Parts of the Cell

Cytosol

The cytosol is the portion of the cytoplasm not contained within membrane-bound organelles. Cytosol makes up about 70% of the cell volume and is composed of water, salts and organic molecules. The cytosol also contains the protein filaments that make up the cytoskeleton, as well as soluble proteins and the cell's organelles.

Nucleoli

The nucleolus is a small, dark staining body within the cell's nucleus. The nucleolus is the site where the large and small subunits of ribosomes are assembled.

Centrioles

Centrioles are paired cylindrical bodies each composed of nine triplets of microtubules. During mitosis centrioles organize to form the spindles and asters. They also form the bases of cilia and flagella.

Microfilaments

Part of the cytoskeleton. Microfilaments are fine filaments made of the contractile protein actin.

Lysosomes

Spherical membranous sacs containing digestive enzymes. Sites of intracellular digestion.

Mitochondria

The cellular powerhouse, mitochondria are rodlike, double membrane structures. The inner membrane is folded into projections called "cristae." Mitochondria are the sites of ATP synthesis.

Cytoskeleton

The cytoskeleton is an elaborate network of rods running throughout the cytosol. The cytoskeleton suports cellular structures and generates various cell movements.

Cytoplasm

Cytoplasm is the region between the nuclear and plasma membranes. It is a gel-like substance residing within the cell membrane holding the organelles, outside the nucleus. In addition to the organelles, it contains cytosol and inclusions (small particles of insoluble substances suspended in the cytosol).

Rough Endoplasmic Reticulum

Membrane system enclosing a cavity called the cisterna, that coils through the cytoplasm. Externally studded with ribosomes, which give it the "rough" appearance. Its ribosomes make all proteins that are exported from the cell; also make the integral proteins and phospholipid molecules of the cell's membranes. Can be considered the cell's membrane factory.

Intermediate Filaments

Part of the cytoskeleton. Intermediate filaments are protein fibers that are the stable cytoskeleton elements. They resist tension forces acting on the cell.

Microtubules

Part of the cytoskeleton. Microtubules are cylindrical structures made of tubulin proteins. They support the cell and give it shape and are involved in cellular and intracellular movements. Microtubules also form centrioles.

Ribosomes

Ribosomes are the assembly line of the manufacturing plant. They are the site of protein synthesis, producing proteins for cellular or extracellular use. Ribosomes are small, dark staining granules. They are not surrounded by a membrane, but are constructed of proteins plus ribosomal RNA. Each ribosome consists of two subunits that fit together. Ribosomes can float freely within the cytosol or be attached to the membranes of the rough ER. Free ribosomes make soluble proteins that function within the cytosol; ribosomes attached to the rough ER make proteins that become part of the cell membrane or are exported out of the cell.

Nucleus

The nucleus is surrounded by the nuclear envelope. It contains fluid nucleoplasm, nucleoli and chromatin. The nucleus is the control center of the cell. It transmits genetic information and provides instructions for protein synthesis.

Plasma Membrane

The outer cell membrane is called the plasma membrane. The structure of the plasma membrane can be described as a fluid mosaic model composed of a lipid bilayer with protein molecules dispersed throughout.

The Cell

Think of the cell as a manufacturing plant. The cell, like a manufacturing plant, has many divisions with specific functions. These functions are carried out by subunits, called organelles.

Peroxisomes

Toxic waste removal system of the manufacturing plant. Peroxisomes are small, membrane-walled sacs that look like small lysosomes. They contain enzymes, most importantly oxidases and catalases. Oxidases neutralize free radicals and catalases break down hydrogen peroxide.

Golgi Apparatus

A stack of smooth membrane sacs close to the nucleus. The golgi apparatus sorts, processes and packages the proteins and membranes made by the rough ER.

Chromatin

Chromatin is a granular, threadlike material composed of DNA and histone proteins. Chromatin is found within the nucleus of the cell.

Smooth Endoplasmic Reticulum

Continuous with the rough ER. Membranous system of sacs and tubules, free of ribosomes. Site of lipid and steroid synthesis, lipid metabolism, drug detoxification. Most cell types have little smooth ER.

Microvilli

Microvilli are cellular membrane protrusions that increase the surface area of the cell and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion.