Photosynthesis and Cellular Respiration Coach Fults Chapter 5

Energy in Living Systems We get energy from the food we eat Producers use sunlight energy to make chemically energy (sugars) for us to consume The Sun is the basis for all energy, but there are some exceptions

Building Molecules That Store Energy Metabolism involves either using energy to build molecules or breaking down molecules where energy is stored Photosynthesis- light energy is converted into chemical energy Autotroph- can make its own food

Breaking Down Food For Energy Heterotroph- organism that has to consume materials to get the energy needed “ EX: humans” Cellular Respiration- is a metabolic process similar to burning fuel. Burning converts almost all the energy to heat, CR releases much of the energy in food to make ATP. This ATP provides cells with energy they need to carry out activities of life.

The Transfer of Energy to ATP In cells, chemical energy stored in food molecules is released gradually in a series of enzyme-assisted chemical reactions. The product of 1 reaction becomes the new reactant for another reaction.

The Transfer of Energy to ATP When cells break down food, some of the energy in the molecules is released as heat, much of the rest of energy is stored temporarily in molecules of ATP ATP delivers energy wherever it is needed Drives most of the cells activities

ATP Adenosine Triphosphate- is a nucleotide with 2 extra energy-storing phosphate groups The phosphate“tail” is unstable b/c it is negatively charged and therefore repel each other.The phosphate groups store energy like a compressed spring.Energy is released when their bonds are broken.

ATP Breaking the outer phosphate bond requires energy. More energy is released than what is consumed. Removal cause ATP to become ADP “adenosine diphosphate.” ATP --> ADP + P + energy This energy drives metabolism; sometimes 2 phosphates can be removed

Photosynthesis “Using the Energy of Sunlight” Plants, algae, and some bacteria capture about 1% of the energy of the sunlight that reaches the earth and converts it to chemical energy thru the process of photosynthesis

Photosynthesis Stages 1. Energy is captured from sunlight 2. Light energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH 3. Energy stored in ATP and NADPH powers the formation of organic compounds using CO 2

Photosynthesis Equation 3CO 2 + 3H 2 O  C 6 H 6 O 3 + 3O 2 light

Stage 1: Absorption of Light Energy The chemical reactions that occur in the 1 st and 2 nd stages are sometimes called the “light reactions” Sunlight is a form of radiation- (energy in the form of waves that travel through space) We only see visible light Many different radiations have diff wavelengths

Pigments Pigments- structures containing light-absorbing substances Pigments only absorb certain wavelengths and reflect others Chlorophyll- absorbs red and blue and reflects green and yellow Plants contain 2 types of chlorophyll 1. Chlorophyll a 2. Chlorophyll b

Pigments Pigments that produce yellow and orange fall leaf colors are called carotenoids. Carotenoids absorb diff. Wavelength than chlorophyll so more energy can be absorbed

Production of Oxygen Thylakoid- clusters of pigments are embedded in the membrane of disk- shaped structures When light strikes a thylakoid in a chloroplast, energy is transferred to electrons in chlorophyll. This energy transfer “excites” the electrons for the 2 nd stage of photosynthesis

Production of Oxygen Excited jump to nearby molecules in the thylakoid membrane. The excited electrons that leave the chlorophyll must be replaced by other electrons Plants get these replacement electrons from water

Production of Oxygen Water molecules are split up by an enzyme inside the thylakoid Chlorophyll molecules take the electrons from the hydrogen atoms (H), leaving hydrogen ions(H + ) The remaining oxygen atoms (O), from the disassembled water molecules combine to form oxygen gas

Stage 2: Conversion of Light Energy Excited electrons leave chlorophyll to form new molecules, including ATP, that temporarily store chemical energy. 1 st an excited electron jumps to a nearby molecule in he thylakoid membrane. Then the electrons is passed along by molecules in the thylakoid membrane.

