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How would you define bioenergetics while relating it to the oxidation-reduction reactions in living systems?
Bioenergetics:
Bioenergetics is the study of energy relationships and energy transformations (conversions) in living organisms.
Bioenergetics and the Role of ATP:
Organisms obtain energy by metabolizing the food they eat or prepare. The food contains potential energy in its bonds. When these bonds are broken down, a large amount of kinetic energy is usually released. Some of this energy is stored in the form of potential energy in the bonds of ATP molecules while the rest escapes as heat. The potential energy stored in ATP is again transformed into kinetic energy to carry out life activities.
Bioenergetics and Oxidation-Reduction Reactions:
For all life processes, oxidation-reduction reactions are the direct source of energy Oxidation-reduction reactions (Redox reactions) involve the exchange of electrons between atoms.
Oxidation:
The loss of electrons is called oxidation.
Reduction:
The gain of electrons is called reduction.
Role of Electrons in Bioenergetics:
Electrons can be an energy source. It depends upon their location and arrangement in atoms. For example; when they are present in oxygen, they make a stable association with oxygen atoms and are not a good energy source. But if electrons are dragged away from oxygen and attached to some other atom e.g. carbon or hydrogen, they make an unstable association. They try to move back to oxygen and when this happens, energy is released.
Role of Redox Reactions:
In living, organisms’ redox reactions involve the loss and gain of hydrogen atoms. We know that a hydrogen atom contains one proton and one electron. It means that when a molecule loses a hydrogen atom, it actually loses an electron, and similarly, when a molecule gains a hydrogen atom, it gains an electron.
Interpret that ATP is the chief energy source of all cells.
ATP (adenosine triphosphate):
The major energy currency of all cells is a nucleotide called adenosine triphosphate (ATP), ATP was discovered in 1929 by Karl Lohmann, and was proposed to be the main energy-transfer molecule in the cell by the Nobel prize winner, Fritz Lipmann in 1941.
ATP: The Cell's Energy Currency:
ATP is the main energy source for the majority of the cellular functions like the synthesis of macromolecules (DNA, RNA, and proteins), movement, the transmission of nerve impulses, active transport, exocytosis, endocytosis, etc.
The ability of ATP to store and release energy is due to its molecular structure.
Sub-Units of ATP:
Each ATP molecule has three subunits:
(a) adenine -a double-ringed nitrogenous base;
(b) a ribose - a five-carbon sugar, and
(c) three phosphate groups in a linear chain.
ATP Transfers Energy Between Metabolic Reactions:
The covalent bond connecting two phosphates is indicated by the "tilde" (~) and it is a high-energy bond. The energy in this bond is released as it breaks and inorganic phosphate (Pi) gets separated from ATP.
Energy Released by breaking off one phosphate bond: The breaking of one phosphate bond releases about 7.3 kcal (7,300 calories) per mole of ATP as follows:
ATP + H2O → ADP + P1 + energy (7.3 kcal/mole)
The energy from ATP is sufficient to drive most of the cell's energy-requiring reactions. In common energy, I reactions only the outermost of the two high-energy bonds break. When this happens, ATP becomes ADP (adenosine diphosphate) and one Pi is released. In some cases, ADP is further broken down to AMP (adenosine monophosphate) and P: as follows:
ADP + H2O → AMP + P1 + energy (7.3 kcal/mole)
Recycling of ADP:
Cells constantly recycle ADP by recombining it with Pi to form ATP the synthesis of ATP from ADP and P (requires the expenditure of 7.3 kcal of energy per mole. This energy is obtained from the oxidation of foodstuff. So, we can summarize that ATP is generated by energy-releasing processes and is broken down by energy-consuming processes. In this way, ATP transfers energy between metabolic reactions.
What is the role of chlorophyll and light in photosynthesis?
Role of Light in photosynthesis:
Sunlight energy is absorbed by chlorophyll. It is then converted into chemical energy, which drives the photosynthetic process. Not all the light falling on the leaves is absorbed. Only about one percent of the light falling on the leaf surface is absorbed, the rest is reflected or transmitted.
The light rays of different wavelengths are not only differently absorbed by photosynthetic pigments but are also differently effective in photosynthesis. The blue and red lights carry out more photosynthesis.
The function of Chlorophyll:
When chlorophyll absorbs light, its electrons are excited and they leave a chlorophyll molecule. The excited electrons are passed through the electron transport chain and their energy is captured for the formation of ATP and for reducing NADP to NADPH.
Role of Chlorophyll in photosynthesis:
The photosynthetic pigments are organized in the form of clusters, called photosystems, in thylakoid membranes of chloroplasts. Chlorophyll-a is the main photosynthetic pigment.
Others are called accessory pigments and include Chlorophyll-b and carotenoids. Chlorophylls absorb mainly blue and red lights. Some wavelengths not absorbed by chlorophyll 'a' are very effectively absorbed by accessory pigments and vice-versa.
