2.2: Cell Structure and Function

The organelles which make up cells (discussed in Topic 2.1) work together to perform complex functions and carry out the working processes of the eukaryotic cell. Topic 2.2 discusses some of these organelle functions, how they work together, and key differences between plant and animal cells.

Vocab List

Written Explanation

Protein Production Chain:

The production and export of proteins in cells is a long and complex process. Firstly, genetic information (DNA) is transferred out of the nucleus in the form of RNA. This information then goes into a ribosome, which translates the information into a fully formed polypeptide (protein). Outputted proteins are then either free floating in the cytoplasm, or are carried in a transport vesicle (vesicles that transport material within the cell). The transport vesicle deposits its materials (proteins in this case) into the golgi apparatus, which packages and processes the proteins. Lastly, secretory vesicles (vesicles that transport material out of the cell) take the proteins from the golgi apparatus and deposit them outside of the plasma membrane (a.k.a. cell membrane).

Diagram of the protein production chain

Chloroplasts:

Chloroplasts are organelles that produce energy for the cell via photosynthesis (more about that in Unit 3). They contain double membranes and have their own DNA and ribosomes. The inside of the chloroplast is called the stroma, and it contains components that actually carry out photosynthesis. These components are called granum (plural: grana). Grana are stacks of thylakoids, which are chlorophyll (a green pigment) covered sacks that absorb sunlight and convert it into chemical energy which the cell can store, much like a solar panel converts sunlight to electricity.

Diagram of a chloroplast

Mitochondria:

Mitochondria are organelles that produce energy for the cell via cellular respiration (more about that in Unit 3). Like the chloroplast, mitochondria have their own DNA and ribosomes, and are enclosed in a double membrane. The inside of the mitochondria is called the matrix. The shape of the inside includes many cristae (singular: crista), which are just folded structures.

Diagram of a mitochondrion (singular of mitochondria)

Plant vs. Animal cells:

Plant and animal cells are both eukaryotic (meaning they contain organelles). They are similar in most ways but differ in a few key areas. Firstly, plants have cell walls outside their membranes to provide more rigidity. There are pores in the cell walls called plasmodesmata that allow materials to flow between cells.

Diagram of a plant cell with a cell wall and plasmodesmata

Secondly, plant cells contain a large central vacuole, which is a sac that holds water. This sac both provides cell rigidity by putting pressure on the cell wall and stores water as needed.

Diagram of a "regular" vacuole in an animal cell next to a large central vacuole in a plant cell

Thirdly, plant cells contain chloroplasts in addition to mitochondria. As you might be able to tell, humans and other animals don't get energy from the sun, while plants do. Plant cells use chloroplasts more in the day, when the sun is present, and use mitochondria more when the sun is not.

Diagram showing mitochondria and chloroplasts in plant and animal cells

Lastly, plant cells do not contain centrosomes, centrioles, and lysosomes. Centrosomes and centrioles are components that help cells reproduce, and lysosomes are organelles that store enzymes to break down things.