Electron Transport Chain The passing along of that electron is what we call the Electron Transport Chain. Excited electrons lose some of their energy as they pass thru proteins in the membrane. The energy lost by the electrons are used to pump hydrogen (H+) ions into the thylakoid. Recall that hydrogen ions are also produced when water molecules are split inside the thylakoid

Electron Transport Chain As the process cont.., hydrogen ions become more concentrated in the thylakoid than outside, producing a concentration gradient across the thylakoid membrane. As a result,H + ions have a tendency to diffuse back out the thylakoid down their gradient thru specialized carrier proteins (that function as an ion channel)

Electron Transport Chain As hydrogen ions pass thru the channel portion of the protein, the protein catalyzes a reaction in which a phosphate group is added to a molecule of ADP; making ATP. Thus the movement of hydrogen ions across the membrane provides the energy to make ATP, which is used to drive the 3 rd stage of photosynthesis

Electron Transport Chain While 1 ETC provides energy used to make ATP, a 2 nd ETC provides energy used to make NADPH NADPH- is an electron carrier that provides the high-energy electrons needed to make carbon-hydrogen bonds in the 3 rd stage of photosynthesis

Electron Transport Chain In the 2 nd ETC, excited electrons combine with hydrogen ions as well as an electron acceptor called NADP +, forming NADPH

Light Dependent Reactions Can Be Summarized as follows: Pigment molecules in the thylakoids of chloroplast absorb light energy. Electrons in the pigments are excited by light and move thru the ETC in the thylakoid membrane. These electrons are replaced by electrons from water molecules, which are split by an enzyme

Light Dependent Reactions Can Be Summarized as follows: Continued…. Oxygen atoms from water molecules combine to form gas. Hydrogen ions accumulate inside thylakoids, setting up a concentration gradient that provides energy to make ATP and NADPH

Stage 3: Storage of Energy Carbon atoms from carbon dioxide from the atmosphere are used to make organic compounds in which chemical energy is stored The transfer of carbon dioxide to organic compounds is called carbon dioxide fixation. The reactions that “fix” carbon dioxide are sometimes called “dark reactions” or light independent reactions

Calvin Cycle The most common method of carbon dioxide fixation is the Calvin Cycle Calvin Cycle- is a series of enzyme- assisted chemical reactions that produces a 3 carbon sugar

Calvin Cycle Steps 1. In carbon dioxide fixation, each molecule of CO 2 is added to a 5 carbon compound by an enzyme 2. The resulting 6 carbon compound splits into two 3 carbon compounds. Phosphate groups from ATP and electrons from NADPH are added to the 3 carbon compounds, forming 3 carbon sugars

Calvin Cycle Steps 3. One of the resulting 3 carbon sugars is used to make organic compounds- including starch and sucrose- in which energy is stored for later use by the organism 4. The other 3 carbon sugars are used to regenerate the initial 5 carbon compound, thereby completing the cycle

Factors that Affect Photosynthesis Amount of light CO 2 concentration Certain temperatures Enzymes, sometimes unfavorable temps. May inactivate certain enzymes

Cellular Respiration Like in most organisms, your cells transfer the energy in organic compounds, especially glucose, to ATP thru a process called Cellular Respiration Oxygen in the air you breathe makes the production of ATP more efficient, although some ATP is made without oxygen present

Aerobic and Anaerobic Respiration Aerobic= oxygen is present Anaerobic= no oxygen present

Cellular Respiration Equation C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O + ATP

Cellular Respiration Steps 1. Glucose is converted into pyruvate, producing a small amount of ATP and NADH

Cellular Respiration Steps 2. When oxygen is present, pyruvate and NADH are used to make a large amount of ATP. Aerobic respiration happens in the mitochondria of eukaryotes and in the cell membrane of prokaryotes. When oxygen isn’t present pyruvate is converted into either lactate or ethanol (ethyl alcohol) and CO 2

Stage 1: Break down of Glucose Glucose is the fuel for cellular respiration, which is formed when carbohydrates such as starch and sucrose are broken down If few carbohydrates are present then the organism can break down fats to make ATP. 1 gram of fat contains more energy than 2 grams of carbohydrates Proteins and nucleic acids can also be used to make ATP, but they are usually used for building important cell parts.

Glycolysis In the 1 st stage of cellular respiration glucose is broken down in the cytoplasm in a process called glycolysis Glycolysis is an enzyme-assisted anaerobic process that breaks down one 6 carbon molecule of glucose to two 3 carbon pyruvate ions.

Glycolysis Recall that a molecule that has lost or gained one or more electrons is called an ion. Pyruvate is the ion of a 3 carbon organic acid called pyruvic acid. The pyruvate produce still has some of the energy that the glucose started with.

