What Is A Cell? Basic Overview Of An Animal Cell

Cells Are The Fundamental Basis Of All Organisms

May 23, 2009

Eukaryotic Cell, Wenche Eikrem and Jahn Throndsen

All organisms are made up of cells. There are single-celled and multi-celled organisms. Here is a brief overview of what a cell consists of, and some of its functions.

There are two cell types, prokaryotic and eukaryotic cells. Prokaryotic cells are simple and only found in bacteria and archaea (various single-celled prokaryotes genetically distinct from bacteria). Eukaryotic cells are much more complex and found in all animals (including humans), plants, protists (eg: protozoans, eukaryotic algae, and slime molds) and fungi.

The Difference Between Prokaryotic and Eukaryotic Cells

Both prokaryotic and eukaryotic cells contain a plasma membrane, organelles and chromosomes, but in a eukaryotic cell, the chromosomes are inside a nucleus. Prokaryotic cells lack a nucleus and instead have DNA (deoxyribonucleic acid) stored in a nucleoid.

While a nucleus has a membrane surrounding it, the nucleoid of the prokaryote has no membrane to separate it from the rest of the cell. Eukaryotic cells are approximately 10 times larger then prokaryotic cells, and are much more complex.

Overview of a Eukaryotic Animal Cell

An animal (e.g., human) cell contains many organelles (“tiny organs”) that all have specific functions that facilitate the cells metabolic function.

Nucleus: within the nucleus are the:

Chromatin: which consists of DNA and proteins
Nucleolus: an organelle involved in production of ribosomes (a nucleus can have several nucleoli)
Nuclear envelope: a membrane enclosing the nucleus

Cytoplasm: substance between the cell membrane and the nucleus
Ribosomes: organelles that make proteins
Golgi apparatus: synthesizes, sorts and secretes cell products
Plasma membrane: a membrane that encloses the cell, providing a barrier but allowing oxygen, nutrients and waste to pass through
Mitochondrion: cell respiration occurs and ATP (adenosine triphosphate, a type of energy) is made
Lysosome: the digestive organelle
Endoplasmic reticulum/ER (rough and smooth ER): membranous sacs and tubes that perform membrane synthesis
Flagellum: locomotory organelle present in some animal cells
Centrosome: initiation of cell microtubules
Perioxisome: specialized metabolic functions. Produces hydrogen peroxide
Microvilli: Projection, which increases surface area of the cell
Cytoskeleton: contains microfilaments, intermediate filaments and microtubules, all of which reinforce the cell’s shape and plays a part in cell movement

Overview of a Eukaryotic Plant Cell

Plant cells are also eukaryotic and contain many organelles with specific functions. Plant cells differ from animal cells, but many organelles are the same.

Nucleus: within the nucleus are the Chromatin, Nucleolus and Nuclear envelope
Ribosomes: organelles that make proteins
Central vacuole: a prominent organelle found in older plant cells. Used for storage and breakdown of waste products
Tonoplast: the membrane that encloses the central vacuole
Golgi apparatus: synthesizes, sorts and secretes cell products
Plasma membrane: a membrane that encloses the cell, providing a barrier but allowing oxygen, nutrients and waste to pass through
Chloroplasts: photosynthetic organelle that converts energy from sunlight into chemical energy
Plasmodesmata: channels through the cell wall that connect the cytoplasm of adjacent cells
Cytoplasm: substance between the cell membrane and the nucleus
Cell wall: an outer layer that protects the cell from mechanical damage and holds the cell’s shape
Mitochondrion: cell respiration occurs and ATP (adenosine triphosphate, a type of energy) is made
Endoplasmic reticulum/ER (rough and smooth ER): membranous sacs and tubes that perform membrane synthesis
Centrosome: initiation of cell microtubules
Perioxisome: specialized metabolic functions. Produces hydrogen peroxide
Cytoskeleton: contains microfilaments, intermediate filaments and microtubules, all of which play a part in cell movement

Although the metabolic requirements of a cell determine its size to a degree, however, generally larger organisms don’t have bigger cells, just more of them.

Resource and further reading:

Campbell and Reece, 2002, 'A Tour of the Cell', in Biology 6th edition, ed. Benjamin Cummings, San Francisco, chap 5.