Related Concept Videos

Position-effect Variegation02:32

Position-effect Variegation

In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
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Positive Regulator Molecules01:45

Positive Regulator Molecules

To consistently produce healthy cells, the cell cycle—the process that generates daughter cells—must be precisely regulated.
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Position and Displacement01:31

Position and Displacement

The position of an object defines its location relative to a convenient frame of reference at any particular time. A frame of reference is an arbitrary set of axes from which the position and motion of an object are described. Earth is often used as a frame of reference, and we often describe the position of an object as it relates to stationary objects on Earth. For example, a rocket launch could be described in terms of the position of the rocket with respect to Earth as a whole. On the other...
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Serial Position Effect01:03

Serial Position Effect

The serial position effect is a cognitive phenomenon where individuals are more likely to recall the first and last items in a list compared to those in the middle. This effect is divided into the primacy effect and the recency effect. The primacy effect is observed when the initial items in a list are remembered better. This occurs because these items are rehearsed more frequently or receive more elaborative processing, allowing them to be encoded into long-term memory more effectively. For...
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Structure and Function of Platelets01:18

Structure and Function of Platelets

The cell fragments known as platelets are disc-shaped, with an average diameter of about 3 μm and a thickness of roughly 1 μm. They play a crucial role in the body's vascular clotting system, which also involves plasma proteins, blood cells, and blood vessel tissues.
Platelets are continually replenished, circulating in the bloodstream for 9-12 days before being removed by phagocytes, primarily in the spleen. A microliter of circulating blood contains between 150,000 and 450,000...
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Formation of the Platelet Plug01:22

Formation of the Platelet Plug

The platelet phase, the second stage of hemostasis, commences around 15-20 seconds after an injury. It follows and overlaps with the vascular phase, during which blood vessels constrict to minimize blood loss.
As the injured blood vessel contracts, endothelial cells undergo contraction, revealing collagen fibers in the basement membrane and underlying connective tissue. Furthermore, the plasma membrane of endothelial cells becomes adhesive, preparing the site for platelet adhesion. Platelets...
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