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Nuclear Envelope: The membrane system of the Cell nucleus that surrounds the nucleoplasm. It consists of two concentric membranes separated by the perinuclear space. The structures of the envelope where it opens to the cytoplasm are called the nuclear pores (Nuclear pore).


JoVE 10692

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein—such as secretory cells in the human pancreas—can contain millions of ribosomes.

Ribosomes are composed of ribosomal RNA (rRNA) and proteins. Ribosomes are not surrounded by a membrane (i.e., despite their specific cell function, they are not an organelle). In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome production. Within the nucleolus, rRNA is combined with proteins that are imported from the cytoplasm. The assembly produces two subunits of a ribosome—the large and small subunits. These subunits then leave the nucleus through pores in the nuclear envelope. Each one large and small subunit bind to each other once mRNA binds to a site on the small subunit at the start of the translation process. This step forms a functional ribosome. Ribosomes may assemble in the cytosol—called free ribosomes—or while attached to the outside of the nuclear envelope or endoplasmic reticulum—called bound ribosomes. Generally, free ribosomes synthesize proteins used in the cytoplasm, while bound ribosomes synthesize proteins that are inserted into membranes, packaged into org

 Core: Biology

The Nucleus

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The nucleus is a membrane-bound organelle that contains a eukaryotic organism’s genetic instructions in the form of chromosomal DNA. This is distinct from the DNA in mitochondria or chloroplasts that carry out functions specific to those organelles. While some cells—such as red blood cells—do not have a nucleus, and others—such as skeletal muscle cells—have multiple nuclei, most eukaryotic cells have a single nucleus. The DNA in the nucleus is wrapped around proteins such as histones, creating a DNA-protein complex called chromatin. When cells are not dividing—that is, when they are in the interphase part of their cell cycle—the chromatin is organized diffusely. This allows easy access to the DNA during the transcription process when messenger RNA (mRNA) is synthesized based on the DNA code. When a eukaryotic cell is about to divide, the chromatin condenses tightly into distinct, linear chromosomes. Humans have 46 chromosomes in total. Chromatin is particularly concentrated in a region of the nucleus called the nucleolus. The nucleolus is important for the production of ribosomes, which translate mRNA into protein. In the nucleolus, ribosomal RNA is synthesized and combined with proteins to create ribosomal subunits, which later form functioning ribosomes in the cytoplasm of the cell. The interior of t

 Core: Biology

Eukaryotic Compartmentalization

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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

Cell Division- Concept

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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

Mitosis and Cytokinesis

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In eukaryotic cells, the cell's cycle—the division cycle—is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome duplication, chromosome distribution to daughter cells, and finally, cell division. The cell cycle is tightly regulated by its regulatory systems as well as extracellular signals that affect cell proliferation. The processes of the cell cycle occur over approximately 24 hours (in typical human cells) and in two major distinguishable stages. The first stage is DNA replication, during the S phase of interphase. The second stage is the mitotic (M) phase, which involves the separation of the duplicated chromosomes into two new nuclei (mitosis) and cytoplasmic division (cytokinesis). The two phases are separated by intervals (G1 and G2 gaps), during which the cell prepares for replication and division. Mitosis can be divided into five distinct stages—prophase, prometaphase, metaphase, anaphase, and telophase. Cytokinesis, which begins during anaphase or telophase (depending on the cell), is part of the M phase, but not part of mitosis. As the cell enters mitosis, its replicated chromosomes begin to condense and become visible as threadlike structures with the aid of proteins known as condensins. The mitotic spindle apparatus b

 Core: Biology


JoVE 11002

The human X chromosome contains over ten times the number of genes as in the Y chromosome. Since males have only one X chromosome, and females have two, one might expect females to produce twice as many of the proteins, with undesirable results.

Instead, in order to avoid this potential issue, female mammalian cells inactivate nearly all the genes in one of their X chromosomes during early embryonic development. In the nuclear envelope surrounding the cell nucleus, the inactivated X chromosome condenses into a small, dense ball called a Barr body. In this state, most of the X-linked genes are not accessible to transcription. In placental mammals, the inactivated X chromosome—maternal or paternalā —is randomly determined (marsupials, however, preferentially inactivate the paternal X chromosome). X inactivation in one cell is also independent of X inactivation in other cells. Thus, about half the embryonic cells inactivate the maternal X copy; the remaining half inactivate the paternal copy, producing a mosaic. When these cells replicate, they produce cells with the same X chromosome inactivated. Notably, Barr bodies get reactivated in cells within the ovaries that become eggs. X inactivation accounts for the appearance of female tortoiseshell and calico cats. These cats are heterozygous for a gene with alleles for black fur and orange fur

 Core: Biology

Meiosis I

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Meiosis is a carefully orchestrated set of cell divisions, the goal of which—in humans—is to produce haploid sperm or eggs, each containing half the number of chromosomes present in somatic cells elsewhere in the body. Meiosis I is the first such division, and involves several key steps, among them: condensation of replicated chromosomes in diploid cells; the pairing of homologous chromosomes and their exchange of information; and finally, the separation of homologous chromosomes by a microtubule-based network. This last step segregates homologs between two haploid precursor cells that may subsequently enter the second phase of meiosis, meiosis II. The exchange of equivalent segments between homologous chromosomes occurs early on during meiosis I, and is referred to as crossing over. This process relies on the close association of such homologs, which are drawn together by the formation of a connective protein framework called the synaptonemal complex between them. To function correctly, the complex requires three parts: (1) vertical lateral elements, which form along the inward-facing sides of two juxtaposed homologous chromosomes; (2) a vertical central element positioned between the chromosomes; and (3) transverse filaments, or horizontal protein threads that connect the vertical and central components. The result has often been compared to a ladde

