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Cell Cycle: The complex series of phenomena, occurring between the end of one Cell division and the end of the next, by which cellular material is duplicated and then divided between two daughter cells. The cell cycle includes Interphase, which includes G0 phase; G1 phase; S Phase; and G2 phase, and Cell division phase.

What is the Cell Cycle?

JoVE 10757

The cell cycle refers to the sequence of events occurring throughout a typical cell’s life. In eukaryotic cells, the somatic cell cycle has two stages: interphase and the mitotic phase. During interphase, the cell grows, performs its basic metabolic functions, copies its DNA, and prepares for mitotic cell division. Then, during mitosis and cytokinesis, the cell divides its nuclear and cytoplasmic materials, respectively. This generates two daughter cells that are identical to the original parent cell. The cell cycle is essential for the growth of the organism, replacement of damaged cells, and regeneration of aged cells. Cancer is the result of uncontrolled cell division sparked by a gene mutation. There are three major checkpoints in the eukaryotic cell cycle. At each checkpoint, the progression to the next cell cycle stage can be halted until conditions are more favorable. The G1 checkpoint is the first of these, where a cell’s size, energy, nutrients, DNA quality, and other external factors are evaluated. If the cell is deemed inadequate, it does not continue to the S phase of interphase. The G2 checkpoint is the second checkpoint. Here, the cell ensures that all of the DNA has been replicated and is not damaged before entering mitosis. If any DNA damage is detected that cannot be repaired, the cell may undergo apoptosis, or

 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

Cell Cycle Analysis

JoVE 5641

Cell cycle refers to the set of events through which a cell grows, replicates its genome, and ultimately divides into two daughter cells through the process of mitosis. Because the amount of DNA in a cell shows characteristic changes throughout the cycle, techniques known as cell cycle analysis can be used to separate a population of cells according to the different phases …

 Cell Biology

The Citric Acid Cycle

JoVE 10741

The citric acid cycle, also known as the Krebs cycle or TCA cycle, consists of several energy-generating reactions that yield one ATP molecule, three NADH molecules, one FADH2 molecule, and two CO2 molecules.

Acetyl CoA is the point-of-entry into the citric acid cycle, which occurs in the inner membrane (i.e., matrix) of mitochondria in eukaryotic cells or the cytoplasm of prokaryotic cells. Prior to the citric acid cycle, pyruvate oxidation produced two acetyl CoA molecules per glucose molecule. Hence, the citric acid cycle runs twice per glucose molecule. The citric acid cycle can be partitioned into eight steps, each yielding different molecules (italicized below). With the help of catalyzing enzymes, one acetyl CoA (2-carbon) reacts with oxaloacetic acid (4-carbon), forming the 6-carbon molecule citrate. Next, citrate is converted into one of its isomers, isocitrate, through a two-part process in which water is removed and added. The third step yields α-ketoglutarate (5-carbon) from oxidized isocitrate. This process releases CO2 and reduces NAD+ to NADH. The fourth step forms the unstable compound succinyl CoA from α-ketoglutarate, a process that also releases CO2 and reduces NAD+ to NADH. The fifth

 Core: Biology

Lysogenic Cycle of Bacteriophages

JoVE 10824

In contrast to the lytic cycle, phages infecting bacteria via the lysogenic cycle do not immediately kill their host cell. Instead, they combine their genome with the host genome, allowing the bacteria to replicate the phage DNA along with the bacterial genome. The incorporated copy of the phage genome is called the prophage. Some prophages can re-activate and enter the lytic cycle. This often occurs in response to a perturbation, such as DNA damage, but can also transpire in the absence of external cues. In some cases, the genes encoded by prophages can alter the phenotype of the infected bacterium, a process known as lysogenic conversion. Some phages encode proteins or toxins called virulence factors that can facilitate bacterial infections. Through lysogenic conversion, normally non-pathogenic bacteria can become highly virulent via infection by a phage carrying virulence factors. For example, such phages are largely responsible for the pathogenicity of the bacterial species that cause botulism (Clostridium botulinum), diphtheria (Corynebacterium diphtheriae), and cholera (Vibrio cholerae). Without lysogenic conversion, these bacteria do not usually cause disease. A particularly well-studied example of lysogenic conversion is that of the Escherichia coli strain O157:H7. Several massive food recalls have stemmed

 Core: Biology

The Angiosperm Life Cycle

JoVE 11108

Plants have a life cycle split between two multicellular stages: a haploid stage—with cells containing one set of chromosomes—and a diploid stage—with cells containing two sets of chromosomes. The haploid stage is the gamete-producing gametophyte, and the diploid stage is the spore-producing sporophyte.

