"Sunlight is the most abundant energy source on this planet. However, the ability to convert sunlight into biological energy in the form of adenosine-5′-triphosphate (ATP) is thought to be limited to chloroplasts in photosynthetic organisms."
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"In strictly chemical terms, cellular respiration reverses the reaction at the core of photosynthesis. Sugar and oxygen react with each other to make water and carbon dioxide, releasing a lot of energy, which is captured for later use." - Paul Nurse
Mitochondria (singular = mitochondrion) are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule. The formation of ATP from the breakdown of glucose is known as cellular respiration. Mitochondria are oval-shaped, double-membrane organelles that have their own ribosomes and DNA.Like mitochondria, chloroplasts also have their own DNA and ribosomes. Chloroplasts function in photosynthesis and can be found in eukaryotic cells such as plants and algae. Carbon dioxide (CO2), water, and light energy are used to make glucose and oxygen in photosynthesis. Like mitochondria, chloroplasts have outer and inner membranes.
Scientists have long noticed that bacteria, mitochondria, and chloroplasts are similar in size. We also know that mitochondria and chloroplasts have DNA and ribosomes, just as bacteria do. Scientists believe that host cells and bacteria formed a mutually beneficial endosymbiotic relationship when the host cells ingested aerobic bacteria and cyanobacteria but did not destroy them. Through evolution, these ingested bacteria became more specialized in their functions, with the aerobic bacteria becoming mitochondria and the photosynthetic bacteria becoming chloroplasts.
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ATP
"Adenosine Triphosphate, or ATP is life's universal energy source. Each molecule of ATP stores energy, acting like a minuscule battery. When a chemical reaction within a cell needs energy the cell breaks ATP's high-energy bond, turning ATP into adenosine diphosphate (ADP), a process that releases energy that the cell can use to trigger a chemical reaction or a physical process, such as each of the steps taken by a molecular motor.
Most of the food you eat eventually ends up being processed in your cells' mitochondria, which use the chemical energy it contains to make a prodigious quantity of ATP.
The key energy-capturing step in cellular repiration is based on the movement of protons, which are single atoms of hydrogen that have been stripped of an electron to give them an electric charge. These protons are pushed out from the centre of the mitochondrion, into the gap between the two membranes that enclose the mitochondrion. This results in the build-up of many more charged protons outside the inner mitochondrial membrane than inside. Although based on chemistry, this is essentially a physical process.
If there is anything remotely like a 'vital spark' that sustains life, it is perhaps this tiny flow of electric charge across a membrane." - Paul Nurse
(Glucose is like charged battery recycled through the biosphere - what keeps it all going)
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"A cell's autonomy lies in its anatomy. And that autonomy, in turn, enables an essential feature of living systems: the capacity to maintain the fixity of an internal milieu -- a phenomenon terms "homeostasis". Loosely meaning, "related to stillness". Claude Bernard - the constancy of the interior environment is the condition of free and independent life. In this shifting physiology's focus from action to the maintenance of fixity (perhaps a dynamic balance (?)) changed our conception of how an organism's body works. A major point of physiological "activity", paradoxically, was to enable stasis.
Bernard and Cannon studied homeostasis in organisms and organs, but it is increasingly recognized as a fundamental feature of cells -- and, indeed, of life. To understand celuular homeostasis, we begin, again, with the membrane that separates the cell from its external milieu, so that its internal reactions can be sequestered and self-contained. The membrane has also evolved pumps to move unwanted substances out of the cell -- again, to maintain a constancy in the cell's internal space. The protoplasm contains chemical buffers so that the acidity or the alkalinity of the cell does not change, even when the chemical environment outside the cell changes. A cell needs energy, and the mitochondria deliver. The proteasome disposes of unwanted, or misfolded, proteins. Specialized storage organelles in some cells ensure that a supply of nutrients can act as a backup repository should there be a shortage externally. Toxic by-products of metabolism are shepherded to the peroxisome to be destroyed."
-- Siddhartha Mukherjee (The Song of the Cell)
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Further from The Song of the Cell:
"In the nucleus - the nucleus is the command center. We might imagine the nucleus as the center of the center of life. The nucleus houses the organism's genome made of long stretches of DNA. The DNA double helix is elaborately folded and packaged around moleules called histones, and tightened and wound further into structures called chromosomes. We still know little about the inner organization of a nucleus. When a cell divides, every chromosome is copied, and the two copies separate in space."
And the most amazing program! All of a person's code is in every cell, just switched on at the particular module it is supposed to be operating, but the point is, each cell carries the whole instruction manual bookmarked for its own particular set of code. (Oh the tangents this launches! Each being contains the entire fabric of creation folded inside, just highlighted at that particular consciousness or point of light it randomly or determinedly happens to be. Oh! As if the entire movie script of all universe and existence is with each being. Individual parts highlighted for quick reference :) )
"The process of switching genes on and off is vital, giving the cell its identity. The set of on/off genes instructs a neuron to be a neuron, and a white cell to be a white cell. During the development of an organism, genes -- or rather proteins encoded by genes -- tell cells about their relative positions and command their future fates. Genes are turned on and off by external stimuli such as hormones, which also signal changes in a cell's behaviours."
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