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Protein Subunits: Single chains of amino acids that are the units of multimeric Proteins. Multimeric proteins can be composed of identical or non-identical subunits. One or more monomeric subunits may compose a protomer which itself is a subunit structure of a larger assembly.

G-protein Coupled Receptors

JoVE 10718

G-protein coupled receptors are ligand binding receptors that indirectly affect changes in the cell. The actual receptor is a single polypeptide that transverses the cell membrane seven times creating intracellular and extracellular loops. The extracellular loops create a ligand specific pocket which binds to neurotransmitters or hormones. The intracellular loops holds onto the G-protein.

The G-protein or guanine nucleotide-binding protein, is a large heterotrimeric complex. Its three subunits are labeled alpha (α), beta (β), and gamma (γ). When the receptor is unbound or resting, the α-subunit binds a guanosine diphosphate molecule or GDP, and all three subunits are attached to the receptor. When a ligand binds the receptor, the α-subunit releases the GDP and binds a molecule of guanosine triphosphate (GTP). This action releases the α-GTP complex and the β-γ complex from the receptor. The α-GTP can move along the membrane to activate second messenger pathways such as cAMP. However there are different types of α-subunits and some are inhibitory, turning off cAMP. The β-γ complex may interact with potassium ion channels which release potassium (K+) into the extracellular space resulting in hyperpolarization of the cell membrane. This type of ligand-gated ion channel is called a G-prot

 Core: Cell Signaling

Protein Organization

JoVE 10678

Proteins are one of the fundamental building blocks of life that carry out many diverse functions in the cell. Proteins are assembled from amino acids. The sequence of amino acids is known as the primary structure of a protein. Local interactions of individual amino acids cause the linear chain to fold into the secondary structures. Interactions of distant amino acids lead to further folding of the protein—the tertiary structure. The assembly of multiple folded chains (subunits) is known as quaternary protein structure. Amino acids that are bound together in a chain are called polypeptides. The amino acids are linked by their amino (–NH3) and carboxyl (–COOH) groups which form peptide bonds. The chain of linked carbon and nitrogen atoms is the backbone of the protein, with the amino acid side chains sticking out perpendicularly. The order of amino acid residues in the polypeptide chain is the primary structure. The amino and carboxyl groups of the protein backbone can form hydrogen bonds. When multiple amino acid residues in close proximity form hydrogen bonds, local structures such as alpha-helices and beta-pleated sheets can form. These are common localized structures, giving rise to the so-called secondary structure of a protein. The tertiary structure of a protein describes the 3-dimensional arrangement of a p

 Core: Macromolecules

Intracellular Signaling Cascades

JoVE 10721

Intracellular signaling cascades amplify a signal originating extracellularly and directs it to its intended intracellular target resulting in transcription, translation, protein modifications, enzyme activation, cellular metabolism, mitosis, and/or apoptosis.

The most basic of signaling cascades involves the activation of second messengers and the release of kinases. Kinases activate or deactivate proteins and enzymes by adding a phosphate group to them. Phosphatases remove phosphate groups resulting in the deactivation or reactivation of proteins. The cyclic AMP (cAMP) pathway is named for its second messenger, cAMP. This pathway is most often initiated when a ligand binds to a G-coupled protein receptor. The G-protein decouples from the receptor and triggers adenylate cyclase to synthesize cAMP from ATP. For each ligand-receptor interaction, multiple cAMP molecules are generated—amplifying the signal. cAMP activates protein kinase A (PKA). PKA is a tetramer molecule with two regulatory subunits and two active subunits. When four cAMP molecules interact with a PKA molecule, it releases the two active subunits. These PKA subunits phosphorylate target proteins and enzymes. In the case of gene expression, PKA activates CREB, a transcription factor in the nucleus. The steps that precede the intracellular signaling cascade that is the lig

 Core: Cell Signaling

Detection of Bacteriophages in Environmental Samples

JoVE 10190

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - Arizona University
Demonstrating Author: Alex Wassimi


Viruses are a unique group of biological entities that infect both eukaryotic and prokaryotic organisms. They are obligate parasites that have no metabolic capacity, and in order to replicate, rely on host metabolism…

