Eukaryotic Cells [detailed]

Eukaryotic Cells

• 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

Components of a Plant Cell

Ribosomes

• 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.

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

• 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.

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

1. Plant cells have chloroplasts, in addition to mitochondria.
2. They contain a green pigment called chlorophyll that captures light.
3. Plant cells have a cell wall:
4. Provides rigidity, shape and protection;
5. Composed of cellulose: a polysaccharide made up of glucose monomers.
6. Only animal cells have lysosomes.
7. This is where digestive processes occur;
8. The plant cell equivalent is the vacuole.

Vacuoles

1. Central vacuole
2. Food vacuole
3. Contractile vacuole

• 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.