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Biology 1 Chapter 8&9. Energy in a Cell. Cell Energy. All living organisms must be able to obtain energy from the environment in which they live.
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Biology 1Chapter 8&9 Energy in a Cell
Cell Energy • All living organisms must be able to obtain energy from the environment in which they live. • Plants and other green organisms are able to trap the light energy in sunlight and store it in the bonds of certain molecules for later use. Autotrophs • Other organisms cannot use sunlight directly. • They eat green plants. In that way, they obtain the energy stored in plants. Heterotrophs
Work and the need for energy • Active transport, cell division, movement of flagella or cilia, and the production, transport, and storage of proteins are some examples of cell processes that require energy. • There is a molecule in your cells that is a quick source of energy for any organelle in the cell that needs it. If cells don’t have this molecule, they will die. • The name of this energy molecule is adenosine triphosphate or ATP for short. • ATP is composed of an adenosine (an adenine and a ribose together) molecule with three phosphate groups attached.
Forming and Breaking Down ATP • The charged phosphate groups act like the positive poles of two magnets. • Bonding a third phosphate group onto ADP to form adenosine triphosphate requires considerable energy. • When ATP is formed, the energy is stored in the bond of the molecule. When this bond is broken, the energy is released. • A molecule with only 2 phosphate groups attached is called adenosine diphosphate, or ADP, and it is formed when ATP is broken down to release energy.
Forming and Breaking Down ATP P P P Adenosine Adenosine triphosphate (ATP) P P Adenosine diphosphate (ADP) P P Adenosine • The energy of ATP becomes available to a cell when the molecule is broken down. + Energy + Energy • When ATP is broken down it releases energy and a phosphate group and reforms ADP which can then be reused to make ATP again.
When ATP is broken down and the energy is released, ADP is formed and a phosphate group is released. The ADP and phosphate is then available to be reused again. It is a cycle between ATP and ADP. • When ATP is broken down and the energy is released, the energy must be captured and used efficiently by cells. • Many proteins have a specific site where ATP can bind.
Trapping Energy from Sunlight • All biological energy originally comes from the sun • The process that uses the sun’s energy to make simple sugars is called photosynthesis. • The general equation for photosynthesis is written as (sunlight) + 6CO2 + 6H2O→C6H12O6 + 6O2
Why are carbs important? Carbohydrates are the main energy molecules used by all organisms. They are what we break down to make ATP!!!
The light-dependent reactions convert light energy into chemical energy. Occurs in the thylakoid. 2. The molecules of ATP produced in the light-dependent reactions are then used to fuel the light-independent reactionsthat produce simple sugars. (the Calvin Cycle). Occurs in the stroma. • Photosynthesis occurs in the chloroplast (which contains the light trapping pigment - chlorophyll). • Photosynthesis happens in two phases. • Photosynthesis depends on 3 things: temperature, light and availability of raw materials.
Light-Dependent Reactions • To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight. • Although there are several kinds of pigments, the most common is chlorophyll. • Chlorophyll absorbs most wavelengths of light except green. Since green is reflected, that is the color our eyes see.
Light-Dependent Reactions • As sunlight strikes the chlorophyll molecules the thylakoid membrane, the energy in the light is transferred to electrons. • These highly energized, or excited, electrons leave the chlorophyll and are passed down an electron transport chain, a series of proteins embedded in the thylakoid membrane. (bucket brigade) • At each step along the transport chain, the electrons lose energy. • This “lost” energy is used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc.
Light-Dependent Reactions • The electrons are re-energized and passed down a second electron transport chain. • Then, the electrons are transferred to the stromaof the chloroplast. To do this, an electron carrier molecule (coenzyme – biological carrier molecules) called NADP+ is used. • NADP+ picks up two excited electrons and a hydrogen ion (H+) to become NADPH which carriers them to the light independent reactions where they will be used. • NADPH will play an important role in the light-independent reactions.
Restoring electrons • To replace the electrons lost by the chlorophyll, molecules of water are split. This reaction is called photolysis. • The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. • The electrons are returned to chlorophyll. • The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration.
Sun Light energy transfers to chlorophyll. Chlorophyll passes energy down through the electron transport chain. Energized electrons provide energy that P to ADP bonds splits H2O forming ATP oxygen released H+ NADP+ NADPH for the use in light-independent reactions Light-Dependent Reactions Sun • Result in: • Electrons • ATP • Hydrogen • Oxygen • 1,2,3 used in the light independent reactions • 4 is released as waste Chlorophyll passes energy down through the electron transport chain. bonds for the use in light-independent reactions
(CO2) Section 9.2 Summary – pages 225-230 (CO2) The Calvin Cycle (Unstable intermediate) (RuPB) • The stroma in the chloroplasts hosts the Calvin cycle. ADP + ATP ATP ADP + NADPH NADP+ (PGAL) (PGAL) (PGAL) (Sugars and other carbohydrates)
The Calvin Cycle • Carbon fixation. • The carbon atom from CO2 bonds with a five-carbon sugar called ribulose biphosphate (RuBP) to form an unstable six-carbon sugar. (CO2) (RuBP)
The Calvin Cycle • Formation of 3-carbon molecules. • The six-carbon sugar formed in Step A immediately splits to form two three-carbon molecules. (Unstable intermediate)
The Calvin Cycle • Use of ATP and NADPH. • A series of reactions involving ATP and NADPH from the light-dependent reactions converts the three-carbon molecules into phosphoglyceraldehyde (PGAL), three-carbon sugars with higher energy bonds. ATP ADP + NADPH NADP+ (PGAL)
The Calvin Cycle • Sugar production. • One out of every six molecules of PGAL is transferred to the cytoplasm and used in the synthesis of sugars and other carbohydrates. After three rounds of the cycle, six molecules of PGAL are produced. (PGAL) (Sugars and other carbohydrates)
The Calvin Cycle • RuBP is replenished. • Five molecules of PGAL, each with three carbon atoms, produce three molecules of the five-carbon RuBP. This replenishes the RuBP that was used up, and the cycle can continue. P ADP+ ATP (PGAL)
(CO2) Section 9.2 Summary – pages 225-230 (CO2) The Calvin Cycle (Unstable intermediate) (RuPB) • The Calvin Cycle results in the production of simple sugar molecules called carbohydrates that are the major source of energy for most organisms. ADP + ATP ATP ADP + NADPH NADP+ (PGAL) (PGAL) (PGAL) (Sugars and other carbohydrates)
Cellular Respiration • The process by which mitochondriabreak down food molecules to produce ATP is called cellular respiration.