Today, most plants grow from seeds and produce flowers and fruit; such plants are called angiosperms. Angiosperms begin as seeds—structures consisting of a protective seed coat, a nutrient supply, and an embryo. The seed develops into a sporophyte—the familiar, flower-producing plant form. The reproductive life cycle of angiosperms begins with flowering. Stamens and carpels contain sporangia, structures with spore-producing cells called sporocytes. Sporophytes produce spores as either eggs or sperm, depending on their origin. For example, male spores—called microspores—are produced within anthers at the tips of stamens. A microspore develops into a pollen grain—the male gametophyte. A pollen grain contains a tube cell and a generative cell, which develops into sperm. A carpel consists of an ovary and its ovules. Female spores, called megaspores, are produced within ovules. A megaspore develops into an embryo sac—the female gametophyte—which contains the egg. Pollination allows

 Core: Biology

The Phosphorus Cycle

JoVE 10935

Unlike carbon, water, and nitrogen, phosphorus is not present in the atmosphere as a gas. Instead, most phosphorus in the ecosystem exists as compounds, such as phosphate ions (PO43-), found in soil, water, sediment and rocks. Phosphorus is often a limiting nutrient (i.e., in short supply). Consequently, phosphorus is added to most agricultural fertilizers, which can cause environmental problems related to runoff in aquatic ecosystems. Phosphorus is present in many important biological structures, such as DNA, cell membranes, bones and teeth. It is not present in the atmosphere in a gaseous form, but is found in minerals, sediment, volcanic ash, and aerosols. As rocks and sediment weather over time, they release inorganic phosphate, which gradually reaches soil and surface water. Plants absorb and incorporate these phosphates into organic molecules. Animals obtain and incorporate phosphates by consuming plants and other animals. When plants and animals die or excrete waste, organic phosphates return to the soil and are broken down by bacteria—in a process called phosphate mineralization—into inorganic forms that can again be used by plants. Natural runoff can transport phosphates to rivers, lakes, and the ocean, where they can be ingested by aquatic organisms. When aquatic organisms die or excrete waste, phosphorus-

 Core: Biology

Lytic Cycle of Bacteriophages

JoVE 10823

Bacteriophages, also known as phages, are specialized viruses that infect bacteria. A key characteristic of phages is their distinctive “head-tail” morphology. A phage begins the infection process (i.e., lytic cycle) by attaching to the outside of a bacterial cell. Attachment is accomplished via proteins in the phage tail that bind to specific receptor proteins on the outer surface of the bacterium. The tail injects the phage’s DNA genome into the bacterial cytoplasm. In the lytic replication cycle, the phage uses the bacterium’s cellular machinery to make proteins that are critical for the phage’s replication and dispersal. Some of these proteins cause the host cell to take in water and burst, or lyse, after phage replication is complete, releasing hundreds of phages that can infect new bacterial cells. Since the early 20th century, researchers have recognized the potential value of lytic bacteriophages in combating bacterial infections in crops, humans, and agricultural animals. Because each type of phage can infect and lyse only specific types of bacteria, phages represent a highly specific form of anti-bacterial treatment. This quality stands in contrast to the familiar antibiotic drugs that we often take for bacterial infections, which are typically broad-spectrum treatments that kill both pathogenic and beneficial bacteria. The w

 Core: Biology

Cross-bridge Cycle

JoVE 10870

As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.

When ATP, that is attached to the myosin head, is hydrolyzed to ADP, myosin moves into a high energy state bound to actin, creating a cross-bridge. When ADP is released, the myosin head moves to a low energy state, moving actin toward the center of the sarcomere. Binding of a new ATP molecule dissociates myosin from actin. When this ATP is hydrolyzed, the myosin head will bind to actin, this time on a portion of actin closer to the end of the sarcomere. Regulatory proteins troponin and tropomyosin, along with calcium, work together to control the myosin-actin interaction. When troponin binds to calcium, tropomyosin is moved away from the myosin-binding site on actin, allowing myosin and actin to interact and muscle contraction to occur. As a regulator of muscle contraction, calcium concentration is very closely controlled in muscle fibers. Muscle fibers are in close contact with motor neurons. Action potentials in motor neurons cause the release of the neurotransmitter acetylcholine in the vicinity of muscle fibers. This ge

 Core: Biology
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