Glycolysis As glucose is broken down, some of its hydrogen atoms are transferred to an electron acceptor called NAD +. This forms an electron carrier called NADH. For respiration to continue, the electrons carried by NADH are eventually donated to other organic compounds

Glycolysis Summarized (Steps) 1. In a series of 3 reactions, phosphate groups form 2 ATP molecules are transferred to a glucose molecule. 2. In 2 reactions, the resulting 6 carbon compound is broken down to two 3 carbon compounds, each with a phosphate group

Glycolysis Summarized (Steps) 3. 2 NADH molecules are produced, and one more phosphate group is transferred to each 3 carbon compound 4. In a series of 4 reactions, each 3 carbon compound is converted to a 3 carbon pyruvate, producing 4 ATP molecules in the process

Stage 2: Production of ATP When oxygen is present, pyruvate produced during glycolysis enters a mitochondrion and is converted to a 2 carbon compound This reaction produces 1 carbon dioxide molecule, 1 NADH molecule, and 1 2- carbon acetyl group. The acetyl group is attached to a molecule called coenzyme A (CoA) forming a compound called acetyl- CoA

Krebs Cycle Acetyl-CoA enters a series of enzyme-assisted reactions called the Krebs Cycle The cycle is named for a biochemist Hans Krebs, who 1 st described it

Krebs Cycle Steps 1. Acetyl-CoA combines with a 4- carbon compound, forming a 6- carbon compound and releasing coenzyme A 2. CO 2 is released from the 6-carbon compound, forming a 5-carbon compound. Electrons are transferred to NAD +, making NADH

Krebs Cycle Steps 3. CO 2 is released from the 5-carbon compound, resulting in a 4-carbon compound. A molecule of ATP is made, and a NADH is produced 4. The existing 4-carbon compound is converted into a new 4-carbon compound. Electrons are transferred to an electron acceptor called FAD, making a molecule of FADH 2 -”another electron carrier”

Krebs Cycle Steps 5. The new 4-carbon compound is then converted to a 4-carbon compound that began the cycle. Another molecule of NADH is produced At the end the NADH and FADH 2 carries most of the energy that glucose and pyruvate started with

Electron Transport Chain In aerobic respiration, electrons donated by NADH and FADH 2 pass thru the ETC. In eukaryotic cells, aerobic respiration occurs in the inner membranes of the mitochondria The energy of these electrons is used to pump hydrogen ions out of the inner mitochondrion membrane

Electron Transport Chain Cont….. The hydrogen ions accumulate in the outer membrane, producing a concentration gradient across the inner membrane. Hydrogen ions diffuse back to the inner membrane thru carrier proteins that add a phosphate group to ADP, making ATP. At the end hydrogen ions and spent electrons combine with oxygen to produce water molecules

Fermentation in the Absence of Oxygen Without oxygen, the ETC does not function b/c oxygen is not there to be the final electron acceptor. Electrons are not transferred from NADH to NAD + So the NAD + is recycled in another way Under anaerobic conditions, electrons carried by NADH are transferred to pyruvate produced during glycolysis

Fermentation in the Absence of Oxygen This process recycles NAD + needed to continue making ATP thru glycolysis The recycling of NAD + using an organic hydrogen acceptor is called fermentation. Prokaryotes produce more than 12 kinds of fermentation

Fermentation in the Absence of Oxygen 2 important kinds of fermentation are lactic acid fermentation and alcoholic fermentation

Lactic Acid Fermentation 3-carbon pyruvate is converted to a 3-carbon lactate. Lactate is an ion of an organic acid called lactic acid.

Lactic Acid Fermentation In vigorous exercise, pyruvate in muscles is converted to lactate when muscle cells must operate w/out enough oxygen. Fermentation allows glycolysis to continuing producing ATP in the muscle cells as long as there is still a glucose supply. Blood removes excess lactate. Lactate can build up in the muscles if not removed quickly, causing muscle soreness and cramping

Alcoholic Fermentation 3-carbon pyruvate is broken down into ethanol (ethyl alcohol), a 2- carbon compound releasing CO 2. Electrons are transferred from a molecule of NADH to the 2-carbon compound, producing ethanol NAD + is recycled thru glycolysis producing ATP, just like lactic acid

Alcoholic Fermentation Wine and beer contain ethanol that was produced during fermentation by yeast Naturally fermented wine contains about 12% ethanol

Production of ATP Glycolysis is an anaerobic process that nets 2 ATP For each molecule of glucose that is broken down, as many as 2 ATP molecules are made directly during the Krebs Cycle, and up to 34 in the ETC, during aerobic respiration