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October, 2006
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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

What is Biology?

JoVE 10647

Biology is the natural science that focuses on the study of life and living organisms, including their structure, function, development, interactions, evolution, distribution, and taxonomy. The scope of the field is extensive and is divided into several specialized disciplines, such as anatomy, physiology, ethology, genetics, and many more.

All living things share a few key traits: cellular organization, heritable genetic material and the ability to adapt/evolve, metabolism to regulate energy needs, the ability to interact with the environment, maintain homeostasis, reproduce, and the ability to grow and change. Despite its complexity, life is organized and structured. The cell theory in biology states that all living organisms are composed of one or more cells. The cell is the basic unit of life, and all cells arise from previously existing cells. Even single-celled organisms, such as bacteria, have structures that allow them to carry out essential functions, such as interacting with the environment and carry out chemical reactions that maintain life, or metabolism. In multicellular organisms, cells work together to form tissues, organs, organ systems, and finally, entire organisms. This hierarchical organization can extend further into populations, communities, ecosystems, and the biosphere. An organism’s genetic material, the biologi

 Core: Biology

Conditions on Early Earth

JoVE 11015

Around 4 billion years ago, oceans began to condense on earth while volcanic eruptions released nitrogen, carbon dioxide, methane, ammonia, and hydrogen into the primordial atmosphere. However, organisms with the characteristics of life were not initially present on earth. Scientists have used experimentation to determine how organisms evolved that could grow, reproduce, and maintain an internal environment. In the 1920s, the scientists Oparin and Haldane proposed the idea that simple biological compounds could have formed on the early earth. More than 30 years later, Stanley Miller and Harold Urey at the University of Chicago tested this hypothesis by simulating the conditions of the early earth's atmosphere and oceans in a laboratory apparatus. Using electricity as an energy source, the Miller-Urey experiment generated amino acids and other organic molecules, showing that the environment of early earth was conducive to the formation of biological molecules. More recent experiments have yielded comparable results and suggest that amino acids may have formed near areas of volcanic activity or hydrothermal vents in the ocean. Amino acids and small organic molecules may then have self-assembled to form more complex macromolecules. For instance, dripping amino acids or nucleotides into hot sand can result in the formation of the corresponding polymer

 Core: Biology

Cell-surface Signaling

JoVE 10877

Hormones—or any molecule that binds to a receptor, known as a ligand—that are lipid-insoluble (water-soluble) are not able to diffuse across the cell membrane. In order to be able to affect a cell without entering it, these hormones bind to receptors on the cell membrane. When a first messenger, a hormone, binds to a receptor, a signal cascade is set off, causing second messengers, proteins inside the cell, to become activated, resulting in downstream effects. Cell membrane receptors have three portions: an external ligand-binding domain, a transmembrane domain, and an internal domain. There are three categories of cell membrane receptors based on the consistency of the structure and function of these domains within each category. One category is ligand-gated ion channels which, when bound to a ligand, undergo a conformational change, allowing ions through a channel formed by the transmembrane portion of the receptor. A second category is G-proteins-coupled receptors which have a distinct structure with seven transmembrane domains. Binding of the external domain to a ligand causes the alpha subunit, one of three subunits attached to the internal portion of the receptor, to disassociate from the receptor and create a cellular response. The third category of receptors, the enzyme-linked receptor—also called catalytic receptor

 Core: Biology


JoVE 10696

Cells with similar structure and function are grouped into tissues. A group of tissues with a specialized function is called an organ. There are four main types of tissue in vertebrates: epithelial, connective, muscle, and nervous.

Epithelial tissue consists of thin sheets of cells and includes the skin and the linings of internal organs and body cavities. Epithelial cells are tightly packed, providing a barrier against injury, infection, and water loss. Epithelial tissue can be a single layer called simple epithelium, or multiple layers called stratified epithelium. In stratified epithelium, such as the skin, the outer cells—which are subject to damage—are replaced through the division of cells underneath. Epithelial cells have a variety of shapes, including squamous (flattened), cuboid, and columnar. Some epithelial tissues absorb or secrete substances, such as the lining of the intestines. Connective tissue is composed of cells within an extracellular matrix and includes loose connective tissue, fibrous connective tissue, adipose (fat) tissue, cartilage, bone, and blood. Although the characteristics of connective tissue vary greatly, their general function is to support and attach multiple tissues. For example, tendons are made of fibrous connective tissue and attach muscle to bone. Blood transports oxygen, nutrients and waste produ

 Core: Biology

Cell Division- Concept

JoVE 10571

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, cell division allows organisms to transfer their genetic material to their offspring. For a unicellular organism, cellular division generates a completely new organism. For multicellular organisms, cellular division produces new cells for…

 Lab Bio

Physiological Correlates of Emotion Recognition

JoVE 10297

Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

The autonomic nervous system (ANS) controls the activity of the body's internal organs and regulates changes in their activity depending on the current environment. The vagus nerve, which innervates many of the internal organs, is an…


Pelvic Exam III: Bimanual and Rectovaginal Exam

JoVE 10163


Alexandra Duncan, GTA, Praxis Clinical, New Haven, CT

Tiffany Cook, GTA, Praxis Clinical, New Haven, CT

Jaideep S. Talwalkar, MD, Internal Medicine and Pediatrics, Yale School of Medicine, New Haven, CT

A bimanual exam is a…

 Physical Examinations II

Marginal Dishonesty: The Adding-to-10 Task

JoVE 10307

Source: Julian Wills & Jay Van Bavel—New York University

Classical economic theory asserts that people are rational and self-interested. In addition to seeking wealth and status, people are motivated by other goals. As a result, financial motives can sometimes be dwarfed by other internal needs, such as maintaining a positive…

 Social Psychology

Cardiac Exam I: Inspection and Palpation

JoVE 10071

Source: Suneel Dhand, MD, Attending Physician, Internal Medicine, Beth Israel Deaconess Medical Center

The cardiac assessment is one of the core examinations performed by almost every physician whenever encountering a patient. Disorders of the cardiac system are among the most common reasons for hospital admission, with conditions ranging…

 Physical Examinations I
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