biology

Ribosome biogenesis

Ribosome biogenesis is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ribosome biogenesis rather than just read about it. In short: Ribosome biogenesis is the process of making ribosomes. In prokaryotes, this process takes place in the cytoplasm with the transcription of many ribosome gene operons.

Key takeaways

Ribosome biogenesis belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ribosome biogenesis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ribosome biogenesis from memory before moving on to harder problems.

Reference excerpt

Ribosome biogenesis is the process of making ribosomes. In prokaryotes, this process takes place in the cytoplasm with the transcription of many ribosome gene operons. In eukaryotes, it takes place both in the cytoplasm and in the nucleolus. It involves the coordinated function of over 200 proteins in the synthesis and processing of the three prokaryotic or four eukaryotic rRNAs, as well as assembly of those rRNAs with the ribosomal proteins. Most of the ribosomal proteins fall into various energy-consuming enzyme families including ATP-dependent RNA helicases, AAA-ATPases, GTPases, and kinases. About 60% of a cell's energy is spent on ribosome production and maintenance. Ribosome biogenesis is a very tightly regulated process, and it is closely linked to other cellular activities like growth and division. Some have speculated that in the origin of life, ribosome biogenesis predates cells, and that genes and cells evolved to enhance the reproductive capacity of ribosomes.

Ribosomes Ribosomes are the macromolecular machines that are responsible for mRNA translation into proteins. The eukaryotic ribosome, also called the 80S ribosome, is made up of two subunits – the large 60S subunit (which contains the 25S [in plants] or 28S [in mammals], 5.8S, and 5S rRNA and 46 ribosomal proteins) and a small 40S subunit (which contains the 18S rRNA and 33 ribosomal proteins). The ribosomal proteins are encoded by ribosomal genes.

Prokaryotes There are 52 genes that encode the ribosomal proteins, and they can be found in 20 operons within prokaryotic DNA. Regulation of ribosome synthesis hinges on the regulation of the rRNA itself. First, a reduction in aminoacyl-tRNA will cause the prokaryotic cell to respond by lowering transcription and translation. This occurs through a series of steps, beginning with stringent factors binding to ribosomes and catalyzing the reaction:GTP + ATP → pppGpp + AMP The γ-phosphate is then removed and ppGpp will bind to and inhibit RNA polymerase. This binding causes a reduction in rRNA transcription. A reduced amount of rRNA means that ribosomal proteins (r-proteins) will be translated but will not have an rRNA to bind to. Instead, they will negatively feedback and bind to their own mRNA, repressing r-protein synthesis. Note that r-proteins preferentially bind to their complementary rRNA if it is present, rather than mRNA. The ribosome operons also include the genes for RNA polymerase and elongation factors (used in RNA translation). Regulation of all of these genes at once illustrate the coupling between transcription and translation in prokaryotes.

Eukaryotes Ribosomal protein synthesis in eukaryotes is a major metabolic activity. It occurs, like most protein synthesis, in the cytoplasm just outside the nucleus. Individual ribosomal proteins are synthesized and imported into the nucleus through nuclear pores. See nuclear import for more about the movement of the ribosomal proteins into the nucleus. The DNA is transcribed, at a high speed, in the nucleolus, which contains all 45S rRNA genes. The only exception is the 5S rRNA which is transcribed outside the nucleolus. After transcription, the rRNAs associate with the ribosomal proteins, forming the two types of ribosomal subunits (large and small). These will later assemble in the cytosol to make a functioning ribosome. See nuclear export for more about the movement of the ribosomal subunits out of the nucleus.

Processing Eukaryotic cells co-transcribe three of the mature rRNA species through a series of steps. The maturation process of the rRNAs and the process of recruiting the r-proteins happen in precursor ribosomal particles, sometimes called pre-ribosomes, and takes place in the nucleolus, nucleoplasm, and cytoplasm. The yeast, S. cerevisiae is the eukaryotic model organism for the study of ribosome biogenesis. Ribosome biogenesis starts in the nucleolus. There, the 35S pre-RNA is transcribed from ribosomal genes as a polycistronic transcript by RNA polymerase I and processed into the 18S, 5.8S, and 25S subunits of the rRNA. Transcription of polymerase I starts with a Pol I initiation complex that binds to the rDNA promoter. The formation of this complex requires the help of an upstream activating factor or UAF that associates with TATA-box binding protein and the core factor (CF). Together the two transcription factors allow the RNA pol I complex to bind with the polymerase I initiation factor, Rrn3. As the pol I transcript is produced, approximately 75 small nucleolar ribonucleoparticles (snoRNPs) facilitate the co-transcriptional covalent modifications of >100 rRNA residues. These snoRNPs control 2'-O-ribose methylation of nucleotides and also assist in the creation of pseudouridines. At the 5' end of rRNA transcripts, small subunit ribosomal proteins (Rps) and non-ribosomal factors assemble with the pre-RNA transcripts to create ball-like knobs. These knobs are the first pre-ribosomal particles in the small (40S) ribosomal subunit pathway. The rRNA transcript is cleaved at the A2 site, and this separates the early 40S pre-ribosome from the remaining pre-rRNA that will combine with large subunit ribosomal proteins (Rpl) and other non-ribosomal factors to create the pre-60S ribosomal particles.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Ribosome biogenesis

Start with the simplest possible case. Write down what Ribosome biogenesis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ribosome biogenesis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ribosome biogenesis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ribosome biogenesis

In research: Ribosome biogenesis appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ribosome biogenesis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ribosome biogenesis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cellular processes, Ribosome, so understanding it makes those chapters shorter.
In everyday life: Look for Ribosome biogenesis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Ribosome biogenesis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ribosome biogenesis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ribosome biogenesis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ribosome biogenesis in simple terms?

Ribosome biogenesis is the process of making ribosomes. In prokaryotes, this process takes place in the cytoplasm with the transcription of many ribosome gene operons.

Why does Ribosome biogenesis matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ribosome biogenesis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ribosome biogenesis.