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Occurs in the chloroplasts. Requires the green pigment cholorphyll. The Chloroplast. Chloroplast: Site of photosynthesis in eukaryotic cells. Thylakoids: Disk shaped membranes containing photosynthetic pigments. Site of light reactions. Grana: Stacks of thylakoids. Stroma: Fluid filled space surrounding grana.
Site of dark reactions. The general equation for photosynthesis is:. Photosynthesis occurs in 2 stages:. Light dependent reactions a. O 2 from the water molecules is released into the atmosphere as waste. Light independent reactions a. In living systems, a small class of molecules functions as electron shuttles: they bind and carry high-energy electrons between compounds in cellular pathways. The principal electron carriers we will consider are derived from the vitamin B group, which are derivatives of nucleotides.
These compounds can be easily reduced that is, they accept electrons or oxidized they lose electrons. Nicotinamide adenine dinucleotide NAD is derived from vitamin B3, niacin. When electrons are added to a compound, the compound is reduced.
A compound that reduces another is called a reducing agent. When electrons are removed from a compound, the compound is oxidized. The molecule NADH is critical for cellular respiration and other metabolic pathways. Its reduced form is FADH 2. ATP, produced by glucose catabolized during cellular respiration, serves as the universal energy currency for all living organisms. A living cell cannot store significant amounts of free energy.
Excess free energy would result in an increase of heat in the cell, which would lead to excessive thermal motion that could damage and then destroy the cell.
Rather, a cell must be able to handle that energy in a way that enables the cell to store energy safely and release it for use as needed. Living cells accomplish this by using the compound adenosine triphosphate ATP. Adenosine triphosphate. The negative charges on the phosphate group naturally repel each other, requiring energy to bond them together and releasing energy when these bonds are broken.
The core of ATP is a molecule of adenosine monophosphate AMP , which is composed of an adenine molecule bonded to a ribose molecule and to a single phosphate group.
The addition of a second phosphate group to this core molecule results in the formation of adenosine diphosphate ADP ; the addition of a third phosphate group forms adenosine triphosphate ATP. The addition of a phosphate group to a molecule requires energy. Phosphate groups are negatively charged and, thus, repel one another when they are arranged in a series, as they are in ADP and ATP.
The release of one or two phosphate groups from ATP, a process called dephosphorylation, releases energy. Hydrolysis is the process of breaking complex macromolecules apart. Water, which was broken down into its hydrogen atom and hydroxyl group during ATP hydrolysis, is regenerated when a third phosphate is added to the ADP molecule, reforming ATP.
Obviously, energy must be infused into the system to regenerate ATP. In nearly every living thing on earth, the energy comes from the metabolism of glucose. In this way, ATP is a direct link between the limited set of exergonic pathways of glucose catabolism and the multitude of endergonic pathways that power living cells.
When ATP is broken down by the removal of its terminal phosphate group, energy is released and can be used to do work by the cell. Often the released phosphate is directly transferred to another molecule, such as a protein, activating it. For example, ATP supplies the energy to move the contractile muscle proteins during the mechanical work of muscle contraction.
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