 Core: Biology

Neuronal Transfection Methods

JoVE 5215

Transfection - the process of transferring genetic material into cells - is a powerful tool for the rapid and efficient manipulation of gene expression in cells. Because this method can be used to silence the expression of specific proteins or to drive the expression of foreign or modified proteins, transfection is an extremely useful tool in the study of the cellular and…


Meiosis II

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Meiosis II is the second and final stage of meiosis. It relies on the haploid cells produced during meiosis I, each of which contain only 23 chromosomes—one from each homologous initial pair. Importantly, each chromosome in these cells is composed of two joined copies, and when these cells enter meiosis II, the goal is to separate such sister chromatids using the same microtubule-based network employed in other division processes. The result of meiosis II is two haploid cells, each containing only one copy of all 23 chromosomes. Depending on whether the process occurs in males or females, these cells may form eggs or sperm, which—when joined through the process of fertilization—may yield a new diploid individual. Although the goal of meiosis II is the same in both males and females—to produce haploid egg or sperm cells—there are some critical differences in this process between the sexes. For example, in a woman’s egg precursor cells, the meiotic spindle apparatus responsible for separating sister chromatids forms off to one side, near the periphery. This asymmetry allows for two cells of unequal sizes to be produced following meiosis II: a large egg, and a smaller polar body that dissolves. This division of cytoplasm ensures that the egg contains enough nutrients to support an embryo. The position of the meiotic spind

 Core: Biology


JoVE 10967

The cytoplasm consists of organelles, an aqueous solution called the cytosol, and a framework of protein scaffolds called the cytoskeleton. The cytosol is a rich broth of ions, small organic molecules such as glucose, and macromolecules such as proteins. Several cellular processes including protein synthesis occur in the cytoplasm.

The composition of the cytosol promotes protein folding such that hydrophobic amino acid side chains are oriented away from the aqueous solution and towards the protein core. However, cellular stressors such as aging and changes in pH, temperature, or osmolarity cause protein misfolding. Misfolded proteins may aggregate to form insoluble deposits in the cytoplasm. Insoluble protein aggregates are implicated in neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. The eukaryotic cytoskeleton consists of three types of filamentous proteins: microtubules, microfilaments, and intermediate filaments. Microtubules–the largest type of filament–are made up of the protein tubulin. Microtubules are dynamic structures that can grow or shrink by adding or removing tubulin molecules from the ends of their strands. They provide structural stability and provide tracks for the transport of proteins and vesicles within the cell. In addition, microtu

 Core: Biology

Quantitative Analysis of Chromatin Proteomes in Disease

1Department of Anesthesiology, David Geffen School of Medicine at UCLA, 2Department of Medicine, David Geffen School of Medicine at UCLA, 3Department of Physiology, David Geffen School of Medicine at UCLA, 4Department of Internal Medicine, Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah

JoVE 4294


An In Vivo Mouse Model to Measure Naïve CD4 T Cell Activation, Proliferation and Th1 Differentiation Induced by Bone Marrow-derived Dendritic Cells

1LamImSys Lab, Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC), 2LamImSys Lab, Instituto de Investigación Sanitaria Hospital 12 de Octubre (imas12), 3CIBER de Enfermedades Cardiovasculares

JoVE 58118

 Immunology and Infection

Correlative Light Electron Microscopy (CLEM) for Tracking and Imaging Viral Protein Associated Structures in Cryo-immobilized Cells

1European Molecular Biology Laboratory, 2Department of Infectious Diseases, Molecular Virology, Heidelberg University, 3Central Facility for Electron Microscopy, Ulm University, 4Heidelberg Partner Site, German Center for Infection Research

JoVE 58154


The CryoAPEX Method for Electron Microscopy Analysis of Membrane Protein Localization Within Ultrastructurally-preserved Cells

1Department of Biological Sciences, Purdue University, 2Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 3Purdue Institute of Inflammation, Immunology and Infectious Disease, Purdue University, 4Bindley Biosciences Center, Purdue University, 5Purdue Institute of Integrative Neuroscience, Purdue University, 6Purdue Center for Cancer Research, Purdue University

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 JoVE In-Press

Databases to Efficiently Manage Medium Sized, Low Velocity, Multidimensional Data in Tissue Engineering

1Department of Biomedical Engineering, University of California, Irvine, 2The Edwards Lifesciences Center for Advanced Cardiovascular Technology, University of California, Irvine, 3Pediatrics-Genetics & Genomics Division-School of Medicine, University of California, Irvine, 4Biological Chemistry-School of Medicine, University of California, Irvine, 5Department of Chemical and Biomolecular Engineering, University of California, Irvine, 6Center for Complex Biological Systems, University of California, Irvine, 7The NSF-Simons Center for Multiscale Cell Fate Research (CMCF), University of California, Irvine

JoVE 60038

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