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#6279.

2424) Chlorophyll

Gist

Chlorophyll is the green pigment in plants, algae, and cyanobacteria that is essential for photosynthesis, the process of converting light energy into chemical energy to create food. It is concentrated in plant cells within structures called chloroplasts and gives plants their characteristic green color. Beyond its primary role in photosynthesis, it's used as a natural green colorant and has been studied for potential antioxidant and anti-aging benefits, though these require more research. 

Chlorophyll is a pigment that gives plants their green color, and it helps plants create their own food through photosynthesis.

Chlorophyll is found in the thylakoid membranes of chloroplasts within the cells of photosynthetic organisms, such as green plants, algae, and cyanobacteria. It is concentrated within the grana (stacks of thylakoids) in plant cells, which are the specific sites where the light-dependent reactions of photosynthesis occur.

Summary

Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (khloros, "pale green") and  (phyllon, "leaf"). Chlorophyll allows plants to absorb energy from light. Those pigments are involved in oxygenic photosynthesis, as opposed to bacteriochlorophylls, related molecules found only in bacteria and involved in anoxygenic photosynthesis.

Chlorophylls absorb light most strongly in the blue portion of the electromagnetic spectrum as well as the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum. Hence chlorophyll-containing tissues appear green because green light, diffusively reflected by structures like cell walls, is less absorbed. Two types of chlorophyll exist in the photosystems of green plants: chlorophyll a and b.

Uses:

Culinary

Synthetic chlorophyll is registered as a food additive colorant, and its E number is E140. Chefs use chlorophyll to color a variety of foods and beverages green, such as pasta and spirits. Absinthe gains its green color naturally from the chlorophyll introduced through the large variety of herbs used in its production. Chlorophyll is not soluble in water, and it is first mixed with a small quantity of vegetable oil to obtain the desired solution.

In marketing

In years 1950–1953 in particular, chlorophyll was used as a marketing tool to promote toothpaste, sanitary towels, soap and other products. This was based on claims that it was an odor blocker — a finding from research by F. Howard Westcott in the 1940s — and the commercial value of this attribute in advertising led to many companies creating brands containing the compound. However, it was soon determined that the hype surrounding chlorophyll was not warranted and the underlying research may even have been a hoax. As a result, brands rapidly discontinued its use. In the 2020s, chlorophyll again became the subject of unsubstantiated medical claims, as social media influencers promoted its use in the form of "chlorophyll water", for example

Details

Chlorophyll is any member of the most important class of pigments involved in photosynthesis, the process by which light energy is converted to chemical energy through the synthesis of organic compounds. Chlorophyll is found in virtually all photosynthetic organisms, including green plants, cyanobacteria, and algae. It absorbs energy from light; this energy is then used to convert carbon dioxide to carbohydrates.

Chlorophyll occurs in several distinct forms: chlorophylls a and b are the major types found in higher plants and green algae; chlorophylls c and d are found, often with a, in different algae; chlorophyll e is a rare type found in some golden algae; and bacterio-chlorophyll occurs in certain bacteria. In green plants chlorophyll occurs in membranous disklike units (thylakoids) in organelles called chloroplasts.

The chlorophyll molecule consists of a central magnesium atom surrounded by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon–hydrogen side chain, known as a phytol chain. Variations are due to minor modifications of certain side groups. Chlorophyll is remarkably similar in structure to hemoglobin, the oxygen-carrying pigment found in the red blood cells of mammals and other vertebrates.

Additional Information

Chlorophyll is a pigment that gives plants their green color, and it helps plants create their own food through photosynthesis.

Green plants have the ability to make their own food. They do this through a process called photosynthesis, which uses a green pigment called chlorophyll. A pigment is a molecule that has a particular color and can absorb light at different wavelengths, depending on the color. There are many different types of pigments in nature, but chlorophyll is unique in its ability to enable plants to absorb the energy they need to build tissues.

Chlorophyll is located in a plant’s chloroplasts, which are tiny structures in a plant’s cells. This is where photosynthesis takes place. Phytoplankton, the microscopic floating plants that form the basis of the entire marine food web, contain chlorophyll, which is why high phytoplankton concentrations can make water look green.

Chlorophyll’s job in a plant is to absorb light—usually sunlight. The energy absorbed from light is transferred to two kinds of energy-storing molecules. Through photosynthesis, the plant uses the stored energy to convert carbon dioxide (absorbed from the air) and water into glucose, a type of sugar. Plants use glucose together with nutrients taken from the soil to make new leaves and other plant parts. The process of photosynthesis produces oxygen, which is released by the plant into the air.

