Eukaryotic Cells
Eukaryotes are much more complex than prokaryotes. Some of their key characteristics are:
- Eukaryotic cells are 10-100x larger than prokaryotic cells.
- Basic cell structure is very complex:
- Membranes found inside of the cells to hold organelles together: membrane bound organelles.
- Eukaryotic cells are often built into multicellular organisms. Example: Humans, any other animal/plant, fungi and protists.
Composition of an Animal Cell
![Image illustrating Eukaryotic Cells [Introduction for detailed courses]](https://d3rw207pwvlq3a.cloudfront.net/attachments/000/035/660/original/Picture3.png?1541570061)
Components of a Plant Cell
![Image illustrating Eukaryotic Cells [Introduction for detailed courses]](https://d3rw207pwvlq3a.cloudfront.net/attachments/000/035/661/original/Picture4.png?1541570125)
Ribosomes
Ribosomes are where proteins are produced inside cells by translating RNA into proteins.
- Made of one large subunit and one small subunit.
- Composed of proteins and ribosomal RNA (rRNA).
- Not surrounded by membrane.
- Exist in large quantities: thousands to millions of ribosomes per cell!
- Two subcategories of ribosomes:
- Free - they float around the cytosol of the cell;
- Bound - stuck to the side of the ER.
Adapted from photo by OpenStax / CC BY
Peroxisomes
- Present in plants and animals;
- Enclosed by a single membrane;
- Function is breakdown of fatty acids and amino acids, as well as detoxification.
- Takes electrons from molecules and produces H2O2 (hydrogen peroxide);
- H2O2 very toxic to cells, but destroyed by enzyme catalase.
Mitochondria and Chloroplasts
Organelles which are capable of growing and dividing (independent of the host cell) and contain their own DNA. These are called semi-autonomous organelles; there are two types:
- The mitochondria
- The chloroplast
Mitochondria
- Found in all eukaryotic cells.
- Surrounded by a double membrane with the intermembrane space between them.
- The inner membrane has a large surface area due to the presence of membrane folds called cristae.
- The inner membrane is the location of the electron transport chain which synthesizes ATP for the cell.
- The inner compartment is called the matrix.
Photo by Kelvinsong; modified by Sowlos / CC BY
Chloroplast
- Found in photosynthetic eukaryotic cells (e.g. plants).
- Surrounded by a double membrane.
- The inner compartment is called the stroma.
- In the stroma, there are stacks of membrane-bound disks called thylakoids;
- A stack of thylakoids is called a granum (grana is plural);
- Inside the thylakoid is the thylakoid lumen;
- The thylakoid membrane contains the photosynthetic machinery required for harvesting energy from the sun.
- CO2 fixation and sugar production occurs in the stroma.
Plant versus Animal Cells
Both plant and animal cells are eukaryotic. However, they have some key differences:
- Plant cells have chloroplasts, in addition to mitochondria.
- They contain a green pigment called chlorophyll that captures light.
- Plant cells have a cell wall:
- Provides rigidity, shape and protection;
- Composed of cellulose: a polysaccharide made up of glucose monomers.
- Only animal cells have lysosomes.
- This is where digestive processes occur;
- The plant cell equivalent is the vacuole.
Photo by ethan davison / CC BY
Vacuoles
We have three main types of vacuoles:
- Central vacuole
- Food vacuole
- Contractile vacuole
Their different roles are:
- Central vacuole: large, occupies most of the volume of mature plant and many fungal cells.
- Maintains proper pressure to support growing plants;
- Performs hydrolytic functions, stores wastes, toxins etc.
- Food vacuoles: contain phagocytosed food.
- Contractile vacuoles: present only in protists/algae, expels water out of cell.