Full Cellular Respiration – Aerobic • The first stage, glycolysis, is anaerobic—no oxygen is required. • The citric acid cycle and the e.t.c. are aerobic (require oxygen to be completed).
Glycolysis • Glycolysis is a series of chemical reactions in the cytoplasm of a cell that break down glucose, a six-carbon compound, intotwo molecules of pyruvic acid, a three-carbon compound. 4ATP 2ADP 2 Pyruvic acid 2ATP 4ADP + 4P Glucose 2PGAL 2NAD+ 2NADH + 2H+
Glycolysis • Glycolysis is not very effective, producing only two ATPmolecules for each glucose molecule broken down. 4ATP 2ADP 2 Pyruvic acid 2ATP 4ADP + 4P Glucose 2PGAL 2NAD+ 2NADH + 2H+
Preparatory Step • Before citric acid cycle and electron transport chain can begin, pyruvic acid undergoes a series of reactions in which it gives off a molecule of CO2 and combines with a molecule called coenzyme A to form acetyl-CoA. Mitochondrial membrane CO2 Outside the mitochondrion Inside the mitochondrion Coenzyme A - CoA Intermediate by-product Acetyl-CoA Pyruvic acid Pyruvic acid NAD+ NADH + H+
The citric acid cycle • The citric acid cycle, also called the Krebs cycle, is a series of chemical reactions similar to the Calvin cycle in that the molecule used in the first reaction is also one of the end products. • For every turn of the cycle, one molecule of ATP and two molecules of carbon dioxide are produced.
The Citric Acid Cycle (Acetyl-CoA) NAD+ Citric acid Oxaloacetic acid NADH + H+ NADH + H+ O= =O Citric Acid Cycle (CO2) NAD+ The mitochondria host the citric acid cycle. NAD+ NADH + H+ O= =O (CO2) ADP+ ATP FAD FADH2
The citric acid cycle • Citric acid forms. • The two-carbon compound acetyl-CoA reacts with a four-carbon compound called oxaloacetic acid to form citric acid, a six-carbon molecule. Acetyl-CoA Citric acid Oxaloacetic acid
The citric acid cycle • Formation of CO2 • A molecule of CO2 is formed, reducing the eventual product to a five-carbon compound. In the process, a molecule of NADH and H+ is produced. NAD+ NADH + H+ O= =O (CO2)
The citric acid cycle • Formation of the second CO2 • Another molecule of CO2 is released, forming a four-carbon compound. One molecule of ATP and a molecule of NADH are also produced. NAD+ NADH + H+ O= =O ADP + (CO2) ATP
Recycling of oxaloacetic acid. • The four-carbon molecule goes through a series of reactions in which FADH2, NADH, and H+ are formed. The carbon chain is rearranged, and oxaloacetic acid is again made available for the cycle. The citric acid cycle NADH + H+ NAD+ FAD FADH2
The Citric Acid Cycle (Acetyl-CoA) NAD+ Citric acid Oxaloacetic acid NADH + H+ NADH + H+ O= =O Citric Acid Cycle (CO2) NAD+ NAD+ NADH + H+ O= =O (CO2) ADP+ ATP FAD FADH2
The electron transport chain • In the electron transport chain, the carrier molecules NADH and FADH2 gives up electrons that pass through a series of reactions (the electron transport chain). Oxygen is the final electron acceptor. Space between inner and outer membranes Electron carrier proteins Enzyme Inner membrane Electron pathway e - H2O 4H+ + O2 NADH NAD+ ADP + ATP + 4 electrons Center of mitochondrion H2O FADH2 FAD • Overall, the electron transport chain adds 32 ATP molecules to the four already produced.
Fermentation • If there is no oxygen present after glycolysis, aerobic respiration cannot occur. Cells can continue producing ATP by using another process (anaerobic, does not require oxygen) called fermentation. • 2 types: • lactic acid fermentation – makes lactic acid • alcoholic fermentation – makes alcohol (ethanol) • Fermentation is a quick process, but does not produce any additional ATP.
No additional ATP are produced, but NAD+ is recycled allowing glycolysis to continue. • The lactic acid - muscle cells • alcoholic fermentation, is used by yeast cells and some bacteria to produce CO2 and ethyl alcohol.
Table 9.1 Comparison of Photosynthesis and Cellular Respiration Cellular Respiration Photosynthesis Food synthesized Food broken down Energy of glucose released Energy from sun stored in glucose Carbon dioxide taken in Carbon dioxide given off Oxygen taken in Oxygen given off Produces sugars from PGAL Produces CO2 and H2O Does not require light Requires light Occurs only in presence of chlorophyll Occurs in allliving cells Comparing Photosynthesis and Cellular Respiration • Notice, the end products of one are the starting products of the other. • Also, photosynthesis takes place in the chloroplast while respiration takes place in the mitochondria.