Glossary: Cells

Cell

A cell is the basic structural and functional unit of an organism and is often called the "building block of life."

Cytoplasm

The cytoplasm forms the inner contents of all cells. It contains the cell’s DNA, organelles, and a fluid portion called cytosol.

Found in: Animal cells, bacterial cells, plant cells

Organelles

Organelles are specialized subunits in a cell that are contained within the cytoplasm. There are several types, and each one has a characteristic shape.

Found in: Animal cells, bacterial cells, plant cells

Function: Each organelle has a specific function in cellular growth, maintenance, or reproduction.

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Animal cell

Animal cells contain a wide variety of organelles to help them carry out their functions.

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Animal cell

There are about 200 different types of specialized cells in the human body. They carry out numerous functions that enable each body system to contribute to homeostasis. A cell has three main parts: the plasma membrane, the cytoplasm, and the nucleus. The nucleus is a large organelle that contains most of a cell's DNA.

Golgi complex

The Golgi body (Golgi apparatus, Golgi complex) is a membrane-bound organelle located in the cytoplasm of eukaryotic cells. Animal cells usually have one or several Golgi bodies, whereas plant cells can have hundreds. Each Golgi body contains stacks of small, flattened, membrane-bound sacs called cisternae.

Found in: Animal cells, plant cells

Function: The Golgi body receives proteins, synthesized by ribosomes on the rough endoplasmic reticulum, via transport vesicles. Enzymes in the cisternae modify these proteins and pack them into vesicles that bud off the Golgi body and transport the proteins to different areas in the cell. The Golgi body also processes and distributes lipids and complex carbohydrates.

Mitochondria

Mitochondria are membrane-bound organelles located in the cytoplasm of eukaryotic cells. Each mitochondrion consists of an outer membrane and an inner membrane with a space between them, called the intermembrane space.

Found in: Animal cells, plant cells

Function: Mitochondria generate adenosine triphosphate (ATP)—the cell's main source of energy—via aerobic respiration, and as a result, they are known as the "power plants" of the cell.

Nucleus

The nucleus is a large membrane-bound organelle that contains the genetic information of eukaryotic cells. A double membrane known as the nuclear envelope, similar in composition to the plasma membrane, surrounds the nucleus, and openings in the nuclear membrane called nuclear pores control the flow of substances in and out. A viscous liquid inside called nucleoplasm contains the contents of the nucleus, which include one or more spherical bodies, known as nucleoli. Each nucleolus contains a cluster of protein, deoxyribonucleic acid (DNA), and ribonucleic acid (RNA).

Found in: Animal cells, plant cells

Function: The nucleus stores information in the form of DNA and controls the activities of the cell by selectively transcribing RNA, which exits via the nuclear pores.

Plasma membrane

The plasma membrane is a lipid bilayer, which is mostly composed of phospholipid molecules that have polar and nonpolar parts. The polar part of each phospholipid is a phosphate-containing "head" that is hydrophilic, or attracted to water. The nonpolar part has two "tails" of fatty acid that are hydrophobic, meaning they do not dissolve in water. As a result, the phospholipid molecules arrange themselves with the heads facing outward toward the cytosol and extracellular fluid, and the tails facing inward toward each other.

Found in: Animal cells, bacterial cells, plant cells

Function: This arrangement creates a selectively permeable barrier, enabling the plasma membrane to surround and protect the cytoplasm while allowing the passage of certain materials in and out of the cell.

Ribosomes

Cells contain a large number of small organelles called ribosomes. Ribosomes are made mostly of rRNA (ribosomal ribonucleic acid), and bacterial cells contain more than 50 associated proteins, whereas plant and animal cells contain 80 associated proteins.

Found in: Animal cells, bacterial cells, plant cells

Function: The primary function of ribosomes is protein synthesis. Proteins synthesized by ribosomes are used by organelles in the cell, by the plasma membrane, or by structures outside the cell.

