it is called messenger RNA, or mRNA. Thus, ribosomes translate mRNA into protein.
To make a protein, ribosomes link together amino acids. The mRNA has the specific order in which the amino acids must be joined, and each protein has a different order of amino acids. The small subunit of rRNA can read the order of amino acids. Linking amino acids together is the function of the rRNA in the large subunit of the ribosome.
Sequence
rRNA Subnits
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The sequence of rRNA is highly complex and derived from multiple genes. The table summarizes the components of the large and small subunit rRNA. Sedimentation rate (S) of the subunit is affected by the size of each subunit. As you can see, the large subunit of rRNA is made of two smaller pieces, while the small subunit is only one piece. The structure of the small subunit of eukaryotic rRNA has been discovered.
Synthesis
All RNA molecules are created by transcription, or making a copy of DNA. The protein that makes a copy of DNA is RNA polymerase. This protein is an enzyme that can read DNA and make an RNA copy. Transcription starts when the RNA polymerase enzyme binds DNA at a specific location called a promoter. Promoters are found 'upstream' of a gene. RNA polymerase reads the DNA in only one direction and continues reading and creating RNA until it reaches the end of the gene. The end of the gene has a special region called a stop codon. This region literally signals the RNA polymerase enzyme to stop copying the DNA.
Importance
Ribosomal RNA characteristics are important in medicine. Both prokaryotes (single-celled organisms, like bacteria) and eukaryotes (organisms whose cells have a nucleus and organelles, like the cells in our bodies) have ribosomes with rRNA. Prokaryotes and eukaryotes differ in the size and sequence of the rRNA in each subunit. Modern medicine exploits this difference using antibiotics. Therefore, rRNA is the target of several antibiotics, including chloramphenicol, erythromycin, and streptomycin.
Ribosomal RNA characteristics are also important in science. We can use rRNA to decide how closely related two species may be. This is because all cells have rRNA and, more importantly, rRNA sequence is specific for each species. How do scientists do this? They find out the rRNA sequence from one organism and compare it to the same type of rRNA sequence of another organism. They are looking for sequence homology, or how alike the sequences are. The more sequence homology between the rRNA, the more related the two organisms.
Lesson Summary
Let's review! Ribonucleic acids (RNA) are a group of large molecules that have many different roles, like coding, decoding, regulation, and expression of our genes. RNA is created by transcription, or making a copy of DNA. RNA polymerase is the protein that makes the copy of DNA.
Ribosomal RNA (rRNA) is part of the ribosome, or protein builders, of the cell. Ribosomes are responsible for translation, or the process our cells use to make proteins. rRNA are responsible for reading the order of amino acids and linking amino acids together. They do this through a highly complex sequence.
rRNA is important to modern medicine, especially in the area of antibiotics. Additionally, science uses rRNA to discover how closely organisms are linked together through studying the rRNA sequence.
Recap of Bolded Terms
| Ribonucleic acids (RNA) |
a group of large molecules that have many different roles in the coding, decoding, regulation, and expression of our genes |
| Ribosomal RNA (rRNA) |
part of the ribosome |
| Ribosome |
the protein builder of the cell |
| Translation |
the process our cells use to make proteins |
| RNA |
ribonucleic acids |
| Transcription |
the process of making a copy of DNA |
| RNA polymerase |
protein is an enzyme that can read DNA and make an RNA copy |
| Stop codon |
a special region at the end of the gene |
| Prokaryotes |
single-celled organisms like bacteria |
| Eukaryotes |
organisms whose cells have a nucleus and organelles |
| Sequence homology |
refers to the 'alikeness' of the sequences |
Learning Outcomes
Once you've finished with this lesson on rRNA, you should have the ability to:
- Define ribonucleic acids (RNA)
- Indicate the function of ribosomal RNA (rRNA)
- Recall the functions of the small and large subunits of rRNA
- Summarize translation and transcription
- Explain the importance of rRNA in modern medicine and in science