Chlorophyll gives plants their green color because it does not absorb the green wavelengths of white light. That particular light wavelength is reflected from the plant, so it appears green.

Plants that use photosynthesis to make their own food are called autotrophs. Animals that eat plants or other animals are called heterotrophs. Because food webs in every type of ecosystem, from terrestrial to marine, begin with photosynthesis, chlorophyll can be considered a foundation for all life on Earth.

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#5821. What does the verb (used with object) conceal mean?

#5822. What does the verb (used with object) concede mean?

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#9773.

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2624.

Mathematical Induction Link:

Mathematical Induction.

From MathsIsFun website.

2423) Neuromuscular junction

Gist

A neuromuscular junction (NMJ) is the specialized synapse where a motor neuron transmits a signal to a skeletal muscle fiber, triggering muscle contraction. This happens when the nerve impulse reaches the neuron's end, causing it to release the neurotransmitter acetylcholine into the synaptic cleft. Acetylcholine then binds to receptors on the muscle fiber, initiating a series of events that lead to a muscle action potential and subsequent contraction. 

When a nerve impulse arrives, it causes the release of the neurotransmitter acetylcholine, which binds to receptors on the muscle fiber, generating an action potential and leading to muscle movement. Disorders affecting the NMJ can lead to muscle weakness and paralysis. 

Summary

A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber.

It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction.

Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy. In the neuromuscular system, nerves from the central nervous system and the peripheral nervous system are linked and work together with muscles. Synaptic transmission at the neuromuscular junction begins when an action potential reaches the presynaptic terminal of a motor neuron, which activates voltage-gated calcium channels to allow calcium ions to enter the neuron. Calcium ions bind to sensor proteins (synaptotagmins) on synaptic vesicles, triggering vesicle fusion with the cell membrane and subsequent neurotransmitter release from the motor neuron into the synaptic cleft. In vertebrates, motor neurons release acetylcholine (ACh), a small molecule neurotransmitter, which diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors (nAChRs) on the cell membrane of the muscle fiber, also known as the sarcolemma. nAChRs are ionotropic receptors, meaning they serve as ligand-gated ion channels. The binding of ACh to the receptor can depolarize the muscle fiber, causing a cascade that eventually results in muscle contraction.

Neuromuscular junction diseases can be of genetic and autoimmune origin. Genetic disorders, such as Congenital myasthenic syndrome, can arise from mutated structural proteins that comprise the neuromuscular junction, whereas autoimmune diseases, such as myasthenia gravis, occur when antibodies are produced against nicotinic acetylcholine receptors on the sarcolemma.

Details

The body contains over 600 different skeletal muscles and each consists of thousands of muscle fibres ranging in length from a few millimetres to several centimetres. The motor nerve fibres innervating them, which arise in the spinal cord, can be more than 1 m in length. However, the area of apposition between the terminal tip of each nerve fibre and the ‘endplate’ of each muscle fibre is usually less than 50 μm (1/20 mm) in diameter. This particular type of synapse is called the neuromuscular junction (see figure). In order to generate the complex and finely controlled movements that we all take for granted, there has to be a very efficient, fail-safe, and one-way transmission between the nerve and the muscle that ensures that muscle contractions faithfully follow commands from the central nervous system. Such neuromuscular transmission depends on the release from the motor nerve terminal of the chemical acetylcholine (ACh), and its binding to a protein receiver on the surface of the muscle, called the acetylcholine receptor (AChR).

When a nerve impulse reaches the motor nerve terminal, specialized proteins forming ion-channels in its cell membrane open transiently, allowing a short-lived entry of calcium into the terminal. Stored inside the nerve terminal, and attached to special sites on the inside of the cell membrane, are small round vesicles filled with ACh. The sudden inrush of calcium causes some of the vesicle membranes to fuse with the nerve terminal membrane, and to release their contents into the synaptic cleft between the nerve and the surface of the muscle fibre.

ACh diffuses rapidly across the ultramicroscopic 50 nm gap and binds to the AChRs that are very densely packed on the tops of the synaptic folds on the muscle fibre. When two ACh molecules bind to each AChR, its central pore (channel) opens, allowing small positively charged ions, mainly sodium, to enter the muscle, resulting in a local reduction in the potential across the membrane (depolarization). The release of many ACh-containing vehicles by a nerve impulse leads to a large depolarization called the endplate potential, which in turn opens the voltage-sensitive sodium channels situated at the base of each synaptic fold. These are responsible for starting an ‘all or nothing’ action potential that is propagated along the muscle fibre in each direction and initiates muscle contraction.

