Shapes of All the Parts of an Animal Cell

Prokaryotes and Eukaryotes

• Animal cells are distinct from plant, archaea and bacteria cells. Animals and plants are eukaryotes. Bacteria and archaea are prokaryotes. Prokaryotes are simple, without interior membrane subdivisions called organelles. Eukaryotes are more complex cells that have organelles and sometimes a nucleus. Many prokaryotes and eukaryotes have a cell wall, a layer that surrounds the entire cell. Bacteria cells have many shapes but are often simply shaped into sausage-like shapes or spirals and have no rigid internal support like animal cells. In addition, animal sperm cells and some prokaryotes have flagella, thread-like protuberances that act in locomotion for the cell.

Animal and Plant Cells

• Animal and plant cells are eukaryotes. Eukaryotes have cell structures called organelles with specialized functions. The major difference between plant and animal cells is the presence of a cell wall comprised of cellulose. Plants have a cell wall; animals do not. Animals also do not have chloroplasts, which function as photosynthetic organelles in plants and algae.

Animal Cell Organelles

• Animal cells parts can be separated into four major types: structural elements, plasma membrane and endomembrane system organelles, energy-producing organelles, and sites of gene expression. Structural elements provide support and locomotion. The plasma membrane and endomembrane system provide most of the functions of the cell. Mitochondria are organelles that produce energy in animals. Within several of these organelles lie structures that assist in gene expression.

Animal Structural Elements

• Structural elements for animals include the cytoskeleton, flagella and cilia. The cytoskeleton is a network of protein filaments that give structure to the cell and move the cell. Flagella and cilia are threadlike extensions outside of the cell body that that provide motility for the cell or move fluid across the cell surface. The human eyelash is comprised of cilia.

Animal Plasma Membrane and Endomembrane System

• The plasma membrane and endomembrane system include the endoplasmic reticulum, the nucleus, the golgi complex, lysosomes and peroxisomes. The endoplasmic reticulum is a network of internal membranes surrounding the nucleus that form compartments and vesicles and participate in protein and lipid synthesis. It is comprised of smooth and rough types. Rough endoplasmic reticulum is studded with ribosomes. The nucleus is usually spherical, surrounded by a double membrane containing chromosomes that is the control center of the cell and is one of two sites of DNA in the animal cell. The golgi complex is outside of the endoplasmic reticulum in the shape of a stack of flattened vesicles resembling pancakes that package proteins. Lysosomes are free-floating vesicles derived from the golgi complex that digest decaying organelle matter. Peroxisomes are free-floating vesicles formed by the endoplasmic reticulum that contain enzymes that carry out various cellular reactions.

Animal Energy-Producing Organelles

• Mitochondria are organelles that produce energy in animals. In plants and algae, energy is produced by chloroplasts. Mitochondria are bacteria-like in their shape. They are sausage shaped with a double membrane that are the sites of oxidative metabolism and produce adenosine triphosphate for cellular energy. Mitochondria's membrane is bent into many folds, called christae. The mitochondrion has an internal matrix, an intermembrane space between the christae and the membrane, and is one of two sites of DNA in the animal cell.

Animal Gene Expression

• The process of gene expression in animals is carried out by a number of structures: chromosomes, the nucleolus and ribosomes. Chromosomes are long thread-like pieces of DNA that contain hereditary information and often form x-shaped pieces of protein. The nucleolus is the command center, functionally and physically, of the cell and nucleus where ribosomes are produced. Ribosomes are small dots on the surface of the rough endoplasmic reticulum. Ribosomes are complexes of protein.