ATP-ADP Cycle

ATP-ADP CYCLE Introduction: Adenosine triphosphate (ATP) is the energy currency used throughout the cell. ATP provides energy for the cell to do work, such as mechanical work, transport substances across the membrane, and perform various chemical reactions. ATP is composed of phosphate groups, ribose, and adenine. In the structure of ATP, there are three phosphate groups attached to adenosine. The last two bonds on the phosphate groups contain especially high energy and are therefore very useful for doing work within living cells. The bonds that hold phosphate groups are easily broken by hydrolysis which results in the release of energy. Fig. 1a. Adenosine triphosphate (ATP) to adenosine diphosphate (ADP) transformation Adenosine Triphosphate (ATP) ● Structure composed of sugar ribose, nitrogen base adenine, and a chain of 3phosphate groups ● Mediates most energy coupling in cells ● Powers cellular work ● Three (3) main kinds of work of a cell: chemical work, transport work, and mechanical work. These are possible through energy coupling, where the cells use an exergonic process to drive an endergonic reaction. ○ chemical work: synthesis of polymers from monomers (pushing of endergonic reactions) ○ transport work: pumping of substances across membranes (against the direction of spontaneous movement) ○ mechanical work: the beating of cilia, contraction of muscles ● Also used to make RNA (since ATP is used as one of the nucleoside triphosphates. Hydrolysis of ATP ● process of breaking down bonds between the phosphate groups ● this happens when a water molecule breaks the terminal phosphate bond ● , abbreviated P I leaves ATP ● Forming Adenosine diphosphate (ADP) ● Energy is released. This comes from the chemical change of the system state of lower free energy and NOT from the phosphate bonds. ● Hydrolysis releases so much energy because of the negative charges of the phosphate groups. These charges are crowded together and their mutual repulsion contributes to the instability of that region of the ATP. The energy equivalent of the triphosphate tail of ATP is compared to a compressed spring. Fig. 1.b. The Hydrolysis of ATP How the Hydrolysis of ATP Perform Work ● Proof that ATP releases heat: in a test set up, the hydrolysis of ATP releases energy in the form of heat in the surrounding water. ● Most of the time when an animal is exposed in a cold environment, the reaction of the body is through shivering. In this reaction of the organism, shivering uses ATP during muscle contraction to warm the body. Since it will also be a disadvantage for organisms to generate heat during ATP hydrolysis, in order to maintain the living conditions inside the cell, the energy released during ATP hydrolysis is used by proteins to perform work: chemical, transport and mechanical ● Hydrolysis of ATP leads to change in the shape of protein and in its ability to bind to another molecule. Phosphorylation (ADP to ATP) and dephosphorylating (ATP to ADP) promote crucial protein shape changes during important cellular process. Fig. 1.c. Phosphorylation (ADP to ATP) and dephosphorylation (ATP to ADP) The Regeneration of ATP ● ATP is renewable it can be regenerated by the addition of phosphate to ADP ● Catabolism (exergonic) provides the free energy to phosphorylate ADP. ● ATP formation is not spontaneous, so there is a need to use free energy for the process to work. ● ATP cycle is the shuttling of inorganic phosphate and energy. ● It couples the cell’s energy-yielding processes (exergonic) to energy-consuming processes (endergonic) ● ATP regeneration happens very fast (10M molecules of ATP used and regenerated per second) ● If ATP could not be regenerated by phosphorylation of ADP, HUMANS would use nearly their body weight in ATP each day. Fig. 1.d. The ATP cycle The Importance of Chlorophyll and Other Pigments Terminology: CHROMATOGRAPHY - is a separation technique used to identify various components of mixtures based on the differences in their structure and/or composition. PIGMENTS - are substances that absorb visible light. Different pigments absorb light of different wavelengths. Light, as it encounters an object, is either reflected, transmitted, or absorbed. Visible light, with a wavelength of 380–750nm, is the segment in the entire range of the electromagnetic spectrum that is most important to life on earth. It is detected as various colors by the human eye. The color that is not absorbed by pigments of objects is transmitted or reflected