Rough endoplasmic reticulum

The endoplasmic reticulum (ER) is a network of membrane-enclosed sacs and tubules in a cell. It extends from the outer nuclear membrane throughout the cytoplasm. Rough ER is continuous with the outer nuclear membrane, and it has numerous, protein-synthesizing ribosomes attached to it.

Found in: Animal cells, plant cells

Function: Ribosomes deposit proteins into the lumen of the rough ER, where they can be modified. Transport vesicles then take the modified proteins to the nearby Golgi body, where they are processed further and sorted for transport.

Smooth endoplasmic reticulum

The endoplasmic reticulum (ER) is a network of membrane-enclosed sacs and tubules in a cell. It extends from the outer nuclear membrane throughout the cytoplasm. Extending from the rough ER, the smooth endoplasmic reticulum forms a network of tubules. It gets its name from the lack of ribosomes on its surface.

Found in: Animal cells, plant cells

Function:. The smooth ER detoxifies drugs and poisons; stores ions; and produces lipids, hormones, and other cellular products, which are distributed throughout the cell by transport vesicles.

Transport vesicles

Transport vesicles fuse with and arise from the edges of the Golgi body’s cisternae.

Found in: Animal cells, plant cells

Function: Ribosomes deposit proteins into the lumen of the rough ER, where they can be modified. Transport vesicles then take the modified proteins to the nearby Golgi body, where they are processed further and sorted for transport. Transport vesicles carry the fully processed proteins throughout the cell or to the plasma membrane for export. Transport vesicles also distribute lipids, hormones, and other cellular products from the smooth ER throughout the cell.

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Bacteria

Bacteria are microorganisms made up of a single prokaryotic cell.

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Bacterial cell

Bacteria are single-celled prokaryotic organisms. Bacterial cells are small, with a typical size range of 0.1 to 5 μm in diameter. The cell's coiled, circular chromosomal DNA is located in a region called the nucleoid, and its nonchromosomal DNA is located in circular plasmids. These structures are not bound by membranes.

Capsule

The capsule is an outer coating, usually composed of polysaccharides, that surrounds the cell wall of gram-negative bacterial cells and some gram-positive bacterial cells.

Found in: Bacterial cells

Function: The capsule protects the cell from phagocytosis and toxic materials, attaches the cell to surfaces or other cells, and helps the cell retain water.

Cell wall

The cell wall of the bacterial cell is external to the plasma membrane. For bacteria that have capsules, the cell wall is located between the capsule and the plasma membrane.

Found in: Bacterial cells, plant cells

Function: The cell wall protects the cell; maintains its shape; and helps facilitate the passage of water, nutrients, gases, and wastes into and out of the cell.

Fimbria

All gram-negative bacteria and many gram-positive bacteria have short projections that support and move them. Fimbriae are short protein tubes that extend from the cell wall and cover the cell's surface.

Found in: Bacterial cells

Function: Bacterial cells can have up to a thousand fimbriae, which attach them to substrate or other cells.

Flagellum

Some bacteria have long projections called flagella, which move them through their liquid surroundings. Flagellated bacteria are classified according to the number and arrangement of their flagella. Some types of bacterial cells have a single flagellum projecting from one of the cell's ends, whereas other types have multiple flagella located all over the entire cell's surface, at the cell's poles, or all at one of the cell's ends.

Found in: Bacterial cells, some animal and plant cells

Plasma membrane

The plasma membrane is a lipid bilayer, which is mostly composed of phospholipid molecules that have polar and nonpolar parts. The polar part of each phospholipid is a phosphate-containing "head" that is hydrophilic, or attracted to water. The nonpolar part has two "tails" of fatty acid that are hydrophobic, meaning they do not dissolve in water. As a result, the phospholipid molecules arrange themselves with the heads facing outward toward the cytosol and extracellular fluid, and the tails facing inward toward each other.

Found in: Animal cells, bacterial cells, plant cells

Function: This arrangement creates a selectively permeable barrier, enabling the plasma membrane to surround and protect the cytoplasm while allowing the passage of certain materials in and out of the cell.