After about a millisecond, the AChR pore closes and ACh unbinds and is broken down by an enzyme, ACh esterase (AChE), that sits in the synaptic cleft. Choline is then taken back into the nerve terminal by special transporters, and used to make more ACh; this is stored in newly-formed synaptic vesicles, themselves made up of recycled nerve terminal membrane. The whole sequence of events, from the inrush of calcium to the initiation of the action potential, takes place in less than two milliseconds.

Many of the earliest studies on chemical synaptic transmission began with the autonomic nervous system, but they were soon extended to skeletal muscles when Dale and his colleagues (1936) showed that stimulation of motor nerves released ACh, and that ACh can induce muscle contraction. The action of ACh could be increased by using a drug, eserine, that inhibits the ACh esterase, and the action of ACh on the muscle could be blocked by the arrow poison, curare. Katz and his co-workers subsequently used intracellular micro-electrodes to measure the endplate potentials and showed that these followed the release of many vesicles of ACh, and that a similar depolarization of the muscle occurred when ACh was applied directly onto the neuromuscular junction with a micropipette.

The neuromuscular junction, unlike most of the nervous system, is accessible to factors circulating in the blood. This can be both an advantage and a disadvantage. For many surgical operations, one of the important roles of the anesthetist is to relax the patient's muscles using an intravenous injection of the otherwise poisonous curare-like drugs — whilst taking over artificially the muscular function of breathing. Similarly, many species of venomous animals, such as snakes and scorpions, make toxins that paralyse their prey, and in some parts of the world this can also be a serious hazard for humans. Such toxins are rapidly absorbed and carried to the neuromuscular junction where they bind with extraordinary efficiency to the AChRs and other ion channel proteins, leading to muscle paralysis which can prevent breathing. Another important toxin is botulinum, which is produced by bacteria contaminating certain foods. Botulinum toxin blocks the release of ACh from the motor nerve terminals, and can cause fatal paralysis in babies; on the other hand it has recently found use as a treatment by local injection into muscles that are subject to uncontrollable severe spasm.

These neurotoxins have also provided marvellous tools for investigating function. For instance, a particular snake toxin, alpha-bungarotoxin, binds very strongly to AChRs and has been of immense use in the study of diseases that affect neuromuscular transmission. In myasthenia gravis (mys: muscle: aesthenia: weakness), the patient suffers from serious weakness and fatigue that can be life-threatening if it involves swallowing and breathing muscles. Myasthenia was first described in 1672 by the very distinguished London physician and anatomist, Thomas Willis. Over three hundred years later, Jim Patrick and Jon Lindstrom at the Salk Institute in California induced a myasthenia gravis-like disease in rabbits by injecting them with AChR protein purified from the electric organs of certain fish. The rabbits responded to the ‘foreign’ protein by making antibodies to it, but these antibodies gained access to the rabbits' neuromuscular junctions, recognized the muscle AChRs, and reduced their function, producing muscle weakness. Following these experimental observations, radioactively-labelled alpha-bungarotoxin was used to show that patients with myasthenia have reduced numbers of AChRs at their neuromuscular junctions, and subsequently that this is caused by serum antibodies that bind to AChRs — just as in the rabbits. Drugs that inhibit the ACh esterase enzyme cause clinical improvement because they prolong the action of ACh, as first demonstrated in 1934 by Mary Walker, a young doctor in London, but nowadays the most important treatment is to reduce the circulating antibodies that bind AChR.

Additional Information

Nneuromuscular junction is a site of chemical communication between a nerve fibre and a muscle cell. The neuromuscular junction is analogous to the synapse between two neurons. A nerve fibre divides into many terminal branches; each terminal ends on a region of muscle fibre called the end plate. Embedded in the end plate are thousands of receptors, which are long protein molecules that form channels through the membrane. Upon stimulation by a nerve impulse, the terminal releases the chemical neurotransmitter acetylcholine from synaptic vesicles. Acetylcholine then binds to the receptors, the channels open, and sodium ions flow into the end plate. This initiates the end-plate potential, the electrical event that leads to contraction of the muscle fibre.

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#5819. What does the noun feat mean?

#5820. What does the adjective febrile mean?

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#9772.