Cytoplasm – Definition, Function, Structure, And Location

The cytoplasm is the fluid inside cells that carries out various functions such as energy production, protein synthesis, and cell division. It also contains organelles such as mitochondria, ribosomes, and lysosomes.

It is a substance found within eukaryotic cells (cells containing nuclei) that provides structural support and performs other vital functions.

Cytoplasm – Definition, Function, Structure, And Location

In this article, we will discuss what cytoplasm is, how it functions, its structure, and where it resides in the cell.

We will also look at some diseases caused by mutations in genes coding for proteins involved in the regulation of cytoplasmic processes.

Cytoplasm Definition

The word “cytoplasm” comes from two Greek words: kytes meaning “cell” and plassein meaning “to mold”. Thus, cytoplasm means “molded cell content”.

The term “cytoplasm”, however, has been used to refer to different things over time. In ancient times, it was used to describe the liquid part of the cell.

Later on, it came to mean the whole cell including the nucleus. Eventually, it became synonymous with the entire cellular interior except for the nucleus.

How Does Cytoplasm Work?

The cytoplasm is a complex mixture of macromolecules, small molecules, ions, and water. The main components are proteins, lipids, carbohydrates, nucleic acids, and metabolites.

Proteins are made up of amino acid chains that fold into specific three-dimensional structures called polypeptides.

These polypeptide chains can be linear or branched; they may have many subunits joined together or one large chain.

They can be either soluble or insoluble and can bind to each other through ionic bonds, hydrogen bonds, disulfide bridges, hydrophobic interactions, van der Waals forces, etc.

What Is Cytoplasm?

The cytoplasm is the fluid part of the cell. It contains most of the cell’s organelles and macronutrients.

The cytoplasm provides the cell with its structure, flexibility, and ability to contract.

It also acts as a storehouse for nutrients such as sugars, fats, vitamins, minerals, and hormones.

The cytoplasm is an intracellular fluid that consists mainly of water and macromolecules called polymers. The main components are:

  1. Proteins – These are made up of long chains of amino acids. They perform many important cellular functions including muscle contraction, blood clotting, hormone secretion, enzyme activation, and DNA replication. There are about 100,000 different kinds of proteins in the body.
  2. Nucleus – This is the component of the nucleus that makes up chromosomes. It is composed of DNA and RNA.
  3. Lipids – These are fats that form membranes. They include phospholipids, cholesterol, triglycerides, sphingomyelin, etc.
  4. Carbohydrates – These are sugar molecules that make glycogen, starch, and cellulose.
  5. Polysaccharides – These are large molecules consisting of sugars linked together. Examples include hyaluronic acid, chondroitin sulfate, heparan sulfate, and keratin.
  6. Minerals – These include calcium, phosphorus, iron, magnesium, sodium, potassium, chloride, bromide, iodine, zinc, copper, etc.
  7. Other organic compounds – These include vitamins, coenzymes, hormones, enzymes, neurotransmitters, etc.

The cytoplasm is divided into four compartments: the nuclear region, the cytoplasm proper, the endoplasmic reticulum (ER), and the mitochondrion.

Nuclear Region

The nuclear region includes the nucleolus, the nucleoplasm, and the chromosomes.

The nucleolus consists of fibrillar centers, dense fibrillar components, granular components, and per chromatin material.

The nucleoplasm is the area between the inner membrane of the nuclear envelope and the chromatin. It contains DNA, RNA, histones, and nonhistone chromosomal proteins.

The chromosomes contain the genetic information needed to make proteins. Each chromosome is composed of tightly packed bundles of DNA strands spiraling around an axis.

The DNA is wound around a core of proteins called histones. The histones help to package the DNA strands so that they cannot unravel.

Endoplasmic Reticulum

The endoplasmic reticular system is a network of tubules and sacs that surrounds the nucleus and extends throughout the cytoplasm.

This network of membranes forms a continuous series of vesicles that function as transport vehicles for materials within the cell.


Mitochondria are double-membrane organelles found in eukaryotic cells. They produce energy by converting foodstuffs into ATP via oxidative phosphorylation.

Functions Of Cytoplasm

Functions Of Cytoplasm

The primary function of the cytoplasm is to provide a framework for the cell’s internal structures.

It also serves as a repository for metabolic waste products produced during metabolism. In addition, it plays a role in intracellular signaling.