 Environmental Microbiology

Antibiotic Selection

JoVE 10807

Researchers use antibiotic resistance genes to identify bacteria that possess a plasmid containing their gene of interest. Antibiotic resistance naturally occurs when a spontaneous DNA mutation creates changes in bacterial genes that eliminate antibiotic activity. Bacteria can share these new resistance genes with their offspring and other bacteria. The overuse and misuse of antibiotics have created a public health crisis, as resistant and multi-resistant bacteria continue to develop. Antibiotics, such as penicillin, are drugs that kill or stop bacterial growth. Bacteria that naturally or artificially acquired antibiotic resistance genes do not respond to antibiotics. Scientists exploit this by designing plasmids—small, self-replicating pieces of DNA—that carry both an antibiotic resistance gene and a gene of interest. Antibiotic resistance is an integral part of DNA cloning that allows a researcher to identify cells that absorbed a DNA of interest. The researcher’s DNA of interest is introduced into bacterial cells using a process called transformation. Bacterial transformation involves temporarily creating small holes in the bacterial cell wall to permit the uptake of external DNA such as a plasmid. Only some bacterial cells absorb new DNA. Since the plasmid includes both the DNA of interest and a gene that confers resistance to a spe

 Core: Biotechnology

Viral Structure

JoVE 10822

Viruses are extraordinarily diverse in shape and size, but they all have several structural features in common. All viruses have a core that contains a DNA- or RNA-based genome. The core is surrounded by a protective coat of proteins called the capsid. The capsid is composed of subunits called capsomeres. The capsid and genome-containing core are together known as the nucleocapsid.

Many criteria are used to classify viruses, including capsid design. Most viruses have icosahedral or helical capsids, although some viruses have developed more complex capsid structures. The icosahedral shape is a 20-sided, quasi-spherical structure. Rhinovirus, the virus that causes the common cold, is icosahedral. Helical (i.e., filamentous or rod-shaped) capsids are thin and linear, resembling cylinders. The nucleic acid genome fits inside the grooves of the helical capsid. Tobacco mosaic virus, a plant pathogen, is a classic example of a helical virus. Some viruses have capsids that are enclosed by an envelope of lipids and proteins outside of the capsid. This viral envelope is not produced by the virus but is acquired from the host’s cell. These envelope molecules protect the virus and mediate interactions with the host’s cells. The viral capsid not only protects the virus’s genome, but it also plays a critical role in interactions with host cells. For i

 Core: Viruses

Endocrine Signaling

JoVE 10719

Endocrine cells produce hormones to communicate with remote target cells found in other organs. The hormone reaches these distant areas using the circulatory system. This exposes the whole organism to the hormone but only those cells expressing hormone receptors or target cells are affected. Thus, endocrine signaling induces slow responses from its target cells but these effects also last longer. There are two types of endocrine receptors: cell surface receptors and intracellular receptors. Cell surface receptors work similarly to other membrane bound receptors. Hormones, the ligand, bind to a hormone specific G-protein coupled receptor. This initiates conformational changes in the receptor, releasing a subunit of the G-protein. The protein activates second messengers which internalize the message by triggering signaling cascades and transcription factors. Many hormones work through cell surface receptors, including epinephrine, norepinephrine, insulin, prostaglandins, prolactin, and growth hormones. Steroid hormones, like testosterone, estrogen, and progesterone, transmit signals using intracellular receptors. These hormones are small hydrophobic molecules so they move directly past the outer cell membrane. Once inside, and if that cell is a target cell, the hormone binds to its receptor. Binding creates a conformational change in the receptor

 Core: Cell Signaling

High-Resolution Complexome Profiling by Cryoslicing BN-MS Analysis

1Institute of Physiology, Faculty of Medicine, University of Freiburg, Freiburg, Germany, 2Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany, 3Signalling Research Centres BIOSS and CIBSS, Freiburg, Germany, 4Logopharm GmbH, Germany

JoVE 60096

 Biochemistry

Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells

1Bristol Centre for Functional Nanomaterials, University of Bristol, 2Department of Materials, Imperial College London, 3Self Assembly Group, CIC nanoGUNE, 4Ikebasque, Basque Foundation for Science, 5School of Cellular and Molecular Medicine, University of Bristol, 6H.H. Wills Physics Laboratory, University of Bristol

JoVE 54785

 Bioengineering
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