Quarter 2, Week 1: ATP and Plant Pigments PDF

QUARTER 2- WEEK 1 THE ROLE OF ATP AND THE IMPORTANCE OF PLANT PIGMENTS Energy is essential to life. All living things must be able to produce energy, store energy for future use, and use energy to carry out life processes. In everyday life, energy is important because it can be used to do work such...

QUARTER 2- WEEK 1 THE ROLE OF ATP AND THE IMPORTANCE OF PLANT PIGMENTS Energy is essential to life. All living things must be able to produce energy, store energy for future use, and use energy to carry out life processes. In everyday life, energy is important because it can be used to do work such as eating, walking, running, talking, and thinking or simply turning the pages of this learning material. Some cellular activities that require energy are active transport, protein synthesis, and cell division. Energy can exist or be stored in many forms such as light, heat, electricity, and chemical bonds in chemical compounds. ATP Structure and Hydrolysis How do organisms carry out essential life processes? Cells in organisms obtain energy from the chemical bonds that hold together certain organic compounds, such as carbohydrates from the food that we eat. This energy in turn is used to produce adenosine triphosphate (ATP). ATP is an organic molecule used for short-term energy storage and transport in the cell. It is composed of three parts: (1) a nitrogenous base (adenine), a sugar (ribose), and three phosphate groups (triphosphate) (Figure 1). The three phosphate groups in an ATP molecule are negatively charged. Recall that molecules having the same charge will tend to repel from each other. Thus, this means that the three phosphate groups are in an unstable arrangement. The third phosphate group is so eager to get further away from the two phosphate groups. A bond between them is broken through hydrolysis (water-mediated breakdown) reaction releasing energy (Figure 2). The remaining free phosphate group and low-energy molecule is called adenosine diphosphate (ADP). ATP-ADP Cycle The hydrolysis of ATP to ADP is reversible (Figure 3). ATP and ADP are like charged and uncharged forms of a rechargeable battery. ATP (charged battery) has energy that can be used to power cellular processes or reactions. Once the energy is used up, ADP (uncharged battery/dead battery) needs to be recharged in order to be used as a power source. ATP regeneration reaction is the reverse of hydrolysis reaction: ATP in Energy Coupling How is the energy released by ATP hydrolysis used to power cells to carry out useful functions? The hydrolysis of ATP not only results to a release of energy but also would simply result in organisms’ overheating because the dissipation of energy would excite nearby molecules, resulting in heat or thermal energy. Energy in a cell needs to be linked to other processes in order to be useful. Energy coupling is the transfer of energy from one chemical reaction to another. An energetically favorable reaction (exergonic, e.g., ATP hydrolysis) is directly linked with an energetically unfavorable reaction (endergonic, e.g., ATP regeneration). Through energy coupling, the cell can perform nearly all of the tasks it needs to function. One example of energy coupling involving ATP is the formation of sucrose (table sugar) from glucose and fructose (Figure 5). In the uncoupled reaction, glucose and fructose combine to form sucrose. In the coupled reaction, there are two reactions that take place: 1. A phosphate group is transferred from ATP to glucose, forming a phosphorylated glucose intermediate (glucose-P). This is an energetically favorable reaction or exergonic reaction. 2. The glucose-P intermediate reacts with fructose to form sucrose. Because glucose-P is relatively unstable, this reaction also releases energy and is spontaneous. The Importance of Chlorophyll and Other Pigments Light from the sun is absorbed by colorful compounds called pigments. The structure and amount of pigments determine the variations in color. The chlorophyll pigment in leaves helps make photosynthesis happen by absorbing light energy from the sun to put together carbon dioxide and water to form glucose or food. All colors of visible light except green are absorbed by chlorophyll, which it reflects to be detected by our eyes. Chlorophyll gives plants their green color and may hide the other pigments found in leaves. If all colors or wavelengths of visible light are absorbed and none are reflected, the pigment appears black to our eyes. On the contrary, if all colors or wavelengths of light are reflected, the pigment appears white to our eyes. Chlorophyll and Accessory Pigments Green plants have green leaves, and the leaves are green because of the green pigment called chlorophyll, which are found in the chloroplasts. The visible light spectrum ranges from red (the longest wavelength) to orange, yellow, green, blue, indigo, and violet (the shortest wavelength). Plants possess pigments that can absorb light in specific regions of the spectrum (Figure 6). Leaves have evolved to produce several other pigments called accessory pigments. Accessory pigments absorb wavelengths of light that chlorophyll cannot absorb effectively, enabling the plant to use more of the sun’s energy (Figures 7 and 8). The following are the types of accessory pigments: 1. Chlorophyll b – It is structurally only slightly different from chlorophyll a but its absorption spectrum is somewhat different. It absorbs more in the blue and orange-red ranges. It looks yellowish green. Captured energy is handed over to chlorophyll a, which is a smaller but more plentiful molecule in the chloroplast. 2. Carotenoids – They absorb light from violet to the greenish-blue range. They appear in various shades of yellow or yellow orange to our eyes. They cluster next to chlorophyll a molecules to efficiently hand off absorbed photons. They are usually found attached to proteins or membranes in the chloroplasts. 3. Anthocyanins – They do not participate in photosynthesis and may appear red, purple, or blue. They occur widely among higher plants. They are pigments that generally give color to flowers but also occur in leaves and fruits. In leaves, these pigments often help to protect against excessive sunlight that can damage some leaf tissues. This is one reason why a young, newly developing leaf is often redder than when it reaches its mature size. 4. Xanthophylls – They pass along light energy to chlorophyll a and act as antioxidants. The molecular structure gives xanthophylls the ability to accept or donate electrons. Xanthophyll pigments produce the yellow color in fall leaves.