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Protein Synthesis in Prokaryotes

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  • 0:00 What Are Prokaryotes?
  • 1:13 Protein Synthesis:…
  • 2:44 Protein Synthesis: Translation
  • 4:40 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
In this lesson, we'll review what prokaryotes are first. Then, we'll explain the steps and process of protein synthesis in prokaryotes and discover what makes it unique from protein synthesis in other cells.

What Are Prokaryotes?

We tend to think of ourselves as individuals. You're only one living thing, right? Well, the truth is we're actually a whole ecosystem! Inside our bodies, particularly our digestive systems, live thousands of bacteria. Bacteria are a type of prokaryote, which is a word for single-celled organisms that don't have a nucleus, or a structure that holds their DNA. Some bacteria make us sick, like Streptococcus pyogenes, which causes strep throat. However, many bacteria live in our intestines without harming us, helping us break down food and regulate our metabolism.

Like all other living things, prokaryotes need proteins for structure and function. Proteins make up everything about us. They give cells structure, allow them to move, make energy, and join together to make multicellular organisms like us. Today, we're going to be looking at the process of making protein in prokaryotes, which is called protein synthesis. There are two main steps in protein synthesis: transcription and translation. Let's look at transcription first.

Protein Synthesis: Transcription

Transcription is the process of copying DNA, the master instructions for the cell, into another molecule called mRNA. DNA is like your birth certificate: it's very important for you, and you only get one original copy. When you apply for a job, you make a copy of your birth certificate for your employer to use. You don't give them the original. The same is true for cells. Cells don't want to move their DNA around all the time. So when they need the instructions to make protein, they make a copy of their DNA to use temporarily - mRNA. After they are done making the protein, your cell can get rid of the mRNA. If it needs to make the protein again, it can go make another copy.

In prokaryotes, transcription occurs in the cytoplasm, or the main compartment of the cell, which is made of a jelly-like substance. RNA polymerase is the protein that actually does the copying of DNA. DNA is one long strand in prokaryotes, but within that long strand are different sections called genes. Each gene codes for one protein.

In prokaryotes, genes are organized into groups called operons. These genes code for proteins that are used for a common function, like metabolizing the sugar lactose, so they're all grouped together. Think of it like organizing your kitchen cabinets. It makes sense to keep all the baking supplies together, since you're likely to need flour, sugar, and baking powder when you bake something.

Protein Synthesis: Translation

Before transcription is even completed, the cell starts to read the mRNA in the cytoplasm and make a protein during translation. Our human cells have to wait until transcription is over, but bacteria are speedy and start translation right away.

In this process, the ribosome, or protein factory, attaches to the mRNA. In prokaryotes, multiple ribosomes attach to the mRNA at once, since more than one gene is encoded on the mRNA in the operon. Each ribosome attaches at a ribosome binding site on the mRNA. This site tells the ribosome where to start making protein.

The ribosome reads the mRNA and tells another molecule, called transfer RNA (tRNA), to go get the building blocks for the protein, called amino acids. The first amino acid in a protein is always methionine. Prokaryotes also add a special group called a formyl group to the methionine, which is not added in other types of cells.

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