and that is the color of the object that we see. Fig. 1.e. The Electromagnetic Spectrum Pigments are the means by which plants capture the sun’s energy to be used in photosynthesis. However, since each pigment absorbs only a narrow range of wavelengths, there is usually a need to produce several kinds of pigments of different colors to capture more of the sun’s energy. CHLOROPHYLL - is the greenish pigment found in the thylakoid membrane inside the chloroplast of a plant cell. Chlorophyll absorbs blue and red light while it transmits and reflects green light. This is why leaves appear green. There are several kinds of chlorophyll. Among these, chlorophyll plays the most important role in photosynthesis. It directly participates in converting solar energy to chemical energy. Other pigments in the chloroplast play the part of accessory pigments. These pigments can absorb light and transfer the energy to chlorophyll a. One of these accessory pigments is chlorophyll b. Some carotenoids also contribute energy to chlorophyll a. Other carotenoids, however, serve as protection for chlorophyll by dissipating excessive energy that will otherwise be destructive to chlorophyll. Structure of chlorophyll ● ● Head - a flat hydrophilic head called porphyrin ring. It has a magnesium atom at its center. Different chlorophylls differ on the side groups attached to the porphyrin. Tail - a lipid-soluble hydrocarbon tail. How does photoexcitation of chlorophyll happen? 1. A chlorophyll molecule absorbs photon or light energy. 2. An electron of the molecule in its normal orbital said to be in its ground state, will be elevated to an orbital of higher energy. The molecule is now in an excited state. The molecule only absorbs photon that has the energy that is equal to the energy needed for it to be able to elevate from the ground state to the excited state. 3. The excited state is unstable. Hence, excited electrons drop back down to the ground state immediately after, releasing energy in the form of heat and photons. This happens in isolated chlorophyll molecules. However, chlorophyll molecule that is found in its natural environment in the thylakoid membrane forms a photosystem together with proteins and other organic molecules to prevent the loss of energy from the electrons. Fig. 1.f. The Photoexcitation of Chlorophyll PHOTOSYSTEM - A photosystem is an aggregate of pigments and proteins in the thylakoid membrane responsible for the absorption of photons and the transfer of energy and electrons. It is composed of: ● ● Light-harvesting complex - is also called the ‘antenna’ complex and is consisted of several different pigments (chlorophyll a, chlorophyll b, and carotenoids) bounded with proteins. When a pigment molecule absorbs a photon, energy is passed on from one pigment molecule to another pigment molecule until the energy reaches the reaction center. Reaction-center complex - is composed of a pair of chlorophyll a and a primary electron acceptor. The primary electron acceptor is a specialized molecule that is able to accept electrons from the pair of chlorophyll a. The pair of chlorophyll in the reaction center is also specialized because they are capable of transferring an electron to the primary electron acceptor and not just boosting the electron to a higher energy level. There are two types of photosystems: ● ● Photosystem II - was discovered later after the discovery of Photosystem I, but functions first in the light reaction of photosynthesis. The chlorophyll-a in the reaction center of Photosystem II effectively absorbs light with a wavelength of 680nm and is thus called P680. Photosystem I - was discovered first. Its reaction center has a chlorophyll called P700 because it is effective in absorbing light with a wavelength of 700nm. PERFORMANCE ACTIVITY 1. Make a 3-5 minute video (. mp4) that contains your reflection about the lesson. The reflection must contain the concepts introduced, and the implications of such to you. The video must contain subtitles regardless of the language or dialect that you will use. If you prefer using Filipino or Vernacular, your subtitles must be translated to English. 2. Save your work in a Google Drive folder, obtain a link, copy, and paste it on the Answer Box. (Note: Embed the link using the embed icon so that the video will open upon clicking.) 3. The link should be restricted. That means, the video creator and the professor only can access the video. The gmail address of the professor is: jgpanilo@mmsu.edu.ph