Eukaryotic Cells & Organelles 2

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The Golgi Apparatus and Golgi Vesicles

The Golgi apparatus releases Golgi vesicles. Lysosomes are a special type of Golgi vesicle.

Structure of Golgi apparatus

The Golgi apparatus is a series of flattened membranous sacs.

Function of Golgi apparatus

Transport vesicles form at the endoplasmic reticulum and fuse with the Golgi apparatus.
The transport vesicles empty proteins and lipids into the lumen of the Golgi apparatus.
As the proteins and lipids travel through the Golgi, they are sorted, packaged and tagged so that they can be sent to the right place.

Structure of Golgi vesicles

Golgi vesicles are membrane-bound, fluid-filled vesicles located in the cytoplasm.
They are small, round and are seen in a high density near the edges of the sacs.
Lysosomes are a type of Golgi vesicle.

Function of Golgi vesicles

Golgi vesicles store and transport modified proteins and lipids from the Golgi apparatus to target cells.
Lysosomes are a special type of Golgi vesicle. They contain enzymes called lysozymes.
- Lysozymes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids and old organelles.

Ribosomes and the Endoplasmic Reticulum

Proteins are made in ribosomes. Proteins may then be folded and processed by the rough endoplasmic reticulum (RER). The smooth endoplasmic reticulum makes and processes lipids.

Structure of ribosomes

Ribosomes can be free floating in the cytoplasm or attached to the cytoplasmic side of the endoplasmic reticulum (ER).
Ribosomes are very small organelles made of protein subunits. This means that ribosomes are not covered by a membrane.

Function of ribosomes

Ribosomes are in charge of protein synthesis.
Protein synthesis is an essential function of all cells. This is why ribosomes are found in practically every cell.

Structure of the ER

The ER is a series of interconnected membranous sacs and tubules.
The membrane of the ER is a phospholipid bilayer embedded with proteins.
The smooth ER (SER) membrane has no ribosomes but the rough ER (RER) membrane has many ribosomes on its surface.

Function of the RER and SER

The RER is responsible for processing and folding proteins.
The SER is responsible for making and processing lipids.

Cell Wall and Cell Vacuole

The cell wall is a structure external to the plasma membrane. Cell vacuoles are found in plant cell cytoplasm.

Structure of cell walls

The cell wall is a rigid covering that protects the cell.
Plant, fungal and algal cells all have cell walls.
- The major organic molecule in fungal cell walls is chitin.
- Plant and algal cell walls are made of cellulose.
  - Cellulose is a polysaccharide made up of glucose units.

Function of cell walls

The cell wall provides structural support and gives shape to the cell.

Structure of cell vacuoles

Plant cells each have a large central vacuole that occupies most of the area of the cell.
These vacuoles are surrounded by a membrane called the tonoplast and contain a weak solution of salts and sugars called cell sap.
Cell vacuoles are found in the cytoplasm of plant cells but are NOT present in animal cells.

Function of cell vacuoles

The central vacuole allows the cell to remain rigid.
When the central vacuole holds more water, the vacuole pushes against the cell wall and pressure is maintained. This stops the plant from wilting.
The vacuole also isolates certain chemicals that are unwanted by the rest of the cell.