The cytoplasm performs many important functions. These include:

  1. Maintenance of Cell Shape – The cytoplasm maintains the cell’s shape by providing structural support.
  2. Transport of Materials Within the Cell – The cytoplasm transports materials such as ions, amino acids, carbohydrates, and nucleotides between different parts of the cell.
  3. Storage of Metabolites – The cytoplasm stores metabolites such as glucose, glycogen, and triglycerides.
  4. Production of Cellular Components – The cytoplasts synthesize and secrete proteins, lipoproteins, glycoproteins, mucopolysaccharides, and polypeptide hormones.
  5. Control of Gene Expression – The cytoplasmic control’s gene expression through transcription and translation.
  6. Communication Between Cells – The cytoplasm communicates with neighboring cells by releasing chemical signals that travel across the membrane.
  7. Intracellular Signaling – The cytoplasm transmits information within the cell by controlling the activity of certain proteins. This process is called signal transduction.
  8. Energy Generation – Cytoplasia produces energy by converting nutrients into ATP.
  9. Organization of the Nucleus – The cytoplasm organizes the nucleus by forming nuclear pores.
  10. Regulation of Membrane Potential – Cytoplasia regulates the electrical potential of the cell membrane.

Structure Of Cytoplasm

The cytoplasms of all animal cells are roughly spherical. However, their size varies greatly depending on the type of cell.

For example, red blood cells are about 5 μm in diameter while the cytoplasm of a neuron is several microns thick.

A typical cytoplasm is approximately 10% protein, 20% lipid, and 70% water.

The remaining percentage is composed of various other substances including salts, sugar, vitamins, enzymes, and hormones.

A typical mammalian cell has a volume of about 1 cubic millimeter. Most of this space is occupied by the nucleus.

The rest of the cell is filled with ribosomes, the rough endoplasmic reticle, Golgi apparatus, lysosomes, mitochondria, microtubules, and numerous other cellular components.

The cytoplasm is made up of three major types of molecules: macromolecules, organelles, and cytomatrix.

Macromolecules are large molecules that cannot be broken down into smaller pieces. Organelles are small components of the cell that perform specialized functions.

They are usually enclosed inside membranes. The cytomatrix is an amorphous substance that holds together all the other molecules in the cell.


A macromolecule is any molecule larger than about 50 angstroms (0.05 microns). Examples of macromolecules include DNA, RNA, proteins, lipids, and carbohydrates.

These molecules are essential for life because they form the basis of genetic material.

Proteins are one type of macromolecule. Proteins are chains of amino acid residues linked together by peptide bonds.

Each protein has a specific structure and function. Some examples of proteins include enzymes, antibodies, hormones, neurotransmitters, and toxins.

Lipids are another type of macromolecular. Lipids are organic compounds made from fatty acids and sugars. They are used for making biological membranes.

Carbohydrates are another type of macromolecule. Carbohydrates are complex molecules containing carbon, hydrogen, oxygen, and nitrogen atoms. They can be either simple or complex.

Simple carbohydrates are monosaccharides (simple sugar), disaccharides (two-sugar molecules), trisaccharides (three-sugar molecules), oligosaccharides (longer chain sugars), and polysaccharides (complex sugar molecules).

Complex carbohydrates contain more than one kind of sugar. Examples of complex carbohydrates include starch, cellulose, and chitin.


An organelle is a component of the cell that performs a specific function.

Some examples of organelles include mitochondria, chloroplasts, ribosomes, lysosomes, peroxisomes, endoplasmic reticulum, Golgi apparatus, centrioles, microtubules, and flagella.

These structures are important because they provide the cell with special functions such as respiration, photosynthesis, digestion, secretion, and reproduction.


A cytomatrix is a combination of macromolecules and organelles that hold together the various components of the cell.

The cytomatrix is responsible for holding cells together and providing them with structural support. It also provides a scaffold on which other cellular components assemble.

The cytomatrix consists of two main parts: the plasma membrane and the cytoplasm. The plasma membrane is a thin layer surrounding the interior of the cell.

It contains channels through which substances enter and leave the cell. The cytoplasm is the bulk of the cell. It is filled with fluid and contains organelles.

The Plasma Membrane

The plasma membrane is composed of phospholipid bilayers. Phospholipid bilayers consist of a hydrophobic part called the lipid tail and a hydrophilic part called the phosphate head.

The phosphate heads face outwards towards the extracellular environment while the lipid tails face inward towards the cytoplasm.

Location Of Cytoplasm

Location Of Cytoplasm

The cytoplasm occupies the interior of the cell. It is surrounded by the plasma membrane.

The cytoplasm is separated from the extracellular environment by two layers of plasma membrane: the outermost layer and the innermost layer.

The outermost layer is known as the plasmalemma. It is composed of lipids and proteins.

Its main functions include maintaining the integrity of the cell wall and providing a permeable barrier against foreign particles.

The innermost layer is known as the tegmentum or ectoplasm.

It is composed of a meshwork of actin filaments and intermediate filament proteins. It provides structural support for the cell and helps maintain its shape.

Location Of Cytoplasm In The Cell

The cytoplasm is located inside the cell. It is bounded by the cell membrane.