Nucleoid

The nucleoid is a region that contains the bacterial cell's coiled, circular chromosomal DNA, as well as nucleoid-associated proteins (NAPs) and RNA. The chromosomal DNA carries the essential genes needed for bacterial cells to survive in normal conditions.

Found in: Bacterial cells

Plasmids

In addition to the DNA located in the nucleoid, bacterial cells have plasmids, small, circular DNA molecules that carry nonessential genes that help them survive in extraneous conditions. Plasmids can replicate themselves, and they are not associated with the cell's chromosome.

Found in: Bacterial cells

Ribosomes

Cells contain a large number of small organelles called ribosomes. Ribosomes are made mostly of rRNA (ribosomal ribonucleic acid), and bacterial cells contain more than 50 associated proteins, whereas plant and animal cells contain 80 associated proteins.

Found in: Animal cells, bacterial cells, plant cells

Function: The primary function of ribosomes is protein synthesis. Proteins synthesized by ribosomes are used by organelles in the cell, by the plasma membrane, or by structures outside the cell.

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Plant cell

Plant cells have a cell wall and use organelles called chloroplasts to carry out photosynthesis.

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Plant cell

Plants are eukaryotes that are composed of several different types of cells, including parenchyma, sclerenchyma, collenchyma, xylem, and phloem cells. Like other eukaryotes, plant cells have three main parts: the plasma membrane, the cytoplasm, and the nucleus. Most plant cells also have a few unique structures, including chloroplasts, a central vacuole, and a cell wall.

Cell wall

The cell wall of the plant cell is external to the plasma membrane. Plants can have three cell wall layers: a thin and flexible primary cell wall composed of polysaccharides, a thicker secondary cell wall composed of cellulose, and an outer middle lamella composed of pectins. In some plant cells, including xylem cells, the secondary cell wall contains lignin, a substance that provides strength and water resistance.

Found in: Bacterial cells, plant cells

Function: The cell wall protects the cell; maintains its shape; and helps facilitate the passage of water, nutrients, gases, and wastes into and out of the cell.

Central vacuole

The central vacuole is a large membrane-bound organelle located in the cytoplasm of plant cells. In most mature plant cells, there is one central vacuole that takes up 30 to 80% of the cell's volume.

Found in: Plant cells

Function: The vacuole stores much of the plant cell's water, storage molecules, and enzymes. In addition to storage, its other main functions are maintaining the cell's rigid structure by creating high hydrostatic pressure within the cell, stabilizing pH by removing protons from the cytoplasm, and removing harmful substances and waste products from the cytoplasm.

Chloroplasts

Chloroplasts are specialized, membrane-bound organelles located in the cytoplasm of plant cells that carry out photosynthesis. Plant cells can have anywhere between one and a hundred chloroplasts, which move around the cell and can divide to replicate themselves.

Found in: Plant cells

Function: Surrounded by two membranes, chloroplasts contain DNA, ribosomes, enzymes, grana, and a thick fluid called stroma. Each granum is a stack of disc-shaped thylakoids that contain the pigment chlorophyll, which converts light energy into chemical energy to produce the food that sustains the plant. Chloroplasts are also involved in the plant's synthesis of fatty acids and amino acids and its immune response.

Golgi complex

The Golgi body (Golgi apparatus, Golgi complex) is a membrane-bound organelle located in the cytoplasm of eukaryotic cells. Animal cells usually have one or several Golgi bodies, whereas plant cells can have hundreds. Each Golgi body contains stacks of small, flattened, membrane-bound sacs called cisternae.

Found in: Animal cells, plant cells

Function: The Golgi body receives proteins, synthesized by ribosomes on the rough endoplasmic reticulum, via transport vesicles. Enzymes in the cisternae modify these proteins and pack them into vesicles that bud off the Golgi body and transport the proteins to different areas in the cell. The Golgi body also processes and distributes lipids and complex carbohydrates.

