Cell Inclusions - Online Tutor, Practice Problems & Exam Prep

Cell inclusions are cytoplasmic molecular aggregates with diverse structures and functions. Common types include storage granules for energy reserves, carboxysomes for carbon fixation, gas vesicles for buoyancy control, and magnetosomes for orientation with Earth's magnetic field. Storage granules, such as carbon and sulfur granules, serve as reservoirs for essential nutrients. Understanding these inclusions is crucial for grasping cellular metabolism and microbial ecology.

Cell Inclusions

In this video, we're going to begin our lesson on cell inclusions. And so inclusions are defined as cytoplasmic molecular aggregates, or in other words, aggregates of molecules in the cytoplasm. And they can be very diverse in both their structure as well as their function. And we'll be able to talk about some of the different types of inclusions down below in this table. Now, some inclusions are stored as insoluble granules, whereas others are enveloped by proteins, a lipid membrane, or both proteins and a lipid membrane. Now granules are defined as small particles that are barely visible by a microscope. And in many cases, granules are referring to vesicles, small little lipid bubbles. Now, down below in this table, once again, we have a bunch of different types of inclusions. This does not include all of the different types of inclusions. It only contains some of the more common types of inclusions that are usually tested on by microbiology professors. And so, notice that we have the inclusion type over here on the far left, and the function over here in the middle, and then a corresponding image on the far right. So the first type of inclusion that we have are the storage granules, which are granules that are used for storage purposes. Almost like a kitchen pantry in a way where you can store items in your kitchen pantry for use at a later time whenever you need it. And so, you can see here that storage granules are aggregates of large polymers that are in excess inside the cell. And so when the cell has a lot of a particular type of molecule, it can store it as these storage granules. And then later at a different time, if that molecule starts to get low, then they can use the storage granules as a source to be able to get more. And so there are many types of storage granules, including carbon granules, which are going to be storing carbon to be used later as an energy source. There are also polyphosphate granules, which are going to be storing phosphate groups, inorganic phosphate groups for later use in biosynthesis to make things like nucleotides and stuff like that. There are also sulfur granules, which are going to be storing sulfur in bacteria that actually use sulfur to generate energy. And so you can see over here, these little bubbles that are inside of the cells represent storage granules that can be inside of cells. Now the next type of inclusion that we have are carboxysomes. And carboxysomes have CO₂ fixing enzymes that are going to be enveloped by a protein shell. And carboxysomes serve as the location of carbon fixation in many bacteria. Now the next type of inclusion that we have are gas vesicles. And as their name implies, these are going to be gas particles enveloped by a protein shell, so they're going to contain gas. And these gas vesicles help to control the cell's buoyancy, which is really just the ability to float in aquatic environments. And so, this buoyancy control allows them to change their elevation within an aquatic environment to get to an area that has more light or more nutrients or less light and more nutrients. Gas vacuoles are basically just groups of gas vesicles in the cell. And so the gas vacuoles are a little bit larger than the gas vesicles themselves. And last but not least, the final type of inclusion that we have here in this table are the magnetosomes. And the magnetosomes are intracellular chains of iron-containing molecules that are enclosed within a membrane. And so, these magnetosomes are used by the cells to orient themselves with the earth's magnetic field. And so here in this image, you can notice there is this chain of these iron-containing molecules, and they help to orient the entire cell with respect to the earth's magnetic field so that the bacteria can have a sense of direction of what is up and what is down and things of that nature. And so this here concludes our brief lesson on cell inclusions. And we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Which of the following statements about gas vesicles is TRUE?

• A. Bacteria use them to align with the Earth's magnetic field.
• B. They store phosphate molecules as granules.
• C. They are used to control the cell's buoyancy in aquatic environments.
• D. They are the site of Carbon fixation.
• E. None of the above are true.

Which of the following inclusion bodies contain iron?

• A. Gas vesicles
• B. Magnetosome
• C. Storage granules
• D. Carboxysomes

Here’s what students ask on this topic:

What are cell inclusions and why are they important?

Cell inclusions are cytoplasmic molecular aggregates found within cells. They can vary widely in structure and function, serving as storage sites for essential nutrients, aiding in cellular processes, and helping cells adapt to their environment. For example, storage granules store excess nutrients like carbon and sulfur, which can be used later for energy or biosynthesis. Carboxysomes contain enzymes for carbon fixation, crucial for photosynthetic bacteria. Gas vesicles help control buoyancy in aquatic environments, and magnetosomes allow bacteria to orient themselves with Earth's magnetic field. Understanding cell inclusions is vital for comprehending cellular metabolism and microbial ecology.

What are storage granules and what types are there?

Storage granules are a type of cell inclusion used to store excess molecules within the cell for later use. They act like a pantry, storing essential nutrients that can be accessed when needed. Common types of storage granules include carbon granules, which store carbon for energy; polyphosphate granules, which store inorganic phosphate for biosynthesis; and sulfur granules, which store sulfur for energy production in certain bacteria. These granules help cells manage resources efficiently, ensuring they have access to vital nutrients during periods of scarcity.

How do gas vesicles function in bacterial cells?

Gas vesicles are cell inclusions that contain gas and are enveloped by a protein shell. They play a crucial role in controlling the buoyancy of bacterial cells in aquatic environments. By adjusting the amount of gas within these vesicles, bacteria can change their elevation in the water column. This allows them to move to areas with optimal light or nutrient conditions. Gas vacuoles, which are larger structures composed of multiple gas vesicles, further aid in this buoyancy control, helping bacteria to thrive in varying environmental conditions.

What are magnetosomes and how do they help bacteria?

Magnetosomes are cell inclusions composed of intracellular chains of iron-containing molecules enclosed within a membrane. They help bacteria orient themselves with Earth's magnetic field, providing a sense of direction. This orientation allows bacteria to navigate their environment more effectively, often moving towards favorable conditions such as optimal oxygen levels. The ability to align with the magnetic field is particularly useful for magnetotactic bacteria, which thrive in specific microenvironments. Understanding magnetosomes is important for studying microbial navigation and behavior.

What role do carboxysomes play in bacterial cells?

Carboxysomes are cell inclusions that contain CO₂-fixing enzymes enveloped by a protein shell. They serve as the site of carbon fixation in many bacteria, particularly those involved in photosynthesis. The enzymes within carboxysomes convert CO₂ into organic compounds, which are then used for cellular growth and energy. This process is essential for autotrophic bacteria, which rely on carbon fixation to produce the organic molecules necessary for their survival. Carboxysomes thus play a critical role in the global carbon cycle and microbial ecology.