The nucleus is the largest organelle in the cell. It is located near the center of the cell.

It has a spherical shape and is surrounded by a double membrane. The nuclear envelope surrounds the nuclei.

This structure separates the nucleus from the cytoplasm and allows for the transport of materials between the two compartments.

The cytoplasmic matrix is an amorphous network of protein fibers and glycoproteins. It holds the cell together by providing mechanical strength to the cell.

The cytoplasms of most eukaryotic cells contain three major types of molecules: polysaccharides, proteins, and lipids. Polysaccharides are long chains of sugar units joined together by chemical bonds.

Glycogen is a type of polysaccharide found in animal cells. Proteins are made up of amino acids linked together by peptide bonds.

They can be either soluble or insoluble. Insoluble proteins form the skeleton of the cell. Lipids are organic compounds containing carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

Fatty acids, triglycerides, sterols, and phospholipids are all examples of lipids.

The cytoplasms of plant cells contain only one type of molecule: cellulose. Cellulose is a polymer of glucose that makes up the walls of plant cells.

Cellular Functions

The cytoplasm performs many important cellular functions. Some of these functions include:

  1. Transporting chemicals into and out of the cell – The plasma membrane acts as a selective filter through which substances must pass before they enter the cell. Molecules too large to fit through the pores will not pass. Molecules too small to fit through the pores may pass but cannot leave the cell. In addition, the plasma membrane also plays a role in regulating the movement of ions across the membrane.
  2. Regulating the flow of ions across membranes – The plasma membrane contains channels that allow certain ions to move freely across it. These channels are regulated by the binding of other molecules to them. For example, calcium ions can bind to specific sites on the channel and block their passage.
  3. Producing energy (ATP) – The mitochondria produce ATP by breaking down nutrients such as sugars, fats, and proteins.
  4. Controlling the growth of the cell – The cytoskeleton controls the growth of the cell. Actin filaments provide mechanical stability to the cell. Intermediate filaments help regulate the size of the cell. Microtubules control the rate at which new material is added to the cell.
  5. Protecting the cell from infection by bacteria, viruses, and other organisms – The cell wall protects the cell from invading microorganisms. Antibodies are produced when B lymphocytes recognize foreign antigens. Phagocytosis is the process by which macrophages engulf particles.
  6. Making sure that DNA is replicated correctly during cell division – Mitochondria play a key role in this process. They take part in the synthesis of ribonucleotides and deoxyribonucleotides. Ribonucleotide reductase converts ribonucleotides to deoxyribonucleotide precursors for DNA replication. Deoxyribonucleotide kinases add phosphate groups to make dNTPs.
  7. Helping to repair damaged parts of the cell – Damaged parts of the cell are removed and replaced with undamaged parts. This process is called mitosis. During mitosis, chromosomes break apart and then rejoin together again. Chromosomes are composed of chromatin fibers. Histones are protein components of chromatin. Nonhistone proteins are also present in chromatin.
  8. Helping to produce new cells – When an organism dies, its cells divide so that there is always enough tissue to replace what has been lost. This process is called regeneration. It occurs throughout the life of an organism.
  9. Helping to control the movement of nutrients into and out of the cells – The endoplasmic reticulum helps transport substances into the cell. Lysosomes contain enzymes that digest waste products. Golgi bodies package materials for secretion.
  10. Helping to regulate the pH of the cell – The cytoplasm contains many types of organelles. Some of these organelles have acidic environments while others have basic ones. An acidic environment is necessary for some chemical reactions to occur.

Final Thoughts

The cell is the smallest unit of living matter. Cells can be found everywhere in the body. There are about 100 trillion cells in the human body.

Each one performs specialized functions within the body. All cells contain nuclei, which house the genetic material. Cells may also contain other structures including:

  1. Nerve endings – Neurons send signals through nerve endings using chemicals known as neurotransmitters.
  2. Muscle cells – Muscles contract or expand to exert force on objects.
  3. Blood vessels – Blood carries oxygen and nutrients to all parts of the body.
  4. Hair follicles – Hair grows continuously because it is made up of dead skin cells.
  5. Skin glands – Glands secrete sweat and oil onto the surface of the skin. Sweat evaporates off the skin.

The cytoplasm is the fluid inside a cell. It performs several important functions including transporting chemicals into and out of a cell.

The cytoplasm also regulates the flow of ions across the plasma membrane. Finally, the cytoplasm provides structural support to the cell.

In conclusion, the cell is the fundamental building block of life. A single-celled organism is called a prokaryote. Prokaryotes include bacteria, algae, fungi, and protozoa.

Eukaryotic organisms are more complex than prokaryotes. Examples of eukaryotic organisms include humans, plants, and animals.

Jennifer Dawkins