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Ribosomes and Mitochondria Study Guide

🗻 Big Picture: Get ready to learn about the functions of ribosomes (cell organelles that are the site of protein synthesis) and mitochondria (the powerhouse of your cells)!


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Introduction

Have you ever been having a fun day hanging out with your friends and started wondering what ribosomes and mitochondria are? Well, maybe not (unless you're us). Even so, they’re crucial to the processes of synthesizing protein and generating all of the energy you need to hang out with your friends in the first place! They might seem complicated, but we’re here to help you learn all about what they are, what they’re made of, and how they work. Let’s get started!

Lesson Objectives

  • Understand the different components that make up ribosomes and mitochondria.
  • Briefly understand the functions of ribosomes and mitochondria.

Ribosomes

Ribosomes are organelles composed of RNA molecules and protein that carry out the process of protein synthesis. Ribosomes are found both freely floating in the cytoplasm or bound to the Rough Endoplasmic Reticulum (rough ER), and the type of protein they produce depend on their location.

  • Detached ribosomes found freely floating in the cytoplasm translate mRNA to create proteins that will remain in the cytoplasm

  • Ribosomes attached to the rough ER generate proteins that will either become part of the membrane or be stored in a small cellular container called a vesicle.

  • Proteins that are to be moved out of the cell are also translated by ribosomes bound to the rough ER.

  • Ribosomes are found in both prokaryotic and eukaryotic cells, but they each use a slightly different process to produce proteins. Luckily, we can use these differences to our advantage. We’ve been able to create antibiotics that decimate infections while causing no harm to any human cells–a huge win for our battle against bacteria.

  • Unfortunately, some prokaryotes use these differences to their advantage too, such as the polio virus which is able to attack our translation mechanism and make us sick. While it generally causes mild flu-like symptoms like fever, fatigue, or nausea, in some severe cases it can cause more serious symptoms like paresthesia, meningitis, or even paralysis.

Ribosome Structure

As we mentioned before, ribosomes are composed of both RNA and proteins. About 37% to 62% of a ribosome is comprised of RNA, while proteins make up the remainder of its composition.

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Ribosomes are divided into two Subunits, one large and one small. When not synthesizing proteins, these two subunits remain unattached. During protein synthesis, the two units combine and work together as one to translate mRNA and form a polypeptide chain from amino acids which will eventually become a functional protein.

  • First, the Small Subunit binds to a single-stranded mRNA molecule. This mRNA provides the instructions for protein synthesis.

  • The small subunit then binds to the large subunit to create what looks like an mRNA sandwich–the large and small subunits on top and bottom and the mRNA in the middle.

  • With the instructions provided by the small subunit, the Large Subunit is able to link together amino acids to form a polypeptide chain. This chain will be released into the cytoplasm where it will fold into its final form as a protein.

  • Prokaryotic and eukaryotic ribosomes differ not only in their process of synthesizing proteins, they also differ in size. Prokaryotes have 70S ribosomes made up of 30S and 50S subunits, while eukaryotes have 80S ribosomes made up of 40S and 60S subunits.

Ribosome Functions

Translate instructions on how to produce a protein from a strand of messenger mRNA from the nucleus.

Synthesize a polypeptide chain by linking together amino acids that are collected from the cytoplasm by transfer ribonucleic acid (tRNA) in a process called peptidyl transfer.

Export the polypeptide chain into the cytoplasm where it will become a new, functional protein in a process called peptidyl hydrolysis.


💡 Ribosome Summary

  • Ribosomes are organelles composed of both RNA and proteins that carry out the process of protein synthesis.

  • Ribosomes either float freely in the cytoplasm or attach to the endoplasmic reticulum; the location of a ribosome determines how the protein it synthesizes will be used.

  • Ribosomes are composed of two subunits, one large and one small.

  • The small subunit binds to mRNA and translates its instructions for protein synthesis.

  • The large subunit synthesizes polypeptide chains based on the mRNA’s instructions.

  • The three main functions of a ribosome are the translation, synthesis, and exportation of proteins.


Mitochondria

Mitochondria are membrane-bound organelles that generate most of the energy a cell uses to function (if you’ve heard it once, you’ve heard it a thousand times–the mitochondria is the powerhouse of the cell 💪). They look like lima beans with ribbon twisted back and forth inside, and are found floating freely throughout the cytoplasm.

Two of the four steps that occur during aerobic cellular respiration (the process by which energy is generated in the cell) occur in the mitochondria: the Krebs Cycle (or citric acid cycle) and Oxidative Phosphorylation.

  • In the Krebs cycle__, the mitochondria modifies acetyl CoA to produce precursors for the next step in cellular respiration–oxidative phosphorylation.

  • In oxidative phosphorylation, electrons from the precursors from the citric acid cycle are used to produce NADH which is then used by enzymes found in the mitochondrial inner membrane to generate ATP–a form of energy stored in chemical bonds.

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Mitochondria Structure

The four distinct parts of mitochondria are the outer membrane, the intermembrane space, the inner membrane, and the mitochondrial matrix.

  • The Outer Membrane is the gateway to a mitochondrion. It contains protein channels called porins that allow the movement of ions and molecules in and out of the organelle, and is similar in both structure and composition to the plasma membrane of a cell.

