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October, 2006
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Organelles: Specific particles of membrane-bound organized living substances present in eukaryotic cells, such as the Mitochondria; the Golgi apparatus; Endoplasmic reticulum; Lysosomes; Plastids; and Vacuoles.

Cell Structure- Concept

JoVE 10587


Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, multicellular organisms like elephants and giant redwood trees. In the mid 19th century, the Cell Theory was proposed to define a cell, which states:

Every living organism is made up of one or more cells.
The cells…

 Lab Bio

Density Gradient Ultracentrifugation

JoVE 5685

Density gradient ultracentrifugation is a common technique used to isolate and purify biomolecules and cell structures. This technique exploits the fact that, in suspension, particles that are more dense than the solvent will sediment, while those that are less dense will float. A high-speed ultracentrifuge is used to accelerate this process in order to separate biomolecules within a density…


Non-nuclear Inheritance

JoVE 11007

Most DNA resides in the nucleus of a cell. However, some organelles in the cell cytoplasm⁠—such as chloroplasts and mitochondria⁠—also have their own DNA. These organelles replicate their DNA independently of the nuclear DNA of the cell in which they reside. Non-nuclear inheritance describes the inheritance of genes from structures other than the nucleus.

Mitochondria aresent in both plants and animal cells. They are regarded as the “powerhouses” of eukaryotic cells because they break down glucose to form energy that fuels cellular activity. Mitochondrial DNA consists of about 37 genes, and many of them contribute to this process, called oxidative phosphorylation. Chloroplasts are found in plants and algae and are the sites of photosynthesis. Photosynthesis allows these organisms to produce glucose from sunlight. Chloroplast DNA consists of about 100 genes, many of which are involved in photosynthesis. Unlike chromosomal DNA in the nucleus, chloroplast and mitochondrial DNA do not abide by the Mendelian assumption that half an organism’s genetic material comes from each parent. This is because sperm cells do not generally contribute mitochondrial or chloroplast DNA to zygotes during fertilization. While a sperm cell primarily contributes one haploid set of nuclear chromosomes to the zygote, an egg cell contribu

 Core: Biology

Eukaryotic Compartmentalization

JoVE 10689

One of the distinguishing features of eukaryotic cells is that they contain membrane-bound organelles—such as the nucleus and mitochondria—that carry out particular functions. Since biological membranes are only permeable to a small number of substances, the membrane around an organelle creates a compartment with controlled conditions inside. These microenvironments are often distinct from the environment of the surrounding cytosol and are tailored to the specific functions of the organelle. For example, lysosomes—organelles in animal cells that digest molecules and cellular debris—maintain an environment that is more acidic than the surrounding cytosol, because its enzymes require a lower pH to catalyze reactions. Similarly, pH is regulated within mitochondria, which helps them carry out their function of producing energy. Additionally, some proteins require an oxidative environment for proper folding and processing, but the cytosol is generally reductive. Therefore, these proteins are produced by ribosomes in the endoplasmic reticulum (ER), which maintains the necessary environment. Proteins are often then transported within the cell through membrane-bound vesicles. The genetic material of eukaryotic cells is compartmentalized within the nucleus, which is surrounded by a double membrane called the nuclear envelope. Sma

 Core: Biology

What are Cells?

JoVE 10687

Cells are the foundational level of organization of life. An organism may be unicellular, as with prokaryotes and most eukaryotic protists, or multicellular where the functions of an organism are divided into different collections of specialized cells. In multicellular eukaryotes, cells are the building blocks of complex structures and can have various forms and functions.

Cells are the building blocks of all living organisms, whether it is a single cell that forms the entire organism (e.g., a bacterium) or trillions of them (e.g., humans). No matter what organism a cell is a part of, they share specific characteristics. A living cell has a plasma membrane, a bilayer of lipids, which separates the watery solution inside the cell, also called cytoplasm, from the outside of the cell. Furthermore, a living cell can replicate itself, which requires that it possess genetic information encoded in DNA. DNA can be localized to a particular area of the cell, as in the nucleoid of a prokaryotic cell, or it can be contained inside another membrane, such as the nucleus of eukaryotes. Eukaryote means "true nucleus." The word prokaryote, hence, implies that the cell is from a group which arose before membrane-bound nuclei appeared in the history of life. Prokaryotic cells lack internal membranes. In contrast, eukaryotes have internal membran

 Core: Biology

Levels of Organization

JoVE 10648

Biological organization is the classification of biological structures, ranging from atoms at the bottom of the hierarchy to the Earth’s biosphere. Each level of the hierarchy represents an increase in complexity that builds upon the previous level.

The most basic levels include atoms, molecules, and biomolecules. Atoms, the smallest unit of ordinary matter, are composed of a nucleus and electrons. Molecules comprise two or more atoms held together by chemical bonds, most commonly covalent, ionic, or metallic bonds. Biomolecules are molecules found in living organisms, including proteins, nucleic acids, lipids, and carbohydrates. Biomolecules are often polymers—large molecules that are created from smaller, repeating units. For instance, proteins are composed of amino acids, and nucleic acids are composed of nucleotides. Biomolecules can be endogenous or exogenous. Endogenous means that the biomolecule is produced inside a living organism. Biomolecules can also be consumed; for example, a cow gets carbohydrates from digesting grass (exogenous), but the grass must produce the carbohydrates through photosynthesis (endogenous). The next hierarchical level comprises subcellular structures called organelles. Organelles are made up of biomolecules and compartmentalize eukaryotic cells. Organelle means “little organ” as

 Core: Biology
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