Mitochondria

Mitochondria are membrane-bound organelles located in the cytoplasm of eukaryotic cells. Each mitochondrion consists of an outer membrane and an inner membrane with a space between them, called the intermembrane space.

Found in: Animal cells, plant cells

Function: Mitochondria generate adenosine triphosphate (ATP)—the cell's main source of energy—via aerobic respiration, and as a result, they are known as the "power plants" of the cell.

Nucleus

The nucleus is a large membrane-bound organelle that contains the genetic information of eukaryotic cells. A double membrane known as the nuclear envelope, similar in composition to the plasma membrane, surrounds the nucleus, and openings in the nuclear membrane called nuclear pores control the flow of substances in and out. A viscous liquid inside called nucleoplasm contains the contents of the nucleus, which include one or more spherical bodies, known as nucleoli. Each nucleolus contains a cluster of protein, deoxyribonucleic acid (DNA), and ribonucleic acid (RNA).

Found in: Animal cells, plant cells

Function: The nucleus stores information in the form of DNA and controls the activities of the cell by selectively transcribing RNA, which exits via the nuclear pores.

Plasma membrane

The plasma membrane is a lipid bilayer, which is mostly composed of phospholipid molecules that have polar and nonpolar parts. The polar part of each phospholipid is a phosphate-containing "head" that is hydrophilic, or attracted to water. The nonpolar part has two "tails" of fatty acid that are hydrophobic, meaning they do not dissolve in water. As a result, the phospholipid molecules arrange themselves with the heads facing outward toward the cytosol and extracellular fluid, and the tails facing inward toward each other.

Found in: Animal cells, bacterial cells, plant cells

Function: This arrangement creates a selectively permeable barrier, enabling the plasma membrane to surround and protect the cytoplasm while allowing the passage of certain materials in and out of the cell.

Ribosomes

Cells contain a large number of small organelles called ribosomes. Ribosomes are made mostly of rRNA (ribosomal ribonucleic acid), and bacterial cells contain more than 50 associated proteins, whereas plant and animal cells contain 80 associated proteins.

Found in: Animal cells, bacterial cells, plant cells

Function: The primary function of ribosomes is protein synthesis. Proteins synthesized by ribosomes are used by organelles in the cell, by the plasma membrane, or by structures outside the cell.

Rough endoplasmic reticulum

The endoplasmic reticulum (ER) is a network of membrane-enclosed sacs and tubules in a cell. It extends from the outer nuclear membrane throughout the cytoplasm. Rough ER is continuous with the outer nuclear membrane, and it has numerous, protein-synthesizing ribosomes attached to it.

Found in: Animal cells, plant cells

Function: Ribosomes deposit proteins into the lumen of the rough ER, where they can be modified. Transport vesicles then take the modified proteins to the nearby Golgi body, where they are processed further and sorted for transport.

Smooth endoplasmic reticulum

The endoplasmic reticulum (ER) is a network of membrane-enclosed sacs and tubules in a cell. It extends from the outer nuclear membrane throughout the cytoplasm. Extending from the rough ER, the smooth endoplasmic reticulum forms a network of tubules. It gets its name from the lack of ribosomes on its surface.

Found in: Animal cells, plant cells

Function:. The smooth ER detoxifies drugs and poisons; stores ions; and produces lipids, hormones, and other cellular products, which are distributed throughout the cell by transport vesicles.

Transport vesicles

Transport vesicles fuse with and arise from the edges of the Golgi body’s cisternae.

Found in: Animal cells, plant cells

Function: Ribosomes deposit proteins into the lumen of the rough ER, where they can be modified. Transport vesicles then take the modified proteins to the nearby Golgi body, where they are processed further and sorted for transport. Transport vesicles carry the fully processed proteins throughout the cell or to the plasma membrane for export. Transport vesicles also distribute lipids, hormones, and other cellular products from the smooth ER throughout the cell.

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