  • The Inner Membrane contains many components of the electron transport chain along with multiple other enzymes and coenzymes. Transporters such as proton pumps and permease proteins also exist in the inner membrane and regulate the transport of molecules such as phosphate, ADP, and ATP into and out of the matrix.

  • The Intermembrane Space sits between the inner and outer membranes and contains the enzymes responsible for citric acid cycle reactions.

  • The Mitochondrial Matrix is a gel-like material found within the inner membrane of the mitochondria, and is where the citric acid cycle takes place. It contains ribosomes to produce proteins used by the organelle as well as mitochondrial DNA.

Mitochondria Functions

Energy Conversion – the primary function of the mitochondria is to supply energy. It produces ATP, the cell’s energy currency that drives cellular mechanisms.

Calcium Storage –the mitochondria maintain the ideal concentration of calcium ions for the cell by absorbing calcium ions until they are needed.

Programmed Cell Death –when cells become old or cease to function, they undergo a process of programmed cell death called Apoptosis. Mitochondria assist with this process by deciding which cells need to be destroyed.

Additional Functions –heat production, steroid synthesis, hormone signaling, cellular metabolism regulation, etc.


💡 Mitochondria Summary

  • Mitochondria are membrane bound organelles primarily responsible for the generation of energy within a cell.

  • Both the Krebs cycle and oxidative phosphorylation occur in the mitochondria.

  • The mitochondria is formed by 4 distinct parts: the outer membrane, the intermembrane space, the inner membrane, and the mitochondrial matrix.

  • The outer membrane regulates the movement of ions and molecules in and out of the mitochondria via porins.

  • The inner membrane contains components of the electron transport chain and transporters such as proton pumps and permease proteins.

  • The intermembrane space exists between the inner and outer membrane and contains the enzymes responsible for the citric acid cycle.

  • The mitochondrial matrix is found within the inner membrane and is where the citric acid cycle takes place.

  • Energy conversion, calcium storage, and apoptosis are all functions of the mitochondria.


FAQs

1. What is a ribosome?

A ribosome is an organelle composed of RNA molecules and proteins that carries out the process of protein synthesis.

2. Where are ribosomes located?

Ribosomes are either freely floating in the cytoplasm or attached to the rough ER.

3. What are the functions of ribosomes?

Ribosomes translate mRNA, synthesize polypeptide chains, and export them into the cytoplasm where they will become a fully functional protein.

4. What are mitochondria?

Mitochondria are membrane-bound organelles that generate the energy necessary for a cell to function.

5. What are the functions of mitochondria?

Mitochondria are responsible for energy conversion, calcium storage, programmed cell death, and additional functions such as heat production, steroid synthesis, hormone signalling, cellular metabolism, etc.

6. What is the structure of mitochondria?

Mitochondria are composed of an outer membrane, intermembrane space, inner membrane, and mitochondrial matrix.

7. Why is mitochondria called the powerhouse of a cell?

Mitochondria are called the powerhouse of the cell because they produce the majority of the energy we need to survive. They do this through the process of energy conversion in which they produce ATP–the molecule that drives cellular mechanisms.

8. How do mitochondria and ribosomes work together?

Ribosomes are the site or place where protein synthesis takes place. Thus mitochondrial ribosomes or mitoribosomes synthesize proteins inside Mitochondria, which are regulated by the genes found in mtDNA (mitochondrial DNA).

We hope you enjoyed studying this lesson and learned something cool about Mitochondria and Ribosomes! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our App and experience our fun VR classrooms - we promise, it makes studying much more fun 😎

Sources:

  1. The Editors of Encyclopaedia Britannica. “Ribosome | Cytology.” Encyclopædia Britannica, 2019, www.britannica.com/science/ribosome. Accessed 10 Nov 2021.

  2. Khan Academy. “Nucleus and Ribosomes.” Khan Academy, 2018, www.khanacademy.org/science/biology/structure-of-a-cell/prokaryotic-and-eukaryotic-cells/a/nucleus-and-ribosomes. Accessed 10 Nov 2021.

  3. “Mitochondrion - Role in Disease.” Encyclopedia Britannica, www.britannica.com/science/mitochondrion/Role-in-disease. Accessed 10 Nov 2021.

  4. British Society for Cell Biology. (2019). Ribosome | British Society for Cell Biology. Bscb.org. https://bscb.org/learning-resources/softcell-e-learning/ribosome/

  5. Gahl, W. (2019). Mitochondria. Genome.gov. https://www.genome.gov/genetics-glossary/Mitochondria

  6. Microscope Master. (2019). Ribosomes - Definition, Structure, Size, Location and Function. MicroscopeMaster. https://www.microscopemaster.com/ribosomes.html

  7. Mitochondrion – much more than an energy converter | British Society for Cell Biology. (2019). Bscb.org. https://bscb.org/learning-resources/softcell-e-learning/mitochondrion-much-more-than-an-energy-converter/

  8. Newman, T. (2018, February 8). Mitochondria: Form, function, and disease. Www.medicalnewstoday.com. https://www.medicalnewstoday.com/articles/320875#function